Acid Sulphate Soils and Acid Drainage, Lower Shoalhaven Floodplain, New South Wales Mark Ian Pease University of Wollongong

University of Wollongong Research Online

University of Wollongong Thesis Collection University of Wollongong Thesis Collections

1994 Acid sulphate soils and acid drainage, Lower Shoalhaven floodplain, New South Wales Mark Ian Pease University of Wollongong

Recommended Citation Pease, Mark Ian, Acid sulphate soils and acid drainage, Lower Shoalhaven floodplain, New South Wales, Master of Science (Hons.) thesis, Department of Geography, University of Wollongong, 1994. http://ro.uow.edu.au/theses/2821

Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected]

ACID SULPHATE SOILS AND ACID DRAINAGE LOWER SHOALHAVEN FLOODPLAIN, NEW SOUTH WALES.

A thesis submitted in fulfilment of the requirements for the award of the degree

MASTER OF SCIENCE (HONOURS)

from

THE UNIVERSITY OF WOLLONGONG

by

MARK IAN PEASE, BSc(Hons)

DEPARTMENT OF GEOGRAPHY

1994 SUMMARY

Rainfall patterns were related to watertable fluctuations over an eight month monitoring period, as a basis for understanding acid drainage development at Jasper's Brush, on the lower Shoalhaven floodplain. The watertable was shown to fall quickly on the floodplain very shortly after rainfall. As the height of groundwater dropped, groundwater acidity increased rapidly and sulphate, iron and aluminium rose to extreme levels. Watertable fluctuations were analysed in a backswamp section, across a large main flood mitigation drain, to understand groundwater movements and the resulting severity of acid drainage in the drain. The severity of acid drainage was also analysed in a small mole drain which was fed by a particularly strongly oxidising environment.

Water quality was analysed along the length of the main drain studied; recurrent drainage of the drain water, through the floodgate upon low tides, allowing more saline creek waters into the drain was shown to have an effect of buffering the acid drainage severity.

Water quality in Broughton Creek was analysed for a month after a minor flood event,

with results (mainly lowered pH and elevated aluminium levels) highlighting the

movement of acid drainage from the floodplain into the creek. The severe adverse effects

on fish were documented. Management options are given. The main option involves

proposing a rise in the watertable by increasing drain water depth (how this may be

achieved is explained) to achieve a reduction in pyritic oxidation, and the likely reduction

in acid drainage severity is estimated. ACKNOWLEDGMENTS

A number of people provided assistance, advice and encouragement during the undertaking of this thesis, without whose help the completion of the thesis would not have been possible. I would like to thank the following people:

- Dr Ann Young (University of Wollongong) and Dr Andrew Nethery (Environment

Protection Authority, Wollongong), my supervisors, for their undivided attention, and advice, including in the field and assistance throughout the time of completion for critical assessment of results and drafts.

- The Environment Protection Authority - Wollongong, for providing financial assistance to myself and for setting up this project.

- The Environment Protection Authority Laboratory - Lidcombe, for being so helpful and providing all water chemistry analysis.

- Mr Roy Lawrie for helping set up the monitoring program on short notice by providing equipment and assistance in digging boreholes.

- Dr Mike Melville for advice on setting up the project, critical assessment of results and

general encouragement.

- Mr Jesmond Sammut for advice and critical assessment of results including a critical

assessment of a draft component.

- Mr Richard Walsh for advice and assistance with many technical aspects of putting the

thesis together, including the TOPCON aerial photograph analyser.

- Assoc. Professor R.W. Young for advice, including in the field and assisting in some

aspects in the completion of this thesis.

- Assoc. Professor E.A. Bryant for advice and assisting in statistical aspects critical to the

completion of this thesis.

- The Environment Protection Authority - Marine and Estuarine Waters Branch,

Bankstown, for advice and use of submerged data loggers.

- Mr Peter Jamieson, Dr Pam Hazelton, Mr John Downey, Assoc. Professor J.

Morrison, Mr Phil Mulvey and Mr Duncan Leadbitter, for advice. - Mr Richard Miller and Mr David Martin for advice and assistance with aspects of cartography.

- Mr David Price for advice and assistance in the laboratory.

- Mr Tony Roper, Mr John Marthick, Mr Robert Wray, Mr Scott Smithers and Mr David

Leffley for advice and assistance on technical aspects.

- All the staff of the Geography Department for their helpful advice and continued encouragement and especially to Mrs Jacqueline Shaw for her constant smile and assistance with general matters.

- All the staff of the Environment Protection Authority - Wollongong, for their helpful advice and continued encouragement and especially to Miss Deborah Taylor, Ms

Jacqueline Cumming and Mrs Deborah Maddison for assistance with general matters.

- Mr Glenn Morris, Miss Melinda Pease and Mr Ross Pease for assistance in the field.

- My mum, Mrs Christine Pease for checking through drafts.

- The 1993/94 postgraduate students for continual encouragement and keeping the social life alive and well: Miss Lynne McCarthy, Mr Richard Walsh, Mr Robert Wray, Mr

Steven Tooth, Mr Brendan Brooke, Mr Rainer Wende and Mr Heqing Huang, Miss

Leanne Wirth, Mr Scott Smithers and Mr Jerry Maroulis.

- The 1993/94 honours students for continual encouragement.

- Miss Karen Wilkinson for always being there and continual encouragement during the final stages.

- Finally, I must thank my family for putting up with me and assisting with some aspects of the thesis. Also to my grandparents for providing accommodation and encouragement during some stages of writing the thesis. TABLE OF CONTENTS

Chapter 1: INTRODUCTION ...... 1 1.1 Introduction ...... 1 1.2 Acid Sulphate Soils and Formation ...... 3 1.3 The Significance of Studying Acid Sulphate Soils ...... 6 1.4 History and Extent of Acid Sulphate Soils Overseas and in Australia ...... 9 · 1. 5 Identification of Acid Sulphate Soils in the Lower Shoalhaven ...... 9 1.6 Significance of this Project ...... 10 1.7 Aims ...... 14

Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA ...... 17 2.1 Introduction ...... 17 2.2 Deposition and Accumulation Required for Acid Sulphate Soil Development ...... 18 2.3 Drainage Network ...... 23 2. 4 Climate ...... 31 2.5 Floods ...... 34 2.6 Sum1nary ...... 35

Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS ...... 36 3. 1 Introduction ...... 36 3.2 Formation of Pyrite ...... 38 3. 3 Oxidation ...... 39 3. 3 .1 Oxidation of Pyrite ...... 39 3. 3. 2 Oxidation Products of Pyrite ...... 42 3 .4 Physiographic Characteristics of the Study Area ...... 44 3.5 Physical and Chemical Properties of Acid Sulphate Soils Analysed in the Study Area ...... 46 3. 6 Levee Soils ...... 52 3.7 Levee toe ...... 54 3.8 Backswamps ...... ··;· ...... 55 3.9 Inter-Section Comparisons ...... 63 3.10 Discussion on Pyrite ...... 65 3.11 Summary ...... 67 Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY ...... 70 4.1 Introduction ...... 70 4.2 Watertable and Drain Water Level Dynamics ...... 70 4.3 Floodplain and Drain Water Levels and pH Dynamics ...... 76 4.3.1 Watertable/pH Relationships in the Floodplain ...... 76 4.3.2 Inter-Bore Comparisons of Groundwater pH ...... 77 4.3.3 Water LeveVpH Relationships Between the Groundwater and Drains ...... 7 8 4.4 Floodplain and Drain, Rainfall, Water Level and Water Quality Dynamics ...... 80 4.4.1 Period 1: 17/2/93 - 19/3/93 ...... 85 4.4.2 Period 2: 24/3/93 - 30/6/93 ...... 88 4.4.3 Period 3: 9/7 /93 - 7 /9/93 ...... 92 4.4.4 Period 4: 7/9/93 - 12/10/93 ...... 93 4.5 Discussion of Rainfall, Water Height/Depth, pH and Water Quality Comparisons from Figures 4.5-4.7, for the Bores and Drains ...... 95 4.6 Linear Regression Analysis of Floodplain and Drain Water Quality Results ...... 98 4. 7 Chemical Analysis ...... 101 4.7 .1 Chloride and Sulphate ...... 102 4.7 .2 Iron ...... 103 4.7 .3 Aluminium ...... 107 4.7.4 Reduction Processes Related to Flooding ...... 107 4.8 Comparisons with Other Areas ...... 110 4.8.1 Background ...... 110 4. 8. 2 Watertable/Drain Water Depth Dynamics ...... 112 4.8.3 Water Quality Analysis ...... 114 4.9 Summary ...... 117

Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS ...... 120 5 .1 Introduction ...... 120 5.2 Water Quality Along the Transect Drain ...... 120 5. 3 Influence of Floodgates on Drainage Water Quality ...... 124 5.4 Summary ...... 130 Chapter 6: BROUGHTON CREEK WATER QUALITY AND IMPACT OF ACID DRAINAGE ON AQUATIC LIFE ...... 132 6.1 Introduction ...... 132 6.2 Effects of Acid Drainage on Aquatic Life ...... 133 6.2.1 Identification of Acid Drainage from Acid Sulphate Soils as an Environmental Threat to Coastal Estuaries ...... 133 6.2.2 Critical Limits of Water Quality Parameters Affecting Aquatic Life ...... 134 6.2.3 Physiologic Changes to Aquatic Life Resulting from Acid Drainage ...... 135 6.3 Recurrent (low volume/high frequency) Acid Drainage ...... 139 6.3.1 Release of Recurrent Acid Drainage ...... 139 6. 3. 2 Water Quality Analysis from Prior Monitoring ...... 140 6.3.3 Water Quality Analysis from this Study ...... 141 6.3.4 Affects on Aquatic Life ...... 143 6.4 High Intensity (high volume/low frequency) Acid Drainage ...... 143 6.4.1 Water Quality Analysis from Prior Monitoring ...... 145 6.4.2 Water Quality Analysis from this Study (Mid-September, 1993 Rainfall Event) ...... 146 6.4.3 Magnitude of Acid Drainage Input into Broughton Creek Following the Mid-September, 1993 Rainfall Event ...... 148 6.4.4 Water Quality Along the Length of Broughton Creek during severe acid discharge (22/9/93 and 29/9/93) ...... 156 6.4.5 Water Quality Recovery in Broughton Creek ...... 161 6.5 Effects on Aquatic Life ...... 164 6. 5. 1 Observations ...... 164 6.5.2 Discussion of Effects ...... 166 6.6 Summary ...... 168

Chapter 7: DISCUSSION AND MANAGEMENT ...... 172 7 .1 Summary of Major Findings ...... 172 7 .2 Management Strategies ...... 175 7. 2. 1 The Need for Geomorphic Analysis ...... 17 5 7 .2.2 Current Amelioration Procedures ...... 177 7 .2.3 Proposals for Remediation Strategies ...... 180 7. 3 Restatement of Aims ...... 184

REFERENCES ...... 186

APPENDICES LIST OF FIGURES

Figure 1.1. Location of the Jasper's Brush study area ...... 2 Figure 1.2. Development of add sulphate soils, following oxidation (from artificial drainage) of potential acid sulphate soils ...... 7

Figure 2.1. Stages of infilling in the evolution of a barrier estuary ...... 20 Figure 2.2. Shoalhaven delta section showing stratigraphy and location of boreholes and C14 dates ...... 22 Figure 2.3. The Shoalhaven floodplain showing the study area, drainage density and floodgates along Broughton .Creek ...... 26 Figure 2.4. Geometrically correct map of a section of the floodplain, highlighting areas of spoil heaps as shown in the 1993 aerial photos ...... 27 Figure 2.5. Mean monthly rainfall for Berry (Berry Sewerage Treatment Plant) and Nowra (Nowra Sewerage Treatment Plant - Bureau of Meteorology Station No. 068048. For 1886-1991) ...... 32 Figure 2.6. Nowra mean temperatures (Station 608048) ...... 33 Figure 2.7. Nowra mean evaporation levels (Station 608048) ...... 33

Figure 3.1. Acid sulphate soil floodplain surface classification ...... 44 Figure 3.2. Location of all soil sampling sites ...... 48 Figure 3.3. Location of bores used in detailed soil analysis. *These soil sampling sites and water quality sampling sites are referred to frequently in Chapter 4 ...... 51 Figure 3.4. Transect of detailed soil sampling sites and bores used for watertable/water quality analysis in Chapter 4 ...... 52 Figure 3.5. Summarised soil analysis - levee/levee toe/backswamp ...... 62

Figure 4.1. Comparison of depth to watertable for; a: the bore (Bsl2) and b: the control bore ...... 72 Figure 4.2. Watertable movement in relation to a drain. Groundwater is being drawn down into the drain in 'a', and water is being drawn from the drain in'b' ...... 73 Figure 4.3. Mean and standard deviation watertable and drain water depth position for the 8 month long monitoring period (17/2/93 - 12/10/93), along the transect outlined in Chapter 3 ...... 75 Figure 4.4. Plots of pH vs depth to watertable for; a: Bsl2 (the bore) and c:Bsl 8, and pH vs drain water depth; b: transect drain, d: road drain and e: gate drain (see Figure 3.3 for locations) ...... 79 Figure 4.5 Water quality analysis between 17 /2/93-12/10/93 at the bore (Bsl2) for a: Rainfall vs Depth to watertable; b: pH vs Chloride/Sulphate ratio; c: Chloride vs Sulphate; d: Aluminium vs Iron ...... 84 Figure 4.6 Water quality analysis between 17/2/93-12/10/93 at the transect drains for a: Rainfall vs Depth to watertable; b: pH vs Chloride/Sulphate ratio; c: Chloride vs Sulphate; d: Aluminium vs Iron ...... 84 Figure 4.7 Water quality analysis between 17/2/93-12/10/93 at the road drain for a: Rainfall vs Depth to watertable; b: pH vs Chloride/Sulphate ratio; c: Chloride vs Sulphate; d: Aluminium vs Iron ...... 84 Figure 4.8. Statistics for the bore (Bs12); a: pH vs depth to watertable, b: aluminium vs depth to watertable and c: aluminium vs pH ...... 99 Figure 4.9. Statistics for the transect drain; a: pH vs drain depth, b: aluminium vs drain depth and c: aluminium vs pH ...... 100 Figure 4.10.Submerged data logger recording for pH and dissolved oxygen for 14/5/93 - 24/5/593 in the transect drain. Readings were taken at a rate of 2/hr...... 105

Figure 5.1. pH along the length of the transect drain analysed between 10/6/93 - 24/8/93. Results shown at distance -50m are representative for sampling done 50m upstream from the floodgate in Broughton Creek...... 122 Figure 5.2 Water quality analysis inside the transect drain floodgate (Fl) between 8/8/93-12/10/93 for; a: Rainfall vs Water depth; b: pH vs Chloride/Sulphate; c: Chloride vs Sulphate; d: Aluminium vs Iron ...... 125 Figure 5.3 Water quality analysis inside the second main drain (F2) between 8/8/93-12/10/93 for; a: Rainfall vs Water depth; b: pH vs Chloride/Sulphate; c: Chloride vs Sulphate; d: Aluminium vs Iron ...... 125

Figure 6.1. pH medians and ranges for drain and Broughton Creek sites (State of Environment Report, 1993, Figure 23) ...... 141 Figure 6.2. Distances in kilometres along Broughton Creek ...... 142 Figure 6.3. Rainfall record for 1991/92/92 from the Berry Sewerage Treatment works, located near the headwaters of Broughton Creek...... 144 Figure 6.4. pH along Broughton Creek after two major rainfall events in 1991 and 1992 ...... 147 Figure 6.5. pH along Broughton Creek as measured from analysis in this thesis on 22/9/93 and 29/9/93, after the major rainfall event which finished on 14/9/93 - see Chapter 4 or Chapter 6 6.4 ...... 147 Figure 6.6. A submerged data logger (SDL) recording showing discharge and drain water depth inside the transect drain floodgate (Fl) between 14/9/93-19/9/93. Readings were taken at a rate of 3/hr...... 150 Figure 6.7. An SDL recording showing pH and dissolved oxygen (from the above recording) ...... 150 Figure 6.8. pH mean and range values immediately inside floodgates along Broughton Creek ...... 153 Figure 6.9. An SDL recording of pH and dissolved oxygen for inside the second floodgate analysed (F2) between 14/9/93-12/10/93. However, for this total length of time three separate recordings were made as indicated on the figure. These were; 14/9/93- 19/9/93, 21/9/93-29/9/93 and 3/10/93-12/10/93. readings were taken at a rate of 3/hr...... 154 Figure 6.10. An SDL recording of pH and dissolved oxygen for outside the second floodgate analysed (F2) between 21/9/93-12/10/93 ...... 154 Figure 6.11. pH taken from the bank of Broughton Creek, 50m upstream and downstream from Fl and F2 (for location see figure 3.3), during outgoing tides ...... 157 Figure 6.12. Water quality analysis along Broughton Creek on 22/9/93 for a: pH; b: Aluminium; c: Iron; d: Chloride vs Sulphate ...... 158 Figure 6.13. Water quality analysis along Broughton Creek on 29/9/93 for a: pH; b: Aluminium; c: Iron; d: Chloride vs Sulphate ...... 158 Figure 6.14. Water quality recovery at 4 sites along Broughton Creek between 14/9/93-12/10/93; a: pH, b: chloride, c: sulphate, d: total iron, e: soluble iron, f: total aluminium and g: soluble aluminium...... 162 LIST OF TABLES

Table 2.1. Radiocarbon dates for samples of unoxidised estuarine sediment and associated shells (Notospisula parva (Lamarck)) in the toposequence in the Shoalhaven River coastal floodplain. Depth of sample 1.2-2.0m (-1.0 to Om AHO) ...... 21

Table 3.1. Soil horizons found following drainage, as assigned for the study area ...... 46 Table 3.2. Soil profile classifications ...... 49 Table 3.2. - Continued ...... 50 Table 3.3. Levee soil results ...... 53 Table 3.4. Levee toe results ...... 55 Table 3.5. Backswamp soil results ...... 57 Table 3.6. Surface and subsurface levee, levee toe and backswamp soil pH ...... 58

Table 4. l. Watertable/water depth summary for all bore/drain site ...... 71 Table 4.2. Summary of pH information from all bores and drain water analysis sites ...... 76 Table 4.3. Mean and standard deviation data from intitial sampling at the three water quality sites in the study area ...... 83 Table 4.4. Water quality summary for the three water quality sites, for periods 1, 2 and 4 (see description above in section 4.4) during the monitoring period ...... 85 Table 4.5. Groundwater (a) and drain water (b) quality comparisons between the study area at Jasper's Brush compared with north coast examples ...... 115

Table 6.1. Critical levels of parameters known to cause effects on aquatic life ...... 135 LIST OF PLATES

Plate 2.1. Aerial view north west from the study area, with the Shoalhaven River in the background. Features shown on the floodplain include Broughton Creek and the main drain (transect drain) around which drain water quality was focussed on in this thesis ...... 18 Plate 2.2. The creek side of a typical floodgate (F2 - Figure 3.3) found along Broughton Creek. This photo was taken on 14/9/93. At the time it was taken, water was being released from this floodgate at 1,250 l/sec ...... 30 Plate 2.3. Immediately inside F2. Floodgates analysed in this thesis (Fl and F2) are built to exactly the same specifications ...... 30

Plate 3.1. Estuarine sediments shown here as part of a spoil heap deposit. These have been oxidised to form an acid sulphate soil and the yellow strands of jarosite can be seen. The ruler is 0.3m long ...... 37 Plate 3.2. Unoxidised pyrite shown here as a core of organic rich soil. This core section was taken at approximately 1.6m depth at Bsl8 (see Figure 3.3 for location) and was 0.2m long ...... 60 Plate 3.3. An acid sulphate soil profile (Bsl2), showing in particular abundant jarosite below 0.7m depth. Groundwater water quality analysis was done from bore Bs12. The core is lm long ...... 60

Plate 4.1. Ochre (green/orange gelatinous material) can be seen here blocking a mole drain, at the road drain water quality sampling site ...... 106 Plate 4.2. Minor flooding on the study area on 14/9/93, taken from 50m south from the transect drain water quality sampling site and looking towards Broughton Creek. All water draing from the spoil heaps and in the drain had a pH of 4.3 ...... 109 Plate 4.3. Shot taken after flooding on 19/9/93. Water was still draining off the spoil heaps and ground surface pH was now 3.2 ...... 109

Plate 5.1. A fence paling can be seen obstructing a floodgate flap, inside the floodgate of the transect drain (Fl). Creek water is entering the drain, thus ameoliorating acid further up the drain ...... 127 Plate 5.2. Blue metal shown on the inside of the transect drain floodgate, due to erosion by acidity, shows the level of water height usually found in the drain. There was no evidence of corrosion on the outside of this floodgate ...... 128 Plate 6.1. Water colouration mid-stream in Broughton Creek on 22/9/93, showing water obviously clearer where pH was lowest (5.1) in the mid-section (6.9km from the mouth) of the creek where acid drinage is compressed (part b). In parts a 0.2km from the mouth (pH 5.8) and c: 1 l.5km from the mouth (pH 6.6) the water appeared dirty ...... 159 Chapter 1: INTRODUCTION

Chapter 1: INTRODUCTION

1.1 Introduction

This study investigates problems associated with acid sulphate soils, of the lower

Shoalhaven River in NSW, about 160km south from Sydney. The floodplains in the lower Shoalhaven, like other coastal plains found along Australia's east coast, are composed of Holocene (last 10,000 years) sediments. In the study area, Holocene sediments are mainly estuarine but may have a thin veneer of alluvium. The estuarine sediments have accumulated behind coastal floodplain barrier systems and their surfaces are very close to modern mean sea level. Along the Shoalhaven River, levees of fluvial sediment have accumulated, but only thin overbank sediments cover estuarine sediments.

Under the influence of a combination of factors, estuarine sediments accumulated and within them, a sulphidic substance iron pyrite (FeS2), developed. When pyrite is brought into contact with air, usually as a result of man-made interference (Melville et al.,

1991), the normally reduced sulphidic sediments oxidise to form sulphates. Upon

oxidation, complex chemical changes take place, generating acidic drainage, often

abnormally high in trace metals such as aluminium, which leaches from the soils and into

estuaries (Dent, 1986). This transformation in the chemical nature of the estuarine

sediments gives rise to acid sulphate soils. Acid sulphate soil by-products are harmful to

aquatic and plant lifeforms and pose damage threats to many engineering structures

(Dent, 1986; Veness, 1990). The Shoalhaven floodplains are the most southern (35°S)

of Australia's twelve floodplains known to have acid sulphate soils (Willett et al.,

l 992a). Acid sulphate soils on floodplains in the lower Shoalhaven were studied by

Norwood (1975) and have been mapped recently by Hazelton (1992) in the Kiama,

1: 100,000 soil landscape sheet, by the Soil Conservation Service.

This study concentrates on the Jasper's Brush area, drained by Broughton Creek, on the

northern side of the Shoalhaven River (Figure 1.1). Acid sulphate soils occur here, and

Norwood' s ( 197 5) work demonstrated that acidity was more severe here than to the Chapter 1: INTRODUCTION 2 .

STUDY SITE ~

PACIFIC , ." Shoalhaven : Heads Nowra >- Crookhaven ~ .-· Heads :::r: CJ :::r: OCEAN

ff] :z0 if a.. JERVIS

0 10km BAY Co 0 0 LO C") 150050'

Figure 1.1. Location of the Jasper's Brush study area. Chapter 1: INTRODUCTION 3 south of the river. Geomorphic and soil characteristics for the study area at Jasper's

Brush and the surrounding landscape were compared with other areas in Australia where acid sulphate soils are known to exist. A detailed monitoring program was developed to analyse the dynamic relationships between rainfall, watertable levels and water quality in a section of the floodplain. Water draining into Broughton Creek was monitored during the second half of the study. A flood event occurred during the monitoring program, after an extended period of dry weather, and this produced an example of pronounced acidity in Broughton Creek. The frequency of monitoring was increased from the time of flooding to account more accurately for the dynamic variations in acid drainage between

the floodplain, drains and Broughton Creek.

This study aimed to investigate acid sulphate soils in the study area, the impacts of acid

drainage on water quality in Broughton ~reek, and possible strategies for acid sulphate

soil management and remediation.

1.2 Acid Sulphate Soils and Formation

"Acid sulphate soils are basically any soils containing appreciable amounts of pyritic

materials, that is FeS2, which have been allowed to oxidise by exposure to air and have

become acid" (Anderson, 1992). While this thesis will describe acid sulphate soils found

in coastal floodplains, since coastal areas are the main regions where acid sulphate soils

are found (Lin and Melville, 1992b; Melville et al., 1993), it is worth noting that acid

sulphate soils or at least acid sulphate drainage can be found in inland areas (Fitzpatrick et

al., 1993; Poelman, 1973; van der Kevie, 1973) or from mine wastes (Miller et al.,

1991; Mulvey, 1990 and 1993).

The origin of pyritic sediments in coastal wetlands can be traced back to the rapid sea

level rise after the Last Glacial (20,000-18,000 years ago) through the Post Glacial

Marine Transgression (14,000-7,000 years ago). As the sea reached close to its present

level, landward progression of marine sediments ceased. Estuarine sediments were

deposited behind coastal sand barriers such as that behind Seven Mile Beach (Figure Chapter 1: INTRODUCTION 4

1.1). The lower Shoalhaven River and Broughton Creek upstream as far as Berry were still tidal. Mangroves line Broughton Creek, and meadows with estuarine palaeochannels remain clearly defined on the floodplain in the study area. Estuarine plants such as mangroves and other halophytes provide large amounts of organic matter,

which accumulate in sediments under low oxygen conditions. Sulphate reducing bacteria

(e.g. Desulpphovibrio sp) flourish under such conditions and they use the organic matter

to reduce the sulphate derived from sea water to form FeS2. which accumulates in

estuarine sediments. This is the source of the sulphidic material required for acid

sulphate soils. Since sea level stabilisation approximately 7 ,000 years ago, the pyritic

sediments in some coastal areas have been buried under alluvial sediments washed down

from valleys and hills higher in the catchment area. Under natural conditions, the pyritic

sediments are usually covered by alluvium and are in areas where the watertable is semi­

permanently above the ground surface, maintaining a reduced environment (Dent, 1986).

Acid sulphate soils form and become capable of producing acid drainage when sediments

containing sufficient amounts of iron pyrite, are oxidised to form sulphuric acid and this

cannot be neutralised by the inherent buffering capacity of the sediment. Clays and shells

are the main neutralising constituents in acid sulphate soils (Dent, 1986; Melville et al.,

1991; 1993 ). There is evidence documenting oxidation of pyritic sediments under natural

conditions due to drought or even dry spells in Australia, given the watertable drops well

below the ground surface (Dent and Pons, 1993; Lin and Melville, 1992b; Melville et al.,

1993). The occurrence of pyritic sediments oxidising to form acid sulphate soils along

the east coast of Australia has vastly increased in the last 50 years due to direct (Lin and

Melville, l 992b) or indirect exposure of pyritic sediments to air by man-made

interference (Melville et al., 1991). Direct exposure of pyritic sediments to air may come

about by physical redeposition of pyrite to the ground surface. Previous causes of direct

exposure to air of pyritic sediments have been from digging for engineering development

and fish ponding (Dent and Pons, 1993 ), and by redeposition at the ground surface for

the purpose of soil fill (Anderson, 1992). However, indirect exposure of pyritic Chapter I: INTRODUCTION 5

sediments to air by drainage to lower the watertable is the most common means of acid

sulphate soil development on Australian coastal floodplains (Dent and Pons, 1993; Lin

and Melville, 1992a; Melville et al., 1993; Willett et al, 1992b ).

Coastal plains underlain by pyritic sediments rarely exceed 3m above Australian Height

Datum high tide level (m AHO) (Dent and Bowman, 1993). As a result of coastal

wetlands being so low in elevation, they have high watertables most of the time, and are

drained very slowly after flooding. In order to make better use of these low lying areas,

which are potentially well suited to agricultural production, many "plains" which are

naturally "wetlands" have been drained (Figure 1.2). Overseas, the production of rice is

common on coastal floodplains affected by acid sulphate soils (Brinkman, 1982; Dent

and Pons, 1993; Kanapathy, 1973). In Australia coastal floodplains are mainly used for

sugar cane production in northern NSW and southern Queensland (Nielsen, 1993). In

northern NSW, in particular, and southern NSW coastal floodplains, including those of

the lower Shoalhaven, are used for pasture to graze cattle for dairy and beef production.

Following drainage, the watertable may drop below pyritic sediments, allowing air to

diffuse through the soil and oxidise the pyrite. Oxidation of pyrite involves a series of

chemical reactions which generate sulphuric acid and leach metals from the soil eg

Aluminium. Overall, the oxidation of pyrite can be represented by the equation:

( 1.1) soild dissolved water colloidal sulphuric acid pyrite oxygen iron III

To prevent saline water moving up the drains, ruining crops or decreasing crop quality,

drains are often blocked by one-way, outward flowing floodgates. If drainage is deep

enough to retain water, the pH of the drainage water may decrease to as low as 2 (Dent

and Pons, 1993) and trace metal concentrations increase as stagnant drainage water

continues to be fed by acid drainage from the adjacent acid sulphate soils. Depending on Chapter 1: INTRODUCTION 6 factors such as the chemical nature of the drained soils and the time between rainfall in which the drains have accumulated acid drainage, a significant rainfall event may discharge water via drains and out over the floodplains in concentrations directly lethal to aquatic lifeforms in receiving waters (Dent, 1986; White et al., 1993). Other less obvious but chronic environmentally degrading effects to aquatic lifeforms (e.g. loss of habitat or growth rate disorders) may also occur as a result of recurrent acid drainage (J.

Sammut, UNSW, pers. comm., 1993). The impact of recurrent acid drainage has likely been underestimated (Leadbitter, 1993a; 1993b; Sammut et al., 1993).

In this thesis, pyritic sediments in their natural, reduced form (Figure 1.2, 1.) will be

referred to as potential acid sulphate soils. Pyritic sediments whether directly or

indirectly oxidised (Figure 1.2, 2.) will be referred to as acid sulphate soils.

1.3 The Significance of Studying Acid Sulphate Soils

Experts both overseas (Brinkman, 1982; Dent, 1986; Dent and Pons, 1993; Pons, 1973)

and in Australia (Bowman, 1993; Dent and Bowman, 1993; Leadbitter, 1993b; Lin and

Melville, 1992b; Stone, 1993; White et al., 1993) recognise a shortage of knowledge on

many features of acid sulphate soils including - distribution, local occurrence, physical

and chemical characteristics, and the environmental problems which they can cause.

Problems are already known to exist, but further research, in particular practical

experimentation, is needed before remediation strategies can be devised. Acid sulphate

soils have reduced the productivity of crops in places (Coulter, 1973; Dent, 1986;

Kanapathy, 1973), including the lower Shoalhaven, but mainly as a loss of quality in

grasses for dairying (P. Morris, farmer, pers. comm., 1993). Acid sulphate soils have

the potential to damage engineering structures. Acid drainage can slowly dissolve

concrete and the reinforcing steel (P. Hazelton, UTS, pers. comm., 1994; van Holst and

Westerveld, 1973), thereby reducing the strength and load bearing capacity of

foundations of high rise buildings, bridges and canals (Anderson, 1992). Overseas, Chapter 1: INTRODUCTION 7 generations of people depending on acid sulphate soils have been impoverished (Dent and Pons, 1993). Families have been economically and socially disadvantaged by developing agriculture on acid sulphate soils (Brinkman, 1982; Brinkman and Pons,

1973).

Development of Acid Sulphate Soils

1. potential acid sulphate soil

watertable close to ground surface river not affected by acid drainage

~~\~~~~~ pyrite layer maintained by reducing conditions below the watertable

2. acid sulphate soil following drainage floodplain drained and becomes more suitable for crop and pasture production air diffuses into the soil air air / I . ' ' .. I y ..!, drain ·--~-...... ,- ~~~~~~~~~--__,..~t;:::::~---...r----~..--

lowered watertable exposes pyrite layer to oxidation, releasing sulphuric acid and mobilising metals such as aluminium and iron into the groundwater ·acidic water with high metal concentrations drains towards the river

Figure 1.2. Development of acid sulphate soils, following oxidation (from artificial drainage) of

potential acid sulphate soils.

In Australia, however, it appears the most significant threat acid sulphate soils poses is

that of environmental degradation to estuarine aquatic lifeforms and to a lesser extent

effects with relation to urbanisation eg bridges and roadworks. "Acidification in

Australian estuaries mainly comes from acid sulphate soils" (Sammut et al., 1993, p.23).

Fish and crustaceans are sensitive indicators of short term environmental change. Acid

drainage may cause rapid change in the physiochemistry of the aquatic environment

causing fish kills, disease, habitat change and other disturbances in fish populations Chapter 1: INTRODUCTION 8

(Sammut et al., 1993). Stemming from damage caused to estuaries by acid sulphate soils, are larger scale problems. Estuaries are a vital (primary) component of the entire oceanographic foodchain (Leadbitter, 1993a). Any lifeform imbalance sustained in an estuary causes a subsequent imbalance in the ecologic food chain, which in turn reduces commercial and recreational rewards (Leadbitter, 1993b). About two thirds of commercially viable fish and shellfish in NSW are dependent on estuaries during some part of their lifecycle (Pollard, 1976). The effects of acidification on Australian estuarine fish species are poorly understood (Sammut et al., 1993), highlighting the need for further research into this topic of such environmental and economic importance.

"The Australian coastline is one of our great natural resources. It is also a region which is undergoing rapid population growth" (White et al., 1993, p.130). Expansion of the coastal population is likely to cause significant degradation of the coastal zone and this will be accentuated in areas of acid sulphate soils (Leadbitter, 1993a). Australia is the

driest of all continents and its estuarine resources are limited (Lin and Melville, 1992a).

Given the benefits people derive from estuaries, the focus should be on ensuring

harmony between the multiple benefits rather than simply permitting multiple, competing

uses (Leadbitter, 1993a). Some areas in which acid sulphate soils occur and where

drainage has been developed are of low production and it may be feasible to return them

to the wetlands they once were. However, many of the areas are either valuable and

highly productive, or have been so modified by the drainage and flood mitigation that

restoration is difficult to justify economically (Anderson, 1992). Overseas studies have

shown some acid sulphate soils can be developed sustainably (Dent and Pons, 1993;

Melville et al., 1993), and innovative management plans are required to address this issue

(Anderson, 1992; Dent and Bowman, 1993). Chapter 1: INTRODUCTION 9

1.4 History and Extent of Acid Sulphate Soils Overseas and in Australia

Acid sulphate soils were first observed when the Dutch drained inland polders in the 17th century. Since then large drainage projects have been implemented both in Holland and more recently in tropical coastal plains. In these areas acid drainage has caused recurring damage to fisheries over many years (Dent and Pons, 1993). The world wide extent of acid sulphate soils has been estimated as approximately 12M ha, with potential acid sulphate soils covering a possible world wide extent of lOOM ha (Dent, 1986).

Very little is known about the history and current extent of acid sulphate soils in

Australia. Drainage networks were formed in the Macleay valley during the 1880's, but the current extensive drainage network in the Macleay valley was developed after 1949, after extensive flooding was experienced (Leadbitter, 1993b). The acid sulphate soils which developed were described by Walker ( 1972), in the first major study of these soils in Australia.

Although the extent of acid sulphate/potential acid sulphate soils in Australia is unknown

(Melville et al., 1993), Galloway (1982) estimates that 1.15M ha of mangroves do exist

in Australia, and all of this may have potential acid sulphate soils (Lin and Melville,

1992a).

1.5 Identification of Acid Sulphate Soils in the Lower Shoalhaven

Investigation of the soils of the lower Shoalhaven floodplain found a close relationship

between geomorphic landsurface and subsurface characteristics and the intensity of

acidity (Norwood, 1975; Willett and Walker, 1982). This was in accord with that

demonstrated for similar soil types described for the Macleay River valley by Walker

( 1972). Considerable differences were found to exist between floodplains to the north

and south of the Shoalhaven River. Acid sulphate soil profile development was most

pronounced, and soil and water were more acidic and more saline on floodplains to the

north of the Shoalhaven River (the study area for this thesis). Chapter 1: INTRODUCTION 1 0

The ecological effects of the development of acid sulphate soils in the area remained unrecognised for some time after these early studies. Acid drainage into Broughton

Creek, the largest tributary of the lower Shoalhaven was first brought to the attention of

the State Pollution Control Commission (SPCC), now (Environment Protection

Authority, EPA) and Shoalhaven City Council after drought breaking heavy rains in

June, 1991. No fish or prawns were observed in the creek for a number of weeks later.

Abnormally clear water observed shortly after the floodwater had started to subside, but

its cause was not known. pH in Broughton Creek at the time was as low as 3.2. A

similar but smaller scale episode in February, 1992 again caused fish to disappear from

the creek for two weeks. Again pH was low, but not as low as was the case in 1991

(Raffell, 1992). Acid drainage was identified as the probable cause and this was

confirmed with ensuing monitoring of drainage canals, showing extreme acidity and

extreme aluminium concentrations. Water in Broughton Creek was shown to be

consistently more acidic and higher in aluminium than the Shoalhaven River (Cumming,

1992; Raffell, 1992; State of Environment Report, 1993). Local fishermen became

interested in developments and suggested that Broughton Creek was increasingly under

the influence of acid drainage, and they identified decreasing fish and prawn stocks and

increasing incidence of fish diseases. It was also pointed out on occasions when the

creek water became surprisingly clear after heavy rain, nets had become full of dying or

dead worms and some dead prawns (C. Weir, fisherman, pers. comm., 1992 - cited

from Cummings, 1992).

1.6 Significance of this Project

A great number of coastal floodplains in Australia have been drained to enhance

productivity of these areas, with acid sulphate soils initially assumed as having high

fertility (Dent and Pons, 1993). These developments took place with little or no warning

of the environmental degradation and engineering problems which were to follow (Stone,

1993). Available knowledge about Australian acid sulphate/potential acid sulphate soils Chapter 1: INTRODUCTION 1 1 and their effects have grown rapidly in the past six years (Leadbitter, 1993a). The current Australian literature deals mainly with identification and description of acid sulphate/potential acid sulphate soils and their effects (Anderson, 1992; Creagh, 1991/92;

1993; Easton, 1989; Environews, 1993; Green, 1993; Melville et al., 1993; Lines-Kelly,

1992; Veness, 1990). Guidelines describing ways in which to positively identify acid sulphate/potential acid sulphate soils and offering basis management options have been drawn up (Acid Sulphate Soils Circular, 1993; Dent, 1986; Mulvey, 1992; Naylor, 1994;

Tweed Shire Council, 1992). However, Australian literature on acid sulphate/potential acid sulphate soils has lacked detailed experimentation in monitoring the dynamics of acid sulphate soils and acid drainage (Dent and Bowman, 1993; White et al., 1993), in proven remediation strategies and in monitoring of any changes to acid drainage (Bowman,

1993; Leadbitter, 1993a; Stone, 1993). Where the ecological impacts of acid drainage were unacceptable, remediation strategies were required. Leadbitter (1993a), speaking of acid sulphate soils in general, not only identified the desperate need for rehabilitation to

become the central theme of estuarine management, but also called for immediate

rehabilitation of the worst affected areas. The concentration of acid drainage at Jasper's

Brush and the impacts of acid drainage from the drained floodplain area on Broughton

Creek are shown to be severe in this thesis. Drainage remediation is likely to be the key

to sustainable management of acid sulphate soils. The best other option to manage acid

sulphate soils is liming (Dent, 1986). Liming has been extensively trialed overseas

(Dent, 1986; Kanapathy, 1973) and in Australia, but has been found to compensate

insufficiently for acid drainage and to be economically unviable (Dent and Pons, 1993).

This project was designed to establish a detailed monitoring program analysing the

Telationships between rainfall, groundwater/drain water levels and water quality (acid

.drainage) across the floodplain and selected drains. Results were to be correlated after

five months to develop remediation designs for the drains. Remediation was to take

place to all drains in the study area, with the monitoring program to continue for a further

five months to document any changes in acid drainage. Chapter l: INTRODUCTION l 2

The study area was owned by the Australian Army and used as a landing ground for parachute exercises. Prior monitoring by Shoalhaven City Council had identified the water quality in drains in the study area as amongst the worst of any area on the surrounding floodplains (P. Jamieson, Shoalhaven City Council, pers. comm., 1993).

The army had plans to modify the drains from the existing deep trench drains to shallow swale drains for safety reasons. This modification should have raised the watertable

(back) closer to the ground surface, and thus should have ameliorated the acid drainage.

However, four months into the monitoring program the Army decided not to go ahead with drainage remediation, due to financial reasons. Hence, the emphasis of the thesis changed from a 'before and after' study, to a more wide ranging study of the flow of acid drainage from the soils to Broughton Creek.

The initial monitoring was continued for 8 successive months, making this monitoring program one of the longest of its type in Australia. Detailed soil surveying of the floodplain was extended, and monitoring of more drains was begun. Particular emphasis was placed on movement of acid drainage from the floodplain into drains and from the drains into Broughton Creek.

Dry weather was experienced during the majority of the monitoring program from

February to September, 1993. In September 1993, a minor flood event occurred (the recurrence interval of this event is discussed in Chapter 6) . The frequency of monitoring on the study area was increased during the flood event, and water quality in Broughton

Creek was monitored also. This allowed assessment of a severe impact of acid drainage on Broughton Creek. Earlier monitoring also demonstrated lower level but recurrent

leakage of acid waters into the creek.

Findings of water quality in Broughton Creek, which was likely affected by recurrent

acid drainage (e.g. during a 2 year monitoring period pH was shown to be more acidic in

Broughton Creek, especially in the central part of the creek where most of the acid Chapter 1: INTRODUCTION l 3 drainage enters the creek, compared with freshwater creeks flowing into the floodplain) and by severe acid drainage after flooding (e.g. lowered pH and elevated alumnium levels in creek waters), allow for the identification of some of the pressures which aquatic lifeforms are faced with in Broughton Creek (State of Environment Report,

1993). This information relating to this South Coast estuary has further, more-wide spread implications for understanding ecosystems elsewhere along the east Coast of

Australia. Many species of fish often found in estuaries (e.g. silver bream), are believed to do most of their breeding in southern estuaries. For some species it is possible that the adult population in any given estuary is more a reflection of the breeding estuary to the south (e.g. Shoalhaven River/Broughton Creek) and not the estuary in which they are caught (Leadbitter, 1993a). The Shoalhaven River, which Broughton Creekjoins, is one of the largest southern breeding grounds of estuarine fish (D. Leadbitter, NSW

Fisheries, pers. comm., 1994).

Professional fishermen have reported significantly reduced fish and prawn stocks in

Broughton Creek, which they believe is due to acid drainage. Broughton Creek as a fishery produced 20 tonnes of prawns during the 1990/91 financial year, which was a relatively dry period. During 1991/92 less than 12kg of prawns were harvested in a live

state, however, a number of tonnes of dead or decaying prawns were brought up (C.

Weir, G. Usher - local fishermen, pers. comm., 1993). No commercial fish statistics are

available for Broughton Creek; however, they are available for the Shoalhaven River

between the 1984-1993 fiscal years (NSW Fisheries data, 1994 ). This data included fish catch statistics for 63 species of fined fish, 5 species of molluscs and 7 species of crustaceans. There was inconclusive evidence to confirm acid drainage was responsible

for influencing catches because the Shoalhaven River is subject to other pollutant sources

and fishing intensity varies in different years. However, it is the firm belief of

professional fishermen that aquatic life in Broughton Creek has been affected by acid

drainage. Broughton Creek is the major tributary of the Shoalhaven River and

consequently plays an important role in the river's ecosystem. The Shoalhaven River Chapter 1: INTRODUCTION 14 forms the base for an active fishing industry and rapidly growing tourism industry (P.

Dalmazzo, NSW Fisheries, pers. comm., 1993), thus the relatively newly recognised

acid drainage problem is a major threat to the estuarine ecosystem there.

Although remediation of drains in the study area did not proceed during this project, it is

still planned in the future. This study thus provides important baseline information for

designing remediation works and for assessing their effectiveness.

1.7 Aims

The project aimed to:

1 . Investigate the extent and characteristics of acid sulphate soils in the study area.

2. Investigate the relationship between rainfall, fluctuating watertables and the

quality of groundwater.

3. Provide information on the conditions required to produce acid drainage from the

study area into the drains and from the drains into receiving waters of Broughton

Creek.

4. Characterise the resultant variations in water quality in Broughton Creek.

5. Provide management options with the aim of reducing acid drainage flow

discharges into Broughton Creek.

The procedures used were:

1. Aerial photo mapping to develop a geomorphic understanding for the floodplains

and drainage pattern. Chapter 1: INTRODUCTION 1 5

2. Soil mapping to identify the distribution of acid sulphate soils, and of any

overlying alluvium.

3. Investigation of the texture, pH and total potential acidity of sediments from the

surface to below the watertable where largely unaltered estuarine sediment is

found.

4. Monitoring of variations in watertable levels and water chemistry in the soils, and

in man-made drains crossing the study area.

5. Monitoring of water quality for two drains crossing the site. Grab sampling was

used to collect samples to determine pH, aluminium, iron, sulphate and chloride.

Yeo-Kal Submersible Data Loggers (SDL) were used when available for remote

logging of pH, dissolved oxygen, depth, temperature and salinity for periods of

up to three weeks (2-4 samples/hr).

6. For selected sites, monitoring ground and surface water quality and determining

concentrations of metals which were reported to be elevated in Broughton Creek

sediments (by a 1990 SPCC Environmental Survey of the lower Shoalhaven

River).

7. Analysis of the relationships between rainfall, watertable levels, and water quality

in soil-water and in the drains which discharge into Broughton Creek.

8. Additional monitoring, focussing on acidity and metal concentrations, of water

quality of Broughton Creek during/after the flood event.

The project thus provides an assessment of the variations in water quality both within the

soils of the plains and through the drains into Broughton Creek, during a prolonged dry Chapter 1: INTRODUCTION 1 6 period and after heavy rainfall. An understanding of these spatial and rainfall-related variations is fundamental to the development of management and remediation strategies and to the prediction of likely ecological impacts within the estuary.

No other documented Australian study on acid sulphate soils caused by artificial drainage is known to include field relationships relating to the above aims, with such an emphasis on water quality results, in as much detail and or for as long a period (although monitoring work outlined in White et al. (1993) from the Tweed area had been going since 1991) as in this study. Willett and Bowman (1990) determined the extent of acid sulphate conditions and assessed the effects of the drains on the development of acid sulphate soils. White et al. (1993) describe preliminary results of a long term program similar to this study in that acid drainage from soil into drains and drains into an estuary was monitored, but these authors concentrate on hydrological characteristics of acid sulphate soils. Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA I 7

Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA

2.1 Introduction

Three main forms of landscapes have been identified in the region; low hillslopes, a coastal sand barrier and coastal floodplains (Wright, 1970). Low hillslopes form the mildly undulating terrain surrounding the river floodplain to the north, west and south.

The hillslopes are cut in strata of Permian age. These are the siltstones, shales and sandstones of the Berry Formation, within the Shoalhaven Group (Wollongong,

1:250,000 Geological sheet, 1966, SI 56-9). To the east, a late Quaternary (Holocene) sand barrier separate the floodplain from the sea. An extensive coastal floodplain exists on both the northern and southern sides of the Shoalhaven River (Figure 1.1). The

Berry Siltstone and underlying Nowra Sandstone probably form the basement on which most of the unconsolidated deposits of the floodplain was deposited (Gutteridge et al.,

1993). Cumming (1992) estimates the lower Shoalhaven River floodplain east of Nowra has 20,000 ha of potential acid sulphate soils.

The study site is located at Jasper's Brush, on the part of the floodplain bounded to the south by the Shoalhaven River and to the east by Broughton Creek (Figure 1.1). The catchment area of Broughton Creek is 183.85km2 (M. Elis, PWD, pers. comm., 1994).

The main study site located on Plate 2.1 and Figure 2.3 is a 203ha property owned by the

Australian Army.

The lower Shoalhaven floodplains, including those surrounding Broughton Creek have developed by estuarine, then alluvial, sedimentation. Their geomorphic character had recently been modified by artificial drainage networks. Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 1 8

Plate 2.1. Aerial view north west from the study area, with the Shoalhaven River in the background.

Features shown on the floodplain include Broughton Creek and the main drain (transect drain) around which drain water quality was focussed on in this thesis.

2.2 Deposition and Accumulation Required for Acid Sulphate Soil

Development

The physiography of the floodplains of the Shoalhaven where acid sulphate soil are found is similar to that of other floodplains along the east coast of Australia, for example, those of the Clarence (Lin and Melville, 1993a and b; Walker, 1960) and the Macleay

(Walker, 1972; Willett and Bowman, 1990). Under natural conditions these floodplains comprise bare tidal flats, marshes with herbaceous vegetation and mangrove swamps along tidal creeks. The lowest parts of such systems are inundated most of the time and have permanently reduc~d sediments, whereas the highest parts have been silted up to spring tide levels and have a predominantly aerated surface soil (Pons et al., 1982). The evolutionary history of the Shoalhaven River, according to Roy (1984), belongs to the Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA I 9

"barrier estuary" system. The Tweed, Richmond, Clarence and Macleay rivers have a similar history.

Barrier estuaries experience complex changes in shoreline morphology during infilling

(Roy, 1984). In youthful stages their shorelines are often rocky and highly irregular

(Figure 2. la) e.g. Crookhaven Heads. Crookhaven Heads remains as an example of such a rocky shoreline. The coastal sand barrier in this case, the barrier behind Seven

Mile Beach blocked off flow from coastal streams, causing sediment to be deposited behind it. As the estuary infills and shallows, smoother sedimentary shorelines initially develop (Figure 2.1 b). Later these become highly irregular as lo bate deltas with bifurcating distributary channels and middle ground shoals prograde and cut off sub­ embayments (Figure 2. lc ). Final stages of infilling are characterised by sinuous channels with smooth levee banks (Figure 2. ld) e.g. Shoalhaven delta.

Times of barrier estuary infilling stages can be identified. Infilling began with the Post

Glacial Marine Transgression (PGMT), 12,000 years ago, when sea levels were believed to be 30-40m below m AHO. During the Transgression there was a rapid landward movement of marine sediments with rising sea levels, resulting in the drowning of prior river valleys by 7,000 years ago (Langford-Smith and Thom, 1969; Roy et al., 1980).

The development of estuarine floodplains resulting from infilling began when sea levels

stabilised (Dent, 1986). While it is widely believed that sea level stabilised to the present

position by 6,000-6,500 years ago (Belperio, 1979; Chappell and Thom, 1986; Melville,

1984; Shepard, 1974), when marine transgression was believed to have ceased (Thom

and Chappell, 1975), there is strong evidence to suggest otherwise (Young et al., 1993).

Young et al. (1993), drawing on numerous examples, claim that sea level pas!sed the present level by 7 ,000 years ago and was significantly higher for much of the Holocene

along the central and southern New South Wales coasts. Only two radiocarbon dates for

the Shoalhaven floodplain sediments were available; these are shown in Table 2.1. Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 20

TIDES ATTENUATED ' ' OCEAN ·------l::-----:·--1------, --- L TIDE : -I -- 1 I I I I I I I

.. ------·---rI ------~---

::::.-_- ~~ ~ =~ ------~ ~I~l I I flood plain I I

coastal barrier n washover, § estuarine mud fluvial sand, flood plain silts, sand LJ tidal delta sand [[IlJ] muddy sand swamp deposits

Figure 2.1. Stages of infilling in the evolution of a barrier estuary (source: Thom et al., 1981) Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 2 1

Sample Laboratory No. Radio.carbon Age Unoxidised estuarine sediments SUA-1311 4280±110 BP Shells SUA-1312 3800±100 BP

Table 2.1. Radiocarbon dates for samples of unoxidised estuarine sediment and associated shells

(Notospisula parva (Lamarck)) in the toposequence in the Shoalhaven River coastal floodplain. Depth of sample 1.2-2.0m (-1.0 to Om AHO). (Source: Willett and Walker, 1982, p.287).

Walker (1970) obtained radiocarbon dates for the Macleay River coastal floodplain. A wood fragment in the upper part of the mottled horizon radiocarbon dated at 3,295±95 years ago and another wood fragment at a depth of 2.8m into unoxidised estuarine sediments radiocarbon dated at 8,530±200 years ago. Dates at around 4,000 years ago for the Shoalhaven floodplain in Table 2.1 are consistent with the age of comparable sediments in the Macleay River. Although both sets of dates are broadly in accord with the proposal of Thom and Chappell (1975), that sea level rise ceased by 6,000 years ago, the effects of marine transgression in the lower Shoalhaven toposequence appear to have continued to 4,000 years ago and even later (Willett and Walker, 1982), strengthening

Young's et al. (1993) argument that sea levels along the coast of New South Wales did not stabilise until significantly later than 6,000 years ago.

Sedimentation in the Shoalhaven proto-estuary was rapid at 5mm per year (Roy, 1984), forming an extensive, subaqueous mud basin -30m thick (Figure 2.2 - Thom et al.,

1981), rich in Notospisular bivalves. In a landward direction the muds interdigitate with fluvial silts and sands, and in a seawards direction with tidal deltaic sand bodies which form flood tide depos.its within the channel of the river mouth (Thom et al., 1981). The

Shoalhaven barrier estuary system is at a mature stage of development as infilling has virtually ceased and river sand has been "leaking" out of the estuary and accreting on the beachface (Wright, 1970). The size of the mature floodplains against the size of the

Shoalhaven River are small compared to the larger, mature floodplains of the Tweed, Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 22

Richmond, Clarence and Macleay Rivers (Roy, 1984). Therefore, little is known about

the depositional history of the lower Shoalhaven. Further discussion is given to this area

in Chapter 3 (section 3.10).

w E

Comerong Island 125 Metres 126 0

10

20

30 ...... • • • .G' • • ,,,,,...... ~ • -,. 0 @ • ~ • @ G' / ""- • "t- • • <.? • G • • // c;g • e • e./ 40 -..-...-._:::-.....e. ---.! --~-..L.-~ __ ..,,,,,,,

0 2 3 Kilometres

Pro-delta mud ~ Beach and nearshote Fluvial sand t-=-:::::--=? I • • I t- -- ;:::! With shell ~ Shelly sand - transgressive 1:-:-1 Fluvial sand Washover sand - tegressive ~withshell HH:u:rn Beach ridge sand ~ ~ Beach and nearshote Levee. silt :>Ii Washover sand - transgressive k;i)!:}~\!i'.@ M ~ shelly sand - regressive le~ J

Figure 2.2. Shoalhaven delta section showing stratigraphy and location of boreholes and C14 dates

(source: Roy, 1984, p.112).

The tidal range of youthful barrier estuaries is weak, but it increases until a strong tidal

regime is achieved in mature systems. The tidal prism (water area x tidal range) in the

estuary basin is directly related to the tidal exchange in the entrance channel. However,

the former may be a passive response to the latter. Thus the reduction in water area that

accqmpanies estuary infilling could cause the observed increase in tidal range without

inducing significant alterations of the tidal discharge through the entrance channel (Roy,

1984). The following tidal prisms represent the volume of water between high and low

water level up Broughton Creek in November, 1989 (T. Roper, PWD, pers. comm.,

1993): Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 23

- Spring 0.99 x 106 m3

- Mean 0.79 x 106 m3

- Neap 0.71 x 106 m3

Stratified salinity conditions occur m the Shoalhaven River due to salt wedge

development (Wright, 1977). This point is discussed in Chapter 6 in relation to acid

drainage in Broughton Creek after flooding.

The tidal influence is both significant and relatively consistent both along the Shoalhaven

River (at least up to the Nowra Bridge - 19.6km from the mouth) and almost along the

entire length of Broughton Creek (T. Roper, PWD, pers. comm., 1993). Limited data

was available to demonstrate this. However, tidal data taken by the PWD between

21/12/91-30/12/91 was used to estimate the average tidal range for the Shoalhaven River

and Broughton Creek between the above dates. The average tidal range estimated for

1.2km upstream from Crookhaven Heads was 0.97m and there was only a small

difference 19.6km upsteam at the Nowra Bridge with a value of 0.86m.

The estimated tidal range immediately at the mouth of Broughton Creek was estimated at

0.85m, 4.4km upstream - 0.82m, and 7 .9km upstream where the furthest testing was

done the estimated tidal range was 0.79m. Water quality analysis in Chapter 6 was

performed in the first 11.5km from the mouth of Broughton Creek, whose total length is

-14km. The tidal range, 11.5km upstream from the mouth was observed to be

significant and is probably about 0.75m.

2.3 Drainage Network

A small number of shallow drains were dug on Berry's property near Mount Coolangatta

in 1829, creating the first major form of artificial drainage in the lower Shoalhaven

(Bayley, 1975). The first form of major artificial drainage in the lower Shoalhaven was

the construction of Berry's canal in 1840 which allowed navigation between the

Shoalhaven and Crookhaven Rivers (Cumming, 1992). Berry's canal was the first cause

of an observed lowering of the watertable in the lower Shoalhaven. This was shown Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 24 from the 1860 and 1870 great floods when flood waters lowered more quickly than in the past (Bayley, 1975).

Floodplains in the lower Shoalhaven were initially drained to increase the amount of useable prime dairy land. During the 1890's the introduction of paspalum grass for cattle feed on 16ha at Berry was found to significantly increase cream production. More land, preferably flat, for which paspalum grass could be sown into was immediately sought after. By 1901 32km2 of floodplains surrounding Broughton Creek were drained with

210km of drains fitted with floodgates and walls. The land was thereafter sold (Bayley,

197 5) with the reclaimation producing good dairy production and good maize yields

(Barton, 1980).

Aerial photo coverage (photo details are given in Appendix A) of the Broughton Creek floodplains from 1949-1993 show some evidence of upgrading (spoil heaps produced from upgrades are shown as bare, bright areas on the aerial photos) of the drains themselves during that period of 44 years. However, it is known that major drainage upgrades were done in the period (J. Downey, Shoalhaven City Council, pers. comm.,

1994). The present drainage network was virtually in place in its entirety by 1949, including all of the drains on and leading off the study area. During 1965-1972 all of the existing drains were upgraded, by the drains being widened and deepened, with a few additional drains being dug as well. All drains leading into Broughton Creek prior to

1965 had already been fitted with floodgates. All floodgates along the Creek were upgraded during 1965-1972. No floodgate upgrades were carried out after 1972 (J.

Downey, Shoalhaven City Council, pers. comm., 1994). No upgrading of the drainage network was apparent from the aerial photos between 1981-1986, and only minor upgrading was done to the entire drainage network between 1986-1993. One noteworthy upgrade during this latter period was, however, made to a large section of the main drain which forms the focus for later discussion throughout this thesis. Re-excavation, with spoil deposited along the drain, took place midway through 1990 (Maj. D. Gallagher, Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 25

Aust. Army, pers, comm., 1994 ); one of the water sampling sites for this project was adjacent to this section.

The present drainage network pattern for floodplains surrounding Broughton Creek is shown in Figure 2.3. The Figure 2.3 base map, showing the area of land prone to inundation and the details of the creek and road names were taken from the Berry

1 :25,000 topographic sheet ( 1986), with some reference to 1:25,000 aerial photos taken on the 22/2/93. Figure 2.3 shows two points of significance to the prediction of the impact of acid sulphate soils on these floodplains. Firstly, the extensive distribution of the drains over nearly all the floodplain (shown as land prone to inundation) indicates extensive lowering of the watertable. A drainage density of ..... 5.75km/km2 is shown in

Figure 2.3; since 230km of drains are found on the 40km2 of land prone to inundation on the northern side of the Shoalhaven River. Secondly, of the 19 drains draining into

Broughton Creek, only one was not blocked by a floodgate, suggesting a very large portion of the acid drainage within channels on the floodplain was stored in the flood mitigation drains.

To gain a visual representation of features such as the length of spoil heaps located along drains a geometrically correct map (Figure 2.4) of the drainage network covering the study area and all drains leading off it was developed using a TOPCON aerial plotter and the I :25000, 22/2/93 aerial photos.

Spoil heaps contain pyritic sediments deposited adjacent to drains from which they were dug. The fact that they bring potentially acidic material directly to the surface where extreme oxidation can take place (with continual wetting and drying), and that after rain their leachate drained straight into drains or Broughton Creek, increased the acid sulphate hazard of the area. The I :50,000, 1970 aerial photos (before completion of major drainage upgrades in 1972) showed spoil heaps along approximately 70% of all drains. Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 26

···· ··· ·. . ... ·. . - area prone to inundation

" - - ... - palaeochannels

• - floodgates

- drains

- study area

- roads

··· ······ .. ··· ...... ·

·· ...... ·

N i 0 1km .·::· ·· ·· .. :

·. ... ·· ....:

Figure 2.3. The Shoalhaven floodplain showing the study area, drainage density and floodgates along

Broughton Creek. Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 27

'----.. - palaeochannels ... - spoil heaps - -drains

0 11<.m

Figure 2.4. Geometrically correct map of a section of the floodplain, highlighting areas of spoil heaps

as shown in the 1993 aerial photos - see Appendix A for photo details.

Spoil heaps were mostly deposited along one side of the drains. Existence of spoil heaps

was most obvious, showing up as bright bare areas on the landscape. With time spoil

heaps are eventua,lly covered by carpet grass (Axonopus afinus) and:bull rush, making

detection of their existence from aerial photos more difficult. Spoil heaps were far less

obvious on the 1993 aerial photos than the photos taken in 1970; and of the spoil heaps

detectable in the 1993 photos, approximately only 30% were bare or free of vegetation

cover. The average size of spoil heaps was 1.5m high x 3m wide. The approximate Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 28 volume of bare spoil heap area estimated from Figure 2.4 was 2,763m3Jkm2. However, the true value is undoubtably higher since some spoil heaps could not be detected.

Figure 2.3 also shows that mapping from aerial photos highlights the inaccuracies of the drainage network shown on the topographic map, as reproduced in Figure 2.3. Some

5km of drains are distinctly seen on the aerial photos, and mapped in Figure 2.4, which are not shown on the topographic map. This shows the worth of geometrically correct maps if management practices were to be applied to an area.

The drainage network is the largest environmental threat in the area by developing an acid sulphate hazard through oxidation of the soil, then transporting acid sulphate products to

Broughton Creek. The drainage network mainly consists of deep, trench, flood mitigation drains (main drains) and was completed with a series of smaller feeder drains

(mole drains). Plate 2.1 shows a section of the floodplain which includes the study area.

The main drains were commonly 3.5m wide x 2.5m deep. Dimensions of the mole drains varied considerably as they were often natural shallow channels which have been modified. These smaller drains are rarely more than l .5m wide x 2m deep. The depth of the larger drains make floodplains surrounding Broughton Creek one of the most deeply drained areas along Australia's east coast where ASS are found. The majority of

Australian coastal floodplains are drained where the majority of the drains rarely exceeding lm in depth (M. Melville, UNSW, pers. comm., 1994), yet still experience severe and well documented acid sulphate problems. Tuckean Swamp on the Richmond

River is drained by a small number of major, 5-lOm wide x 3m deep drains, supplemented with a large number of small drains with depths

Melville, UNSW, pers. comm., 1994). Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 29

The lower Macleay has been extensively drained, with 40km of excavated drains dug.

Drainage in this area was designed to drain a two and a half year flood to 0.3-0.6m AHD within 6-10 days. To achieve this, most drains were constructed to an invert level of

-0.6m AHO and terminate where the natural surface level of the back swamp (lowest area) reduces to a level of O. lm AHD. All drains were blocked by floodgates, This extent of drainage in relation to m AHD in the lower Macleay, implemented in the

1950's, has promoted the development of severe acid sulphate soils and consequent acid drainage has caused major fish kills (NSW Agriculture and Fisheries, 1989). The extent of drainage in relation to m AHO of floodplains surrounding Broughton Creek is far greater than the lower Macleay. The larger flood mitigation drains of the Broughton

Creek area have commonly been dug to an invert level of -1.2m AHD in back swamp areas.

All floodgates blocking the drains flowing into Broughton Creek are made from concrete.

The gates are located on the outside of the structures and are made from vertically suspended steel plates, lined on the inside with thick rubber (Plate 2.2). The inside of the floodgates consist of 1-4 chambers, each with dimensions 2m high x 2m wide x lOm long. The two floodgates later studied in detail have 3 chambers (Plate 2.3).

The creation of an artificial drainage network on the floodplain near Broughton Creek has altered the wetland character of the area. Where natural vegetation survives, this change to a drier environment may change the character of vegetation found on such areas (Lin and Melville, 1992a). However, changes of drainage patterns in association with watertable positions alone do not always promote changes in vegetation species and growth rates. For example, when an area is drained, salts may rise to the ground surface and accumulate in concentrations too high for continued existence or normal growth rates

(M. Melville, UNSW, pers. comm., 1994). Areas affected by acid sulphate soils typically have sparse vegetation (Lin and Melville, 1992a). On the Shoalhaven Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 30

Plate 2.2. The creek side of a typical floodgate (F2 - Figure 3.3) found along Broughton Creek. This photo was taken on 14/9/93. At the time it was taken, water was being released from this floodgate at

1,250 l/sec.

Plate 2.3. Immediately inside F2. Floodgates analysed in this thesis (Fl and F2) are built to exactly the same specifications. Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 3 1 floodplain, drainage was carried out to improve pasture land and in fact very little natural vegetation remains except along the major creek banks.

Two species of mangroves grow along Broughton Creek. The larger of the two species, the white or grey mangrove (Avicennia marina) is the most widespread mangrove in

Australia; the river mangrove (Aegiceras corniculatum) is smaller and close to its

southern limit on the east coast (Galloway, 1982). Avicennia is the most common of the

two species and is found up to 7km upstream in Broughton Creek (Gutteridge, 1993).

Two introduced grasses, kikuyu (Penn.isetum clandestin.um) and carpet grass (Axonopus

affinus) dominate the vegetation cover over the floodplain. Some isolated Swamp

Sheoak (Casuarina glauca) also exist on the floodplain, in isolated clumps or scattered

along drains or channels. In the drains, a sedge (Eleocharis equisetina) is found and

particularly thrives in the drains containing acidic water. Paspalum grass, as has already

been discussed in this chapter was introduced on the floodplains during the 1890's. This

appears to be a good example of a change in vegetation species after strong development

of acid sulphate soils. All paspalum had disappeared from the floodplains during 1976-

77 (D. Failes, local farmer, pers. comm., 1993), around 5 years after major drainage

upgrades were made.

2.4 Climate

Historical rainfall records from Berry Sewerage Treatment Plant and the Bureau of

Meteorology station (No. 068048) at Nowra Sewerage Treatment Plant indicate that the

rainfall is spread throughout the year (Figure 2.5). The driest period at both Berry and

Nowra is from August to November, yet 25% of the annual rainfall is received in this 4

month period. January to June is the wettest period at both centres when approximately

60% of the annual rainfall is received. In Chapters 4 and 6, the spread of rainfall

throughout the year is shown to be important in explaining the severity of the Jasper's

Brush acid drainage problem. Mean annual rainfall for the floodplain, varies from north

to south. At Berry, in Broughton Creek's catchment area, at the northern end of the Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 32 floodplain the mean annual rainfall is 1,416mm, but at Nowra it was only 1,058mm

(Gutteridge et. al., 1993). Although rainfall is not strongly seasonal, fluctuations in rainfall do affect the watertable position, and the soil profiles are subject to cycles of wetting and drying. This affects the surface and, because of the deep drains, also the subsoil (Norwood, 1975).

-E -E CtS -c:: '(ij a: >. 100 ..c:...... c:: 0 ~ c:: CtS Q) ~

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Figure 2.5. Mean monthly rainfall for Berry (Berry Sewerage Treatment Plant) and Nowra (Nowra

Sewerage Treatment Plant - Bureau of Meteorology Station No. 068048. For 1886-1991)

The rainfall record for the Jasper's Brush study area is not likely to be accurately

represented by either of the above records. The study area is at least lOkm from both

Berry and Nowra, and is at a lower elevation than either of these stations. An accurate

rainfall record is essential for this study since a major focus is to understand the

dynamics between rainfall and watertable levels. Therefore, daily rainfall records

recorded by Ken Jones, a farmer whose property is located approximately l.2km north­

east from the study site (Figure 3.3), were used as the rainfall data in relation to the field monitoring results here. Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 33

The average monthly temperatures recorded at the Nowra RAN Air Station (No. 608048) show an obvious summer peak with February temperatures the highest (22°C) for the year and a winter drop in temperatures to 13°C between July and September as shown in

Figure 2.6 (Gutteridge et al., 1993).

24

~ Mean temperature 22 I 0 0 ,._Cl) 20 :::s rn...... Cl) c.. 18 E Cl) c: 16 -ca Cl) ~ 14

12--...... ---.-----~--~------.-----~--~---~----~--~ Jan Feb Mar Apr May Jun Ju I Aug Sep Oct Nov Dec

Month

Figure 2.6: Nowra mean temperatures (Station 608048)

90

~ Mean evaporation 'I -E 80 E -c: 0 70 -...... ca 0 c.. ca 60 >Cl) c: ca Cl) ~ : 50

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Figure 2. 7. Nowra mean evaporation levels (Station 608048) Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 34

Mean evaporation levels (Figure 2.7) overall show a late summer/early autumn elevation

(>80mm per month) and late winter/early spring depression (>50mm per month).

2.5 Floods

The first attempts to develop a village at Berry from 1868 were seen to be impractible after flooding resulted in 1870 and 1873. The township was thereafter established in its present, more elevated position. The 1870 flood also caused destruction of a settlement at Terara, on the southern side of the Shoalhaven River (Bayley, 1975). Along

Broughton Creek, the elevation of the ground surface drops moving away from the levees until rising again near the colluvial hillslopes, thus naturally trapping floodwater.

Extended duration of flooding and inparticular flood peaks are accentuated as tides can

hold back water in Shoalhaven River, not allowing flood water to escape from

Broughton Creek (T. Roper, PWD, pers. comm., 1993). Hence the installation of deep

trench drains to move water off the floodplain quickly was conducted so pasture did not

die of prolonged inundation. Yet, major flooding still poses a potential threat to the area,

prompting the PWD (1990) report for the flood risk of the lower Shoalhaven.

The study area receives floods to a height of 1.3m AHD at a recurrence interval of 25%

(once in 4yrs) and 3.85m AHD at a recurrence interval of 5% (once in 20yrs) (T. Roper,

PWD, pers. comm., 1993; PWD, 1990). Major flooding in August, 1974 caused

flooding on the study area to 3.5m AHD, with local farmers confirming this observation.

The level of the flood reported in this study (mid September, 1993 - more detail given in

Chapter 6), unfortunately were not available due to the PWD flood gauge

malfunctioning. However, what can be said is that the 1993 flood reported here was

minor and could be classified as a common event. The implementation of the drainage

network described in section 2.3 has vastly increased the efficiency with which water is

drained off the floodplain after flooding during the past 20 years or so (D. Failes, dairy

farmer, pers. comm., 1993). The association between local flooding and acid drainage

to receiving waters in Broughton Creek is discussed in Chapter 6. Chapter 2: PHYSICAL CHARACTERISTICS OF THE STUDY AREA 35

2.6 Summary * The evolutionary history of the lower Shoalhaven, according to Roy (1984), belongs

to the "barrier estuary" system. The Tweed, Richmond, Clarence and Macleay Rivers

have a similar history.

* A limited understanding of the lower Shoalhaven's depositional history existed.

Further discussion is given to this point in Chapter 3.

* The tidal influence along the Shoalhaven River (at least 19.6km upstream) and along

the length of Broughton Creek analysed in this review (l 1.5km from the mouth in the

creek's 14km stretch) is significant.

* A drainage density of -5.75kmfkm2 is shown in Figure 2.3; since 230km of drains

are found on the 40km2 of land prone to inundation on the northern side of the

Shoalhaven River. Secondly, of the 19 drains draining into Broughton Creek, only

one was not blocked by a floodgate, suggesting that a very large portion of the acid

drainage transported from the floodplain into the drains was likely stored in the drains.

* Large volumes of spoil (including oxidiseable pyrite) from drainage construction was

deposited on the floodplain with an estimated density of 2,763 m3fkm2.

* The drainage network mainly consisted of deep trench drains (main drains) with

dimensions 3.5m wide x 2m deep (dug to invert levels of -1.2m AHD) and smaller

drains (mole drains) with dimensions rarely exceeding l.5m wide x 2m deep.

* Local climate conditions are described including a description of the flooding history for the floodplain. The Jasper's Brush study area was found to receive floods to a

height of 1.3m AHD at a recurrence interval of 25% (once in 4yrs) and 3.85m AHD at

a recurrence interval of 5% (once in 20yrs) (T. Roper, PWD, pers. comm., 1993; PWD, 1990). Chapter 3: ACID SULPHATE SOIL DEVELOPl\.1ENT AND DESCRIPTIONS 36

Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS

3.1 Introduction

The essential chemical processes involved in forming acid sulphate soils are, firstly, the

formation of pyrite (by reduction and accumulation) in a water logged, anaerobic

environment (usually under mangroves), and subsequently, the oxidation of this pyrite

following natural or artificial drainage (Dent, 1986). The involvement of bacteria is

important in these processes (van Breeman, 1973). The development of oxidation

products after oxidation of pyrite in soils associated with mangrove sedimentation has

received insufficient recognition in Australia as a potential source of environmental

degradation to estuarine ecosystems (Lin and Melville, 1992a).

Before the quality of water leached from coastal soils can be understood and hence

meaningful coastal zone management strategies established, the soils from the coastal

zone need to be identified and their physical and chemical characteristics assessed (Arakel

and Hongrun, 1992). It was not the aim of this study to provide a finely detailed and

large scale assessment of the physical and chemical characteristics of acid sulphate soils

in the entire Shoalhaven floodplain. Instead, detailed soil analysis was done in a small

area in conjunction with water quality monitoring, and some further analyses were done

to characterise the soils on the floodplain surrounding Broughton Creek. The theme of

this study is the interaction between water quality and soil characteristics. The main aim

of the soil analysis was to understand acid drainage in the study area by identifying the

distribution of soils with certain physical and chemical properties; this also allowed

comparison with the physical and chemical characteristics of acid sulphate soils in other

areas of Australia.

General descriptions of pyrite and acid sulphate soil formation processes are given in this

chapter. Further detail is given when water quality results are discussed in Chapter 4.

Plate 3.1 shows excavated pyritic sediment deposited on a spoil heap beside a main Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 37 drain, located 40m south of a drain water sampling site (more detail is given on this sites location in chapter 4). The sediment in Plate 3.1 had been subject to direct oxidation for

3 years, and the photograph illustrates several features dealt with in sections 3.2 and 3.3, i.e. yellow jarosite staining, the grey estuarine sediment, the presence of shells and the red/orange colouration of iron oxides.

All equations quoted in this chapter are taken from Dent (1986) unless other wise stated.

Plate 3.1. Estuarine sediments shown here as part of a spoil heap deposit. These have been oxidised to form an acid sulphate soil and the yellow strands of jarosite can be seen. The ruler is 0.3m long. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 38

3.2 Formation of Pyrite

Pyrite is formed by reaction between the sulphate ion from sea water in the pores and

spaces of old plant roots (Rickard, 1972) and iron oxides present in sediments. An

anoxic environment with a sufficient supply of organic matter and of dissolved sulphate -

thus allowing the reduction of sulphate to sulphides through the action of reducing

bacteria - is required before the chemical reaction to form pyrite can take place (Pons,

1973; Berner, 1984; Dent, 1986). According to Dent ( 1986) the essential conditions for

pyrite formation can be summarised as:

an anaerobic/anoxic environment

a source of dissolved sulphate

organic matter

a source of iron

time.

The formation of pyrite with iron III oxide as a source of iron may be represented by the

following overall equation (Dent, 1986):

iron III sulphate organic dissolved oxide ions from matter oxygen from the seawater sediment

Chemical and physical characteristics of any acid sulphate soils are largely the result of

the relationship between the acid-neutralising capacity and the pyrite content. A soil

containing pyrite is only a potential acid sulphate soil if the potential acidity represented

by the pyrite is greater than the acid-neutralising capacity of the soil (Dent, 1986). The

neutralising capacity of the soil is provided by:

carbonates

exchangeable bases

easily-weatherable silicates. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 39

Calcium carbonate stands out in both its rate of reaction and neutralising capacity.

3.3 Oxidation

Pyrite is very stable under reducing conditions and stable when completely dry.

Drainage brings about oxidising conditions because air diffuses far more rapidly down

into the soil through air-filled pores, than through saturated soil. This initiates the

oxidation of pyrite and the generation of acidity. The vast majority of pyrite oxidation

has occurred on coastal floodplains as a result of deliberate exclusion of tidal action and

lowering of the water table (Melville et al., 1993). Pyrite oxidation has also occurred

after natural drainage as a result of a fall in sea level or severe dry period (see Chapter 1).

Excavation through sulphidic sediments and mining sulphidic ores and coals may also

oxidise pyrite, but this process does not necessarily produce acid sulphate soils (Dent,

1986).

3.3.1 Oxidation of Pyrite

Oxidation is essential in the initial formation of pyrite and then later in its conversion to

jarosite. Oxidation of organic matter is required before pyrite can be formed. Oxidation

of organic matter provides the energy requirements of sulphate-reducing bacteria. The

amount of sulphide produced is directly related to the amount of organic matter

metabolised. The presence of dark grey organic matter still remaining in sediment of the

study area can be seen in Plate 3.2 (shown in section 3.8 with an acid sulphate soil

profile - Plate 3.3). Sulphate ions serve as the electron sink for bacterial respiration and

the ions are thereby reduced to sulphide:

(3 .2)

This reduced sulphide can then react with iron bearing sediments to produce pyrite

(FeS2). This remains stable in the anoxic environment of saturated estuarine sediments.

When these are drained, the sulphide is re-oxidised to sulphate ion. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 40

Oxidation of pyrite in acid sulphate soils takes place in several stages, involving both chemical and microbiological processes. Initially, dissolved oxygen reacts slowly with pyrite, yielding iron II, and elemental sulphur:

(3 .3)

Further oxidation of sulphur by oxygen is very slow, but may be catalysed by autotrophic bacteria at pH values close to neutrality. pH is a measure of hydrogen ion

(H+) concentration in solutions (Dent and Bowman, 1993). This oxidation releases hydrogen ions and sulphate ions:

(3.4)

Initial acidification may also be brought about by chemical oxidation of amorphous iron

II monosulphide. However, generally only very small amounts of FeS are present, even in intensely black horizons:

(3.5)

Once the pH of the oxidising system is brought below 4 (by the hydrogen ions released in the initial oxidation reactions), Fe3+ becomes appreciably soluble and brings about rapid oxidation of pyrite, by electron transfer:

3 2 FeS 2 + 2Fe + ~ 3Fe + + 2S (3.6)

The half time of this reaction is of the order 20-1,000 minutes (Stumm and Morgan,

1970). Reaction of iron III with sulphur is also very rapid and the overall oxidation of pyrite by iron III may be represented as: Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 4 1

(3.7)

Thus at low pH, acidification can continue even in the absence of free oxygen. In the presence of oxygen, the iron II produced by these reactions is oxidised to iron III. At pH values <3.5, chemical oxidation is a slow process with a half time of the order of

1,000 days (Singer and Stumm, 1970). However, autotrophic bacteria, which seem to be ubiquitous in sulphidic and sulphate soils, overcome the kinetic barriers that exist in purely chemical systems. At low pH, Thiobacillus f errooxidans (T. ferrooxidans) oxidises reduced sulphur species and also iron II, thereby returning iron III to the

system:

T .ferrooxidans (3.8)

The rapid catalytic oxidation of pyrite by Fe3+ ions is limited by pH, because Fe3+ is

appreciably soluble only at pH values <4 and because T.ferrooxidans does not grow at a

higher pH. Where concentrations of estuarine shells occur, pH will be locally higher

than usual (Plate 3.1) with shells or calcium carbonate having a buffering effect, the

oxidation of pyrite is probably slow. Iron III oxides and pyrite may be in contact, but

the rate of oxidation will be constrained by the insolubility of iron ill (Dent, 1986).

The rate at which pyrite oxidises depends on the oxygen concentration of the soil. In

pyritic soils, the oxygen concentration at a specific depth depends on oxygen diffusion

and consumption. Several authors (McKibben and Barnes, 1986; Mathews and Robins,

197 4; cited in, Ritsema and Groenenberg, 1993) postulated rate laws to describe the

oxidation process of pyrite, but the rate of pyrite oxidation remain~ poorly understood

(Dent and Pons, 1993). The extent to which pyrite oxidises under natural conditions,

and the rate at which carbonates dissolve in drained acid sulphate soils to neutralise the

rapid acid production following oxidation, under natural conditions have not been

studied (Ritsema and Groenenberg, 1993). Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 42

3.3.2 Oxidation Products of Pyrite

Most of the acidity generated by the oxidation of pyrite by iron III (Equation 3.7) is spent in the subsequent oxidation of iron II back to iron III (Equation 3.8). The net result, with iron III hydroxide as an end product, may be expressed as:

1 FeSz + 102 + ~HzO ~ Fe(OHh + 2so~- + 4H+ (3.9) ochre

This releases 4 moles of hydrogen per mole of pyrite oxidised.

Iron Oxides

Where the pH of the soil remains above 4, iron III oxides and hydroxides precipitate directly by oxidation of dissolved iron II. Where active oxidation of pyrite is taking place, colloidal iron III oxides commonly appear in drainage water. Goethite is the most common iron oxide identified as a precipitate in soils. Sometimes it may be slowly transformed to haematite:

2Fe0.0H -> Fe203 + HzO (3.10) goethite haematite

Haematite is not common in young acid sulphate soils produced by artificial drainage.

Jarosite

Characteristic pale yellow deposits of Jarosite [KFe3(S04)z(OH)6] precipitate as pore

fillings and coatings on ped faces (Plate 3.1) under strongly oxidising, severely acid

conditions; when pH is less than 3.7 jarosite formation from pyrite may be represented

as:

(3.11) Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 43

At higher pH values, jarosite is metastable with respect to goethite and ultimately it is hydrolysed to the iron oxide:

(3.12)

In the field, brown rims of iron oxides become visible around the yellow jarosite deposits within 10-20 years of drainage. Brown and red mottles in acid sulphate soils are predominantly goethite, sometimes associated with jarosite and sometimes with haematite (van Breeman, 1973).

Sulphates

Most of the iron mobilised by oxidation of pyrite remains in the soil profile, but only a small fraction of sulphate is retained, as jarosite or gypsum. Most sulphate, being soluble, is lost to drainage, although some diffuses downwards to the reduced substratum and is reduced once again to sulphide. Gypsum may be formed in acid

sulphate soils with high shell or lime contents by the neutralisation of acidity by calcium carbonate:

(3.13)

However, a great deal of carbonate is required to neutralise an acid sulphate soil.

Calcium carbonate's neutralising capacity is 20 moles acid kg- 1. As one mole of pyrite is

equivalent to four moles H+ (Equation 3.9), the acidity from the oxidation of 1 % by

mass of pyrite sulphur is balanced by 3% by mass of calcium carbonate (Equation 3.13).

The different stages of oxidation do not necessarily occur at the same point. Pyrite can

be distinguished from its oxidation products; jarosite, iron oxides and gypsum. In

horizons where there is a reserve of pyrite to be oxidised, this is confined to the cores

and peds, whereas upon oxidation jarosite iron oxides and gypsum are closely associated Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 44

with pores and ped faces. The products of pyrite oxidation can be seen in the directly

oxidised soil in a spoil heap in the study area (Plate 3.1) with the oxidation products

transported away from the pyrite source. Yellow jarosite cores and joint fillings,

sometimes with iron oxide coatings, can be seen emplaced in a clay matrix which would

still contain some dispersed pyrite.

Further chemical reactions associated with acid sulphate soils will be discussed in

relation to the influence they have on acid drainage characteristics in the study area.

These include acid hydrolysis of silicates, release of Al3+ ions and reduction processes

related to flooding (Chapter 4).

3.4 Physiographic Characteristics of the Study Area

The landsurface classification employed in this study is the same as that first employed

for Australian acid sulphate soils in Walker (1972). This classification is applied to the

floodplains surrounding Broughton Creek in Figure 3.1.

2m levee

-m (AHO) 1m

backswamp

Om ------~------.... older estuarine clays and sands

(not to scale)

Figure 3 .1. Acid sulphate soil floodplain surface classification. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 45

Recent sediments of low pyrite content overlie older sulphidic clays; these recent alluvial sediments were deposited by flooding after the period when sea levels stabilised and the accumulation of pyrite-forming sediments ceased. Alluvial sands were still being deposited over the floodplains, for example as a result of the March, 1973 floods

(Bayley, 1975). Levees of alluvium flank the main channels, burying the older sulphidic

sediments and the depths of alluvial sediments are thickest adjacent to the main channels

such as Broughton Creek. The levees surrounding Broughton Creek often reach

between l.7-2.2m AHD, but are closer to 2.0m AHD adjacent to the study area (lower

Shoalhaven flood mitigation map, PWD, 184/71, 1967). Moving from the levees, away

from Broughton Creek the relief of the ground surface was reduced. Any sloped areas

are termed levee toes. Levee toes are characterised as having less alluvial soil between

the ground surface and old estuarine sediments than the levees. Moving further away

from Broughton Creek from the levee toes, the land surface becomes almost flat and the

thickness of alluvial sediments is further reduced so that older estuarine sediments may

be exposed at the surface in the lowest areas. Estuarine sediments are exposed in the

study area. These flat areas are known as backswamps. Backswamps surrounding

Broughton Creek commonly lie between 0.2-0.6m AHD (Lower Shoalhaven flood

mitigation map, 1967), but in some places are as low as 0-0.lm AHD. The study area at

Jasper's Brush is one of the lowest backswamp areas on the floodplain, commonly 0.2-

0.4m AHD (J. Downey, Shoalhaven City Council, pers. comm., 1993).

Of the floodplains surrounding Broughton Creek the following percentages (Flood

Mitigation map, 1967) and surface areas (Hazelton, 1993) are estimated for levee, levee

toe and backswamp areas:

- Levee (15%), 7.05km2

- Levee toe (25%), 1 l.75km2

- Backswamp (60%), 28 .2km2 Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 46

Hazelton ( 1993) mapped a further 18km2 with potential acid sulphate risk extending up

major tributaries, of which most drain into Broughton Creek.

In detail, soil patterns were complex. It may expected that relationships exist between

the pyrite content, the depth of the soil profile at which pyrite is concentrated, the

sequential development of tidal landforms, and oxidation characteristics (Dent, 1986).

3.5 Physical and Chemical Properties of Acid Sulphate Soils Analysed in the Study Area

In describing the physical and chemical properties of the soils, at different depths in the

three physiographic units in this study, after drainage, the following nomenclature in

Table 3.1 has been derived from Dent (1986) and Lin and Melville (1992b):

Unit Desciption Ao Organic horizon; surface mineral horizon distinguished by a concentration of organic matter, not severely acid. Hi Acid organic horizon. Bg Transitional horizon; not severely acidic, mottled brown with reddish iron oxide mottles and nodules. Bi Oxidised gley horizon; severely acidic, strongly mottled grey with reddish iron oxide and yellow jarosite mottles. ~ Reduced gley horizon; not acidic, dark grey to black, pyrite rich.

Table 3.1 Soil horizons found following drainage, as assigned for the study area.

The legend including all horizons and sub-horizons used to describe profiles is shown in

Table 3.2.

The physical and chemical characteristics of the soils have been described using 4 levee

(L), 8 levee toe (Lt) and 22 backswamp (Bs) soil profiles, whose locations are shown on

Figure 3.2. More detailed chemical analysis is given to: levee profiles 1, 3 and 4; levee Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 47 toe profiles 2, 5 and 7; backswamp profiles 1, 5, 10, 12 and 22. All profiles were dug to 2.5m unless the water table was reached and digging became too difficult. These profiles were chosen to assist in describing pH, grain size and Total Potential Acidity

(TP A) in the different horizons of soils in the three different topographic positions.

Sampling and analysis methodology is outlined in Appendix B. The profiles were located in or adjacent to the study area, and horizon development was typical of profiles representing levees, levee toes and backswamps.

Most emphasis was placed on describing physical and chemical characteristics in the backswamp profiles in the study area, Bs7-18 along the transect from which water table

data was collected. Particular attention was given to Bs12 since this was the profile used for ground water analysis. Figures 3.3 and 3.4 locate the profiles found within the study

area.

(Total Potential Acidity) TPA

A simple test was required to estimate the potential acid drainage hazard for the

floodplains surrounding Broughton Creek. Peroxide (H202) pretreatmant techniques

have been used for pyrite-S extraction (e.g. Calvert and Ford, 1973; Willett and Walker,

1982; Dent, 1986 - cited in Lin and Melville, 1992b). However, it was found by using

this method the pH value after H102 treatment did not precisely reflect the actual acidity

of the sample (Konston et al., 1986). Konston et al. (1986) suggested that determination

of Total Potential Acidity (TP A) by titration is a better technique . . Determination of TPA

by titration was carried out using the method of Dent and Bowman (1993).

In assessing the potential acid sulphate hazard in an area Total Actual Acidity (TAA) is

also measured and subtracted from TPA, with the qualitative measure of acid sulphate

hazard represented as Total Sulphate Acidity (TSA), i.e. (TPA - TAA = TSA). TPA is

the total potential acidity which will develop when a sulphidic soil is drained and all the Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 48 reduced sulphur species are oxidised. T AA is the total actual acidity which includes not just free acid due to previous sulphate oxidation but, also, what is often a much bigger reservoir of acidity (and soluble aluminium) absorbed on the clay and organic matter and in acid salts. T AA is a measure of the lime requirement to neutralise the acidity (for method see - Dent and Bowman, 1993). In this study TPA was measured as an estimate

of the maximum acidity risk.

\. ·· ." > -area prone to inundation * - soil sampling sites '- ..,., '"" - palaeochannels

• - floodgates

-- -roads

Lt2 BRUSH * ········· , I *Bs18 (...,. --, .· .· I Bs7·17 I .. · <.-'~-,..- ... ,_, '" *BS1 L I , L \., *Bs20. * 17 * ' , r...,, L3 *Bs19 r *Bs4 *BsS

.. Bs3 ' ...... · \ * ' I I

N

Bomaderry •. · ··.i ' i "'" *Lt4 Belong ·... 0 1km / ·· ... .·.- ..

Figure 3.2. Location of all soil sampling sites. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 49

Ao Organic Horizon • -Organic very dark brown (7.5 YR 2/ 1)

• -Grayish brown (lOYR 4/2) fine sand

Hi Acid Organic Horizon • -Fibrous in darkish red (2.SYR 3/3) clay

Bg Transitional Horizon -Yellowish red (5YR 5/8) streaks II in brown silty clay

-Red (2 .5YR 4/6) Fe(III) streaks in • redish brown (5YR 5/ 3) clay -Brown ( lOYR 5/3) clay

• -Dark yellowish brown ( 10.S YR 4/4) fine sand • Bj Oxidised Gley Horizon -Abundant Jarosite (2.5Y 8/5) mottles in horizontal cracks in dark brown ( lOYR 4/3) silty clay

- Minor Jarosite (2.SY 8/4) mottling in light olive brown (2.SYR 5/4) clay

-Yellowish brown ( lOYR 5/6) fine loamy sand GjReduced • Gley Horizon -Very dark grey (2.SY 3/0) silty clay loam

-Dark grey (2.SY 4/0) to grey (2 .5YR 5/0) loam •~ -Not sampled

Table 3.2. Soil profile classifications; a: legend; b: levee profiles; c: levee toe profiles; d: backswamp

profiles. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 50

Levee Profiles © Levee Toe Profiles

L1 L2 L3 L4 Ltl Lt2 Lt3 Lt4 Lt5 Lt6 Lt7 Lte 0 0

-E E ...... - ...... ~ ~ ..,J ..,J c. c. . Q) Q) A .A 0 0

2 2

@) BackswamJL(Bs) Profiles

2 3 4 5 6 7 e g 10 11 12 0 13 14 15 16 17 1e

-E -.....,~ c. Q) Ci 2

19 20 21 22 0

-E ...... ,~ c. Q) 0

2

Table 3.2. - Continued. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 5 1

It is unlikely under natural conditions, or even with drainage, that all pyrite in any area would oxidise fully in a short period, to achieve acidity expressed for the full potential

TPA value in any area. Furthermore, a lot is yet to be learnt about acid sulphate soils, for example storage capacities of acid in floodplains and speed of drainage (Dent, 1986;

Leadbitter, 1993a). In some acid sulphate soils the value of T AA may be similar to TP A, creating a small potential future risk value. However, the same soils may, for example, experience extreme drought, then extreme flooding, and a large portion of total TPA and total T AA may be released in a short period into an estuarine ecosystem. Therefore,

there may be a high risk to an area with a potential low TSA risk. Ultimate or long term

management practises surely should be applied to manage a worse case scenario; this

scenario is most accurately represented by TP A calculations alone, as used in this study.

• - bores/soil sampling sites • - water quality sites Control bo re * - - trench drains _,-- - drainage channels Rainfall recording site * '- ,.... - paleochannels

0 scorn

r'" _road drain \ ( ...... \. transect drain - ---- \ \ \ I ~ l I ,,-.,,. I I / I ...... 'I , 1~-~,~'""";~"":--7~-17-~-~---¥-- gate drain l ' ' ...... ,., ' ( \ J ..... _,. r

Figure 3.3. Location of bores used in detailed soil analysis. *These soil sampling sites and water

quality sampling sites are referred to frequently in Chapter 4. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 5 2

1.50 -r------'------, west east backswamp profiles 1.00 - transect drain 17 ------\ \ ~ 0.50 16 15 14 13 12 1110 9 8 7 E Cl 0.00 I <( ----1-----~------r---~------~1- -1----t---- ~ -0.50 ·a; I -1 .00

-1.50 = borehole depths V.E. = 30 -2.00 ""T------,------.------,------.,.------.--' 0 100 200 300 400 500

Distance (m)

Figure 3.4. Transect of detailed soil sampling sites and bores used for watertable/water quality analysis

in Chapter 4.

3.6 Levee

The four profiles on levee soils showed little colour variation with depth. The surface

horizon for each profile was organic-rich and very dark brown (7.5YR 2/1), and

extended down to about 0.5m in depth. Below this an Ao horizon, a greyish brown

(lOYR 3/3) clay, of around 0.3m thickness was found in all profiles. A dark yellowish

brown (10.5YR 4/4), Bj transitional horizon extended from around lm depth to at least

2.5m depth. The lack of variation in colour down the levee profiles is a reflection of the

dominance of alluvial soils to depths of 2.5m. This interpretation is supported by the

grain size, pH and TPA values for the three profiles analysed (Table 3.3).

On the levees, mean percentage clay and silt fractions increased marginally from the

surface to lower transitional horizons clay (25-31 %) and silt (33-40%). The mean

percentage sand fraction was highest at the top of the profiles (Ao horizon 38%, Bg

transitional horizon 41 % ). Thus there was a general decrease in sediment size down

levee profiles, due to a decreasing alluvial content and/or pedogenic clay transport.

Soils of the levees had a mean pH value of 4.9 at the surface and become increasingly

more acid down the profile (as measured in the laboratory); the mean pH value at depth Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 53 absence of jarosite in all profiles. An increase in acidity down levee profiles suggests some pyrite did exist and that some oxidation had taken place. This may have been the result of pyrite re-deposition during floods, since two of the four levee profiles (L3 and

L4) had a 0.3m thick layer at around lm depth with a yellowish brown (10.5YR 4/4) appearance, representing possible oxidation.

In the levee profiles TPA values were consistently around 0.4 mol/kg throughout all horizons indicating a common sedimentary history.

Ao Bg Bg ® Location Property 0-0.8 (m) 0.8-2.0 (m) 2.0-> (m) 0.15 (m) 1.0 (m) 2.0 (m) L1 % clay 22 25 32 % silt 28 40 44 %sand 40 35 24 L3 % clay 28 25 29 % silt 39 33 45 %sand 33 42 26 L4 %clay 24 23 32 % silt 31 31 30 %sand 41 46 38

%Clay ® Mean 25 24 31 St. dev. 3 1 2 %Silt Mean 33 35 40 St. dev. 6 5 8 %Sand Mean 38 41 29 St. dev. 4 6 8

L1 pH (before oxi) 4.7 4.3 4 © pH (after oxi) 4.4 4.1 3.8 TPA 0.4 0.39 0.37 L3 pH (before oxi) 5 4.1 3.8 pH (after oxi) 4.8 3.9 3.4 TPA 0.42 0.44 0.4 L4 pH (before oxi) 4.6 4 3.8 pH (after oxi) 4.5 3.9 3.4 TPA 0.43 0.45 0.41

Table 3.3. Levee soil results; a: grain size, b: mean grain size, c: pH{fPA. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 54

3.7 Levee toe

Organic very dark brown (7.5YR 2/1) soils like those in the levee dominate in the Ao surface horizon of levee toe profiles, but these seldom extended deeper than 0.3m depth.

Deeper soil horizons in the levee toe profiles were more complex than in levee profiles, presumably as a result of a thinning of alluvial surface sediments (Figure 3.1). In the

two levee toe profiles (Lt3 and Lt4) which were furthest from Broughton Creek, towards

Bomaderry (Figure 3.2), a brown (lOYR 5/3) clay occured to around l.5m depth. In

other levee toe profiles the transitional horizon soils with yellowish red (5YR 5/8) streaks

in brown silty clay and/or red (2.5YR 4/6) iron III streaks in reddish brown (5YR 5/3)

clays extend to around lm depth. Other than levee toe profiles 3 and 4, an oxidised

horizon existed in these levee toe profiles, with minor jarosite (2.5Y 8/4) mottling in light

olive brown (2.5YR 5/4) clay. A reduced gley horizon with dark grey (2.5Y 4/0) to grey

(2.5YR 5/0) loam occurred at around 2m depth in the three levee toe profiles (Lt5, 6 and

7) found closest to the study area (Figure 3.2).

The mean percentage grain size fractions of clay (35-46%) and silt (32-35%) down levee

toe horizons remained very consistent, but the mean percentage sand fractions were more

variable and were highest at 36% in the Bj oxidised horizon (Table 3.4). Mean clay

percentage fractions were higher than silt and sand fractions in the Ao, Bg and Gj

horizons.

Associated with relative high mean percentage fractions of clay in the levee toe profiles

was an increase in soil acidity down the profile, except where a Gj horizon was found,

resulting in a sharp rise in soil pH (see Table 3.4). The levee toe surface soil with the

only pH value above 5 (5.3) was obtaine,d at Lt4, the closest profile to Bomaderry. The

mean pH for surface soils of the all 8 levee toe profiles was 4.8; at an average depth of

l .43m, jarosite was found and mean pH fell to 3.1 (Table 3.6). The mean pH of 5.8

taken from levee toe profiles in Table 3.4c was representative for the Gj horizon. TP A

values were highest in the Ao horizon with a mean of 4.4 mol/Kg. While the TP A for corresponding horizons of all levee toe profiles were similar, there was a consistent Cha12ter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 55 horizons of all levee toe profiles were similar, there was a consistent decrease in the TPA

value until the Gj horizon, indicating a change in chemical response within the soils.

Ao Bg Bj Gj 0 Location Property 0-0.3 (m) 0.2-0.6 (m) 0.8-1.6 (m) 1.6-2.5 (m) 0.2 (m) 0.5 (m) 1.1 (m) 2.0 (m) Lt 2 % clay 40 45 33 % silt 41 41 40 %sand 19 14 37 Lt 5 %clay 48 51 35 47 % silt 30 32 30 33 %sand 22 18 35 20 Lt 7 %clay 45 36 36 45 % silt 26 32 29 37 %sand 29 30 35 18

%Clay ® Mean 44 46 35 46 St. dev. 3 6 1 1 % Silt Mean 32 35 32 35 St. dev. 13 16 5 2 %Sand Mean 23 21 36 19 St. dev. 15 17 1

Lt 2 pH (before oxi) 4.8 3.9 3.5 © pH (after oxi) 4.4 3.7 3 TPA 0.41 0.35 0.31 lt5 pH (before oxi) 4.1 3.3 3.1 5.6 pH (after oxi) 3.7 3 2.7 2.6 TPA 0.47 0.39 0.35 0.43 Lt? pH (before oxi) 4.7 3.4 3 6 pH (after oxi) 4.3 3 2.6 2.7 TPA 0.42 0.4 0.34 0.39

Table 3.4. Levee toe results; a: grain size, b: mean grain size, c: pH{fPA.

3.8 Backswamps

The colour of the surface soil (Hj - acid organic horizon) was the same for each of the 22

backswamp profiles analysed; some fibrous material occurred in dark red (2.5YR 2/1)

clay. The thickness of the Hj horizon in the backswamps rarely exceeded 0.3m and there

was no obvious variation across different areas of the floodplain. The Bg horizon of

nearly all backswamp horizons included red (2.5YR 4/6) iron streaks in reddish brown

(lOYR 5/3) clay and it was commonly underlain by yellowish red (5YR 5/8) streaks in Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 56 brown silty clay. Soil sampling by a class group from the University of Wollongong on the study area, revealed iron mottling to be particularly strong and high in the profile

(within the upper 0.5m) in palaeochannels which were dry at the time. The Bg horizon commonly graded out by 0.6m depth and in every profile it was underlain by the oxidised Bj horizon containing either numerous jarosite (2.5Y 8/5) mottles in horizontal cracks in dark brown (lOYR 4/3) silty clay and/or minor jarosite (2.5Y 8/4) mottling in light olive brown (2.5YR 5/4) clay. The only significant area not containing abundant jarosite was around backswamp profiles 3, 4, 5 and 6 just west of Jorans Creek. Out of the 12 profiles used for water quality analysis (Bs7-18) only two profiles (Bs14 and

Bs15) contained no abundant jarosite. Under the Hj horizon in every backswamp horizon, a reduced gley (Gj) horizon was found at around lm depth. Only 3 of the 22 backswamp profiles (Bs3, 4 and 22) did not contain a very dark grey (2.5Y 4/0) silty clay loam in the Gj horizon. Shells were commonly found just below the Bg horizon between depths of -lm to -l.2m AHD, and commonly graded out by -2.6m to -2.9m

AHD. The shell species found included in order of prevalence: Notospisula parva

(Lamarck), Conuber sordidum, Anadara trapezia, Irus crenatus (Child, 1965; Child and

Currey, 1972; Clark, 1990). The shell frequency of occurrence could be considered as

sparse (C. Woodroffe, UW, pers. comm., 1994).

In Plate 3.3 a fully developed acid sulphate soil from Bs12, the profile where chemical

water quality analysis was conducted, is shown. Moderate jarosite can be seen from

depth 0.4-0.7m and abundant jarosite from 0.7-lm. The vertical orientation of the

jarosite cores in particular in the Bj horizon was an indication of watertable fluctuations

being strongest in the Bj horizon (R. Lawrie, Dept. of Agriculture, pers. comm., 1993).

The existence of iron in this profile (mainly as coatings on jarositic core) can be seen

from below the Hj horizon at 0.2m depth. ChaI?ter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 57

Ao Bg Bj Gj 0 Location Property 0-0.2 (m) 0.2-0.6 (m) 0.6-1.1 (m) 1.1-2.5(m) 0.15(m) 0.4 (m) 0.9 (m) 1.8 (m) Bs 1 % clay 38 34 28 48 % silt 50 42 62 42 %sand 12 24 10 10 Bs 5 %clay 38 39 29 45 % silt 42 41 46 47 %sand 20 20 15 8 Bs 10 %clay 30 35 23 42 % silt 46 40 47 48 %sand 24 5 30 10 Bs 12 %clay 39 38 30 41 % silt 42 54 45 52 %sand 19 8 25 7 Bs 22 %clay 42 40 34 45 % silt 33 44 56 43 %sand 15 16 20 12

%Clay ® Mean 37 37 29 44 St. dev. 4 3 4 3 %Silt Mean 43 44 51 46 St. dev. 6 6 7 4 %Sand Mean 18 15 20 9 St. dev. 5 8 8 2

Bs 1 pH (before oxi) 4.2 3.7 3 6.4 © pH (after oxi) 3.3 3 2.5 1.9 TPA 0.53 0.39 0.3 0.46 Bs 5 pH (before oxi) 4.1 3.8 3.6 6.6 pH (after oxi) 3.1 2.9 2.8 2.1 TPA 0.51 0.4 0.33 0.44 Bs 10 pH (before oxi) 3.8 3.6 3.1 6.2 pH (after oxi) 3.1 3 2.7 1.8 TPA 0.88 0.51 0.22 0.7 Bs 12 pH (before oxi) 4.1 3.3 2.9 6.5 pH (after oxi) 3.2 2.7 2.5 1.8 TPA 0.58 0.41 0.32 0.48 Bs 22 pH (before oxi) 4.3 3.8 3.4 6.3 pH (after oxi) 3.1 3 2.6 1.9 TPA 0.86 0.49 0.23 0.65

. Table 3.5. Backswamp soil results; a: grain size, b: mean grain size, c: pH{fPA. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 58

Location Presence of (surface soil) pH jarosite pH (depth m)

L1 4.7 2.5* 4 L2 5.2 2.5* 3.9 L3 5 2.5* 3.8 L4 4.6 2.5* 3.8 mean 4.9 2.50 3.9 st. dev. 0.3 0.00 0.1

Lt1 4.7 1.3 3.3 Lt2 4.8 1.6 3.5 Lt3 4.6 1.9 2.7 Lt4 5.3 1.8* 3.6 Lt5 4.6 1.3 2.7 Lt6 4.4 1.2 2.9 Lt? 4.7 1.4 2.8 Lt8 4.9 1.3 3.1 mean 4.8 1.43 3.1 st. dev. 0.3 0.24 0.4

Bs1 4.2 0.8 2.9 Bs2 4 0.8 3.3 Bs3 4.4 1.2 3.2 Bs4 4.3 1.2 3.4 Bs5 4.1 0.9 3.3 Bs6 4.2 0.9 3.3 Bs7 4.3 0.8 2.9 Bs8 4.2 0.85 3 Bs9 4 0.85 3.2 Bs10 3.8 0.75 3.3 Bs11 4.2 1 3 Bs12 4.1 1.05 2.9 Bs13 4.3 2.9 Bs14 4.4 1.1 3.2 Bs15 4 0.95 3 Bs16 4.1 1. 1 3 Bs17 4.3 1.4 3.1 Bs18 3.8 0.2 3.7 Bs19 4.2 0.8 3.1 Bs20 4.1 0.8 3.1 Bs21 4.1 1 3 Bs22 4.3 1.3 2.9 mean 4.2 0.94 3.1 st. dev. 0.2 0.24 0.2

* = No Jarosite found

Table 3.6. Surface and subsurface levee, levee toe and backswamp soil pH. Depths are for distances

below the ground surface. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 59

Powter (1993) conducted iron (total) analysis adjacent to Bs 12 and obtained the following result:

- Hj (0-0.2m) 50,300 (mg/kg)

- Bg (0.5-0.6m) 33,340 (mg/kg)

- Bj (0.9-lm) 29,320 (mg/kg)

- Gj (1.7-2m) 51,460 (mg/kg)

Samples analysed within the strongly oxidised spoil heap located lOOm down the drain from Bsl2 showed excessive iron concentration of 46,700-266,950 mg/kg. These data indicate that iron may have been leached out of the Bg and Bj horizons during oxidation, and that considerable reserves of pyrite and, probably aluminium remain in the Gj horizon.

In all backswamp profiles from the Hj to the Bj horizons, the percentage of the clay fraction decreased with depth (37-29%), as was also found in Norwood (1975). This

supports the notion of an upward growth of the soil profile with deposition, rather than a

downward development of the profile through leaching and translocation of the clay to

the lower profile (Norwood, 1975). However, both in Norwood's (1975) study and

here, the percentage clay decreased sharply at a point between the Bg and Bj horizons.

The change in clay content was thought by Norwood ( 197 5) to be a rough indicator of

the boundary of the upper levels of the estuarine deposits and the overlying fill. This

assumption would appear plausible; however, the situation is not so simple since the Gj

horizon was also analysed in this study and showed another sharp rise in the mean

percentage clay fraction ( 44% ). Thus the coarser texture of the Bj horizon in the

backswamp and levee toe profiles (Figure 3.5) may be a pedogenic and not a

depositional change. Silt was the dominant grain size fraction in all horizons for the

backswamp profiles, ranging from 43% in the Hj horizon to 51 % in the Bj horizon.

Sand was, however, by far the least significant of the grain size fractions in all horizons

ranging from 9% in the Gj horizon to 20% in the Bj horizon. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 60

Plate 3.2. Unoxidised pyrite shown here as a core of organic rich soil. This core section was taken at approximately 1.6m depth at Bsl8 (see Figure 3.3 for location) and was 0.2m long.

Plate 3.3. An acid sulphate soil profile (Bsl2), showing in particular abundant jarosite below 0.7m depth. Groundwater water quality analysis was done from bore Bs12. The core is lm long. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 6 1

Depths between transitional boundries of alluvial, lagoonal and intertidal sediments are estimated below and are shown to be almost identical (in relation to local high tide level; m AHD) to those for the Clarence floodplain in Lin and Melville (1992b, p.7):

Jasper's Brush Clarence

Alluvial >0.2m >Om

Lagoonal 0.2-1. lm O-l.2m

Intertidal

Further evidence to support the above transitional boundaries for the study area lie with

the analysis of diatoms, carried out by Associate Professor Masatomo Umitsu, visiting

from the University of Nagoya, Japan, between May and September, 1994). An

analysis of diatoms from bore profile Bs12 showed freshwater species, (Nitzschina

pa/ea) and benthic freshwater species, (Achnanthes minutissima) dominated all species

found in the first 0.5m of the profile. Below lm depth there was a clear dominance of

marine/brackish diatom species, with the most prevalent species being Nitzschia

cocconeiformis. The full complement of diatom species found down this profile is

shown in Appendix E.

There was a gradual drop in mean pH from the Hj (4.2) to the Bj (3.1) horizons in all

backswamp profiles (Table 3.6) with a sharp rise in the Gj horizon (pH 6.4) (Table 3.5).

There was little variation in the pH of soils throughout the floodplain in the Hj and Bj

horizons; however, three significant points dealing with pH from profiles used in water

quality analysis in the study area can be seen from Table 3.6. Of all 22 backswamp

profiles, the thickness of the Hj horizon was least (0.08m) and depth to the Bj horizon

least besides a permanent swamp (Bs18) devoid of vegetation. The surface pH was

which was lowest (pH 3.8) and pH in the Bj horizon highest (pH 3.7) at Bsl8. Thus at

Bs 18 where the surface covering of alluvial sediments was thinner than any other

backswamp profile analysed, the products of pryrite oxidation were closer to the ground Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 62

pH % Grain size TPA (mol/Kg) 2 3 4 5 6 7 0 20 40 60 0.2 0.3 0.4 0.5 0.6 0 ® a DA 0 a

-...... E a D 0 A a .c_, 0. Q) 0

2 a 0 D

0 ® a A 0 a a

a A 0 a a -E ...... - a %clay .c_, 0 %silt 0. a A %sand 01:21. a Q.) 0

2 a - A 0 a a

@) 0 a A ID a

a A a 0 a -E ...... ,, a AC 0 a .c_, 0. Q.) a a 0 a 0 2

Figure 3.5. Summarised soil analysis - levees; a: L3, levee toes; b: Lt5 and backswamps; c:Bsl2.

surface than all other backswamp profiles. Two other profiles in the study area with

noticeably lower surface soil pH values were Bs9 (pH 4) and BslO (pH 3.8) located on

either side, within 5m of a large drain, later referred to in the water quality analysis (Chapter 4). Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 63

Surface soil samples show high TP A values (>0.51 mol/kg), with the highest value of

0.86 mol/kg located closest to Berry at Bs22 (Table 3.5). There was a steady drop in the value of TPA from the Hj the Bj horizons, with the lowest value recorded at BslO. In the Gj horizon TP A values sharply rose again.

3.9 Inter-Section Comparisons

In Figure 3.5, three profiles, with one representative each for a levee, levee toe and backswamp profile are shown. A reduction in thickness and increase in complexity from the surface Ao organic horizon through to the Bj oxidised horizon is shown from the levee, to the levee toe, to the backswamp profiles. There is also a reduction in surface soil thickness and reduction in the depth to the unoxidised horizons from the levee to backswamp profiles. The above description for levee, levee toe and backswamp acid sulphate soil distribution and development resembles that for the Macleay Floodplain

(Walker, 1972; Willett and Bowman, 1990) and the Clarence Floodplain (Lin and

Melville, 1992b). One other noteworthy feature here, as was similarly found from the above other works, was the shallow depth at which jarosite was found in the backswamps. There were indications of jarosite almost exclusively within 0.2-0.25m of the ground surface throughout the backswamp. This observation is one which makes management difficult, as described in Chapter 7.

The relative percentage fractions of clay, silt and sand became increasingly more diverse from the levee to backswamp profiles. The percentage of clay was always lowest in the

soils of the Bj horizon (if present) in the levee toes and backswamps and clay dominated mean percentage grain size fractions in the levee toes, where sand dominated the same

parameters for the levees and silt for the backswamps. There was also an overall reduction of sand from the levees to backswamps with mean percentage sand fractions

by far the lowest in the Gj backswamp horizons. These observations were all closely in

accord with those for grain size analysis in Lin and Melville (1993b) and Walker (1972).

The acidity of the soil increased from the Ao to the Bj horizons from the levee to backswamp profiles. Soil acidity would be assumed higher in the Bj horizon of the Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 64 backswamp profiles where the development of abundant jarosite was greatest than in the

Bj horizon levee toe profile; however, the mean pH values in the Bj horizons for both the levee toe and backswamp profiles were 3.1 (Table 3.1 ). Soil acidity dropped sharply in the Gj horizon and was lowest in the backswamps. The above description for soil acidity in the various horizons throughout the floodplain, for the study area, were very similar with those for the same area in Norwood (1975) and similar as elsewhere (Lin and Melville, 1992b; Walker, 1972; Willett and Bowman, 1990); although there was a noticeable trend for an overall -0.3 unit drop in soil pH amongst all horizons in the study area. For example the lowest soil pH measured in the backswamp elsewhere (as above), for the Go horizon (same as Bj here) was 3.4, where mean soil pH for the Bj horizon here was 3.1±0.2.

Soil pH was noticeably less acidic throughout all horizons on the levees, levee toes and backswamps, on the southern side of the Shoalhaven River (Norwood, 1975; Willett and

Walker, 1982) than here. It was found in Willett and Walker (1982) that soil pH was <4

(minimum - 3.9) in levee toe profiles only. The lowest soil pH in any backswamp horizon was 5.1. Reasons for an apparent decrease in soil acidity on the southern side of the Shoalhaven River are given in section 3.10.

Backswamp TP A values showed more variation down the profiles than those of the levee and levee toe (Figure 3.5). This was to be expected since the textural transition between backswamp horizons was greatest, indicating estuarine sedimentation. As expected,

TPA values between 0.46-0.7 mol/kg in the backswamp, Gj horizon were higher than those of any other horizon in the levee or levee toe profiles. However, what was not expected was the decrease .in TPA down from the surface through to the Bg and Bj horizons in nearly all of the levee, levee toe and backswamp profiles. Additionally, the highest TPA values for any one horizon were found in the surface horizon of the backswamp profiles, opposed to the Gj horizon of the backswamp profiles as would be expected. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 65

3.10 Discussion on Pyrite

The analysis of TP A in this study was undertaken with the aim that it would represent the potential acidity of the pyrite content in different horizons throughout levee, levee toe and backswamp profiles. While the TP A values did accurately show potential soil acidity in this study, they did not represent the potential acidity of the pyrite content alone. TP A

was shown to be high in the Gj horizon of the backswamp profiles, as would be

expected where the influence of old estuarine deposits was strongest. This was shown

where upon complete oxidation with hydrogen peroxide, the pH values ranged from 1.8-

2.1 (Table 3.5c) and were considerably lower than pH after treatment with hydrogen

peroxide in any other horizon in the levee, levee toe or backswamp profiles (Tables 3.3c

and 3.4c ). There was the trend for pH after treatment with hydrogen peroxide to be

lowest in the lowest horizon and highest in the surface horizon of the levee, levee toe and

backswamp profiles analysed, yet, as was not expected, TPA values in nearly every

levee, levee toe and backslope profile were highest in the surface horizon. Possible

reasons for this are that organic acidity, aluminium and variable charge polymer surfaces

can increase the potential soil acidity represented in a TPA value (Lin and Melville,

1992b; M. Melville, VNSW,pers. comm., 1994). High organic levies are also likely to

promote high TPA values. Which of the above factors or combination of the above

factors have led to the high values of TPA in surface soils is uncertain, but it is known

the influence is strongest in the surface horizon (with probable accumulation around

vegetation roots) and decreases down the profile until reaching the Gj horizon.

Although the presence of factors other than pyrite content raise the TP A risk higher than

expected in surface horizons, it was only in backswamp profiles, that TPA values rose

above 0.5 mol/kg. The values of TP A >0.5 mol/kg have been generally considered

necessary for the development of severe acid sulphate soils. Despite values above 0.51

mol/kg found in the Gj horizon of the backswamps, TP A values anywhere in the

floodplain could not be classed as extreme (M. Melville, UNSW, pers. comm., 1994);

therefore, pyrite concentrations throughout the floodplain can be classified as not extreme. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 66

The potential acid sulphate hazard for the floodplain was to be calculated in Chapter 7, as per Dent and Bowman (1993), using TPA as the analytical acid measure. However, due to the inadequacies of the TP A method to accurately measure the potential acid hazard from the pyrite content in the soil, the above task was not attempted. However, the

results from the TPA analysis will remain useful in this study. A TPA risk hazard not

only represents the risk of acidity of an ecosystem, but is an indicator of other pyritic

oxidation products such as soluble iron and aluminium. Iron and aluminium are

damaging to the survival and growth of aquatic lifeforms and some plant species (Dent,

1986; Dent and Bowman, 1993). The higher the TPA risk, the higher the combined

risk.

Acid sulphate soils on the Shoalhaven Floodplain, amongst other areas where these soils

exist along the NSW coast, are found to contain much greater potential sulphuric acidity

from high pyrite levels compared with overseas examples such as the Pearl River Delta,

China (Lin and Melville, 1992a). This is considered to be the result of a slower accretion

rate of the intertidal surface for the Australian examples (the Pearl Delta has prograded

more rapidly), allowing more pyrite accumulation in the sediment at the given elevation

for a given time (Lin and Melville, 1992b). However, as has been indicated here by

TP A analysis, the pyrite content within the floodplain surrounding Broughton Creek was

not as high as the Clarence and Tweed Floodplains (M. Melville, UNSW, pers. comm.,

1993).

As a result of the limited detailed geomorphic work done over the Shoalhaven Floodplain

to date, to propose why the pyrite content appears higher in northern NSW compared

with the Shoalhaven is difficult. One reason may deal with the more temperate climate of

the Shoalhaven area compared with north coast areas such as the Tweed. The more

tropical the climate the denser mangrove will grow (van Breeman, 1982). Organics from

mangrove contribute by far the highest input towards developing high pyrite contents

than organics from any other form of vegetation (Lin and Melville, l 992a). The Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 67

darkness of the Gj horizon here did not appear as evident here as is indicated in Lin and

Melville (1992b) or as was observed on the Tweed Floodplain during an (ASS

Conference field trip led by M. Melville in 1993). C. Woodroffe (pers. comm., 1994)

also suggests unoxidised sediment often appeared higher in organic content (as judged

by colour) in the Mary River and other estuaries of the Northern Territory than on the

Shoalhaven.

In order to estimate the likely pyrite concentration in an area, first a sound understanding

of the depositional history of the area is necessary. However, since the depositional

history of the study area is poorly understood, only broad assumptions can be given

explaining the apparent low pyrite concentrations here. It was suggested in Chapter 2

that sea level had not stabilized in the study area possibly not until significantly after

4,000 years ago. In any case, there were indications that the depositional environment

has been variable. Pons et al. (1982) propose that the most conducive environment for

high concentrations of pyrite would be one with a rapid accumulation of mangrove

organics, forming a thick layer while sea levels were rising and for sedimentation rates to

be thereafter low during a prolonged period (5,000-6,000 years) of stable sea levels.

These conditions have not been operative in the lower Shoalhaven, and recent work by

Woodroffe and Umitsu indicates a far more complex and recent sedimentation pattern

than that suggested even by Roy (1984).

A significantly higher than normal pyrite content does not occur in the acid sulphate soils

at Jasper's Brush, yet extreme concentrations of pyrite oxidation products were found in

the acid drainage at Jasper's Brush. Reasons for this are given in later chapters.

3.11 Summary

* The formation of pyrite was outlined, with essential conditions for development

identified as; an anaerobic/anoxic environment, a source of dissolved sulphate (sea

water), organic matter (usually mangroves), a source of iron, time and the Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 68

oxidation of pyrite by exposure to air. Oxidation of pyrite in coastal areas is usually

associated with high, often extreme, acidity and mobilisation of iron and aluminium

from the soils.

* Three geomorphic zones across the floodplain of differing acid sulphate soil

development were identified (levees, levee toes and backswamps) and these were in

accord with examples from the north coast of NSW.

* A classification system was assigned to acid sulphate soil development in the

Shoalhaven floodplain.

* In the levee soils, only minor changes were found in the parameters analysed,

including colour, grain size, pH and total potential acidity (TPA). This indicated a

common sedimentary history. The complexity of soil horizons increased in the levee

toe soils, including a decrease in the depth of alluvium. There were now signs of

pyrite oxidation. Soil complexity and pyritic oxidation was extremely obvious in

backswamp soils, with colour, grain size, pH and TPA varying significantly down

the profile. Alluvial surface soils were very thin (rarely exceeding 0.2-0.25m depth)

in the backswamps. All of the above transitional changes (including grain size

fractions, and pH and TPA levels) were broadly in accord with those of acid sulphate

soils found on the north coast of NSW (Lin and Melville, 1992b; Walker, 1972;

Willett and Bowman, 1990).

* The analysis of TPA did show potential soil acidity in this study, but did not represent

the potential acidity due to the pyrite content alone. Surprisingly, TPA values in

nearly every levee, levee toe and backswamp profile were highest in the surface

horizon. However, the TPA analysis indicated the pyrite concentration was not

severe and was not as high as has been found on the north coast of NSW, perhaps

because of differing sedimentary histories or sedimenatary environments. Chapter 3: ACID SULPHATE SOIL DEVELOPMENT AND DESCRIPTIONS 69

* Following all analysis of the soils on the lower Shoalhaven floodplain here, it can be

said acid sulphate soils are very well developed, but the severity of toxicity and

potential toxicity is not as severe as is suggested for acid sulphate soils on the north

coast. Therefore, the composition of the soils alone cannot account for the

extreme levels of acid drainage ( as severe as on the north coast) detailed later in

Chapters 4, 5 and 6. Reasons for this are given in Chapter 7. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 70

Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY

4.1 Introduction

Oxidation of pyritic sediments has occurred since their deposition in the early Holocene

as a result of the interaction of climate and the hydrological regime, for example when

groundwater is lowered during severe drought. Landuse changes have brought about

human activities in the coastal zone leading to an acceleration in this natural process,

principally through alteration of the hydrologic regime. The rate at which acidic

soil/water is produced and moved into streams will determine the acid, iron and

aluminium concentrations in streams (White et al., 1993).

In Australia very little work has been done on understanding the interaction of processes

on the production of acid drainage (White et al., 1993). Here, aspects of climate and

hydrology are described and discussed with reference to the literature to gain an

understanding of the rate and severity in which acid drainage is produced in the study

area.

This chapter addresses the second major aim of this thesis - i.e. the investigation of the

relationship between fluctuating watertables and the quality of groundwater - and also

part of the third major aim - i.e. the provision of information on the conditions required

to cause acid drainage from the study area to flow into the drains and then from the drains

into receiving waters of Broughton Creek.

4.2 Watertable and Drain Water Level Dynamics

In beginning to investigate the relationship between fluctuating watertables and the

quality of groundwater, the movement of groundwater in relation to drainage water was

analysed. It was investigated whether watertable movements were responding differently

on the drained floodplains compared with an undrained area where a control bore was

located. As there are no undrained floodplains in the lower Shoalhaven, a control bore to Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 7 l measure watertable fluctuations was located on a bedrock ridge, as close as possible to the study area. The control bore chosen had been dug in 1981 and was located on land

7 .6m above AHD, approximately 200m north of the rainfall recording site (Figure 3.3).

Mean, standard deviation, median, minimum and maximum watertable/drain depth values for all bores and drain sites are shown in Table 4.1, and discussed further in sections 4.2 and 4.3. The main drain analysed here is referred to as the "transect drain" and the mole

drain analysed as the "road drain". Measurements for water depth and pH only were

taken at a third drain location (Figure 2.3). This site named "gate drain" was in a main

drain, connected to the road drain.

Bs7 Bs8 Bs9 Bs10 Bs11 Bs12 Bs13 Bs14 Bs15 Bs16 Bs17 Bs18 transect road gate control drain drain drain bore Mean -0.70 -0.62 -0.63 -0.57 -0.48 -0.43 -0.47 -0.56 -0.37 -0.32 -0.65 -0.30 1.46 1.21 0.89 -2.09 st . dev. 0.25 0.28 0.23 0.28 0.30 0.29 0.25 0.25 0.23 0.24 0.15 0.27 0.16 0.18 0.14 0.39 Median -0.73 -0.60 -0.66 -0 .63 -0.51 -0.45 -0.50 -0 .56 -0 .39 -0 .29 -0.67 -0.26 1.44 1.17 0.87 2.23 Minmum -1 .11 -1 .08 -0.92 -0.89 -0.90 -0.91 -0.90 -1.00 -0.72 -0.74 -0.90 -0.81 1.20 1.04 0.78 -2.50 Maximum 0.05 0.20 0.18 0.18 0.17 0.14 0.08 0.00 0.13 0.13 -0.15 0.12 2.13 1.97 1.57 -1.34

Table 4.1. Watertable/water depth (not AHD) summary for all bore/drain sites.

In sections 4.2 and 4.4, attention will focus on the bore "hole" (Bsl2) from which

groundwater water quality samples were taken. A rainfall/watertable plot is shown in

Figure 4. la, for this bore (labelled "the bore" - Bs12) whose watertable fluctuations were

typical of the floodplain bores; it had the watertable near to the ground surface during a

relatively wet period in mid March, 1993. The watertable dropped to 0.91m below the

ground surface with a corresponding decrease in rainfall until early July. It rose to

0.47m below the ground surface in response to rainfall on the ~th, 7th and 9th of July,

and then declined again until heavy rainfall was received on the 13-14th of September.

Figure 4.1 b, representing watertable fluctuations of the control bore located on undrained

land, showed a smaller decrease from the period in late April until early July. The

watertable in this control bore (Figure 4. lb) only rose 0.04m between field visits on the Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 7 2 0.2

rainfall 0 -E 60 watertable -0.2 -Q) -E • :c CCI E -0.4 i -m 40

--. -1 .4 - E Q) .c -1 .8 ~ Q) -::CCI ~- -2.2 0 .c- a -2.6 '3

-3 C\J ('I') ('I') v l() <.o <.o I'- co co (J) 0 ~ ~ ~ t::: ~ Q! ...... I'- (") I'- ...... v co C\J <.o (J) (") ;::: ...... v co ...... l() en ...... (") ...... C\J ...... C\J C\J C\J ...... C\J (") ------...... Date (1993) Figure 4.1. Depth to watertable (not ARD) for; a: the bore (Bs12) and b: the control bore.

30/6/93-9n /93 where for the corresponding period in the bore the watertable rose 0.44m. The watertable level in the control bore showed no major decline between 9n /93-7/9/93 . Rises in the watertable of 0.78m in the control bore and 0.64m from the floodplain were

experienced between 7/9/93-14/9/93. The watertable dropped rapidly on the floodplain

in the 11 days till 25/9/93, the watertable in the control bore continued to rise for 2 days

after the heavy rain on 14/9/93 and then declined slowly.

Although it is difficult to cmppare watertable fluctuations between two areas, when one

area is on a floodplain and the other is not, it seems evident from Figures 4.1a and 4.1 b

that the floodplain was prone to greater water rises in response to rainfall and in particular

to low intensity rainfall events. This was expected since more water accumulates on

floodplains after rainfall. Another obvious feature was a more rapid drop in the Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 7 3 watertable following rainfall on the drained floodplain (Figure 4. la) compared with the undrained area (Figure 4. lb). This indicated that the flood mitigation drains were performing their task of draining water quickly off the floodplain after rainfall.

The second step in this initial investigation was to determine whether groundwater was being drawn down into the drains (Figure 4.2a), thus causing direct oxidation of adjacent acid sulphate soils (Willett and Bowman, 1990) with the oxidation products being fed into the drains, or whether drain water was drawn into the floodplain (Figure 4.2b ), with drain water influencing groundwater quality. ®

water drain movement drain

Figure 4.2. Watertable movement in relation to a drain. Groundwater is being drawn down into the drain in 'a', and water is being drawn from the drain in 'b'.

At Jasper's Brush the groundwater was acting as a source in supplying water to the

transect drain during the period of monitoring from 17 /2/93-12/10/93 (neglecting any

effects from down slope water movements of which there was no information).

Examples of this are shown in Figure 4.3; all mean bore levels were higher than the mean

drain level. This was in accordance with watertable movements in relation to a drain as

shown in Figure 4.2a. Thus the main drain analysed at Jasper's Brush determined

groundwater height and had been causing oxidation of adjacent acid sulphate soils. This

conclusion is reaffirmed by the analysis of groundwater and drainage water quality

described in sections 4.4 and 4.8. In the sites described by both Willett and Walker

(1990) for the lower Macleay, and by White et al. (1993) for the Tweed the water level of

the drains was described as being higher than the groundwater level during field analysis. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 7 4

This was in accordance with watertable movements in relation to a drain as shown in

Figure 4.2b. The relationship between groundwater level and drain depth was likely to be different at Jasper's Brush, compared with areas on the north coast of NSW on the

lower Macleay and Tweed Rivers, because of drainage specifications and landuse. In

both examples from the north coast, drains studied had not been dug to invert levels as

low nor were they as deep as at Jasper's Brush:

Jasper's Brush dug to -l.2m AHD 1.4m deep

lower Macleay - Willett and Bowman ( 1990) dug to -0.3m AHD 0.5m deep

Tweed - White et al. (1993) dug to 0.4m AHD 0.6m deep

The main drains at Jasper's Brush had been dug at least 0.9m deeper than either of the

main drains in the above examples from the north coast of NSW. It is not clear here how

drains dug to different levels and of different depths can be used in determining the

relationships between groundwater movements and drain water depths. Hydraulic

factors such as pore water pressure and surface runoff patterns are likely to influence

ground movements in different ways where drainage specifications are different.

Different landuses in different areas are likely to affect groundwater movement. At

Jasper's Brush, floodplains are only used for low intensity dairying and beef production,

thus vegetation cover is predominantly grass (no reliable evapotransporation values were

available for the study area). Along the north coast of NSW (Tweed, Clarence) where

acid sulphate soils are found, a common landuse is sugar cane production. Sugar cane is

a water succulent plant, causing high evapotranspiration levels, (White et al., 1993) and

as a result water would not be permitted to move into drains as easily as in areas where

only grass cover is found. White et al. (1993) investigating the role of

evapotransporation from drained areas of land used for sugar cane production in

understanding the dynamics between watertable movements and drain water levels and

water chemistry. It was apparent from the present study that watertable movements in

relation to drains varied between locations along the NSW coast. Unknowns here Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 7 5 include; there was no data available for interflow or downslope flow which may affect the water levels on the Shoalhaven floodplain. And on average, precipitation exceeded evaporation in all months of the year, suggesting increases in depth to the watertable was due to decreased rainfall in this monitoring period.

Another point of interest shown in Figure 4.3 is that there was no obvious change in depth to the watertable moving away from the transect drain (for descriptions of bore locations see Chapter 3, section 3.5 and Appendix A). This would suggest watertable

levels for the area of the floodplain at least 400m away from the transect drain, in Figure

4.3, were dominated by deep drainage and that the influence of drainage from small

shallow channels was minimal.

1.50 .,.------, east backswamp profiles west 1.00 I ' - transect drain 17 0.50 14 13 12 1110 7 9 8 I 0 0.00 -:r ---- i- I ~-- -1- --- <( --1------T--f-----1-tt t l • • ~ ·0.50 l 1 'Qi I -1.00

·1.50 = mean and standard deviation watertable position V.E. = 30 l ·2.00 -'-r------,..------,.------.,------,...------,-1 0 100 200 300 400 500

Distance (m)

Figure 4.3. Mean and standard deviation watertahle and drain water depth position for the 8 month

long monitoring period (17/2/93 - 12/10/93), along the transect outlined in Chapter 3.

Further evidence to suggest groundwater levels were dominated by the deep artificial

drains lies with the mean groundwater levels of bores Bs7-9 on the western side of the

transect drain being lower than any bore on the eastern side of the transect drain, despite

little variation in ground surface elevation on both sides of the drain. The reason for this Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 7 6

is likely to be the result of the location of the bores in relation to other main drains.

Bores on the western side of the drain were within a small area bounded by drains to the

east, south and west; bores on the eastern side of the drain, had other, more distant

drains to the north east, south and west (Figure 3.3). Thus the higher density of drains

affecting bores Bs7-9 is represented in Figure 4.3 with depth to the watertable below m

AHD being greater for those bores than for bores Bs 10-17. Soil texture analysis

between the bores on either side of the transect drain showed no obvious variation and

could not account for the above watertable differences. More extensive ground surface

surveying would be useful in confirming deep drainage as the cause rather than other

factors such as surface runoff patterns.

4.3 Floodplain and Drain Water Levels and pH Dynamics

Acidic groundwater (pH <3.5) is one of the primary indicators of the existence of acid

sulphate soils (Melville et al., 1993; Mulvey, 1992; 1993). This section identifies the

existence of acidic groundwater and discusses the relationship between water movements

and pH of the floodplain and drain waters. Mean, standard deviation, median, minimum

and maximum pH values for all bores and drain sites are shown in Table 4.2.

Bs7 Bs8 Bs9 Bs10 Bs11 Bs12 Bs13 Bs14 Bs15 Bs16 Bs17 Bs18 transect road gate drain drain drain Mean 3.2 3.3 3.5 3.4 3.5 3.2 3.4 3.5 3.2 3.5 3.6 3.1 3.0 2.9 3.1 st. dev. 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.8 0.8 0.7 0.7 0.6 0.6 0.5 0.6 Median 3.2 3.3 3.5 3.4 3.5 3.2 3.4 3.4 3.1 3.5 3.6 3.1 3.0 2.9 3.2 Minimum 2.7 3.0 3.1 3.0 3.1 2.8 3.0 2.9 2.8 2.8 3.1 2.8 2.8 2.8 2.5 Maximum 5.7 5.7 5.4 5.0 5.3 5.5 5.5 5.5 5.5 5.2 5.2 4.7 4.3 3.9 4.0

Table 4.2. Summary of pH information from all bores and drain water analysis sites (see Figure 3.3).

4.3.1 Watertable/pH Relationships in the Floodplain

There was found to be little variation, in regard to pH change in response to watertable

fluctuations, amongst the 11 bores in the transect across the transect drain (all data,

including the rainfall record for the monitoring period, is given in Appendix C). The bore located 50m east from the transect drain had been chosen to describe pH change in Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 77 response to watertable fluctuations. The trends in this bore (Figure 4.4a) were typical of those in the 10 other bores along the profile transect and this was the bore used in later detailed water quality analysis (chloride, sulphate, iron and aluminium) in relationship to the watertable and pH.

Three important points may be observed in Figure 4.4a: * Rapid rises in the the watertable from shallow depth (about 0.5m below the ground

surface) noted on 19/3/93 and 14/9/9/3 caused pH to rise rapidly. However, the

rapid rise in the watertable from deeper in the profile (from 0.91m on 30/6/93

to 0.47m on 7/9/93) was not associated with a rapid rise in pH.

* pH was highest (4. 9-5.5) on the three occasions when the watertable was at or above the ground surface (0-0.14m). After the watertable had begun to subside even

marginally (by 0.03-0.13m) on the occasions when the watertable had been at or

above the ground surface, within 5 days, pH responded by decreasing rapidly (by

1.5-2.3 pH units).

* While the watertable was about 0.5m below the ground surface, or deeper, the pH

was relatively stable between 2.8-3.3.

Therefore, groundwater pH responded closely to fluctuations in the watertable, but

particularly when the watertable rose close to the ground surface.

4.3.2 Inter-Bore Comparisons of Groundwater pH

Bores Bs7, Bs 15, Bs16 and Bs18 were located in or adjacent to three types of water

courses, two of which were natural. Bore Bs15 (located in a palaeochannel) and bores

Bs7 and Bs18 (adjacent to a palaeochannel and semi-permanent swamp respectively) had

the lowest mean pH value (2.8) of all bores (Table 4.2). Bore Bs16, located in a man­

made channel beside the runway had a mean pH value of 3.7. The reasons for bores in Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 7 8 or adjacent to natural water courses continuing the most acidic groundwater is most likely due to the soil profile development in those areas and/or ground surface water movements. Soil profile analysis reported in Chapter 3 showed more thickly developed zones of abundant jarosite from bores adjacent to the natural water courses. Surface runoff from the floodplain flows through the palaeochannels; this was observed on

17 /2/93 when 28mm of rainfall fell in a 12 hour period, just prior to a field survey. In these and other areas of naturally low elevation such as the semi-permanent swamp adjacent to bore Bs18, jarosite was close to the ground surface. Bore Bs16, however, was located in a trench approximately 200m in length and 0.3m in depth. Jarosite in the soil surrounding Bs16 was considerably deeper than in the soils adjacent to the paleochannels. Hence, groundwater beneath the man-made channel at Bs16 was less acidic probably because jarosite was deeper in the surrounding area.

Of the remaining bores not located in or adjacent to a water course, the bore (Bsl2) used in the water quality analysis showed the lowest pH values (mean of 3.4±0.6, median of

3.2 and minimum of 2.8). No striking differences in soil profile development amongst the 12 bores could account for this variation. However, the bore was constructed with

0.15m diameter PVC pipe where all other 11 bores were constructed with 0.05m

diameter PVC pipe. It is proposed the greater volume of air in contact with water in the

bore may have resulted in some degree of secondary oxidation reactions, further reducing

acidity (secondary oxidation is discussed in section 4.4). The possibility of secondary

reactions occurring in groundwater sampling bores is worthy of further research.

4.3.3 Water Level/pH Relationships Between the Groundwater and

Drains

Figure 4.4a-e shows pH and water level fluctuations in the 3 drains immediately leading

off the study site and and watertable fluctuations in 2 bores near those drains (bore Bs12

and bore Bs18, closest to the road drain). It might be expected that the relationship

between depth of water in a drain and pH would correspond with the relationship Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 7 9 ® 7.0 .------0.2 ----- pH o E' 6.0 ~ watertable -0.2 ~ ca 5.0 -0.4 ~ :c •• a. '• iii 4.0 I I \ -0.6 3: ' , \ I I I l .8 ', I I I ,,, -0.8 £ 3.0 -- .... _..------· , "' a. -1 ~ 2.0

7.0 r------;:======:------, 2.5 ® ----- pH 6.0 :[ 2 .t= water depth a. 5.0 (I) :c "O a. 1.5 Cii 4.0 ,, ~ , , ., c: ,, .... ',,_ .. ______, .. --, ______, '''. - ~ 3.0 Cl

@) 7.0 0.2 0 6.0 E -0.2 ~ ca 5.0 t:: -0.4 Q) :c ,, a. I iii 4.0 I -0.6 3: \ I ,_ ' I '•I .8 -... \ , \ -0.8 .t= , ... ,----" , ..... _ I I ' ,1 \ a. 3.0 Q) ' ------' ' -- I ... - - -1 Cl 2.0 -1 .2 @ 7.0 2.5 ----- pH 6.0 2 .s .t= water depth a. Q) 5.0 "O :c ..... a. 1.5 Q) iii 4.0 3: c: ______, "iil 3.0 ...... ', ', --- .. --... \ ... q 2.0 0.5 ® 7.0 2.5 6.0 .s 2 .t= a. Q) 5.0 "O :c ..... a. 1.5 Q) 4.0 iii 3: c: 3.0 ... ·e - Cl 2.0 0.5 (") (") lO

Figure 4.4. Plots of pH vs depth to watertable for; a: Bs12 (the bore) and c: Bs18, and pH vs drain

water depth; b: transect drain, d: road drain and e: gate drain (see Figure 3.3 for locations). Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 8 0 between depth to watertable and pH in the bores closest to that particular drain. The overall trends for depth to watertable and pH are comparable for the transect drain and bore Bsl2 (Figures 4.4a and 4.4b), and also the road drain, and its closest bore (-200m apart) Bsl8 (Figure 4.4c and 4.4d). However, there were noticeable variations in trends between water depth and pH between these two drains and bore Bsl8. There are two likely reasons for this. Bore Bs18 was not located on the bore transect, but adjacent to a semi-permanent swamp, where jarosite was found relatively high in the profile (see

Chapter 3). Bore Bs18 was the only bore located in the catchment of the road drain. The relationship between depth to watertable and pH for bore Bs18 was unlike that relationship for any of the transect bores in a line from the transect drain. The second reason is related to differences in drain design. The transect drain, crossing the bore transect, is a main drain as described in Chapter 2. The road drain was a smaller mole drain. Common fluctuations between surrounding groundwater movements and pH with drain water depth and pH (Figures 4.4c and 4.4d) for the road drain were not as easy to distinguish as those for the transect drain (Figure 4.4a and 4.4b).

Comparisons of Figures 4.4d and 4.4e shows comparable trends in water depth and pH for the road drain and gate drain. The more acidic water draining from the road drain into the gate drain highlights the active role the road (mole) drain had in contributing towards the development of acid drainage in a main drain. This last point is discussed further in section 4.4.

4.4 Floodplain and Drain, Rainfall, Water Level and Water Quality

Dynamics

In this section, more detailed description and explanation is given for pH fluctuations in response to rainfall and the consequent change in groundwater and drainage water quality. Further detail is given describing groundwater and drainage water quality with chloride, sulphate, iron and aluminium levels being reported here. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 8 l

Low groundwater pH ( <3 .5) alone is not a good indicator of the extent of pyritic oxidation (Mulvey, 1993). Development of groundwater with pH below 3.5 can have causes other than pyritic oxidation; conversely acidity due to pyritic oxidation can be neutralised by the soil mineral fraction or by shells. However, a combination of low pH

( <3.5), elevated sulphate concentrations and a chloride/sulphate ratio less than 4, is a certain indicator of pyritic oxidation; the combination of pH and the chloride/sulphate ratio gives some understanding of the extent of pyrite oxidation (Mulvey, 1992; 1993).

The sulphate concentration in sea water is approximately 2,700 mg/l (parts per million -

ppm) and chloride is 19,400 ppm with the chloride/sulphate ratio on a mass basis being

7.2:1 . The ratios of the dominant ions in a saline water remain approximately the same

when the saline water is diluted. Thus estuaries and coastal creeks and associated

groundwater will normally have ratios for dominant ions similar to those in sea water. In

shallow coastal waters, the principal potential sources of sulphate are the seawater and

pyritic oxidation, but the chloride/sulphate ratios will differ depending on the relative

importance of those sources (Mulvey, 1993).

Analysis of chloride and sulphate was chosen to identify beyond any reasonable doubt

the existence of pyritic oxidation at Jasper's Brush and consequently to gain an

understanding of the extent of pyritic oxidation in the groundwater and drainage water.

Following pyrite oxidation (see Equation 1.1) a number of oxidation products develop

other than high levels of hydrogen ions (see Chapter 3). These include iron and

aluminium dissolved from the soil. High aluminium levels are particularly important

because they result in reduced productivity, impaired growth and even death of plants

and fish (Dent, 1986; Dent and Pons, 1993; Mulvey, 1992; 1993). The analysis of

soluble iron and aluminium was chosen here to gain an understanding of the distribution

and concentration of these metals at Jasper's Brush. Soluble levels only were Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 82 determined, although it was recognised that toxicity of dissolved metals can be ameliorated by organic chelation and precipitation and flocculation (see Chapter 5). pH

<3.5 and soluble aluminium levels >3ppm is a combination widely considered to indicate extreme oxidation and toxicity to aquatic lifeforms (Dent, 1986). The vast majority of the values measured from the study area lie in these extreme ranges, as indicated below.

To simplify the description of the relationships between rainfall and both groundwater and drainage water movements and water quality fluctuations, the eight-month-long monitoring program was divided into 4 periods according to broad rainfall patterns and corresponding watertable fluctuations during that time. The 4 periods were:

Period 1: 17 /2/93-19/3/93 - moderate rainfall promoting a shallow, but variable

watertable.

Period 2: 19/3/93-30/6/93 - long term dry period promoting a continual increase in the

depth to watertable.

Period 3: 30/6/93-9n/93 - intermittent rainfall promoting an initial rise then general

stability in the watertable depth. Period 4: 9n /93-12/10/93 - intensive, short term rainfall initially promoting minor flooding/rapid watertable rise.

Chloride, sulphate, iron (soluble) and aluminium (soluble - aluminium speciation is discussed in section 4.8) levels in Figure 4.5 are results from the analysis of single grab samples. Four replicate samples were analysed for chloride and sulphate for the 3 water quality sites (Figure 3.3) on 17 /2/94 and 23/2/94, and 2 for iron and aluminium.

Standard deviations were considered small enough to permit analysis of single samples to give accurate results, as shown by Table 4.3. Additionally, standard deviations from the samples taken on 17 /2/94 would be higher than normal as these samples were taken shortly after significant rainfall, to the extent where the watertable was at the ground surface in the bore, thus causing mixing in the sample of surface and soil waters. Cha[!tcr 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 83

date (1993) the bore transect drain road drain the bore transect drain road drain chloride sulphate

29 310 40 32 560 330 28 290 44 31 490 390 17/2 27 340 39 30 600 320 28 330 45 31 560 390

Mean 28 317.5 42 31 552.5 357.5 St. dev. 0.82 22.17 2.94 0.82 45.73 37 .75

55 530 170 220 990 1700 23/2 55 530 170 220 980 1700 54 530 170 230 950 1700 55 520 170 210 980 1700

Mean 54.75 527.5 170 220 975 1700 St.dev. 0.50 5.00 0.00 8.16 17.32 0.00

aluminium iron

17/2 0.9 30.3 10 0.4 6.4 4.2 0.9 29.8 8.1 0.4 6.1 2.9

Mean 0.9 30.05 9.05 0.4 6.25 3.55 St.dev. 0.00 0.35 1.34 0.00 0.21 0.92

23/2 52 10.7 89.6 18.2 4.7 92.8 52.7 10.5 88.3 18.2 5 93 .2

Mean 52.35 10.6 88.95 18.2 4.85 93 St.dev. 0.49 0.14 0.92 0.00 0.21 0.28

Table 4.3. Mean and standard deviation data from intitial sampling at the three water quality sites in

the study area as measured in ppm.

All results for each period are inclusive for the dates representative for the first and last

sampling day in each of the 4 periods (some sampling day results are used in two

periods). Section 4.4 is discussed with reference to Figure 4.5a-c, Figure 4.6a-c and

Figure 4.7a-c. Mean and standard deviation summary data quoted in regards to Figures

4.5-4.7 for each site, for periods 1, 2 and 4, are given in Table 4.4. All water quality

results for this section are shown in Appendix C. The above data is not shown for

period 3 in Table 4.4 because sampling in the study area was intermitten during this

period due to resources being taken elsewhere, for reasons described in section 4.4.3.

Raw data and mean, standard deviation, median, minimum and maximum values for

chloride, sulphate, chloride/sulphate ratio, iron and aluminium are given in Appendix C.

For the speciation of aluminium used see 4.8.1. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 84

80 0.2 r;:::=====:::------...'.F..'.:igu~re::_4:·~6 2.5 Figure 4.7 ---rainfall ---rainlalt @ 60 I ® -0.2 . ~ waterdeplh e 'iii .s -0.4 1" 40 ~ -0.6 ~ ;\!! 0 20 ·0.8 i -1 0

-1.2

10 @ .g ~ 6 ~ ~ !!l :g :l1 ()

""° 0

12000 3000

10000 ~chloride @) 2500 @) @) e 8000 2000 '[ .% s . 6000 1500 ~ ~ "'0 4000 1000 % ti Cf) 2000 500

120 350 @) @) 100 0 @) 300 '[ 250 s 80 200 I § 60 ·2 150 _g E 40 ;i! 100 { 20 50 Oo o

0 0 0

Figures 4 .5-4.7. Water quality - Figure 4.S; a: Rainfall vs Depth 10 watcrtable. b: pH vs Chloride/Sulphate ratio, c: Chloride vs Sulphate and d: Soluble Aluminium vs

Soluble Iron for the bore (Bsl2). Drain wa1cr quality for th e tran sec t drain - Figure 4.6 and lhe road drain - Figure 4.7 for; Rainfall vs Drain water depth. h: pH vs

Chloride/Sulphate ratio, c: Ch loride vs Sulphate and d: So luble Aluminium vs Soluble Iron (sec Figure 3.3 for location) . Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 85

4.4.1 Period 1: 17/2/93 - 19/3/93

Rainfall vs Depth to Watertable/Drain Water Depth

The watertable was first measured in the bore as a high level of O.Olm above the ground

surface on 17 /2/94 (Figure 4.5a). This level quickly dropped to 0.43m below the ground

surface over the next 9 days despite 19mm of rainfall during that period. After 63.Smrn

of rainfall over 17 days from the 26/2/93-15/3/93, the depth to watertable decreased to

0.3m. The watertable then rose to 0.02m above the ground surface on the 19/3/94 with a

further 13.Smrn of rainfall. In the transect drain (Figure 4.6a) and the road drain (Figure

4.7a), there were only minor fluctuations (ranges of 0.12m and 0.08m respectively)

during this period.

Period Field pH - -~~!!?!.~~~...... ~.':l.IP.~~~.E'.l ...... S.!{~.Q~ ...... !~ .'?.~ ...... ~!~!!1 .iD.i.':l.~ ...... P .e~ ...... Bore Mean 4 41 .4 131 .1 0.43 14.4 21 .1 St. dev. 0.7 13.9 83 .6 0.26 25.9 27 .5

P1 Transect drain Mean 3.2 456.4 814.3 0.55 8.2 28.2 St. dev. 0.3 232.2 334.8 0.16 5.8 20

Road drain Mean 3.2 126 1180 0.12 48 62.1 St. dev. 0.2 47 .8 4096.3 0.03 35.1 29 .6

Bore Mean 3.1 170.56 1292.5 0.16 154.9 44.3 St. dev. 0.3 80 .9 725.9 0.05 119.9 30 .3

P2 Transect drain Mean 2.9 1100.4 891 .3 1.1 14.4 35.7 St. dev. 0.1 1619.7 270.7 1.3 4.5 10.6

Road drain Mean 2.9 196.3 1871.9 0.15 151.6 82.8 St. dev. 0.1 41 .3 647.1 0.15 72.8 17.8

Bore Mean 3.7 34 98.4 0.36 3.2 6.6 St. dev. 0.8 8.9 23.7 0.03 2.7 1.6

P4 Transect drain Mean 3.4 273 .3 334 6.6 26.7 St. dev. 0.5 115.7 238.7 2.6 18.4

Road drain Mean 3.1 119 897.5 0.14 39.5 42.7 St. dev. 0.1 50 .6 449.9 0.02 14.4 23.6

Table 4.4. Water quality summary for the three water quality sites, for periods 1, 2 and 4 (see

description above in section 4.4) during the monitoring period. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 8 6 pH vs Chloride/Sulphate Ratio

The watertable fluctuations in the bore (Figure 4.5b) were closely followed by the fluctuations in pH (section 4.3). The pH started at 4.9 on 26/2/93 and after 9 days

dropped to 3.3. As the watertable rose, the pH followed, remaining steady near 3.8

while the watertable was at about 0.4m depth, but rising quickly to 5.1 when the

watertable reached the ground surface on 19/3/93.

The trends for pH fluctuations in the transect drain (Figure 4.6b) were similar to those in

the bore. However, the water was more acidic with a smaller standard deviation in the

transect drain (3.2±0.3) than in the bore (4.0±0.7). In the road drain (Figure 4.7b), as

in the bore and transect drain, pH decreased as the water level rose. Mean pH for the

period in the road drain (3.2±0.2) was similar to that in the transect drain.

Chloride/sulphate ratios were very low in the study area, indicating strong pyritic

oxidation. The chloride/sulphate ratio did not rise above 0.9 for this period in the bore;

the mean chloride/sulphate ratio for the bore in this period was 0.43±0.26. The

chloride/sulphate ratio in the transect drain was similar (0.55±0.16) to that in the bore.

In the road drain, the mean chloride/sulphate ratio was the lowest (0.12±0.3) and

showed the smallest standard deviation of the three water quality sites for this period.

This suggests the road drain was being fed by a catchment with a stronger oxidising

environment than the other 2 sites, and/or further oxidation is occurring in the road drain.

This point is expanded later in this chapter.

Chloride and Sulphate

Chloride was . low throughout this period in the bore with a mean of 41.4±13.9ppm

(Figure 4.5c). Minor fluctuations in chloride could be seen in the transect drain (Figure

4.6c) with the two lowest values corresponding to the times of highest water depth in this

drain. The mean chloride concentration of 456.4±232.2ppm was somewhat higher than Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 8 7

in the transect drain. In the road drain (Figure 4.7c), chloride concentrations were again

low with a mean of 126±47.8ppm.

The concentration of sulphate in the bore (bores were not pumped prior to sampling)

showed a stronger trend than chloride, being highest when the depth to watertable was

lowest and vice versa. A similar, but weaker trend could be seen in both drains with the

lowest values recorded when drain depth was highest. The overall mean concentration of

sulphate increased from the bore (13 l.1±83.6ppm) to the transect drain

(814.3±334.8ppm) and the road drain (1180.1±496.3ppm). This supports the assertion

made earlier, that the road drain sub-catchment was the more oxidising of the two

studied, or that the acidic runoff was more diluted in the transect drain's catchment.

Iron and Aluminium

The mean concentration of iron was lowest in the transect drain (8.2±5.8ppm - Figure

4.6d), higher in the bore (14.4±25.9ppm - Figure 4.5d), but was considerably higher in

the road drain (48±35.lppm - Figure 4.7d). Fluctuations of iron were shown to be

closely related to those described below for aluminium.

The key factors in the concentration of aluminium in the bore were two peaks on 23/2/93

and 12/3/93. The concentration of 52ppm from a sample collected on 23/2/93 was

5 lppm higher than the concentration of the sample taken 5 days earlier. Possible reasons

for this include a drop in pH of 1.5 units during this 5 day period, increasing the

concentration of soluble aluminium in solution, along with 15mm of rainfall on 20/2/93

having the effect of flushing aluminium in a soluble form, from the soil into

groundwater, when the watertable was falling. Similar reasoning is proposed for the

larger rise in aluminium from 7ppm on 8/3/93 to 68ppm on 12/3/93.

Two peaks of aluminium rising from 10-48ppm and from 7-50ppm also occurred in the

transect drain from the two previous sampling days. In both cases these peaks occurred Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 88 on the next sampling day after the sampling days which registered the corresponding peaks in the bore (after 3 and 12 days respectively). This observation indicates a movement of acid drainage from the floodplain into the drain with two periods of lag.

Different or more variable oxidation processes may also occur in the floodplain. This may account for a smaller range of aluminium in the transect drain (44ppm) compared to the bore (68ppm) for this period.

The average concentration of aluminium for the period was greater in the road drain

(62.1±29.6ppm) than in the transect drain (28.2±20ppm) or the bore (21.1±27.Sppm).

In all cases, but particularly in the 2 drains, the fluctuations in aluminium levels largely

corresponded to the pattern of fluctuation in sulphate and iron levels. Also, the levels of

both aluminium and sulphate were lowest in the bore (groundwater), higher in the

transect drain and highest in the road drain. This reaffirms the observation from the

chloride/sulphate ratio that the road drain was being fed by a catchment with a stronger

oxidising environment than the bore. This also suggests these two drains could be acting

to trap and accumulate soluble aluminium.

4.4.2 Period 2: 24/3/93 - 30/6/93

Rainfall vs Depth to Watertable/Drain Water Depth

The depth to watertable in the bore during this period showed (except on 10/6/93) a

continual drop from at the ground surface on 19/3/93 to -0.9lm on 30/6/93; only

62.5mm of rainfall was recorded for this 103 day period. The most rapid drop in

watertable occurred, early in this period after the relatively wet period in early to late

March (see section 4.3.1). This drop in the watertable of 0.26m in 9 days from 24/3/93-

2/4/93, occurred despite l 1.5mm of rainfall. Rainfall up to 10.5mm on three other days

between 2/4/93-2/6/93 slowed the decrease in the depth to the watertable, and 16mm of

rainfall recorded on 3/6/93 did cause the watertable to rise slightly. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 8 9

The depth of water in the transect drain showed an overall decrease from 19/3/93-30/6/93 of 1.56-1.29m. This decrease of 0.37m was far less than the decrease of 0.91m for the change in depth to the watertable experienced in the bore for the same period. The road drain fluctuated but showed only a slight overall decrease in drain water depth of 0.06m.

pH and Chloride/Sulphate Ratio

The relative water depths for the bore and transect drain for this period, as in the previous

period, showed overall correspondence with pH (greater water elevation leading to

higher pH and vice versa). The mean pH was less acidic in the bore (3.1±0.3) than in

the drains, with the transect drain 2.9±0.14 and the road drain 2.9±0.12. Both in the

bore and in the drains, pH varied far less in this period of consistently low water

elevations than in the preceding wetter period. An interesting point was that pH

stabilised between 2.8-3.0 upon reaching the zone of abundant jarosite at 0.7m below the

ground surface in the bore on 6/5/93. This stable pH was an indication of how low

groundwater pH at this location in the floodplain was likely to fall, since the continuing

drop in the watertable throughout June did not promote any further drop in pH. Any

further drop in the watertable below the maximum of -0.9lm experienced here would

also be unlikely to promote a further drop in pH below approximately 2.8, since the

oxidised zone graded out below lm and no jarosite was found beyond l.15m depth.

The chloride/sulphate ratios for the bore and the road drain were very low with little

variation in values of 0.16±0.05 and 0.15±0.15 respectively. The chloride/sulphate ratio

was highest in the transect drain at 1.1±1.3. However, more noteworthy was the

increase in the chloride/sulphate ratio of 4.61 from 0.72-5.33 in the 28 days between

2/6/93-30/6/93. The reason for this is a rise in the chloride concentration due to seawater

incursion, and this is discussed further in Chapter 5. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 90

Chloride and Sulphate

Apart from the rapid rise in the chloride concentration after 2/6/93 in the transect drain, chloride was at very low levels with little variation between the bore and the road drain; the bore had the lower mean value of l 70.6±80.9ppm compared with the road drain

196.3±41.3ppm.

In the bore, the concentration of sulphate was closely related to the depth to the

watertable, with a pronounced rise in sulphate to 2,200ppm when the depth to the

watertable was greatest (on 30/6/93) from a level of 33ppm on 19/3/93. Although the

rate of increase slowed when the watertable reached the zone of abundant jarosite, the

sulphate concentration did not stabilise here, as the pH had done.

There were noticeable differences in mean sulphate concentrations m the bore

(1,292.5±725.9ppm), the transect drain (891.3±270.7ppm) and the road drain

(1,871. 9±647 .1 ppm). In the bore and the transect drain, the sulphate concentration rose

from 19/3/93-30/6/93. However, the range in the sulphate concentration in the transect

drain was only l,040ppm compared with 2,167ppm for the bore. In the transect drain

there was an initial rapid rise, then a flattening off, whereas sulphate levels rose steadily

in the bore. The overall sulphate concentration in the road drain was higher than the bore

and transect drain, but the concentration here showed no apparent relationship between

drain water depth or pH.

The sudden drop in sulphate in the transect drain of 920ppm on the 27 /4/93 to 240ppm

on the 6/5/93 was a feature of this period. Reasons for the drop are unclear, but may be

related to 8mm of rain falling between 29/4/93-30/4/93. No rainfall was recorded 34

days prior to 29/4/93. It is possible the sample collected on 6/5/93 was diluted by local

surface runoff, as concentrations of all ions determined were low. However, as the drain

level was also low, this seems improbable and no good reason for the variation were

obvious. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 91

Iron and Aluminium

Iron rose throughout this period in the bore from 1.3ppm on 19/3/93 to 340ppm by

30/6/93. There was one obvious rise in iron from 90-192ppm from 6/5/93-14/5/93. By

6/5/93 the watertable had been in the zone of abundant jarosite (0. 7-1.0m) for

approximately 4 days, with iron apparently being released there, since there was a rise in

iron for the whole time the watertable was in the zone of abundant jarosite. For

approximately the 43 days the watertable was above the zone of abundant jarosite, iron

rose by 83.7ppm (1.9ppm per day), but the 60 days the watertable was in the zone of

abundantjarosite, iron rose by 255ppm (4.3ppm per day).

Mean iron was consistently low in the transect drain (14.4±4.5ppm), much lower than

the bore (154.9±119.9ppm) or the road drain (15 l.6±72.8ppm). It seems soluble iron

was precipitated out in the transect drain, but was released into groundwater of the bore

from the surrounding soils and remained in solution in the smaller road drain. Possible

reasons are again believed to be associated with the buffering effect of more saline creek

water moving up the drain as described in Chapter 5.

Aluminium in the bore steadily rose from 0.2ppm on 19/3/93 to 48ppm 75 days later on

2/6/93 (0.6ppm per day). A rapid 52ppm rise in aluminium to lOOppm in 8 days was

then recorded by 10/6/93 (6.5ppm per day). The reason for this may have been 16mm of

rainfall on 3/6/93, flushing aluminium from the soil after it had been accumulating during

this dry period since it corresponded with a slight rise in the watertable. Aluminium in

the bore thereafter dropped to 81 ppm by 30/6/93.

Aluminium in the transect drain behaved similarly to sulphate, when compared with the

bore. Towards the end of this period (from 16/6/93) aluminium levels dropped in the

transect drain, 6 days after the relative drop shown in the bore. This supports the

suggestion of a lag in oxidation products from the floodplain into the drain. The steep

rise in aluminium described for the bore from 2/6/93-10/6/93 was not seen in the transect Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 92 drain. This was again attributed to the compositing effect of groundwaters from a relatively large area diffusing into an accumulation area, as may be indicated by the transect drain (35.7±10.6ppm) having a similar mean aluminium concentration to the bore (44.3±30.3ppm), but a much lower standard deviation. The mean aluminium for the road drain (82.8±17.8ppm) was noticeably higher than either the bore or transect drain for this period, corresponding to its lower pH and higher sulphate levels.

4.4.3 Period 3: 9/7/93 - 7/9/93

In early July it was known that this project required a different approach to the one

originally proposed, since remediation works were not proceeding (see Chapter 1). In

order to obtain results which could effectively be used to understand acid drainage at

Jasper's Brush while acquiring results useful in devising management options, some of

the water sampling resources were diverted to focus on new issues. All water quality

results which were available by mid July were analysed. Rainfall and watertable results,

when compared with the water quality results in the bore, were found to correlate well

enough and over a long enough period to understand, in broad terms, groundwater

movement in response to rainfall and the consequent production of oxidation products. It

was decided that the frequency of water quality sampling in the bore could be reduced,

but depth to watertable and pH measurements should still be taken on each field visit,

providing enough information to continue to analyse the relationships between the

floodplain and transect drain in particular. The frequency of original sampling was

maintained for the transect drain. pH and drain depth data were collected upon each field

visit for the road drain but only a few further chemical analysis were performed for this

drain. The focus of the study shifted to water quality in Broughton Creek and it was

considered important to concentrate on the link from floodplain sediments to main drains

to the creek. The behaviour of the smaller road drain, although recognised as a highly

polluted source, was less important because of its low volume and because it drained a

different subcatchment within the study site. The above new direction in analysing the

water quality of acid drainage is discussed in Chapter 5. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 93

Rainfall vs Depth to Watertable/Drain Water Depth

The watertable in the bore rose 0.44m to be 0.47m below the ground surface by 9/7 /93 in response to 44mm of rainfall between 30/6/93-9/7 /93. The depth to the watertable was maintained at a fairly consistent level (0.47-0.60m below the ground surface) from

9/7 /93 until the end of the period in which time a further 53mm of rainfall was received.

Again, the fluctuations in the transect drain were in a similar but more muted pattern to those in the bore.

pH

The range of pH and the bore (0.2) as the transect drain (0.4) was low during this period; in the road drain it was slightly greater at 0.8 pH units.

Chloride/Sulphate Ratio - Aluminium

The few water quality samples taken during this period showed that again the bore and road drains had higher iron and aluminium levels than the transect drain, with chloride being consistently low in the transect drain.

4.4.4 Period 4: 7 /9/93 - 12/10/93

Rainfall vs Depth to Watertable/Drain Water Depth

A flood (whose recurrence interval is discussed in Chapter 6 - section 6.4) was experienced at Jasper's Brush and Broughton Creek after 133mm of rain fell in 3 days

(12/9/93 - 56mm; 13/9/93 - 70.Smm; 14/9/93 - 6.5mm). From 9/7 /93-14/9/93 the watertable rose 0.64m to be a height of 0.14m above the ground surface at the bore on

14/9/93. The watertable dropped to 0.37m below the ground surface by 29/9/93, as no further rainfall was experienced. A further 14.Smm of rain between 1/10/93-4/10/94 caused a relatively large watertable rise of O. l 7-0.20m below the ground surface from

29/9/93-7 /10/93, due to the soil still being close to saturation after the flood. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 94

The trends for drain water depth fluctuations in both drains, with time, throughout this period corresponded to watertable fluctuations described for the bore. Drain water depth increased 0.73m to 2.13m depth in the transect drain and 0.78m to l.97m depth in the road drain from the 7/9/93-14/9/93. By the 12/10/93, drain water depth had decreased to

1.47m in the transect drain and l.18m in the road drain.

pH vs Chloride/Sulphate Ratio

In the bore, pH rose from 3.2-5.5 from 7/9/93-14/9/93, but dropped back down to 3.2

only 2 days later. pH then experienced another rise of 1.2 units to 4.4 from the 19/9/93-

21/9/93 and another fall of 1.1 units on 25/9/93, before stabilising between 3.1-3.2 from

3/10/93. Trends in pH which changed from 7/9/93-12/10/93 in both drains, were similar

to those described over that period for the bore, with the most obvious difference being

pH only rising to 4.3 in the transect drain and 3.8 in the road drain on 14/9/93. This was

probably due to the influence of relatively acidic runoff moving off the spoil heaps and

into the drains on 14/9/93, and to the water sampled in the bore being diluted by runoff

from the non-acidic ridges.

The chloride/sulphate ratio remained low in the bore (0.36±0.03) and road drain

(0.14±0.02) for this period. The chloride/sulphate ratio in the the transect drain was

3.05 on 14/9/93, but dropped to 0.52 by 19/9/93, thereafter ranging from the 0.52-0.65.

Chloride and Sulphate

Sulphate concentrations rose in the transect drain and road drain after the 14/9/93.

Chloride ranged from 24-47ppm in the bore, 110-430ppm in the transect drain and 56-

180ppm in the road drain between 19/9/93.-12/10/93. Sulphate ranged from 66ppm-

130ppm in the bore, 38-700ppm in the transect drain and 420-1500ppm in the road

drain. In both drains, sulphate concentrations rose as the flood receded; in the bore, the

level remained low in association with a watertable close to the surface. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 95

Iron and Aluminium

Iron remained low in the bore, transect drain and road drain. Mean iron for the bore was

3.2±2.7ppm, for road drain 39.5±14.4ppm; in both cases these values were well below

the dry weather readings. In the transect drain, iron was 6.6±2.6ppm, a value

comparable to the readings in the March wet period and slightly lower than the

intervening drier periods.

Aluminium remained low in the bore with a mean of 6.6±1.6ppm, not rising above 8ppm

throughout the period. The flood in early to mid September caused the generation of far

less soluble aluminium than the 3 other periods in this analysis because groundwater

levels and pH remained high. In the transect drain for period 4, mean aluminium was

26.7±18.4ppm; the level rose 52ppm from 2ppm on 14/9/93 to 54ppm on 12/10/93, at

the same time that sulphate levels rose rapidly. For soluble aluminium to increase in the

drain by this amount after the flood, when levels remained considerably lower in

groundwater for this period indicated that the transect drain was accumulating aluminium

from a continual supply and large volume of groundwater; thus the effects of the flood in

creating acid drainage were felt for at least 1 month. In the road drain, only three

samples were taken and values were high (50-190ppm).

4.5 Discussion of Rainfall, Water Height/Depth, pH and Water Quality Comparisons from Figures 4.5-4. 7, for the Bores and Drains

It has been shown in section 4.4 how, in the floodplain, rainfall patterns dictated

watertable trends. There was also a relationship between pH and watertable trends, with

changes observed as the watertable moved through an acid sulphate soil profile.

Sulphate and aluminium levels were closely related in the bore and 2 drains; iron levels

also followed the same trend in the bore and road drain, but were consistently low in the

transect drain. Chloride levels were very low except in the transect drain; this indicated

that there had been considerable leaching since the estuarine sediments were emplaced. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 96

This thesis will now concentrate on discussion of the relationships which dictate the quality of water draining from the floodplain.

It has been shown that groundwater entered the transect drain and that water quality in the transect drain was largely a reflection of the water quality from the floodplain; water quality in the transect drain was closely related to that in the bore. Major fluctuations in pH and water quality variables in the bore were echoed in the transect drain, with a lag time of several days. However, despite these strong relationships between water quality fluctuations at both sites, drain water quality was not identical to groundwater quality.

Other factors in the drain appeared to influence drain water quality at any particular time.

The overall range of pH was less for the transect drain than the bore, as were sulphate, iron and aluminium levels. This may indicate a smoothing effect as water of varying quality moved from a relatively large floodplain area into the transect drain. Also, different chemical processes were likely to occur in the transect drain, i.e. acid drainage severity was higher in the bore than "average" compared to all other bores with a smaller diameter (150mm vs 50mm). This has already been suggested as possibly resulting because of secondary oxidation. One feature peculiar to the transect drain was the sudden increase in chloride level in late June. This was thought to be due to leakage of estuarine water into the drain because the floodgate was not closing fully (see Chapter 5).

While it might be expected that this saline incursion had some buffering effect, pH in fact only rose slightly but soluble aluminium levels declined. However, the cause of these changes in drain water quality was difficult to determine as there was some rainfall and an associated rising watertable, which also tended to increase pH and decrease aluminium and sulphate levels.

It has been shown in results from section 4.2 and described here how the water quality in the transect drain, the larger of the two types of drains (mole/main) found at Jasper's

Brush, was largely controlled by groundwater quality. However, it was more difficult to understand water quality fluctuations in the road drain. Yet there are many small feeder Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 97 drains on the floodplain and it is important to try and understand the role they play in influencing water quality. The difference in fluctuations of drain water depth between the road drain and transect drain was a probable key to explaining the variation in water quality between the two drains. Whereas the fluctuations in the transect drain followed rainfall patterns, those in the road drain were more irregular, reflecting the pattern of runoff from a very small sub-catchment. As the road drain is smaller than the transect drain, the characteristics of the water it received from the floodplain will be different Its relatively low pH (lower than the bore), low chloride/sulphate ratio (lower than the bore) and high sulphate concentration (higher than the bore) throughout the monitoring period is an indication that it is fed from a strongly oxidising environment; this explains the relatively high concentrations of iron and aluminium. The road drain is largely fed by surface runoff over spoil heaps of which there is a higher density in this drain's catchment than in the catchment of the transect drain. Also the road drain would be fed by shallow groundwater movement through soils where jarosite was observed to be closer to the ground surface (Chapter 3) than in the transect drain's catchment. These reasons explain why higher concentrations of oxidation products are fed into the road

drain compared with the transect drain, but may not be the only reasons why such high

concentrations of sulphate, iron and aluminium were found in the road drain. We must

consider the size of this drain also.

The road drain is smaller and from field observations, obviously more stagnant than the

transect drain. A most prominant feature was the almost complete blockage of the road

drain at most times by reeds and ochre (a gelatinous deposit rich in iron oxide). Thus,

the chemical and biological environment of water in the two different types of drains was

different. This ~aises a point to be developed further in Chapter 5, that where a drain was

subject to a degree of amelioration and buffering by saline sea water (indicated by high

chloride levels) the severity of acid drainage was reduced compared with a stagnant

drain. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 9 8

4.6 Linear Regression Analysis of Floodplain and Drain Water Quality Results

It has already been shown in this chapter that when depth to groundwater drops, pH decreases and aluminium levels increase. This same scenario was also shown for the drains with decreasing drain water depth.

A statistical relationship was performed between pH vs depth to watertable (Figure 4.8a),

aluminium vs depth to watertable (Figure 4.8b) and aluminium vs pH (Figure 4.8c) for

the bore and pH vs drain water depth (Figure 4.9a), aluminium vs drain water depth

(Figure 4.9b) and aluminium vs pH (Figure 4.9c) for the transect drain, using linear

regression analysis. The aim of this exercise was to see how statistically accurate the

above relationships were. Statistically accurate pH and/or depth to the watertable and

drain water depth relationships could be used as a means of accurately predicting the

concentration of aluminium in the study area. Future field visits to measure simply pH

and/or depth to the watertable and drain water depth would provide a fast estimate of

aluminium concentrations.

Rsquared (r2) measures the proportion of the variation around the mean, explained by the

linear model. The remaining variation is attributed to random error. Rsquared is 1 if the

model fits perfectly, and 0 if the fit is no better than the simple mean model. The

statistical significance of r2 was tested using the F test, at a 95% confidence level. The fit

of the model to the data was evaluated using 95% confidence limits for the regression

line.

Bore

The pH vs depth to watertable was noticeably significant for the bore with an r2 - 0.559,

meaning that 55.9% of the variation in the data set was explained around the line (mean).

The statistical significance was also noticeable with P>F - 0.0000, meaning there would

be

6.0

N - 31 5.0 r2 - 0.559 4 . 0 .· F - 36.7412

.. P>F - 0.0000 3.0 ..... ;...... -- . . ~ ... .··

2.0-r-~-.--~-,--~-,--~-,--~-,-~-,-~ -1.2 -1 . 0 -0.8 -0 . 6 -0. 4 -0.2 0.0 0.2 Depth to watertable (m) ®120-.---~~~~~~~~~ y = -25.89x + 123.120 1 00

80 ::.... ' N -31 ' 60 r2 - 0.456

' ·,_ __ _ -...... ~ :~ ~ 40 ...... F - 24.2811 ' ...... P>F - 0.0000 . ' , 20 . ... ' . . ... ' .. , .. o-t-~-.--~-,--~-...-~-.--~-.--~~---j -1.2 -1.0 -0.8 -0 . 6 -0.4 -0.2 0.0 0.2 Depth to watertable (m)

©120-.-~~~~~~~~~~~~---., y = -7 4.24x + 1.262

100

80 "E N - 31 .e,c. ' E 60 ' ' ::i r2 - 0.212 ·2 ".' . .E .. ' ' .. ' ' . ::i 40 ' .. F - 7.7646 <( : . .. . -. -..., . ' ' P>F - 0.0093 20 .' . .. ' ' . ' •• ..' o-r-~~.-~~r------"-,..~~--.--~---;' 2.0 3 .0 4 .0 5 .0 6 .0 7 . 0 p-t Figure 4.8. Statistics for the bore (Bsl2); a: pH vs depth to watertable, b: aluminium vs depth to watertable and c: aluminium vs pH. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 100 ® 1.0-.------~ y = 1.52x + 0.852

6.0

N - 37 5 .0 :c_ r2 - 0.686 .. .. 4.0 ...... F - 76.5129 -·· .-· ...... · ..-::: ...... P>F - 0.0000 3 .0

2.0 1.0 1 .5 2.0 2.5 Drain water depth (m)

@120 y = -47.05x + 103.167

100

80 N - 37 Ec.. .e: E 60 r2 - 0.251 ·c:::i .. . .E ::i F - 11.6912 < 40 .. ·-. ·-. P>F - 0.0016 20 ' ' . ' ' ' ' . . . ' ' ' ' .. ' ' 0 ' ' 1.0 1 .5 2.0 2.5 Drain water depth (m) © 120-.------~ Y = -32.16x + 133.149 100

80 N - 37 Ec.. .e: E 60 . r2 - 0.391 ::i . ·c: • I . .E ..k• . ::i 40 ' F - 22.6421 < !I"':. ' ...... •(., ' ,, ', .. , ' P>F - 0.0000 ' ' 20 "\ ' ' .. ' .. .. ' ·: . ' ~ 0 2.0 3.0 4.0 5.0 6.0 7.0 p-1 Figure 4.9. Statistics for the transect drain; a: pH vs drain depth, b: aluminium vs drain depth and c:

aluminium vs pH. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 101

The proportion of variation explained around the mean was less for aluminium vs depth to watertable (r2 - 0.456) and less again for aluminium vs pH (r2 - 0.212). However, the statistical strength of P>F was still <1 % for aluminium vs depth to watertable (P>F -

0.000) and for aluminium vs pH (P>F - 0.0093).

Transect Drain

The proportion of variation explained around the mean for pH vs drain water depth in the transect drain was particularly noticeable at r2 - 0.686 and P>F - 0.0000. The r2 value dropped to 0.250 for aluminium vs drain water depth, and the P>F was 0.0016. The r2 value rose again to 0.393 for aluminium vs pH, with P>F - 0.0000.

Bore vs Transect Drain Comparison

Differences in the proportions of variation explained around the mean at a 95% confidence level have been explained. All r2 values documented were observed to be significant (to varying degrees). The statistical strength at 95% confidence limits was also observed to be significant for all values generated. The general "strength" of these results was described on the basis of the data sets coming from an environmental setting, where the influence of variables affecting the parameters measured was likely to be high.

The most accurate way to predict aluminium for the bore was shown to be with depth to watertable and with pH for the transect drain.

4.7 Chemical Analysis

Oxidation of pyrite can play a major role in altering the quality/chemistry of water drained from acid sulphate soils, overwhelming the buffering capacity of the natural dissolved carbonate system and increasing acidity, mobilising iron and aluminium as toxic dissolved species, and generating iron hydroxide precipitates. The chemical reactions which accompany pyrite oxidation are largely mediated by microbial communities, and

involve a number of sequential steps (Simpson and Pedini, 1985). The above summary of the role which oxidation of pyrite plays in producing acid drainage was in keeping Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 102 with the results of this study. It was not in the interests of this study to give a detailed account of chemical relationships within the parameters already discussed, but the following section outlines how the sequence of equations in Chapter 3 fits with the processes of acid drainage production and explains some of the features observed.

4.7.1 Chloride and Sulphate

The main aim of analysing chloride and sulphate here was to use the chloride/sulphate ratio to prove acidic ground and drainage water was the result of pyritic oxidation, and then to gain an understanding on the extent to which oxidation had occurred from the soils (see Chapter 3). However, some noteworthy features were revealed from the analysis of chloride and sulphate. The primary reason for analysing chloride is due to it's relationship with sulphate in the chloride/sulphate ratio as it is a component of the groundwater of estuarine soils, but is not involved with the oxidation of pyrite (Mulvey,

1990; 1993). The relatively high levels of chloride in the transect drain opposed to the levels in the bore and road drain have implications in regards to remediation strategies discussed in Chapter 7.

When oxygen enters the soil system pyrite starts to oxidisei which results in an immediate production of sulphate (Equation 3.4) (Ritsema ~ Groenenberg, 1993). This was seen in groundwater analysis from the b~re sulphate followed the fluctuations of groundwater movements more closely than any other parameters

analysed. This was seen particularly in period 2 as sulphate increased proportionally

with a decrease in the watertable and consequent drying of the soil profile. The levels of

sulphate in the transect drain and road drain have been shown to be different, but at the

same time representative for drains being fed by catchments with different oxidising

characteristics.

In short, the analysis of the chloride/sulphate ratio in association with acidic drainage

from the study area identified a strong oxidising environment. For an environment such

as the one studied, the chloride/sulphate ratio should have been around 7 under natural Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 103 conditions. The chloride/sulphate ratio for groundwater samples throughout the 8 month monitoring period showed values far below 7 with an overall mean of 0.26±0.17 and dropping to as low as 0.11. This mean chloride/sulphate value for the bore along with pH of 3.4±0.6, placed the groundwater sampled in the seveth most severe class of pyrite oxidation from a scale of 8, in Mulvey's (1993) summary of groundwater conditions in regards to soil sulphides. This class describes the soil's behaviour as having little buffering capacity. Little buffering capacity from these soils would be expected since no shells were found within lm from the ground surface of any bore dug on the study area.

The watertable did not fall below 0.91m below the ground surface during the 8 month monitoring period.

While the analysis of chloride, sulphate and the chloride/sulphate ratio has shown to be a good indicator of the overall pyritic oxidation (mainly from groundwater) a number of chemical processes occur in acid sulphate soils under different environmental conditions which lead to changes in pH (for example) and are more accurately explained by changes in ions such as iron and aluminium. The very low chloride levels (as expected) also indicate that there has been very substantial leaching, and thus probable alteration of the sediments.

4.7.2 Iron

Oxidation of an acid sulphate soil is the initial cause of lower pH (Equation 3.5) and can reduce the pH to about 4.5, where the rate of ferrous iron oxidation slows down significantly (Nordstrom, 1982); thus the acid production accompanying pyrite oxidation depends on the fate of iron (van Breemen, 1973). In this process, there is a conversion of solid mineral pyrite to dissolved iron (Fe2+) and dissolved sulphate (Simpson and

Pedini, 1985). Once the pH of the oxidising system is brought below 4 (by the hydrogen ions released in the initial oxidation reactions), ferric iron becomes appreciably soluble and brings about rapid oxidation of pyrite, by electron transfer (Equation 3.6) with the overall equation represented by Equation 3.7 (Dent, 1986). Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY l 04

At low pH, acidification can continue even in the . absence of free oxygen. It was described in Chapter 3 how the further reduction in pH below 3.5 is a slow process

unless catalysed by autotrophic bacteria (Equation 3.8) (Dent, 1986) to the point where,

as pH falls below 3, these are the only important oxidisers of pyrite (Nordstrom, 1982).

The seemingly free ability of groundwater pH to fall from pH of 3.5 to below 3,

particularly in period 2 also suggests a high involvement of autotrophic bacteria in the

chemical processes that occurred in the study area. One point of interest here was the

apparent rise in soluble iron in period 2 on 14/5/93, which was the second sampling day

in that period when a pH as low as 3 was recorded, suggesting bacterial involvement

increased at pH 3, leading to an increase in the rate of pyritic oxidation. However, this

reaction would increase the less soluble ferric iron, and thus may not be the sole cause in

the apparent rise of total soluble iron on 14/5/93.

In the presence of oxygen in Equation 3.8, the relatively soluble form of ferrous iron is

converted to the more insoluble ferric form (Simpson and Pedini, 1985). The soluble

iron produced in Equation 3.8 may undergo secondary oxidation if placed in a stronger

oxidising environment such as a drain, with this process occurring at a distance from the

original source of iron (Dent and Bowman, 1993). This secondary oxidation involves

the insoluble, ferric form of iron precipitating ferric hydroxide (ochre), with three

additional hydrogen ions generated when the solution is hydrolysed at pH greater than 3,

as shown below:

hydrolysis at pH>3 Fe(OHh(s) + 3H+ (4.1) ochre

Equation 4.1 follows equation 3~8 and is completed as Equation 3.9. Another

characteristic in this series of reactions (following on Equation 4.2) is the depletion of

dissolved oxygen values. Figure 4.10 shows a 10 day SDL recording from the transect

drain. There was a reduction in dissolved oxygen values after 3 days and a

corresponding decrease in pH. Dissolved oxygen values approaching Oppm between 6-7 Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 105 days was another feature from Figure 4.10. The ANZECC (1992) water quality guidelines recommend dissolved oxygen should not fall below 8ppm in estuaries, highlighting another component of the severe acid drainage problem from the Shoalhaven

Floodplain. Hydrolysis may occur as the result of rain raising the pH in a drain or acidic drainage water being transported into less acidic creek water. Hydrolysis of ferric iron can be seen at the road drain sampling site in Plate 4.1 by the amount of ochre, with this gelatinous substance acting to almost block this drain.

------pH 7 a E --- dissolved oxygen c.. 6 s 6 55 Cl >. x :a 5 0 4 a:l > 4 0 en en .. -...... ,--.....-- -- 2 i:5

2+--~~-~--~-----~----~----~~---'-0 0

Figure 4.10. Submerged data logger recording for pH and dissolved oxygen for 14/5/93 - 24/5/593 in

the transect drain. Readings were taken at a rate of 2/hr.

The reason for lower total soluble iron levels found throughout the monitoring period in

the transect drain as opposed to the bore, was probably due to ferrous (converting the

ferric and precipitates) iron falling out of solution once in the more strongly oxidising

environment of the drain. Water in the transect drain was continually more acidic and

less variable than the bore very probably due to additional hydrogen ions given off in the

secondary reaction experienced in the drain. The large, transect drain was observed to

contain orange floe coating on reeds. It was shown throughout the entire monitoring

period that total soluble iron levels were significantly higher in the road drain than the

transect drain. However, the road drain was almost blocked with ochre, highlighting the

point made earlier that the road drain was fed by a significantly stronger oxidising

environment than the transect drain. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 106

Plate 4.1. Ochre (green/orange gelatinous material) can be seen here blocking a mole drain, at the road drain water quality sampling site. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 107

4.7.3 Aluminium

The severely acid environment of an acid sulphate soil (developed by direct oxidation or a microbiological mechanism - as described above) enhances the weathering of silicate minerals. High contents of dissolved silica and Al3+ are a striking characteristic of acid water, due to breakdown of aluminosilicate minerals such as clays (van Breemen, 1973).

When the pH of a system falls below 5, aluminium ions come into solution (Dent and

Bowman, 1993). Dissolved aluminium activity is directly related to pH; as pH decreases, soluble aluminium increases (van Breemen, 1973), usually logarithmically

(Dent and Bowman, 1993).

In this study also it was shown that soluble aluminium levels overall increased with

decreasing pH, especially in the groundwater. Significant peaks in soluble aluminium

from the groundwater, described in section 4.4 appear to be the result of a response of

flushing soluble aluminium into solution. It can therefore be said that rainfall patterns

influenced the acid sulphate soils in the study area, which in turn accounted for soluble

iron levels. While these same climatic patterns broadly controlled the amount of soluble

aluminium in the soils at a certain time, the effect of short term rainfall may be to flush

high levels of aluminium into groundwater from surrounding soils.

Soluble aluminium levels in both drains have already been described as a function of (a)

the catchment areas from which they receive their acid drainage and (b) influences from

within the drains themselves, such as chloride levels promoting different buffering

capacities.

4.7.4 Reduction Processes Related to Flooding

In most soils, flooding is followed within a few hours or days by exhaustion of

dissolved oxygen by aerobic micro-organisms. In a flooded soil, decomposition of

organic matter is continued by anaerobic bacteria which reduce nitrate, manganese

oxides, and ultimately iron III oxides and sulphate (Dent, 1986). Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 108

The response to flooding of acid sulphate soils is very variable (Dent, 1986). After flooding in the study area (from the bore), pH as expected, increased from 3.2 before the flood on 7 /9/93 to 5.5 when measured close to the height of the flood on 14/9/93 (Figure

4.2). This increase of 2.3 pH units was likely to be the result of reduced oxidation of pyrite and of a dilution effect from the rain. The influence of dilution on groundwater quality on 14/9/93 was probably strong, since the water level was 0.14m above the

ground surface and iron levels were shown to be very low (Figure 4.5d). However, in

some circumstances, reduction of iron III oxides back to iron II could contribute to a

higher pH, especially if soils remain water logged for some time.

Following a pronounced dry period, acidity generated by oxidation of pyrite at some

depth in the soil migrates towards the surface and may produce efflorescence of acid

salts: for example hydrated NaAl(S04)2, Al2(S04)3. Dissolution of these salts by

flooding liberates acidity. Subsequently, reduction processes in the soil produce Fe2+.

The iron maybe oxidised at the soil-water interface, liberating further acidity into the

floodwater (Dent, 1986):

2+ 1 5 + Fe +-0 +-H 0 ~ Fe(OHh + 2H (4.2) 4 2 2 2

Plate 4.2 (14/9/93) and Plate 4.3 (19/9/93) show the transect drain, adjacent to the drain

sampling point and looking down the drain. Flood levels were high and surface runoff

extensive initially, but they decreased 5 days after the assumed flood peak. Surface

water flowing into the drain from direct contact with jarosite in the spoil heaps was more

acidic (pH 4.3 on 14/9/93) than surface runoff over the grassed floodplain (pH 5.5).

This acidity may have been due to oxidation of the iron II from the spoil heaps. Plate 4.2. Minor flooding on the study area on 14/9/93, taken from 50m south from the transect drain water quality sampling site and looking towards Broughton Creek. All water draing from the spoil heaps and in the drain had a pH of 4.3.

Plate 4.3. Shot taken after flooding on 19/9/93. Water was still draining off the spoil heaps and ground swface pH was now 3.2. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 110

4.8 Comparisons with Other Areas

4.8.1 Background

In this chapter discussion has focussed around the dynamics and water quality of acid drainage in the study area. In this section, dynamics and water quality of acid drainage from the study area are compared with NSW north coast examples. Due to the lack of literature on this aspect of Australian Acid Sulphate Soil research, only three similar pieces of work (Willett and Bowman, 1990; Willett et al., 1992b; White et al., 1993) could be used for comparison.

A set of criteria was set in Willett and Bowman (1990, p.4) for indicators of acid

sulphate conditions in and around drains, as follows:

* extensive Fe (III) stains on the drain surface, or Fe (Ill) stained drain water, * acidic drainwater (pH <3.5), * jarosite present in spoil dredged from the bottom of drains and exposed to

aeration on the banks,

* corrosion of steel and galvinised fence posts and wires.

All of the above criteria were prominently evident in the study area.

Aluminium Speciation

Aluminium leached from acid sulphate soils is considered as the most detrimental ion and

oxidation product with respect to the survival, growth etc for aquatic life (Driscoll et al.,

1980). It is important to understand that different aluminium species exist, each having

different effects on aquatic life. Very little is known about aluminium chemistry and its

effects on aquatic life in estuaries affected by acid sulphate soils (Leadbitter, 1993b). As

other authors (M. Melville; J. Sammut, UNSW, pen; comm., 1994) have also noted,

there is a lack of uniformity in the literature reporting findings about aluminium chemistry

in acid drainage/estuaries. For example, even if an aluminium species is referred to, Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 111 quite often the details of analytical method used are not given. Different methods of analysis can influem:e the exact form of aluminium determined and thus its likely toxicity.

Furthermore, it is also not uncommon to find that the aluminium species has not been specified at all; the method of analysis is not given, and a level of 'aluminium' is simply reported.

Aluminium speciation here is referred to in the context of Driscoll et al. ( 1980). Driscoll

et al. (1980) refers to 4 aluminium species, two of which are related to the aluminium

species analysed here. The 4 aluminium species are:

1) Total - acid digestion.

2) Total monomeric - no acid digestion.

3) Non-labile monomeric - separated by cation exchange and analysed as

monomenc.

4) Labile (inorganic) monomeric - = (2) - (3). Including free AI3+ and aqueous

inorganic complexes.

The labile monomeric or inorganic species is the toxic species, which is referred to in

relation to effects on aquatic life (Willett and Bowman, 1990; Willett et al., 1992b;

White et al., 1993). Aluminium species analysed here (referred to as soluble (filtered)

aluminium) in all acid drainage dynamics results (see Appendix C) are comparable to the

total monomeric species (2) from Driscoll et al. (1980). Samples were also taken for

total aluminium analysis from Broughton Creek (Chapter 5). Total aluminium analysed

here is comparable to the total aluminium (1) analysed by Driscoll et al. (1980). The

soluble aluminium levels reported here are, therefore, not directly comparable to the

values reported in toxicity studies. The method used here (for all water quality

methodology - see Appendix A) is a standard procedure for wastewater analysis and can

be related to levels of aluminium in many aquatic environments. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 112

4.8.2 Watertable/Drain Water Depth Dynamics

The rate at which the water level drops during a dry period on a drained floodplain, at the

study area was similar to that described in White et al. (1993). The following

comparison is made from bores located approximately 30m from drains. The dry period

(period 2) already described for the study area from 19/3/93-30/6/93 had a watertable

reduction rate of 0.008 m/day (the bore - depth to watertable: 0-0.91m). The monitoring

of groundwater fluctuations, during a dry period between 19/6/93-15n/93 from White et

al. (1993; Figure 11) showed a watertable reduction rate of 0.007 m/day (depth to

watertable: 0.08-0.27m). This fall in depth to the watertable from White et al. (1993)

was considered sharp, and after piezometric analysis was largely attributed to the

sugarcane extracting water from the soil profile. Grasses (see Chapter 2) dominate the

vegetation cover in the study area. As they are shallow rooted, these grasses are likely to

be far less water-extracting than sugarcane. Sugarcane was playing a large role in

aerating the soil in White et al. (1993), but grasses were assumed not to have had such a

large effect in the study area. Therefore, since the watertable reduction rate in the study

area was even greater than by the Tweed River in White et al. (1993) it is concluded (for

at least a dry period) the influence of seepage to the deep drains to sharply lower the

watertable was significant in the study area. Further analysis using soil hydraulic

conductivity would be required to more completely understand watertable movements ..

It was shown in section 4.2 how, in the study area, the drains (or at least main drains)

have acted to lower the watertable and that groundwater was being fed into the drains.

This was not the case in the areas studied, by Willett and Bowman, ( 1990) and White et

al. (1993). There, water from the drains was fed into the groundwater. Willett and

: Bowman (1990, p.10) state for the lower Macleay floodplain "There was no evidence

that the flood mitigation drains had caused any oxidation of the adjacent soils. It appears

that some areas of the backswamps are undergoing oxidation." In the Jasper's Brush

study area, because the drains have increased the depth to the watertable in the

floodplain, Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAlN WATER QUALITY I 1 3 it is proposed the drains have caused additional oxidation throughout the study area.

However, this leaves the question of how acid drainage enters the main drains on the north coast if water from the main drains is feeding the groundwater? Willett and

Bowman ( 1990) proposed that, during significant rainfall, products of severe soil acidification (low - pH, high - sulphate, iron and aluminium) enter surface runoff in some way. Runoff water enters the main drains via the network of smaller mole drains.

Two explanations were given for oxidation products from the soil entering surface runoff; there were shallow occurrences of jarositic material including significant areas of jarositic surface crusts resulting in direct contact; and the acidic products rose through the soil profile with water rising by capillary action or because the groundwater is under pressure. On the Tweed Floodplain, during the monitoring from White et al. (1993) both main drains and mole drains were subirrigating the floodplain. However, Willett et al.

(l 992b) suggested that acid dainage entered the main drain for the same Tweed study area in White et al. (1993) by acidity being leached out of the soil with time and that the source of acidic water was water draining from the profile rather than surface drainage water. This explanation describes a situation similar to that of the Jasper's Brush study area.

In White et al. (1993) it was shown that water quality improved in a main drain during a dry period when the input of acid drainage decreased and stream water intruded up the drain through a leaky floodgate. During the dry period the watertable was located in the

unoxidised pyrite layer. In the study area, water quality in the transect drain and road drain overall worsened during the prolonged dry period (period 2). Upon a field visit to

the study area on 25/2/94, conditions were very dry. No moisture was evident in the

bottom of any bore. It was highly likely the watertable was located in the largely

unoxidised pyrite layer at this time, e.g. as unoxidised pyrite was found only 0.2m

below the oxidised (adundant jarosite) horizon. However, on 25/2/94, pH at the transect drain sampling point was 2.5, 0.3 pH units lower than at any stage during the monitoring

period when the watertable was within the depth of the bores. Two possible Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 114 explanations for this are (a) the further involvement of secondary reactions in the transect drain, or (b) groundwater rise into the drain by capillary action. For this period of monitoring, drains in the study area were, therefore, interacting differently with acid drainage compared with areas analysed on the north coast for at least certain periods during dry and/or semi-wet conditions.

During flooding, surface runoff will enter the drains, contributing towards the "acid drainage" component of the drainage water. It is difficult to estimate what proportion of the "acid drainage" component in the drains is composed from acidic surface runoff. In the study area, for the minor flood already discussed in section 4.4.4, groundsurface water movement was greatest on 14/9/93. On this day the pH of water on grassed floodplain areas was as low as 5.1, with the majority of samples being about 5.5 (Table

4.2). Over areas of freshly exposed spoil, rich in surface jarosite encrustations, surface water had a much lower pH of 4.3. The proportion of surface water flowing into the transect drain from over an area of spoil as rich in jarosite as the one described above is probably less than 5%. At the transect drain sampling location the pH of the drain water was 4.3. Water was flowing down the transect drain quickly at this time (0.6m/sec), and the drain sampling point was located "upstream" from the spoil heap in question. Indeed

no directly exposed spoil existed "upstream" from the drain sampling point and a considerable amount of water with pH above 5 would have entered the drain. It is

suggested acid drainage water leached from the soils of the floodplain (which also had a

low pH during flooding) formed a significant proportion of drain water in order for the

transect drain pH to be 4.3. Therefore, the means by which acidity mainly entered the drains through flooding did not correspond directly to north coast examples (Willett and

Bowman, 1990; White et al., 1993) as described above.

4.8.3 Water Quality Analysis

The suite of groundwater quality parameters analysed are shown as mean values in Table

4.5a for the entire 8 month monitoring period. The severity of these values have been Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 115

discussed in section 4.4. Only two groundwater samples were found from Willett and

Bowman (1990) that could be used as a means of comparison with the study area. But it

can be seen in Table 4.5a that oxidation products from the study area are at least as severe

as the two samples taken from the lower Macleay. From the study area, mean pH was

equally as acidic, the chloride/sulphate ration was lower (suggesting greater oxidation in

the study area), iron was comparably high and aluminium significantly higher. The

lower aluminium values from Willett and Bowman (1990) could be expected as they

recorded the inorganic fraction (the labile species "4" of Driscoll et al. 1980).

Source/location Field pH Chloride Sulphate Cl/S04 Iron Aluminium 0 ppm Willett and Bowman (1990) (surface) 3.4 261 689 0.38 12.8 0.63 (0.25m depth) 4.8 779 1570 0.47 210 4.2

the bore (from this study) (mean) 3.4 111 .3 754 0.26 96 36.1 (st. dev.) 0.6 87.5 778 0.17 112.9 31.9

® Source/location Field pH Chloride Sulphate Cl/S04 Iron Aluminium ppm

Willett and Bowman (1990) 3.9 241 187 1.29 0.4 0.19

White et al. (1993) 3.7 51.8 265 0.2 5.9 6.1

transect drain (from this study) (mean) 3.1 1179 763 1.42 11.3 35.4 (st. dev.) 0.3 1381 335 1.36 5.7 15.7

Road drain (from this study) (mean) 3 163 1495 0.14 106.3 73.6 (st. dev.) 0.3 63 717 0.11 78.3 27.9

Table 4.5. Groundwater (a) and drain water (b) quality comparisons between the study area at Jasper's

Brush compared with north coast examples. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 116

The suite of drain water quality parameters analysed are shown as mean values in Table

4.5b. Table 4.5b shows mean values for the transect drain (equivalent to Willett and

Bowman's main drain) and road drain for the entire 8 month monitoring period. The main drain sample shown in Table 4.Sb from Willett and Bowman (1990) was the sample with the highest values for oxidation products, taken from 19 samples from different points in 6 drains. The main drain sample shown in Table 4.Sb from White et al. (1993) was the sample again with highest levels of oxidation products, taken from 5 samples from different points along a single main drain. The explanation for groundwater (Table 4.5a) for the comparison between the severity of oxidation products in the study area and other areas is similar to that for drainage water (Table 4.Sb). The other main point to note is that the severity of road drain oxidation products is by far the greatest amongst the sites for all parameters.

To summarise the comparison of groundwater and drainwater between the study area and

2 areas on the north coast, the following 4 points are drawn from Tables 4.Sa-b:

1) Average bore water from the study area was much more acidic than from Willett

and Bowman, (1990) at 0.25m depth, since most samples were taken from at

least that depth.

2) The chloride/sulphate ratio was lower, iron higher and aluminium not directly

comparable but obviously severe in Jasper's Brush groundwater.

3) In the main drain from the study area, pH was lower, the chloride/sulphate ratio

comparable or higher, iron much higher and again aluminium not comparable

but severe.

4) The overall water quality of the road drain was worse than the main drains. Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 117

Therefore, given the well-documented effects on aquatic life in the north coast rivers, the levels shown in this study were clearly cause for concern.

4.9 Summary

* Watertable movements were found to be responding differently on the drained

floodplains (mainly by falling significantly faster after rainfall), compared with

undrained areas. Groundwater was found to be drawn down into the drains, thus

allowing direct oxidation of adjacent soils. Hence the oxidation products were fed

into the drains. This groundwater/drain water relationship was unlike that described

in Willett and Walker (1990) for the lower Macleay, and by White et al. (1993) for

the Tweed. At these two north coast locations, the water level of the drains

was described as being higher than the groundwater level during field analysis.

* Interaction between rainfall and deep drainage on the floodplain by the main drains

was controlling groundwater levels. The drains controlled the lowest level to which

groundwater could fall, as levels in the drain remained relatively stable except during

very high rainfall.

* Rainfall patterns dominated watertable fluctuations. Watertable fluctuations (position

along the soil profile) dominated groundwater pH levels. Rapid rises in the watertable

caused pH to rise rapidly, especially when the watertable rose to, or above the ground

surface. Similarly, when the watertable was at or near the ground surface, only a

minor watertable decrease was required for the pH to drop rapidly. While the

watertable was about 0.5m below the ground surface (approximately -0.2m AHD), or

deeper (while remaining in the oxidised section), pH was relatively stable between

2.8-3.3.

* pH dropped to lowest levels in each bore at the position down each bore where

jarosite was observed to be most abundant (see Chapter 3). Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 118

* Groundwater and pH levels were found to fluctuate in the same way as drain water

and pH levels (greater water depth = lower pH), for the bores and drains in the same

catchments.

* Sulphate and aluminium levels were closely related in the bore and two drain water

quality sampling sites; iron levels also followed the same trend in the bore and road

drain, but were consistently low in the transect drain. Chloride levels were very low

except in the transect drain; this indicated that there had been considerable leaching

since the estuarine sediments were emplaced.

* It has been shown in results from section 4.2 and described here how the water

quality in the transect drain (main drain) found at Jasper's Brush, was largely

controlled by groundwater quality. However, it was more difficult to understand

water quality fluctuations in the road drain (mole drain). Yet, mole drains are

believed to have been significantly contributing the total proportion of acid

drainage (amount of oxidation products) fed into Broughton Creek.

* A statistical analysis was performed between pH vs depth to watertable, aluminium vs

depth to watertable and aluminium vs pH for the bore; and pH vs drain water depth,

aluminium vs drain water depth and aluminium vs pH for the transect drain. All

Rsquared values documented were significant. The statistical strength at 95%

confidence limits was also significant for all values generated.

* Discussion was given relating the oxidation and levels of oxidation products found

(pH, chloride/sulphate, iron and aluminium) with chemical processes. The use of the

chloride/sulphate ratio was found to be a very good indicator of pyritic oxidation, but

could not be strictly used as a measure for precisely predicting the levels of oxidation

products, due to other influences occurring in the floodplain. The chloride/sulphate Chapter 4: DYNAMICS BETWEEN GROUNDWATER AND DRAIN WATER QUALITY 119

ratio indicated severe oxidation (of pyrite) had taken place in the floodplain. The

relationships between the geomorphology of the study area and different oxidation

product levels agreed with processes described in the literature. These relationships

include a high likelihood of bacterial involvement in oxidation mechanisms, during the

development of the highest levels of oxidation products (particularly iron and

aluminium).

* Comparisons were made between the Shoalhaven floodplain and north coast sites in

regard to water level and water quality fluctuations in the groundwater and the drains.

Indicators of acid sulphate soil development and acid drainage and water quality levels

were largely comparable between areas. While some acid drainage dynamics were

also comparable (e.g. watertable reduction rates), others were not. For example,

oxidation products predominantly entered the drains in the Shoalhaven floodplain

through groundwater movement, even during flooding. Oxidation products

predominantly entered drains on the north coast from surface runoff. Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 120

Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS

5.1 Introduction

The role of flood mitigations drains in developing an acid drainage problem on the lower

Macleay is described by Willett and Bowman (1990, p.2) as the drains having "increased the rate of transfer of acidity and salinity from the backswamps to the rivers and creeks."

On the Tweed, water quality in a main drain improved during dry periods as depth to the watertable increased (Willett et al., 1992b; White et al., 1993). Drainage of a floodplain,

therefore, plays an important role in the development of acid drainage, and drains form

the important link in transporting acid drainage developed in the backswamps to the

creeks.

In this chapter, water quality along the length of the transect drain is analysed. Water

quality near the transect drain floodgate is analysed in order to understand aspects of the

floodgate's role in affecting water quality along the length of the drain and releasing acid

drainage into Broughton Creek under dry weather and flood conditions. Water quality

analysis immediately inside floodgates is extended to include the floodgate connected to

the main drain, which is fed by the road drain (Plates 2.2 and 2.3; Figure 3.3). Thus

two main drains, and their water quality, including near the estuary, are considered.

This chapter contributes to this theses third major aim - i.e. the provision of information

on the conditions requried to discharge acid drainage from the study area into the drains

and from the drains into receiving waters of Broughton Creek.

5.2 Water Quality Along the Transect Drain

On the north coast the water quality in main drains improved from backswamp areas

towards the floodgate (creek interface). This was believed to be a function of acid

drainage entering the drain from the backswamps and the floodgates leaking, allowing

better quality creek water to intrude up the drains (Willett and Bowman, 1990; Willett et Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 1 2 1 al., 1993). Similar trends occurred in the study area. The issue of floodgates leaking and water quality improving from the floodgates up the drain is developed in the next section (5.3). In this section, water quality along the transect drain is described in relation to Figure 5.1 showing pH for a relatively dry period between 10/6/93-24/8/93.

It can be seen in Figure 5.1 that pH in the transect drain clearly became less acidic towards the floodgate. The sampling point shown in Figure 5.1 as furthest up the drain

(775m) is the transect drain sampling point referred to in previous water quality analysis.

Five major points are evident from Figure 5.1, as follows:

1) pH was most acidic (2.7-3.5) furthest up the drain; the position of this

sampling point could be referred to as roughly located in the central backswamp zone

between the creek and hillslopes.

2) Acidity decreased suddenly at around 400m along the transect drain. This

distance from the floodgate does correspond closely with estimated boundary from levee

toe to backswamp acid sulphate soils, so that soil water entering the first 400m of the

drain could be expected to be less acidic.

3) The sampling point at 360m along the transect drain shows pH values

clustered in two groups, around pH 3.2 and 5.0. This was believed to be a function of

the more acid drain water from further up the drain being forced down the drain at certain

times, and creek water leaking through the floodgate and intruding up the drain at other

times to this point. It was thought that rainfall on or closely prior to sampling days

represented by lower drain pH values (-3.2), could be the cause of a "down-drain" push

of acidity. However, no rainfall was received on sampling days from the cluster of low

pH values. Rainfall was received on 1 sampling day (15mm on 9/7/93) from the less

acidic cluster (pH -5.0). Eleven millimetres of rain was received in the 2 days prior to

27/7/93; when pH was low; but llmm of rain was also received in the 2 days prior to

30/6/93 when pH was high. Therefore, no clear evidence existed linking small rainfalls

to times of increased/decreased drain acidity at this point. Another explanation was Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 122

9 • 10/6/93 -0-- 22/6/93 30/6/93 --0-- 9/7/93 8 2317/93 ~2717/93 17/8/93 --0-- 24/8/93

7 2 ' 6 6 8 I a. 5

4

3

2 -100 0 100 200 300 400 500 600 700 800 Distance from floodgate (m)

Figure 5.1. pH along the length of the transect drain analysed between 10/6/93 - 24/8/93. Results

shown at distance -50m are representative for sampling done 50m upstream from the floodgate in

Broughton Creek.

required, but no clear reason was found. An interaction of rainfall and tidal movement

controlling groundwater drainage is a possible explanation.

4) pH for the location immediately inside the floodgate was overall least acidic

and had the largest range (4.7-6.6) of all sampling points along the length of the transect

drain. Reasons for this are discussed in section 5.3.

5) Values shown with a distance of -50m are from sampling done in Broughton

Creek 50m upstream from the floodgate (measured on low tides). Here pH was

consistently less acidic (6.0-6.9) th~n than the equivalent samples for any drain sampling

site.

It is clear from the above points that, at least in terms of pH, water quality did vary

reasonably consistently along the length of a main drain, during a relatively dry period. Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 1 2 1

Similar trends to those above in terms of pH along the length of a main drain, during a dry period, have been observed for the Tweed Floodplain (Willett et al., 1992b -

23/11/91). However, where pH also increased in the main drain in Willett et al. (1992b) from the backswamp towards the floodgate, the proportion of acidic drain water (pH <4) along the length of the drain (.-27%) was considerably smaller than measured for the length of the transect drain (at least .-42% for 75% of sampling days). Willett et al.

(1992b) also found that .-66% (or 0-2.3km) of the length of the drain from the floodgate had a pH of >7, where for the period of sampling, pH did not exceed 7 in any part of the transect drain. Therefore, in the study area, a greater proportion of acidic (pH <4) water existed in a main drain and was located closer to the creek than on the Tweed. However, the Tweed drain was longer and may have drained a catchment with a lower proportion of acid sulphate soils.

Analysis of sulphate, iron and aluminium along the length of the main drain in Willett et al. (1992b) showed similar trends compared to pH during a dry period (23/11/93) as described for groundwater and drainwater in the study area (Chapter 4). Where pH was high (6.3) adjacent to the hillslopes, sulphate (9.6ppm) in particular and also aluminium

(l.6ppm - total dissolved aluminium by atomic absorption) were low (Willett et al.,

1992b). At the sampling point where pH was lowest (3.5) - in a backswamp area with a strong oxidising environment - iron (3.4ppm) and aluminium (4.4ppm) were highest.

Thereafter, pH and sulphate values steadily increased whereas iron and aluminium values

steadily decreased towards the floodgate. Similar trends with distance along a main

drain.

However, there was no ameliorating effect down-drain during high flow of 0.6m/sec, at

the time of peak flow measured during the flood on 14/9/93. pH was 4.3 for the entire

775m length of the transect drain. Thus, acid drainage from backswamp areas on this

occasion dictated pH for the length of a main drain in the study area. The influence of

backswamps in the Tweed on pH along the length of a main drain, during a flood with Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 124 flow rate of l.4m/s on 8/2/90, (White et al., 1993) was not as great, pH became less acidic, ranging from pH 3.6, 2.85km up the drain to 4.7 at the floodgate. Water quality trends for chloride, sulphate, iron and aluminium along the length of this drain were similar to those described for the same drain during a dry period (White et al., 1993;

Willett et al., 1992b).

Discussion is given to other water quality parameters (chloride, sulphate, iron and aluminium) in response to flooding in the study area in section 5.4. However, prior to discussing this, section 5.3 describes how the above water quality parameters vary as a function of floodgate operation, leading to discharge of acid drainage into Broughton

Creek.

5.3 Influence of Floodgates on Drainage Water Quality

The leaking of floodgates, allowing more saline creek water into a drain, has been

identified as means by which water quality in a drain may improve (Bush, 1994). A

floodgate may leak because of a poor seal, with leaking intensity and frequency likely to

increase as the floodgate becomes older. Floodgates may also leak when debris such as

grass or tree branches are trapped in the gate flaps. Floodgates along Broughton Creek

have been well designed (Plate 2.3) and leakage into the drains was minimal unless

complete flap closure was obstructed by debris. An example of how closing of one of

the three floodgate flaps from the transect drain floodgate was obstructed, promoting

leakage, can be seen in Plate 5.1 with a wooden paling jammed in the flap.

Seawater has great ability to neutralise acidity. The neutralising capacity of seawater is

36-45ppm m-3 (2-2.5 moles nr3) and Shoalhaven River water <18ppm m-3 (

(NSW Department of Water Resources, unpublished data; cited in Dent and Bowman,

1993 ). Plate 5.1 was taken on 8/8/93, 1.5 hours before high tide for that day. The effect

of this leakage to improve water quality inside the transect drain floodgate can be seen in

Figure 5.2a-d. On 8/8/93, immediately inside the floodgate, pH was 6.2, the chloride/sulphate ratio 9, iron O. lppm and aluminium 0.8ppm. At the transect drain ChaE:tcr 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 125 Figure 5.2 Figure 5.3 ® 80 ® 80 ---ra!nfall 0.8 - 60 60 O.B - 'E ------water depth .s 'E .s .s 0.6 % .s 0.6 li 40

0 0 0 0 ® 7.0 10 ® 7 10 Ql CD 6.0 8 (ii 6 8 (ii .c: .c: Q_ Q_ 5.0 6 'S 5 6 'S I I ~ Q_ Q_ Ql ~ 4.0 4 4 4 :E --<>--pH ~ 0 0 :E :E 3.0 -0---ratio 2 0 3 2 (.)

2.0 0 2 0

@) 12000 3000 @) 12000 3000 10000 2500 10000 2500 ----0-- chloride 'E 'EQ_ 'E 'EQ_ Q_ 8000 2000 Q_ 8000 2000 ----o--- sulphate s s .!;!, s CD 6000 1500 -ra 'O 6000 1500 -ra 'O"' '>= .c: ·c: .c: 0 0 4000 1000 Q_ :E 4000 1000 % :E 'S (.) (/) (.) (/) 2000 500 2000 500

0 0 0 0 @) 120 350 @) 120 350 300 300 100 --<>--- aluminium 100 'E 250 'EQ_ 250 Q_ 80 -O---iron 80 s 200 '[ s 200 '[ E E 60 s 60 s 150 c: ·"c: 150 c: ·"c: _g .E e .E 40 40 100 - 100 <" <" 20 50 20 50 0 0 0 0 15/9 29/9 13/10 4/8 18/8 1/9 15/9 29/9 13/10 4/8 18/8 1/9 Date (1993) Date (1993)'

Figures 5 .2-5.3. Water quality analysis inside the Lransect drain noodgate (Fl) shown as Figure 5.2 and inside the second main drain floodgate (F2) shown as Figure 5.3

for; a: Rainfall vs water depth : b: pH vs Chloride/S ulphate ratio: c: Chloridc vs Sulphate; d: Aluminium vs Iron (for site locations sec Figun; 3.3). Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 126 water quality site, 775m further up the drain on this day, pH was 3.2, iron 8.4ppm and aluminium 48ppm. Therefore, the leaking of the transect drain floodgate shown in Plate

5.1, was the obvious reason for improved water quality inside the floodgate compared with further up the drain.

Water quality analysis of the Tweed River main drain described by Willett et al. ( l 992b) showed pH as 7 .3, iron as 0.2ppm and aluminium as 0.8ppm immediately inside the floodgate (on 23/11/91). The values for pH and iron were similar to those on 8/8/93 from the study area.

Obstructions such as that shown in Plate 5.1 are not likely to occur at all times in all the floodgates along Broughton Creek. An indicator that the presence of reasonably acidic drainage water at least on a semi-regular basis immediately inside the transect drain floodgate is the more usual situation, was given by the degree to which the concrete had been corroded (high blue metal exposure) from around the semi-permanent water level

(Plate 5.2). Acid drainage is known to attack concrete foundations (Holst and

Westerveld, 1972). On no portion on the creek side of the floodgate was corrosion of concrete evident.

Between 26/8/93-31/8/93, 24.5mm of rainfall was received in the study area. Field observations showed that some time between 24/8/93-7 /9/93, the piece of wood

obstructing the transect drain floodgate was dislodged. The chloride/sulphate ratio reduced sharply from 8-4 between 24/8/93-7 /9/93 (Figure 5.2b). This was probably the

result of drain water moving down the drain to the floodgate from an oxidising

environment, with an decreased chloride component (Figure 5.2c). The relatively small

amount of rainfall described here did not cause acidic drainwater to move to the

floodgate, but the 50% reduction in the chloride/sulphate ratio did indicate the rainfall

brought drainwater further towards the floodgate from an oxidising and unbuffered

environment. This poses a question; if significant rainfall was received, would acid Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 127 drainage, characterised by high levels of oxidation products, pass into the creek unmodified?

Plate 5 .1. A fence paling can be seen obs true ting a floodgate flap, inside the floodgate of the transect drain (Fl). Creek water is entering the drain, thus ameoliorating acid further up the drain. Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 128

Plate 5.2. Blue metal shown on the inside of the transect drain floodgate, due to erosion by acidity, shows the level of water height usually found in the drain. There was no evidence of corrosion on the outside of this floodgate. Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 129

The flood already described for the study area resulted after 133mrn of rainfall was received between 12/9/93-14/9/93. As shown by Figure 5.2b-c, pH and the chloride/sulphate ratio decreased while iron and aluminium increased on 14/9/93, indicating the concentration of acid drainage was greater during the flood peak compared with any time of sampling during the earlier, relatively dry period. Following the flood peak on 14/9/93 until 12/10/93, pH overall dropped. Iron remained low but aluminium rose. One other noteworthy feature from Figure 5.2 was the sudden rise of sulphate and aluminium on 3/10/93 after 12.5mm of rainfall was recorded between 1/10/93-3/10/93.

It seems as though the l 33mrn of rainfall received, mainly in 2 days, finishing on

14/9/93, caused acid drainage to leach from the backswamps and move down to the floodgate, with effects of concentrated oxidation products lasting for at least 28 days, until the completion of monitoring on 12/10/93. The sudden rise in sulphate and aluminium observed on 3/10/93 was probably the result of a flushing effect of oxidation products from the floodplain when by that stage the soil profile would have been

saturated after the main flood and/or the application of the process described in Chapter

4, (Equation 4.2) where the production of acidity is liberated by flooding. Thus only a

relatively small amount rainfall following the flood had a major impact on water quality

immediately inside the floodgate.

Water quality in this chapter has so far dealt with the transect drain. Figure 5.3a-d shows

the same parameters as in Figure 5.2a-d, but for the floodgate of the main drain

connected to the road drain (mole drain) (see Figure 3.3). The road drain was found to

have oxidation products in extreme concentrations (see Chapter 4). The influence of

oxidation products from the road drain are particularly evident inside this floodgate (F2),

as opposed to the transect drain floodgate (Fl) in terms of pH (Figure 5.2b vs 5.3b) and

aluminium (Figure 5.2d vs 5.3d) for the relatively dry period between 8/8/93-7/9/93. F2

was slightly obstructed by grass so it did not have as much creek water entering it and

consequently its acid drainage was not ameliorated to the same degree as Fl for the

period. After flooding on 14/9/93, pH, the chloride/sulphate ratio, iron and aluminium Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 130 did not show as much variation inside F2 as Fl. Nor was the feature of elevated sulphate and aluminium values evident on 3/10/93 in F2. Oxidation products were suggested to be initially more concentrated inside the F2 during and soon after flooding as a result of that drain being fed by a catchment with significantly greater area of exposed spoil and less grass cover (due to more intense grazing). This would have allowed surface runoff to transport oxidation products directly into the main drain.

Oxidation products inside F2 seem to have been more dictated from surface runoff than from stored soil water. Smaller reserves of oxidation products would be held in surface soil layers and, with the rainfall already described for just prior to 3/10/93, the significant portion of reserve generated before the onset of the main flood would have been mostly transported into drains immediately after the heaviest rain, with little remaining by

3/10/93.

This chapter has looked at water quality along one main drain with the emphasis to

highlight water quality immediately inside two floodgates. Once acid drainage is located

inside a floodgate its next move is into the more environmentally sensitive creek. The

next chapter looks at how acid drainage was transported into the creek, what happened to

it once there and what likely effects it was having on aquatic life.

5.4 Summary

* The quality of water in main drains improved on the north coast from backswamp

areas towards the floodgate (creek interface). This was believed to be a function of

acid drainage entering the drain from the backswamps and the floodgates leaking,

allowing better quality creek water to intrude up the drains (Willett and Bowman,

1993; Willett et al., 1993). Similar trends occurred in the study area.

* A floodgate may leak because of a poor seal, with leaking intensity and frequency

likely to increase as the floodgate becomes older. Floodgates may also leak when

debris such as grass or tree branches are trapped in the gate. Chapter 5: ACID DRAINAGE MOVEMENT ALONG DRAINS 1 3 1

* The most severe water quality levels for any portion of the north coast drains

analysed were at least comparable with those here, and similarly severe levels of acid

drainage were found in a larger portion of a main drain in the Shoalhaven floodplain

than the main drain analysed on the north coast (White et al., 1993; Willett et al.,

1993).

* The 133mm of rainfall received, mainly in 2 days, finishing on 14/9/93, caused acid

drainage to leach from the backswamps and move down to the floodgate, with

effects of concentrated oxidation products, immediately inside the floodgate, lasting

for at least 28 days, until the completion of monitoring on 12/10/93.

* Water quality immediately inside the floodgate of a main drain, also fed by the road

drain (mole drain) showed a tendency to deteriorate more quickly after rainfall than

inside the transect drain floodgate. This was thought to be largely due to the

contribution of acid drainage from the road drain, since this drain was located in a

stronger oxidising environment that the transect drain. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 13 2

Chapter 6: BROUGHTON CREEK WATER QUALITY AND IMPACT OF ACID DRAINAGE ON AQUATIC LIFE

6.1 Introduction

Acidification of Australian waterways is largely caused by drainage from acid sulphate soils in freshwater and tidal environments and thus, a variety of freshwater and estuarine fish are affected. The effects of acidification in Australian freshwater and estuarine species are however, poorly understood (Sammut et al., 1993).

This chapter shows that both recurrent (low volume/high frequency) and high intensity

(high volume/low frequency) acid drainage was discharged into Broughton Creek and that there was good evidence to indicate that this acid drainage had affected aquatic life in a variety of ways. There are three points which contribute to the suggestion that there is good evidence to show that aquatic life is affected by acid drainage in Broughton Creek.

These are:

1. Anecdotal evidence from local professional fishermen and Shoalhaven City Council

field analysis identified prolonged periods when fish and prawns dissappeared form

Broughton Creek after major rainfall episodes. This was thought to be due to acid

drainage and not just from other factors such as salinity decreases. Reasons for this

include large numbers of dead prawns being found after rain events.

2. Water quality results from this thesis in Broughton Creek, after a rainfall episode,

were consistent with water quality criteria recognised as being harmful to aquatic life

in the literature.

3. Our observations and those from professional fishermen of creek water (water

clarification) in Broughton Creek were consistent with the occurrence of acid drainage

in the literature resulting from the flood in this thesis. Additionally, how these

observations related to water quality parameters coincided with aquatic life

dissappearing from Brouhgton Creek. Such events had been identified in Broughton

Creek for the previous three years. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 133

In this chapter, levels of oxidation products from acid drainage (pH, aluminium and iron), associated in the literature with specific physiologic responses in aquatic life, are described.

This chapter fullfills the fourth major aim of the thesis - i.e. to characterise variations in water quality in Broughton Creek caused by acid drainage.

6.2 Effects of Acid Drainage on Aquatic Life 6.2.1 Identification of Acid Drainage from Acid Sulphate Soils as an Environmental Threat to Coastal Estuaries

Anecdotal reports in Australia, dating back to the turn of the century, identified fish kills which are now believed to have been linked with acid drainage (Neilson, 1993;

Leadbitter, 1993b). A detailed description of a fish kill, from Magela Creek, northern

Australia, in Bishop (1980) identified deoxygenation as a primary cause, but suggested other water quality parameters were probably also involved. Fish kills from the same area were later linked to acid drainage from acid sulphate soils; low pH and dissolved

aluminium as well as low dissolved oxygen were shown to be primary causes (Brown et

al., 1983; Noller and Cusbert, 1985). When a large fish kill on the Tweed, on the north

coast of NSW was described in March 1987, pH and aluminium were again recognised

as primary causes (Easton, 1989). These incidents, particularly the 1987 event, were

arguably the driving force behind acid sulphate soils being recognised as a direct

environmental threat to Australian coastal estuaries, and along with Walker (1972),

formed the benchmark from which present research related to acid sulphate soils was

derived. Further work concerning the effects of acid drainage on estuarine aquatic life

has identified pH, aluminium, iron and dissolved oxygen as the major constituents in

harming aquatic life (Callinan et al., 1992; Willett et al., 1992b; Sammut et al., in press).

At the time of writing, the understanding of this field had begun to undergo change. For

example, Sammut et al. (in press) reports that the clinical signs of exposure to low

dissolved oxygen are similar to acid-exposure and that this may have caused confusion in

the interpretation of some fish kills. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 134

Identification of the two modes by which acid drainage is released from drained floodplains into estuaries - high intensity (low frequency/high volume - predominantly associated with significant rainfall episodes) and recurrent (high frequency/low volume - predominantly associated with daily tidal exchange) discharges - suggests that estuarine aquatic life can be harmed in different ways (Leadbitter, 1993a and b; Sammut et al.,

1993).

Acute effects can be considered as those responsible for making short term survival of aquatic life impossible. Acute effects from acid sulphate drainage usually occur during and/or immediately after rainfall episodes. Chronic (or lag) effects are considered not to be as directly lethal to aquatic life as acute effects. Chronic effects are likely to be most severe for prolonged periods after rainfall episodes, but in some locations have been probably occurring all year round. Sammut et al. (1993, p.26) notes that "Fish are sensitive indicators of short and long term environmental change. In acid sulphate soils, the oxidation of pyrite (FeS2) may cause rapid changes in the physiochemistry of the aquatic environment causing fish kills, disease and other disturbances in fish populations". Consequences of both acute and chronic effects maybe equally damaging to the overall functioning of coastal estuarine ecosystems.

6.2.2 Critical Limits of Water Quality Parameters Affecting Aquatic Life

In the study area and elsewhere (Brown et al., 1983; Callinan et al., 1992; Leadbitter,

1993b; Sammut et al., 1993) when pH becomes more acidic in drainage water, there is a general trend for aluminium and iron levels to become higher. Dissolved oxygen levels usually show a corresponding decline during a lowering of iron. Therefore, water quality declines markedly in response to increasing acidity (Dent and Pons, 1993;

Melville et al., 1993). These broad trends are maintained when drainage water flows into more saline creek or river waters, but levels of each parameter are changed, (usually with an overall improvement in water quality) depending upon the buffering capacity of the receiving waters. Table 6.1 outlines levels of each parameter known to cause effects on Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 135 aquatic life, but note that these levels are for the freshwater environments. Nevertheless, many estuarine organisms tolerate pH-neutral freshwater from time to time, and are likely to be even more sensitive to low pH because of the preference for more alkaline waters:

Parameter Level Response pH <6.6 Undesirable for a range of reasons (ANZECC, 1992) 3 to 4 Lethal to many species (Sammut et al., 1993) <3 Lethal to most species (Sammut et al., 1993) Aluminium (inorganic 0.1-5ppm Potentially lethal to most species (Driscoll et al., 1980} monmeric) Aluminium (total monmeric 0.13ppm Increased fish mortality in fresh water (McCahon et al., 1989) or souble; as here Iron (total) >0.5ppm Undesirable for a range of reasons (ANZECC, 1992) Dissolved oxygen <6ppm Undesirable for a range of reasons (ANZECC, 1992)

Table 6.1. Critical levels of parameters known to cause effects on aquatic life.

6.2.3 Physiologic Changes to Aquatic Life Resulting from Acid Drainage

Acute Effects

Under acute conditions, potentially lethal toxicity generally occurs at pH 4.0 or less

(Alabaster and Lloyd, 1980; Buckler et al., 1987; Langdon, 1988; Leivestad and Muniz,

1976). This is a result of gill damage and associated disturbances in oxygen transport

and ion regulation (Wendelaar Bonga and Dederen, 1986 - cited in Sammut et al., 1993).

The toxicity of acidified water is believed to be amplified by association with inorganic

monomeric aluminium species (Driscoll et al., 1980; Langdon, 1988). Gills have been

identified as the main site for aluminium toxicity, since aluminium induces a calcium

deficiency, and thus increases the permeability of the gills (Norrgren et al., 1991). It

was found in Freda and McDonald (1988) that when calcium is leached from the gills,

the uptake of sodium and chloride is inhibited and a passive loss of these ions results.

Sammut et al. (in press) documented gill diffusion and skin damage in fish exposed to

acidified water, in estuaries of the north coast of NSW. They used histopathology as

their analytical tool and their descriptions of gill and skin damage are consistent with

those in the international literature on acid effects as described above. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 136

Fish exposed to low dissolved oxygen may gasp at the surface or display erratic opercular movement in an effort to increase oxygen uptake. Fish with acid-induced gill damage sometimes behave in a similar way, as their damaged gills cannot efficiently extract oxygen. Irritation to the gills caused by excessive mucus or precipitated aluminium and iron may also cause the fish to behave as if they are exposed to low dissolved oxygen. The similarity in behaviour has caused confusion in the assessment of some fish kills (Sammut et al., in press).

Calcium deficiencies following exposure to sub-lethal pH may cause bone deformities

(Beamish et al., 1975), reduced fertility (Mount, 1973), egg abnormalities and increased larval mortality (Kwain and Rose, 1985; McCormick et al.,, 1989; Wendelaar Bonga and

Dederen, 1986). The recruitment of juvenile fathead minnows in soft water was affected at pH 6.0 and failed completely at pH 5.2 (McCormick et al., 1989).

The role of inorganic aluminium with acidified water as an agent in increasing lethality is difficult to determine because of a range of complicating factors such as salinity, and different species tolerances, but it is known that effects are most pronounced in juveniles

(Johanssen et al., 1973; McCormick et al., 1989). An example of how increased inorganic aluminium levels at different pH alters lethality is shown in the following

comparison using East Coast Striped Bass, a common freshwater species in the USA, from Buckler et al. (1987):

pH 5.0 100% mortality at 0 and 1 and 3ppm aluminium

pH 7.2 20% mortality at Oppm aluminium

75% mortality at lppm aluminium

100% mortality at 3ppm aluminium

Iron has been identified as another potentially lethal biotoxin at low pH (Sammut et al.,

1993). Death of fish has been reported after iron was absorbed into digestive tracks, Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 137 causing lesions on various internal organs (Cruz, 1969). Amorphous iron oxides may precipitate on the gills of fish and crustaceans (Simpson and Pedini, 1985), where the precipitate may stimulate excessive mucus production (Fromm, 1980; McDonald, 1983).

Both these mechanisms of gill disturbances can cause oxygen transport deficiencies in fish, and lead to death (Sammut et al., 1993). Eggs and larvae may also be affected following smothering by iron oxide precipitates (Sammut et al., 1993). The precipitation of iron oxides/oxyhydroxides may render tidal flats unproductive by smothering biotic and abiotic surfaces (Sammut et al., in press).

Epizootic Ulcerative Syndrome (EUS) or red spot disease, is an ulcerative skin disease affecting estuarine and freshwater fish (Sammut et al., 1993), and there is increasing evidence linking EUS outbreaks to acid drainage from acid sulphate soils in Australia

(Callinan et al., 1992; Sammut et al., in press) and overseas (Pearce, 1980). EUS has in the past been identified as a chronic effect (Leadbitter, 1993a and b; Sammut et al.,

1993), mainly because it is not a direct threat to short term survival. It may be appropriate to reclassify EUS as an acute effect here, because there is growing evidence to suggest it is predominantly linked to high intensity acid drainage. EUS develops a short time after significant rainfall and the effects from a particular episode only last for a limited period (Sammut et al., 1993; and in press).

EUS is economically damaging to the fishing industry (Callinan et al., 1992; Leadbitter,

1993a and b; Virgona, 1992). It has been suggested EUS costs the fishing industry on

Australia's, east coast about $IM annually, mainly in discarded fish (Callinan et al.,

1992). Given the widespread nature of EUS, the real cost may be several million dollars annually (Leadbitter, 1993b), as a large proportion of affected catches are probably being discarded before reaching markets, where comparisons can be made.

A disease such as EUS will not kill a fish directly, but may accelerate death due to such features as feeding disorders, decreased immunity to other diseases, and increased Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 138 susceptibility to secondary infections (Fraser et al., 1992; Lilley et al., 1992). There is evidence to suggest that a disease such as EUS may have greater long term effects on fish populations than effects directly causing death. Merrimam and Vaughan (1987) found that - neglecting fishing mortality - by modelling the effects of a 0.5% decline in the survival of young menhaden over a 30 year period there was a reduction in the fish population to 60% of normal numbers.

EUS is considered to be primarily caused by the invasion of an infectious agent; the oomycete fungus Aphanomyces sp. (Callinan et al., 1992; Fraser et al., 1992). In a laboratory experiment, it was found exposing fish to fungal spores did not induce EUS lesions unless skin was abraded prior to exposure (Callinan and Fraser, unpublished data

- cited in Sammut et al., 1993). Since up to 80% of some species have been found affected by EUS during heavy outbreaks of the disease on the Clarence River, Northern

NSW (Virgona, 1992), it is suggested that factors other than simple exposure to the fungus are necessary for EUS outbreaks to occur in wild populations (Callinan et al.,

1992; Sammut et al., 1993; and in press). There is a growing body of evidence suggesting EUS outbreaks only occur when susceptible fish are exposed to both

Aphanomyces sp. propagules (zoospores and/or hyphae) and increased stress levels

(Sammut et al., in press). Stress could be due to poor water quality, e.g. low pH and low dissolved oxygen, following exposure to large volumes of acid drainage after flooding from areas of acid sulphate soils (Sammut et al., 1993; Virgona, 1992).

Chronic Effects

Other physiologic responses may result from recurrent acid drainage, compounding

stress levels and affecting growth rates. Energy required for osmoregulation may double from normal conditions to be around 40% under acidic conditions (Wendelaar Bonga and

Dederen, 1986). Stress and diseases may increase when forms of aquatic life are forced to move from desirable habitats, with overcrowding of new habitats resulting (Sammut et al., 1993). Corneal damage can result from acidification (Daye and Garside, 1976), Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 139 making the location of food difficult. Clinical signs of corneal damage have been noted in mullet exposed to low pH in an artificial drain (J. Sammut, UNSW, pers. comm.,

1994). The amount of food available to all food chain levels within an estuarine ecosystem can also be assumed to be reduced from normal levels as there is evidence to suggest some species of single celled algae at the bottom of the food chain are highly sensitive to acidic conditions (ANZECC, 1992).

Iron oxyhydroxides may affect habitat away from the source of acidity as the precipitate can by transported to and deposited at other sites. This is an example of how acidification can affect other parts of the catchment (Sammut et al., in press). Sammut et al. (in press) argue that habitat loss is the most significant of the known impacts of acidification. They note that habitat may remain degraded long after the pH returns to background levels, because of loss of food resources, macrophytes and the coating of the channel by iron oxyhydroxides.

6.3 Recurrent (low volume/high frequency) Acid Drainage

Leadbitter ( 1993b) comments that the media and public attention focus on physiologic damage of acute effects, and implications of wider ecosystem effects are often

overlooked. Obviously large kills of fish are more news worthy than subtle changes in

estuarine health. However, chronic toxicity is likely to be more widespread and more

common than episodes of acute toxicity (Leadbitter, 1993b). Leadbitter's comments

concerning the north coast rivers appear to be equally valid for Broughton Creek.

Sammut et al. (in press) notes that frequent high discharges can cause long term impacts

in tidal reaches. Acidification can occur continuously for periods of more than 6 weeks

in tidal reaches (J. Sammut, UNSW, pers. comm., 1994).

6.3.1 Release of Recurrent Acid Drainage

Floodgates have been releasing acid drainage into Broughton Creek during low tides, as

has been observed on the north coast (Sammut et al., in press). The vertically suspended

floodgate flaps in the study area were found to open, releasing acid drainage into Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 140

Broughton Creek, when the water level in the drains was ~0.02m above the height of the water in the creek. Therefore, whether the floodgate flaps open or not depends on the interaction between drain water depth and creek water height, but this was observed to happen on most low tides (3 out of 4 field visits between the relatively dry period between 29/7/93-21/8/93), and usually for approximately 40 minutes.

6.3.2 Water Quality Analysis from Prior Monitoring

Sampling of pH (showing medians and ranges) by Shoalhaven City Council between

March, 1992 and December, 1992 indicated that recurrent acid drainage was probably

discharging, into Broughton Creek. This point is demonstrated in Figure 6.1. Figure

6.1 is reproduced from the Shoalhaven State of Environment Report (1992; Figure 23).

Site numbers from 347 to 362 are for readings taken at floodgates moving upstream

along Broughton Creek, for 11.Skm (from the mouth). Distances upstream (taken mid­

stream) corresponding to each site number in Figure 6.1 can be seen in Figure 6.8.

Distances in lkm intervals are shown along Broughton Creek in Figure 6.2

It can be seen from Figure 6.1 b that on almost all occasions drainage water from canals

immediately inside the floodgates did not meet acceptable criteria. pH levels showed

severe acidity at nearly all sites. pH, when measured approximately 50m downstream

from the same floodgates and on low tides (Figure 6.lc), showed less acidity than for

corresponding sites inside the floodgates. However, an examination of the range of

results downstream from floodgates, on the bank, indicates waters of Broughton Creek

waters were also very acidic from time to time. Mid-stream Broughton Creek sites (with

distance upstream; 10 - 1.2km, 349 - 5.5km, 354 - 9.2km, 357 - l 1.7km) from Figure

6. ld, show that there was an overall decrease in acidity compared with creek waters

closer to floodgates (Figure 6. lc ), but pH levels at times still fell below acceptable levels. L11aptcr 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 141

•• ••••.•••••• KEY •.••••. ...•.. SHOALHAVEN CllY COUNCIL 1992 pH RESULTS · BROUGHTON CREEK Range { iMedlan

10

9 / / / / / / / / / / / / / s / Ac~ptao1e / / / /, / / / 7 / - / ,,, . / I / / / ,.-; / T 1 1 I 6 • pH I l I 5 I

4

3 l • I 2

0 ' ' ' s s § ii) := s s § :g § § 5 § :g s 5 :g 5 § M ~ § :g § § § :g 5 5 c 5 :g :g :g § § 5 0 ::::: N ..., ...,

SITT NUMBERS· (Number of_R_esu_n~s) ______

Figure 6.1. pH medians and ranges for drain and Broughton Creek sites (State of Environment Report,

1993, Figure 23)

Some limited analysis for aluminium at the Broughton Creek sites was also done as a part

of Shoalhaven City Council's monitoring. Like pH, total aluminium levels were highest

in the central part of the creek, where they ranged between 0.25-0.9ppm.

6.3.3 Water Quality Analysis from this Study

On 7 /10/93, a flow meter (provided by Wollongong PWD) was set up inside the

floodgate of the second main drain analysed. pH was measured inside, upstream and

downstream of the floodgate on an out going tide. pH was measured again after the

drain had stopped discharging, with any variation noted. Volumes of water involved in

the discharge were calculated.

Water discharged from the floodgate for 70 minutes during which time the peak

discharge was 911/sec and discharge averaged 47 l/sec. Assuming an average flow rate

(0.05m/sec) and cross-sectional area of water in the floodgate of 2.84m2, 56, 17 60 litres Chapter 6: BROUGHTON CREEK WATER QUALITY & lMPACT .. ON AQUATIC LIFE 142

·:·::·::·:::.' - area prone to inundation

I - distance upstream (km)

\.. /" - palaeochannels

• - floodgates

--- - roads

J/\SPERS . ·· ··· ·...... · BRUSH ,- / l""\

...... · ' ' ' I \

I N I I I llulu1l(J 0 1km I .· ·.·:.· ··· / ·· ..:

/ ·.. ··. .

Figure 6.2. Distances in kilometres along Broughton Creek. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 143 of water was discharged into Broughton Creek as a result of this episode, one which is clearly not unusual but typical of outflows at low tide. pH inside the floodgate remained at 3.3 throughout the experiment. However, whereas pH in Broughton Creek 50m upstream from the drain remained at 6.1 while the tide was going out, pH 50m downstream changed from 6.1 before discharge occurred, to 5.8 upon discharge completion. Water flowing from the drain formed a glassy plume as it moved into the

creek. When the tide turned and began to move upstream the plume spread across the

-60m width of the creek. These changes are thought to be typical of recurrent discharge

into the creek. Such plumes may be chemically different because of the density

differences between the acid outflow and tidal outflow (Sammut et al., in press). The

significance of plumes with different densities is discussed later in this chapter.

6.3.4 Affects on Aquatic Life

There has been no scientific analysis done on effects of recurrent drainage in Broughton

Creek, although such programs at this time are being devised (T. Roach - Marine and

Estuarine Waters Section, Bankstown, EPA). Anecdotal reports from professional

fishermen (G. Usher and C. Weir) have identified EUS as occurring, on average, in 5%

of total fish catches for about the last 5 years. During this time, EUS was most common

on sea mullet (Mugil cephalus). The prevalence of EUS rose dramatically after

significant rain; similarly there has been a disappearance of fish and prawns for

prolonged periods after heavy rain.

6.4 High Intensity (high volume/low frequency) Acid Drainage

An acid drainage problem was first identified for Broughton Creek on 1st August 1991,

when an 8km stretch of the creek turned clear, after drought breaking rain in June and

July. The clear water was associated with very low pH levels and, in places, clouds of

flocculating white particles. Drainage from acid sulphate soils was identified as the likely

cause. Following this event, fish and prawns were absent from the creek for a prolonged

time and dead worms were found in nets during discolouration of the creek (Raffell,

1992). Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 144

A similar scenario occurred in Broughton Creek on 3rd March 1992, again after heavy

rainfall in the previous month. But on this occasion, pH levels were not so low and the

extent of water clarification was only Skm. The apparently smaller scale acid drainage

effect observed in Broughton Creek, in March 1992 was attributed to a lesser amount of

flushing of oxidation products from acid sulphate soils, where prior rainfall was not as

great as was the June and July rainfall from 1991 (Raffell, 1992). The greater amount of

rainfall prior to the acid event in 1991 compared with that in February, prior to the acid

event in 1992 can be seen in Figures 6.3. Figure 6.3 shows rainfall from the Berry

Sewerage Treatment Works. The treatment works are located on land with low relief,

very close to the headwaters of Broughton Creek and, therefore, located well within

Broughton Creeks catchment area.

700 ,-~~~~~~~~~~~~~~~~~~======;;:======::::;:;i~ WJ 1991 soo I Dilll 1992 500 E 11'1 1993 .s 400 ~ ·c:c:a 300 a: 200

100

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

Figure 6.3. Rainfall record for 1991/92/92 from the Berry Sewerage Treatment works, located near the

headwaters of Broughton Creek. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 14 5

This section is primarily concerned with the analysis of water quality in Broughton Creek in response to the rainfall episode already described for mid-September 1993. Figure 6.3 shows that for at least total rainfall, for the two broad periods of rainfall inducing two separate acid drainage events, in 1991, 1992 were significantly higher than the high intensity event analysed in detail here (1993). No flood recurrence interval data was available for the 1993 event, but Figure 6.3 shows that at least equally significant events as was received in 1993 (the 1991 and 1992 events were probably significantly more intense) occurred annually for 3 years running. Therefore, this study gives the most comprehensive set of analysis to date for a high intensity acid event in Broughton Creek,

it does not describe a 'worst case' scenario. Rather, it describes a fairly common event,

and thus emphasises the seriousness of the problem caused by drainage of acid sulphate

soils.

6.4.1 Water Quality Analysis from Prior Monitoring

As has already been outlined, pH was low on 1/8/91 where clarification of creek water

occurred. On this occasion, at low tide, pH reached its lowest level of 3.1 at 9.5km from

the mouth. pH was below the acceptable level of 6.6 until beyond l l .5km upstream

from the creek mouth and was below 5 for a 5km stretch, between the 6km and 1 lkm

reaches from the mouth (Figure 6.4).

Acidity associated with the clarification event measured on 3/3/92 was not as evident in

Broughton Creek. pH was again below the acceptable level of 6.6 for an extended

distance from the mouth (10.7km), but the lowest level on this occasion was only 5.6.

An aluminium level of 0.28ppm (speciation not given) was recorded at this low pH

point, 6km from the mouth. Aluminium of 24.6ppm in an unknown drain was recorded

on this day too. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 146

6.4.2 Water Quality Analysis from this Study (Mid-September, 1993

Rainfall Event)

This section will begin by comparing pH and distances of water clarification along

Broughton Creek for the event analysed in this study. Figure 6.5 shows pH again lowest in the central reaches of the creek on 22/9/93. This is probably the result of trapping of acid drainage by tidal movement as more saline waters push upstream, and by fresher water pushing down from the headwaters. Also, the majority of acid drainage was released in the central part of the creek from the floodgates as shown in Figure 6.2. pH was lowest (5 .1) at 7 .3km from the mouth and was below the acceptable level of 6.6 for the first l l .2km stretch of the creek. Acidity following the mid-September 1993 flood was reduced in all sections of the creek by 29/9/93. But again pH was lowest (6.1)

7 .3km from the mouth.

Water clarification was most obvious and pH was likely to be lowest for the creek, around 22/9/93, following the mid-September 1993 flood. It is not known whether the days of sampling following the 1991 and 1992 floods corresponded to the worst acidification for those events. Nevertheless, overall acidity was seen to be significantly less on 22/9/93 than on 1/8/91. Acid drainage conditions in Broughton Creek in late

July/early August 1991 were obviously more severe than the 1993 event.

Field sampling techniques and lab methods for water quality analysis in Broughton Creek were the same as those described for the floodplain analysis in Chapter 4; and Appendix

A. Raw data for creek sampling results is shown in Appendix D. However, duplicate and triplicate samples were taken from Broughton Creek to more accurately account for the expected low ion concentrations there compared with the floodplain and drains

(Chapters 4 and 5). All Broughton Creek samples were surface samples due to a limited availability of sampling resources. While taking surface samples does not indicate whether or not stratification of layers with differing acidities exist in a creek, it does measure the most severe acidification as thi s is always found closest to the surface (J. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 14 7

Sammut, UNSW, pers. comm., 1994). Samples described in section 6.4.3 were taken from the creek bank (on low tide), and section 6.4.4 mid-stream from a boat (on low tide).

9 .. B :; :; : ; : ; :; : ; : :; :; :; :; :; :; :; :; : ; :; : ; : ; :; : ~ :; :; : ; : ; :; : ; : ; :; :; : ; :; : ; :; ;: ; : ; ;: ~ :; :; :; : ; : :; : ; : ···· ·· ··· ···· ··········· ·· ······· ··· ··············· ········ ·· ···· ·· ·· ··· ············ ·· ··· .... ··· ··· ···· ··· .. . .. ···· · ·· ·· ····· ··· ·· ··· ., T:;:; :; ); J Acceptable pH Range 6.5-e.5 I: ;:; ;::;: :;:;:::;: ;: ; ;:;:; 7 •' . , ::::::::::::: ::: . :. : . :. : .: .:.: .:.:. : .: .: . :. : .: . : , :.: ,:. :.: ,: .:. ::.:: ··: .... . ·· · ·· : ::::: ······· ··· ·········· ····· ·················· ····· ····· ························ ·· ······························ ····· ········ ·· ..,.,... ········· ·· ···· ·· ········ ·· Q.) O') 6 c: cc Cl:: 5 :I: 0.. 4 --- pH range August 1, 1991 3 --- pH range March 3, 1992

2 ~ Cleared waters August 1, 1991 111 Cleared waters March 3, 1992

i!l·'\./.''.'·:~ ··...... ,..... :.:<:·::<·;,_·'·:~:.'.::>.'L::.;,_>'.:._:-:,_.-\ ·· ..·· :... ,...... : ·'· ...... ::~···· : ...... · . . . ./· ...... • .. 2 3 4 5 6 7 8 9 10 11 12 13 14

Di stance from mouth (km)

Figure 6.4. pH along Broughton Creek after two major rainfall events in 1991and1992.

9

I ...... ··· ········· ···· ·· ························ ··· ······ ····· ·· ··· ·· ·· ····· ··· ·· B ...... ·················· ·· ······················ ············ ··························· ······················· ···· ················ ····· ········· ·········· .. ;::: :;:: :: :~:; T· ... ·.· ·· ···· ············ ····· ··· ···· ·· ·· ···· r :::: :::: : ::::: 7 .. ;::; :;::;::;;:; Acceptable pH Range 6.5-8.5:/:: ;~::; ?: ; '. '. '. • ' ~ :~ : :~ :~ :~ :~ '. ~ :~ : ~ : ~ : :: :: :: :: ~ :~ :~ :~ :~ :~ :~ :~ :~ : :: :: : : : :: : : :~ : :~ ;~ :~ . :~ ;~ ; ~ ~ ;~ ~

Q.) 6 O') c: cc Ck: 5 :I: 0.. 4 ___ pH range September 22, 1993 3 ___ pH range September 29, 1993

2 ~ Cleared waters Sept 22, 1993

Ill Cleared waters Sept 29, 1993 !

2 3 4 5 8 9 10 11 12 13 14

Di stance f ram mouth (km) Figure 6.5. pH along Broughton Creek as measured from analysis in this thesis on 22/9/93 and

29/9/93. after the major rainfall event which finished on 14/9/93 - see Chapter 4 or Chapter 6: 6.4. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 14 8

6.4.3 Magnitude of Acid Drainage Input into Broughton Creek Following the Mid-September, 1993 Rainfall Event

It was mentioned in Chapters 4 and 5 that, when minor flooding occurred in the study area, large volumes of water were flowing down the drains and into the creeks. An attempt is made here to estimate the total volume of acid drainage released into Broughton

Creek from 14/9/9/3-16/9/93 (immediately after the flood described in section 6.4).

Volume data was only available for this 2 day period because these were the only days for which a flowmeter was installed at a floodgate. The majority of acid drainage released into Broughton Creek seemed to occur in this 2 day period, despite flow into the creek continuing at reduced rates until about 22/9/93. All calculations for this section are shown in Appendix D, but a summary is given here. Five steps were invloved in this exercise including several assumptions. The 5 steps are as follows:

1. Average discharge for the 50.5 hour time interval was calculated by averaging the

readings taken during the time frame.

2. As is described in detail below - it was apparent that upon high tides, some amount of

creek water entered through the floodgate and into the drain (along the bottom), even

though drain water was probably still discharging from the drain (along the surface)

at the same time. For the purpose of this exercise water was not assumed as

discharging from the drain when water was believed to be entering it. The 20 minute

intervals from the SDL recording spreadsheet were totalled and subtracted from the

initial 50.5 hour period (to give the revised time of total discharge). This was done

when analysis of pH and dissolved oxygen readings with the spreadsheet showed

obvious change (increased pH, increased dissolved oxygen) at the beginning and end

of the high tide intervals.

3. Average flow was multiplied by the revised time of assumed total discharge. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 149

4. The total discharge from the transect drain during this "total" 50.5 hour interval

during the mid-September, 1993 flood event is calculated on the basis of total

discharge per floodgate flap. The total discharge per floodgate flap for the transect

drain floodgate allowed for the calculation of discharge from all drains that entered

Broughton Creek for the time interval analysed, according to the number of

floodgate flaps (known) for each drain, assuming flows/velocities from all

drains were similar.

5. The total discharge for all drains is calculated and the amount of total discharge is

represented in terms of - to what capacity it would fill Broughton Creek upon a low

tide, with further assumptions in relation to the likely low tide capacity of Broughton

Creek made.

Average discharge from the transect drain between 1315 hours on 14/9/93 to 1545 hours on 16/9/93 was calculated at 5.2xl06 l/hr. If uniform steady flow at this average rate was assumed, 2.62x108 litres of water (total volume) would have moved through the floodgate for the 50.5 hour period. However, uniform steady flow did not occur because of the tidal influence affecting discharge rates; flows out of the drain are slowed on high tides when creek water is acting to push the floodgate flaps closed. In Figure

6.6, an SDL recording from 14/9/93-19/9/93 shows drain water depth fluctuating with tides (the depth shown is for the adjusted levels representing actual drain depths for the location where flow/depth measurements for discharges were made). This indicates that average discharge alone would not be an accurate parameter for calculating total volume.

Ideally, a height recorder in the creek would be additional equipment necessary to accurately calculate total volumes released. It was noted in section 6.3. l that floodgates discharge once the creek water height falls ~0.02m below the drain water height. By comparison of these 2 parameters, exact times of drain discharges would be possible.

However, this problem is to some extent overcome by other information given by the

SDL for this Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 150 period (Figure 6.7). In Figure 6.7 it can be seen that there is a good correlation between increasing drain depth and increasing pH, and dissolved oxygen.

2000

1600 • 2

(j Ql ::..UI 1200 1.5 g Ql e> ..c: ca Ci. ..c: Ql u 800 Cl UI i5 discharge 400 • 0.5 water depth

0 00 W ~ N 0 00 W ~ N O 00 W ~ N N M ~ ~ ~ W ~ 00 00 m O ~ ~ ~ Time (hrs)

Figure 6.6. A submerged data logger (SDL) recording showing discharge and drain water depth inside

the transect drain floodgate (Fl) between 14/9/93-19/9/93. Readings were taken at a rate of 3/hr.

7 8 ~ E c. .8:: 6 6 1ij ~ 0 I I ' I I I I 4 ~ '•-' _.•- ...... : I I I . > ' ..._,I I I • 4 ~------~'·-' . -. I . 0 -.. -· •• J Cl) Cl) ------pH 2 i5 3 ---dissolved oxygen

Time (hrs)

Figure 6. 7. An SDL recording showing pH and dissolved oxygen (from the above recording). Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 151

On 14/9/93, observations indicated that there was flow out from the drain into the creek throughout the day and this may have continued until 16/9/93. The better water quality shown by the SOL at approximately 12 hourly intervals may reflect up-drain movement of a saline wedge below a discharging acidic upper layer. The same scenario, (including during flooding) has also been identified in northern NSW. "Stratification may occur in the floodgated situations as a result of the migration of salt wedges during periods of tidal intrusion. On the north coast, these occur because of floodgate leakage or impaired operation (debris, etc.). The salt wedges can then cause marked pH stratification because the lower stratum is acid-neutralised or acid water is displaced by tidal water" (J.

Sammut, UNSW, pers. comm., 1994). This assumption is plausible because; this floodgate is located on the outer bank of the largest bend in Broughton Creek, and one of the deepest sections in Broughton Creek is adjacent to this floodgate (G. Usher, professional fisherman, pers. comm., 1994). Large volumes of denser, saline water are probably stored in Broughton Creek, adjacent to this floodgate. It appears as though more saline creek waters entered through the floodgates and move at least along the bottom of the drains (The bottom of the SOL where the probes are located was only placed -0.3m off the bottom of the drain), even during discharge during flooding.

However, to give a conservative estimate of outflow, the volume for these periods when water quality improved (with total time of 13.5 hours until 1545 hours on 16/9/93) was subtracted from the initial total volume calculated. The revised value is 1.92xl081itres.

In order to calculate a value for the total volume of water released into Broughton Creek via all floodgates during this 50.5 hour period, the above value of 1.92xl08 litres was divided by 3 (6.42x108 I/flap) to be representative for the water that flowed from each of the 3 flaps of the transect drain floodgate. Along Broughton Creek there were 18 floodgates with a total of 38 floodgate flaps. In multiplying 6.42xl07 litres by 38, a value of 2.43x 109 litres was calculated, estimating the total volume of water released into

Broughton Creek via flood mitigation drains in the "total" 50.5 hour interval analysed

between 14/9/93-16/9/93. In order to determine what proportion of the above value may Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 152 have had in the total volume of Broughton Creek on a low tide, the volume of Broughton

Creek was required first. Unfortunately, it was not possible to obtain an estimate of the flood flows in the creek at the time.

The length of Broughton Creek where flood mitigation drains were found extended for

l 1,500m. The average width was calculated by increasing the size of a 1:25,000 aerial photo 300% and measuring the width at 500m intervals. The estimated average width of

Broughton Creek was 52.5m. After extensive depth sounding of the total length of

Broughton Creek the average low tide depth has been found to be approximately 3m (G.

Usher, professional fisherman, pers. comm., 1993). The total volume of Broughton

Creek for low tides was estimated as l.81xl09 litres. Therefore, the total discharge from

all floodgates between 1315 hours on 14/9/93 to 1545 hours on 16/9/93 produced

enough acid drainage to fill Broughton Creek on a low tide 1.34 times (134% capacity).

At the time of maximum discharge (18,600 I/sec) from the transect drain on 14/9/93, pH

was 4.3 and soluble aluminium 0.8ppm. By keeping in mind the above results, the

impact of acidity discharged into Broughton Creek from this event can be appreciated by

considering pH results shown on Figure 6.8. Figure 6.8 shows average pH and range

from Shoalhaven City Council monitoring along Broughton Creek, during March 1992

to December 1992. Average pH inside the transect drain floodgate (site number 348)

was more acidic than the majority of floodgates connected to Broughton Creek, but three

drains in a central section of the creek (distances upstream - 7.4, 8.15 and 8.2km) were

more acidic than the transect drain and nearly all drains were at times severely acidic.

It has already been identified (see Figures 6.6 and 6.7) that creek water was apparently

moving into the drain and causing fluctuations in pH and dissolved oxygen. These

spikes apparently caused by creek water moving into the drain increased in duration and

regularity during the 5 day period to 19/9/93, when discharge was decreasing, thus

supporting this assumption. Outside these spikes of improved water quality, during this Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 153

5 day period, pH showed a slight reduction to below 4 by the fifth day and dissolved

oxygen showed a more rapid reduction from 7.0ppm on 14/9/93 to be as low as 3.7ppm

by 19/9/93. Possible contamination of the dissolved oxygen probe during this time was

not considered to influence the above result, since dissolved iron was only found to be

::;4ppm during 14/9/93-19/9/93 and so there was little chance of ferric oxhydroxide

flocculants accumulating around the probe.

6 I f 5 I I :r c. I I f t I 1 f 4 I I I I I I 3 I ! ! 21

(.:I A ~ ?> IO IO -to :,.. "';,, "' :,.. °';,, °' -Q Q -Q -Q - VI VI VI VI VI VI 0 N to (;,- c;; c;; c;; - 'A VI VI VI VI A c;;"' A VI c;;"' t c;; A c;;"' w"' c;;"' c;; ~ VI VI VI VI 'A c;; 'A"' ~ ~ .!!: .£ ~ .!!: $. .!:!! ~ ~ .!:!! $. A A A ~"' .l:!! ~"' ~ ~ Distance upstream (km) [Shoalhaven Council site numbers]

Figure 6.8. pH mean and range values immediately inside floodgates along Broughton Creek.

Changes in pH and dissolved oxygen from an SDL located just inside the floodgate of

the second main drain (F2 - see Figure 3.3) recording are shown in Figures 6.9. The

sampling rate was again 3 readings per hour, but this recording was taken between

14/9/93-12/10/93 in 3 intervals; 14/9/93-19/9/93, 21/9/93-29/9/93 and 3/10/93-12/10/93.

A noteworthy point from Figure 6.9 for the first period (14/9/93-19/9/93, corresponding

to the same period in Figures 6.6 and 6.7) is, that the short term fluctuations in pH were

only over a narrow range (<1 pH unit). The stretch of creek adjacent to F2 (located

4.4km from the mouth) is straight, thus it is likely that denser creek water was not forced

up into this floodgate, as was apparently the case on the large creek bend adjacent to the

transect drain floodgate (Fl - located 7.4km from the mouth). pH inside F2 between Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 154

8 8 ----pH ------dissolved oxygen 7 .i'-..t.. ,LJ\ • . ~ W ·~.,....., I ' 1' ~ ~ ~--..- l•I I I 6 I 1' ..ft ' \ •,,/' '"' '. ·.. ~ ~~"'· ,. !'~ ' ,• =a 5 I '.1 V1 ,, /". I \ II 1,, I I/ I 4 " I

3

0 II) 0 (') (() (') (() .,... (t:J .,... (t:J ,.....

Time (hours)

Figure 6.9. An SDL recording of pH and dissolved oxygen for inside the second floodgate analysed

(F2) between 14/9/93-12/10/93. However, for this total length of time three separate recordings were

made as indicated on the figure. These were; 14/9/93-19/9/93, 21/9/93-29/9/93 and 3/10/93-12/10/93.

readings were taken at a rate of 3/hr.

10

7 8 'E Q.

ii.I I .9: 6 ,, ,, c: . ., .•l 6 . I x ~5 I 0 "C 4

Time (hours)

Figure 6.10. An SOL recording of pH and dissolved oxygen for outside the second floodgate analysed

(F2) between 21/9/93-12/10/93. Setup was as above. Times of instrument start-ups and shut-downs

both both SDL's used for Figures 6.9 and 6.10 were identical. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 15 5

14/9/93 and 19/9/93 declined, but more sharply than in Fl, ranging from 4.4-3.1; whereas in Fl, it fluctuated diurnally but the lowest levels only fell from 4.2-3.8.

Dissolved oxygen showed no prominent trend for this period, but a significant point was that dissolved oxygen levels as low as 0.35ppm were recorded. The greater acidity and lower dissolved oxygen levels for this period inside F2 compared with Fl was expected, as detailed earlier (see Chapters 3, 4 and 5), because the second main drain was fed by a stronger oxidising environment than the transect drain.

Evidence of decreasing outward flow from F2, from 21/9/93, can be seen similarly in

Figure 6.9 as has been described for the transect drain (Figures 6.6 and 6.7). Acidity and dissolved oxygen levels gradually fell and the intensity of fluctuations increased.

This again is likely from creek water intruding into the drain as outflow discharges declined. Outward flow down the drain had virtually ceased by 22/9/93 and a lot of debris was jammed in the floodgates at this time. However, pH was still commonly

around 3.0 and dissolved oxygen around 4.5ppm by 12/10/93; this shows that oxidation

products were still being washed out of the floodplain, and moving down the second

main drain to be in a position to be pushed out at low tides into the creek, as late as 1

month after the rainfall producing the flood had ceased. Prolonged periods of recurrent

discharge have also been reported by Sammut et al. (in press).

Another SOL was located in Broughton Creek l.5m outside F2 and set for the same

times and intervals from between 21/9/93-12/10/93 (Figure 6.10) as the SOL inside this

floodgate (Figure 6.9). This was done to analyse water quality as the flood receded and

to quantify water quality under recurrent drainage. It can be seen that pH gradually rose

adjacent to the floodgate, in the creek from a maximum level of around 4.0 on 21/9/93 to

6.9 by 12/10/93. However, evidence of recurrent drainage can be seen here from the

consistent pH levels dipping to as low as 3.2. These very short term periods of low

levels of acidity corresponded in time closely with similar periods of low level acidity

inside the drain. The recurrent discharges of severe acidity into Broughton Creek shown Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 156 in Figure 6.10 are probably the result of drain water height being larger than creek water height (tidal exchange).

Dissolved oxygen showed a gradual decline from around 8.lppm on 21/9/93 to be

5.8ppm by 12/10/93, but remained between 6-8ppm for the majority of this period.

Sammut et al. (1993) found that, after heavy rainfall, an SDL recorded significant

reductions in pH (-8-3.5) and dissolved oxygen levels (-8.4-0ppm) down stream of a

barrage (floodgate) from a catchment draining acid sulphate soils in the Richmond River

area. Studies on the Richmond and Clarence Rivers have shown that, during periods of

about 2 weeks after major rain events, significant falls in dissolved oxygen

concentrations consistently occurred in most representative floodplain tributaries and at

some main stream sites (Sammut et al., 1993). Here, in the post-flood phase, the

changes were not major. In fact, the percentage saturation of dissolved oxygen varied

only slightly.

These patterns are confirmed by grab samples from Broughton Creek, as shown in

Figure 6.11. In Broughton Creek, both above and below Fl and F2, pH is shown to

have been significantly reduced after rainfall in mid-September, 1993 especially

compared with prior dry weather conditions. Acidity was ameliorated after 14/9/93 until

at least 12/10/93, but did not quite recover to the background levels. Data for Figure

6.11 was taken on outgoing tides, and again here recurrent drainage for both before and

after the rainfall episode is shown by acidity commonly being greater downstream (50m)

from both floodgates (but especially below F2).

6.4.4 Water Quality Along the Length of Broughton Creek during severe

acid discharge (22/9/93 and 29/9/93)

Clarification of creek waters on north coast rivers (M. Melville, UNSW, pers. comm.,

1993) and Broughton Creek (R. Cumming, EPA, pers. comm., 1993) commonly occurs

in main streams 6-9 days after significant rainfall. Initial signs of water clarification in Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUA TIC LIFE 1 5 7

Broughton Creek, resulting from the large input of acid drainage, following the mid­

September rainfall episode, was first observed on 19/9/93, 5 days after rainfall had

ceased. By 21/9/93 water clarification on the bank at F2, was striking. Water quality

along the length of Broughton Creek was investigated in a boat on 22/9/93 and 29/9/93.

7r-~~::::~.-~--~-~--~-~~--~__;, __ ;;~::-~~~~~~~~~~~ ------0------q----- 6 ~------~==--o- ,~ ---o--- -· --~:·- -- ~-:·· 5 - ,', ~CT .... , :c • .0 c.. F1 (upstream) [J 4 -----

---- •- -- - F2 (upstream) 3 ----o- --- F2 (downstream)

4/8 18/8 1/9 15/9 29/9 13/10 Date (1993)

Figure 6.11. pH taken from the bank of Broughton Creek, 50m upstream and downstream from Fl

and F2 (for location see figure 3.3), during outgoing tides.

As noted earlier, pH on 22/9/93 was highest at the mouth (5.8) and in the upstream

section of the creek (6.8); it was lowest (5.1) in the central section (6.9km from the

mouth) as shown in Figure 6 .12a, where the effect of water clarification was greatest.

Plate 6.1 shows this effect, with part A showing brown coloured water 0.2km from the

mouth, part B showing the light green coloured water 6.9km from the mouth and brown

coloured water again in part C l l .5km from the mouth.

As expected, both soluble and total aluminium levels were highest in the central section

of the creek (Figure 6.12b). The maximum soluble aluminium level of 0.7±0.02ppm

was recorded with a pH of 5.1 units at 6.9km from the mouth. The maximum total

aluminium level of l.2±0.14ppm was recorded with a pH of 5.1 units at 7.4km from the

mouth. Creek water of this quality would be considered to be harmful to aquatic life. Chapter fi: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE ISB Figure 6.12 @) 8.0 Figure 6. 13

7.0

I a. 6.0

5.0

@ 1 5 . I ---- Aluminium (soluble) "E a. --- Aluminium (total) .9' E ·::lc: .E 0.5. ::l ,.. A, Ci; J ~ ---- ...... ' 0 1- 1 ------r' ~ - 'i © l ---- iron (soluble) "E i -- - iron (total) a. / .9' - c - _g 1--- T 1 ______- __ -_ __r-.._1 ___ __..-- 0 @) 6000 800 @)

---- chloride "E 600 "E a. 4000 --- sulphate a. .e, .9' Q) 400 Q) "O 1ii .c - ~ a. :c: 2000 ::; () 200 (J)

0 ------0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Distance upstream (km) Distance upstream (km)

Figures 6 . 12-6.13. Water quality analysis along Broughton Creek on 22/9/93 (Figure 6.12) and 29/9/93 (Fig ure 6. 13) for: a: pH ; h: Aluminium: c: Iron: d: Chloride vs

Sulphate. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 159

Plate 6.1. Water colouration mid-stream in Broughton Creek on 22/9/93, showing water obviously clearer where pH was lowest (5.1) in the mid-section (6.9km from the mouth) of the creek where acid

drainage is compressed (part b). In parts a: 0.2km from the mouth (pH 5.8) and c: 11.Skrn from the

mouth (pH 6.6) the water appeared dirty. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 160

Maximum aluminium toxicity has been found to occur in fresh water at pH 5.0-5.2

(ANZECC, 1992), and continual exposure of fish to water with concentrations of total filterable aluminium (equivalent to soluble aluminium) of 0.13ppm has been shown to cause increased mortality in fresh waters (McCahon et al., 1989).

Trends for soluble and total iron for along the length of the creek were very similar to those for aluminium except that both iron levels rose upstream (Figure 6.12c ). The maximum soluble iron level of 0.3±0.0ppm was recorded 6.9km from the mouth. The maximum total iron level of 0.6±0.0ppm was recorded 7.4km from the mouth. Thus the highest levels of soluble iron and aluminium occurred about 7km upstream, where, like aluminium, pH was lowest.

Flocculation of small snow-like particles (probably of aluminium hydroxide) were observed on 22/9/93 from 4.6-11.0km from the mouth, but was most evident at approximately 7km from the mouth. On this day, an SDL was used to see whether different densities and salinities of water could be detected in the creek, but the

instrument was faulty on the day. Since all results here are from surface samples, certain

water quality levels cannot be assumed to be having their full potential effects on aquatic

life if it is not known whether acid drainage was found in all layers of the creek in any

one location. However, for at least 7km upstream from the mouth, the bottom of the

creek could be seen along with floes clearly visible on the bottom. This suggests the

stream, or at least this section of the creek, was not stratified and that acid drainage was

evident at all depths there.

The effects of acid drainage were somewhat reduced in the creek by 29/9/93. pH ranged

from 6.4-6.9 for the length of the creek and did not drop significantly in the central

section of the creek (Figure 6.13a). Soluble aluminium in all reaches was low

(0.05±0.02ppm), but total aluminium levels were still significant beyond 6.9km from the Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 161

mouth and peaked at 0.55±0.07ppm 9.8km from the mouth (Figure 6.13b). Soluble

iron levels were not high, but increased along the length of the creek from 0.04±0.0ppm

near the mouth to 0.2±0.0ppm 1 l.5km upstream. Like total aluminium, total iron

increased from around the 7km (7.4km) mark; then continued to increase to 0.6±0.0ppm

by 1 l.5km upstream, as did pH (Figure 6.13a and c).

A reduction in soluble and total aluminium and iron levels would be expected with the

overall drop in pH observed from 22/9/93-29/9/93. The shift of the highest levels of

aluminium and iron further upstream by 29/9/93 is an indication that the freshwater push

from further upstream had slowed and polluted water was pushed upstream by tides.

The advancement of tidal water up the creek by 29/9/93 can be shown with higher

concentrations of chloride and sulphate levels, especially up to -5km from the mouth

(Figure 6. l 3d). On 22/9/93 both chloride and sulphate levels were low, indicating

dominance by fresh floodwaters (Figure 6.13d). There was a noticeable increase in

sulphate and iron upstream from 9.8km on 29/9/93, which may indicate a source of

sulphate oxidation feeding into the creek near this location. The Berry Sewerage

Treatment Works is located on low relief land, near the headwaters of Broughton Creek,

and did discharge waste into Broughton Creek. These discharges could influence

sulphate levels in the upper portion of the creek through photorespiration. However, pH

was also rising, so there remains some uncertainty about the reason for this result.

6.4.5 Water Quality Recovery in Broughton Creek

An extension from the previous section is given here to indicate low water quality

improved in different parts of the creek, during the month after the mid-September

rainfall episode. This section refers to Figures 6.14a-g, where sampling at 0.2km,

4.5km, 7.4km (samples were not taken at this location on every sampling day) and

l l .5km was done. Water quality recovery in Broughton Creek is discussed in this

section in reference to two periods; period 1 - 14/9/93-21/9/93 and period 2 - 21/9/93-

12/10/93. Period 1 is representative of when oxidation products from high intensity acid Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 162 ~ a.-~~~~~~~~~~~~--,

7

J: a. 6

5

4 ® 8000 ...... ' e 6000 .. -----· a. S: , .a.. G> 4000 / ' -0 "O ', ·c: I "' -.- --.. CJ"' 0 I .a / ' :2 - (.) 2000 ,,,er--- _... I • I - ct' / 0 "' I - @ 1000 .. • ' 800 --.. ----· ea. S: 600 G> 1ij .r: a. 400 :5 en 200

0 @ 4 " 3 ea. S: c: _g 2

~...... I - ... 0 • -- -~- -~--~...._ -~=---=---=: @ 4

ea. 3 S: c: _g 2 G> 1i :i 0 en CD ea. S: 3 •

• -- • -- 0.2 (km)

- o- - 4.5 (km)

- .. - - 7.4 (km)

--0-- 11 .5 (km)

~ a-'.a.- o L-~_!•~-~~~:;:::!:~~i.c----~o-~-ci--....-~=====;L-_J 10/9 1 5/9 20/9 25/9 30/9 5/1 0 10/10 15/10 Date (1993)

Figure 6.14. Water quality recovery at 4 sites along Broughton Creek between 14/9/93-12/10/93; a:

pH, b: chloride, c: sulphate, d: total iron, e: soluble iron, f: total aluminium and g: soluble aluminium. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 163 drainage were severe, but decreasing in all reaches of the creek. Period 2 is representative of when the presence of oxidation products became increasingly less obvious. All distances are measured upstream from the mouth of Broughton Creek.

Period 1: (14/9/93 - 21/9/93)

Water quality was worst in Broughton Creek following the mid-September rainfall episode at the height of the flood peak on 14/9/93. On 14/9/93 pH was highest (6.4)

11.5km upstream (above the zone of acid drainage input into the creek), and continued to decrease to the central part of the creek (7.4km upstream) where the pH was 5.1, and pH at the mouth was 5.8. The low chloride (maximum - 390ppm at 0.2km) and sulphate levels in all reaches of Broughton Creek on 14/9/93 was an indication of the dominant effect of flood water moving down the creek over tidal water moving up the creek. The influence of high volumes of acid drainage entering the creek during the height of the flood peak measured is shown as total iron and aluminium and to a lesser extent soluble iron and aluminium were highest on 14/9/93, just down stream from the central part of the creek (4.5km) and at the mouth.

By 19/9/93, when flood waters had subsided, there was evidence to suggest more saline

creek water had begun to move back up the creek, improving water quality as it went, but

trapping some pollutant waters upstream. pH had risen to an acceptable level at 0.2km

(6.8), since 14/9/93. The chloride levels rose 3,7 lOppm at 0.2km and

11.5km, between 14/9/93-19/9/93. As expected, iron and aluminium levels (both total

and soluble) dropped most dramatically at 0.2km, but from 4.5km and further upstream,

soluble iron and aluminium stabilised at low but significant levels. pH had maintained

stability and was relatively acidic (5.3) in the most central location (7.4km) on 21/9/93.

Acidity had actually increased by 0.1, at this location from 19/9/93. Acidity dropped

upstream and downstream from this point on 21/9/93, but again pH stabilised or

decreased at all locations on 21/9/93. The reason for this was probably due Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 164 to tidal water downstream (indicated by the stabilisation of chloride at 0.2km) and the lessening of flood flows allowing an acid slug to form in the central part of the creek.

This acid slug in the central part of the creek was particularly obvious by 21/9/93, by the clarification of the water and an increase in total and soluble iron and aluminium at 4.5km and 7.4km, on 21/9/93. A highest soluble aluminium value of 3.2ppm was recorded at

7.4km, on 21/9/93.

Period 2: (21/9/93 - 12/10/93)

Water quality overall continued to improve upstream from the mouth, throughout this period, except at 11.5km, where pH dropped from 7.4-5.7, between 3/10/93-7/10/93.

Soluble aluminium was also high (0.lOppm) at 11.5km on 7/10/93. This was thought to be the result of a remnant acid slug developed earlier in the month, moving further upstream (by which time flood waters had completely subsided), or of some other unknown factor.

There was a continual influence of chloride up the creek throughout this period at all locations except 11.Skm. But where total and soluble iron and aluminium levels overall dropped throughout this period at all location except 11.Skm, decreases were slight.

Clarification of creek waters which originated around the 19/9/93, persisted until

approximately 3/10/93. Water quality as a result of mid-September flood event was not

severe by 12/10/93 in Broughton Creek, but the effects (mainly total and soluble iron and

aluminium) were still evident in the creek for approximately 1 month after the flood -

inducing rainfall had ceased.

6.5 Effects on Aquatic Life 6.5.1 Observations

There are reports of fish dying in Broughton Creek in 1991, as a result of acid drainage

in Broughton Creek. Apparently, between 50-100 sea mullet and a small number of

silver bream (Acanthopagrus australis) had died and been found dead at approximately Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 165

11.Skm from the mouth, in early August 1991 (R. Cumming, EPA, pers. comm.,

1993). There is other evidence suggesting both acute and chronic drainage affects

aquatic life in Broughton Creek (see Chapter 1). There is, also, strong anecdotal

evidence suggesting acid drainage from the mid-September flood had significant impact

upon aquatic life in Broughton Creek.

While travelling the length of Broughton Creek in a boat, at dawn on 22/9/93, when

effects from acid drainage were most obvious, there was no sign of fish life in any part

of the creek. Under normal conditions early in the morning, many small mullet can be

seen breaking the surface of the water, during any time of the year, along any stretch of

the creek (G. Usher, professional fisherman, pers. comm., 1993). This observation was

made 8 days after significant rainfall was received and a flood had occurred; but water

flowing out of Broughton Creek on 22/9/93, even on the low tide, was by no means

excessive. Acid drainage is suggested as a likely cause for this observation. As was

shown here, there was an overall improvement in water quality by 29/9/93. Fish were

observed from the boat on 29/9/93 from a distance of 4.8km from the mouth.

Noticeable reductions in prawn and fish stocks were observed in Broughton Creek by

professional fishermen after the mid-September rainfall episode (G. Usher, pers. comm.,

1993). At a location 4km from the mouth of the creek 50kg of prawns were caught on

the 21/9/93. The next day, clarification of the water was observed and only lOkg of

prawns were caught. The next day (23/9/93), not one prawn was caught, and no prawns

were caught in two further trips until the 13/11/93. On 13/11/93, 0.5kg of prawns were

caught and these were apparently significantly smaller than usual for that time of year.

This was a similar scenario to other times in the previous 3 years after significant rainfall.

Netting of the creek in two trips between 20/9/93 and 8/10/93 saw no fish caught. On

13/10/93, netting within the first 1.5km of the creek produced a catch of 21kg. Species

caught on this occasion included silver bream (the majority), luderick (Gire/la cyanea), Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 166 sea mullet and flathead (Platycephalus sp.). Three kilos of flathead (5 fish) were caught on this occasion. This was considered to be high. Flathead have been observed elsewhere as slow movers away from acidity (Leadbitter, 1993b; Sammut et al., 1993), and this is an indication that a number of flathead had congregated at this lower end of the creek, in order to escape from the previous acidity. Another noteworthy feature of this catch was the occurrence of EUS in about 15% of the catch, mainly affecting the silver bream. This proportion was high. EUS was also observed when another professional fisherman caught approximately 40kg of mullet on 2/10/93, approximately 11.8km up the creek, of which 30-40% were affected. It appeared as though these fish were trapped above the slug of acidity which has been described as lingering in the mid section of the creek for at least 3 weeks after significant rainfall.

One other noteworthy point was that professional fishermen set eel traps (for shortfinned

Anguilla reinhardtii and longfinned A. australis eels) along the length of the creek. No

eels were caught until 2 weeks after 14/9/93; thereafter they were caught in small

numbers along the creek, and there was a noticeable increase in prevalence towards the

mouth of the creek (G. Usher, professional fisherman, pers. comm., 1994). A similar

scenario occurred on the north coast in the Tuckean Swamp and Rocky Mouth Creek, in

the Richmond River catchment, whereby large losses of eels occurred after high intensity

acid drainage in March, 1993 (J. Sammut, UNSW, pers. comm., 1994). Eels are

thought to be more tolerant to poor water quality than other fish but are still affected by

low pH (Sammut et al., 1993). This observation may also hold for Broughton Creek.

6.5.2 Discussion of Effects

Water quality has been shown to be severely reduced in Broughton Creek from acid

drainage in response to the flood event described in this thesis. Water quality in

Broughton Creek may normally be expected to be more severe from acid drainage

following the proportion of rainfall which has been described, since a significantly higher

than normal amount of rainfall was received higher in the catchment in mid-September Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 167

1993 (P. Jamieson, Shoalhaven City Council,pers. comm., 1994). This may have acted to dilute and flush a larger than normal portion of the acid drainage from the creek. It has also been shown that more, or at least equally severe, episodes of severe acid drainage have impacted upon Broughton Creek on a fairly regular basis (at least once a year from

1991-1993).

The effects on aquatic life in Broughton Creek from acid drainage are considered to be less severe than other areas on the north coast, despite the severity of acid drainage produced within the floodplain being measured as extreme. The reason for this is that

Broughton Creek is considered to be a more open system than the areas on the north coast where effects have been more obvious. On the north coast, many natural pathways for fish have been partially blocked by floodgates and/or barrages (Sammut et al., 1993).

Water quality is often acceptable for aquatic life to survive upstream from these obstacles, and fish when possible often move past them. But following rain events, fish are practically trapped and often cannot escape in time from acid drainage after a rainfall episode. Fish that die upstream from these obstacles have been assumed to comprise of a large proportion of fish kills (Callinan et al., 1992). There is not the same network of obstacles in Broughton Creek and fish do not move through floodgates. This may explain why fish kills are not experienced on the scale of those on the north coast.

Another reason may be because of lower buffering capacities on the north coast. The tidal range is often close to zero (J. Sammut, UNSW, pers. comm., 1994), where effects are felt greatest on the north coast; but, as was described in Chapter 2, the tidal range is quite strong along the length of Broughton Creek, accounting for the high salinity levels for this creek in the lower Shoalhaven. The greater tidal exchange in Broughton Creek would allow for easier escape of aquatic life during high intensity events and for greater amelioration of toxic effects during recurrent discharges.

Despite some stream water parameters not being as severe in Broughton Creek compared with examples from northern NSW, the potential impact on aquatic life in Broughton Chapter 6: BROUGHTON CREEK WATER QUAUTY & IMPACT .. ON AQUATIC LIFE 168

Creek may be similar~ It has already been stated here that Sammut et al. (in press) argue that habitat loss is the most significant of the known impacts of acidification. It was shown here that fish move out of Broughton Creek (their natural habitat) for extended periods after high intensity acid drainage, which has occurred annually between 1991-

1993. The severe acid drainage problem in Broughton Creek described in this analysis can be assumed to have developed after the completion of deep flood mitigation works

(see Chapter 2) -20 years ago. "Homeostasis cannot occur if the rate of environmental change exceeds the ability of fish to modify their physiological and behavioural processes to survive frequent extreme events" (Sammut et al., 1993, p.35). It is believed that the frequency of high intensity acid drainage events which have occurred in the recent past in

Broughton Creek was having a severe impact on aquatic life mainly due to habitat loss, as the rate of environmental change (water quality) in Broughton Creek over the last 20-

30 years would have far out weighed the scope of physiological and behavioural change by fish.

6.6 Summary * Anecdotal reports in Australia, dating back to the turn of the century, identified fish kills which are now believed to have been linked with acid drainage (Neilson, 1993;

Leadbitter, 1993b).

* Identification of the two modes, in which acid drainage is released from drained floodplains into estuaries - i.e. high intensity (high volume/low frequency -

predominantly associated with significant rainfall episodes) and recurrent (low

volume/high frequency - predominantly associated with daily tidal exchange)

discharges - suggests that estuarine aquatic life can be harmed in different ways

(Lead bitter, l 993a and b; Sammut et al., 1993 ). Acute effects can be considered as

those which make for short term survival of aquatic life to be often impossible to

sustain. Acute effects from acid drainage, related to acid sulphate soils, usually occur

during and/or immediately after rainfall episodes. Chronic (or lag) effects are not as

directly lethal to aquatic life as acute effects. Chronic effects are likely to be most Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 169

severe for prolonged periods after rainfall episodes, but in some locations have been

probably occurring all year round.

* In the study area and elsewhere (Brown et al., 1983; Callinan et al., 1992; Leadbitter,

1993b; Sammut et al., 1993) when pH becomes more acidic in drainage water, there

is a general trend for aluminium and iron levels to become higher.

* Random sampling of pH (showing medians and ranges) by Shoalhaven City Council

between March, 1992 and December, 1992 indicated that recurrent acid drainage was

probably occurring into Broughton Creek. This observation was confirmed by water

quality analyses during this study.

* An acid drainage problem was first identified for Broughton Creek on 1st August

1991, when an 8km stretch of the creek turned clear, after drought breaking rain in

June and July. A similar scenario occurred in Broughton Creek on 3rd March 1992,

again after heavy rainfall in the previous month. On both occasions, fish and prawns

were absent in Broughton Creek for extended periods after the heavy rains. The

intensity and potential impact was less for the event analysed in this study than for

those in 1991 and 1992; but this thesis describes a fairly common event, and thus

emphasises the seriousness of the problem caused by drainage of acid sulphate soils.

* A submerged data logger identified movement of saline creek waters into the drains

even during flooding, as had been identified on the north coast (Sammut et al., in

press).

* The total discharge from all 18 floodgates between 1315hrs on 14/9/93 to 1545hrs on

16/9/93 produced enough acid drainage to fill Broughton Creek on a low tide 1.34

times (134% capacity). Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 170

* Submerged data loggers located immediately inside and outside a floodgate of a main

drain identified oxidation products still being washed out of the floodplain and in a

position to be pushed out at low tides into the creek, as late as 1 month after the

rainfall producing the flood had ceased.

* Water quality in Broughton Creek was found to be such that it would have been

harmful to aquatic life. Mid stream analysis showed that the maximum soluble

aluminium level of 0.7±0.02ppm was recorded with a pH of 5.1 units at 6.9km from

the mouth. The maximum total aluminium level of 1.2±0.14ppm was recorded with a

pH of 5.1 units at 7.4km from the mouth. Creek water of this quality would be

considered to be harmful to aquatic life. Maximum aluminium toxicity has been found

to occur in fresh water at pH 5.0-5.2 (ANZECC, 1992), and continual exposure of

fish to water with concentrations of total filterable aluminium (equivalent to soluble

aluminium) of 0.13ppm has been shown to cause increased mortality in fresh waters

(McCahon et al., 1989).

* As flood waters receded, more saline creek water steadily moved up Broughton

Creek (as shown by increasing chloride levels). A consequent improvement of

water quality was seen to progress up the creek, but a slug of acid drainage

apparently accumulated in the central part of the creek, from approximately 5

days after the rainfall, as shown by rises in soluble aluminium and iron and

clarification of the water.

* Water quality has been shown to be severely reduced in Broughton Creek from acid

drainage in response to the flood event described in this thesis. Aquatic life was

reported to be affected in a variety of ways following the mid-September rainfall

episode in Broughton Creek, including a noticeable increase in prevalence of red spot

(EUS) disease. Chapter 6: BROUGHTON CREEK WATER QUALITY & IMPACT .. ON AQUATIC LIFE 171

* The acute effects on aquatic life in Broughton Creek from acid drainage are considered

to be less severe than other areas on the north coast, despite the severity of acid

drainage produced within the floodplain being measured as extreme. Despite this, the

potential impact on aquatic life in Broughton Creek may be similar in the longer term. Chapter 7: DISCUSSION AND MANAGEMENT 172

Chapter 7: DISCUSSION AND MANAGEMENT

7.1 Summary of Major Findings

* An acid drainage problem was first identified for Broughton Creek on 1st August

1991, when an 8km stretch of the creek turned clear, after drought breaking rain in

June and July. A similar scenario occurred in Broughton Creek on 3rd March 1992,

again after heavy rainfall in the previous month. On both occasions, fish and prawns

were absent in Broughton Creek for extended periods after the heavy rains. The

intensity and potential impact was less for the event analysed in this study than for

those in 1991and1992; but this study describes a fairly common event, and thus

emphasises the seriousness of the problem caused by drainage of acid sulphate soils.

* A drainage density of -5.75kmfkm2 is shown in Figure 2.3; since 230km of drains

are found on the 40km2 of land prone to inundation on the northern side of the

Shoalhaven River. Secondly, of the 19 drains draining into Broughton Creek, only

one was not blocked by a floodgate, suggesting that a very large portion of the acid

drainage transported from the floodplain into the drains was likely stored in the drains.

* Large volumes of spoil (including oxidiseable pyrite) from drainage construction was

deposited on the floodplain with an estimated density of 7 ,763 m3Jkm2.

* The drainage network mainly consisted of deep trench drains (main drains) with

dimensions 3.5m wide x 2m deep (dug to invert levels of -1.2m AHD) and smaller

drains (mole drains) with dimensions rarely exceeding 1.Sm wide x 2m deep.

* Three geomorphic zones across the floodplain of differing acid sulphate soil

development were identified (levees, levee toes and backswamps) and these were in

accord with examples from the north coast of NSW, with the same calssification used. Chapter 7: DISCUSSION AND MANAGEMENT 173

* In the levee soils, only minor changes were found in the parameters analysed,

including colour, grain size pH and total potential acidity (TP A). This indicated a

common sedimentary history. The complexity of soil horizons increased in the levee

toe soils, including a decrease in the depth of alluvium. There were now signs of

pyrite oxidation. Soil complexity and pyritic oxidation was extremely obvious in

backswamp soils, with colour, grain size, pH and TP A varying significantly down the

profile. Alluvial surface soils were very thin (rarely exceeding 0.2-0.25m depth) in

the backswamps. All of the above transitional changes (including grain size fractions,

and pH and TPA levels) were broadly in accord with those of acid sulphate soils

found on the north coast of NSW (Lin and Melville, 1992b; Walker, 1972; Willett

and Bowman, 1990).

* The analysis of TP A did show potential soil acidity in this study, but did not

represent the potential acidity due to the pyrite content alone. Surprisingly, TPA

values in nearly every levee, levee toe and backswamp profile were highest (higher

than the unoxidised - lowest horizon) in the surface horizon. However, the TP A

analysis indicated the pyrite concentration was not severe and was not as high as has

been found on the north coast of NSW, perhaps because of differing sedimentary

histories.

* Watertable movements were found to be responding differently on the drained floodplains (mainly by falling significantly faster after rainfall), compared with

undrained areas. Groundwater was found to be drawn down into the drains, thus

allowing direct oxidation of adjacent soils. Hence the oxidation products were fed

into the drains. This groundwater/drain water relationship was predominantly unlike

that described in Willett and Walker (1990) for the lower Macleay, and by White et al.

( 1993) for the Tweed. At these two north coast locations, the water level of the drains

was described as being higher than the groundwater level during field analysis. Chapter 7: DISCUSSION AND MANAGEMENT 174

* Interaction between rainfall and deep drainage on the floodplain by the main drains

was controlling groundwater levels. The drains controlled the lowest level to which

groundwater could fall, as levels in the drain remained relatively stable except during

very high rainfall.

* Rainfall patterns dominated watertable fluctuations. Watertable fluctuations (position

along the soil profile) dominated groundwater pH levels. Rapid rises in the watertable

caused pH to rise rapidly, especially when the watertable rose to, or above the ground

surface. Similarly, when the watertable was at or near the ground surface, only a

minor watertable decrease was required for the pH to drop rapidly. While the

watertable was about 0.5m below the ground surface (approximately -0.2m AHD), or

deeper (while remaining in the oxidised section), pH was low between 2.8-3.3.

* Sulphate and aluminium levels were closely related in the bore and two drain water

quality sampling sites; iron levels also followed the same trend in the bore and road

drain, but were consistently low in the transect drain. Chloride levels were very low

except in the transect drain; this indicated that there had been considerable leaching

since the estuarine sediments were emplaced.

* Comparisons were made between the Shoalhaven floodplain and north coast sites in

regard to water level and water quality fluctuations in the groundwater and the drains.

Indicators of acid sulphate soil development and acid drainage and water quality levels

were largely comparable between areas. While some acid drainage dynamics were

also comparable (e.g. watertable reduction rates), others were not. For example,

oxidation products predominantly entered the drains in the Shoalhaven floodplain

through groundwater movement, even during flooding. Oxidation products

predominantly entered drains on the north coast from surface runoff, therefore, mainly

during flooding. Flooding is not necessary for this to occur on the lower Shoalhaven. Chapter 7: DISCUSSION AND MANAGEMENT 175

* The 133mm of rainfall received, mainly in 2 days, finishing on 14/9/93, caused acid

drainage to leach from the backswamps and move down to the floodgate, with effects

of concentrated oxidation products, immediately inside the floodgate, lasting for at

least 28 days, until the completion of monitoring on 12/10/93.

* Submerged data loggers located immediately inside and outside a floodgate of a main

drain identified oxidation products still being washed out of the floodplain and in a

position to be pushed out at low tides into the creek, as late as 1 month after the

rainfall producing the flood had ceased.

* Water quality in Broughton Creek was found to be such that it would have been

harmful to aquatic life. Mid stream analysis showed that the maximum soluble

aluminium level of 0.7±0.02ppm was recorded with a pH of 5.1 units at 6.9km from

the mouth. The maximum total aluminium level of 1.2±0.14ppm was recorded with a

pH of 5.1 units at 7.4km from the mouth. Creek water of this quality would be

considered to be harmful to aquatic life. Maximum aluminium toxicity has been found

to occur in fresh water at pH 5.0-5.2 (ANZECC, 1992), and continual exposure of

fish to water with concentrations of total filterable aluminium (equivalent to soluble

aluminium) of 0.13ppm has been shown to cause increased mortality in fresh waters

(McCahon et al., 1989).

7 .2 Management Strategies 7.2.1 The Need for Geomorphic Analysis

Acid sulphate soils on the Shoalhaven floodplain have been analysed to try to understand

processes involved with the generation and release of acid drainage from the floodplain

into the drains, thence Broughton Creek, mainly by relating rainfall patterns, watertable

fluctuations and water quality levels. These relationships indicate significant effects on

aquatic life, and emphasise the need for new management strategies to reduce the adverse

impacts of acidification. However, before proposing management plans for the study

area, some further mention of the geomorphic setting of these soils is essential. Chapter 7: DISCUSSION AND MANAGEMENT 176

Management strategies for environmental and industrial problems associated with acid sulphate soils cannot be accurately made until the areas of acid sulphate soils are more accurately mapped and the geomorphology of these areas better understood. There has been a wealth of Australian literature describing coastal development along the east coast of Australia (e.g. Thom, 1984; Young et al., 1993), but there needs to be an enhanced awareness in the recognition of the Quaternary history and environmental development of the coastal landscape (Melville et al., 1991). Enhanced awareness of the coastal quaternary history needs to be both large scale and small scale (Bowman, 1993). The

Shoalhaven coastal floodplain, illustrates this point since there has been little geomorphic work since that of Thom et al. (1981). In Thom et al. (1981), organic rich estuarine muds were assumed to be found at depths of around 30m below the present sea level for the majority of the floodplain surrounding Broughton Creek, including the study area.

This conclusion was based on drilling done on the southern side only of the Shoalhaven

River. Also pedological work discussed earlier in Chapter 3 (Norwood, 1975) showed acid sulphate soils - and thus evidence of estuarine sedimentation - across the floodplain, but considerable variations in pH indicated significant differences in the past sedimentary environment. Furthermore, drilling in May 1994 in the Shoalhaven floodplain showed organic rich sediments of apparent estuarine origin extending to 3m below present sea level; thereafter lighter coloured sediments possibly of Pleistocene age were found. It indicated a variable depth of estuarine sedimentation, to over 20m near the Shoalhaven

River, but no more than 3.5m on the study area (C. Woodroffe, UW, pers. comm.,

1994). Obviously far more information is requried concerning the presence of pyritic

sediments and the sequences of deposition before the results of their oxidation can be

predicted reliably. Programs to relate findings from coring and dating of sediments

within coastal floodplains with factors such as grain size and sulphur contents would be

invaluable information in understanding the environmental development of the coastal

landscape and potential risks of acid drainage on estuarine aquatic life. Chapter 7: DISCUSSION AND MANAGEMENT 177

7 .2.2 Current Amelioration Procedures

It was not an aim of this study to provide a detailed chemical analysis of the character of the acid sulphate soils across the floodplain. However, the analysis of total potential acidity (TP A) in Chapter 3 was to be used here for a prediction of the acid sulphate hazard of the floodplain and estimate what volumes of lime would be necessary to neutralise the acid. The TPA test was found to be unsuitable for such an exercise. What is done here instead is a discussion of two types of amelioration procedures which were

being carried out on the floodplain with the results being encouraging in decreasing acid drainage concentrations.

It has been shown overseas that the use of lime to neutralise acid sulphate drainage

particularly for large areas, was not economically viable for most types of landuse. Also,

there may be side effects on the environment and plants, also rising from excessive use

of lime (Dent, 1986). However, liming has been trialed for improved pasture on the

floodplain with very encouraging results shown after only 1 year (P. Morris, dairy

farmer, pers. comm., 1994). Trials were done on a 6ha section of a property, located

north from the study area, approximately lOkm up Broughton Creek between the creek

and the hillslopes (in an east-west orientation). Trialing consisted ofliming 12m strips of

land with different tonnages per hectare. Tonnages of 0.2-0.8 tonnes/ha were applied to

every second adjacent strip with intermediate strips left unlimed. Surface soil and soil to

depths of 0.5m showed pH values commonly between 3.7-4.0 units throughout the

trialing area. After 1 year, surface soil and soil to depths of 0.5m showed higher pH

values where lime had been applied, averaging 5.0-5.7 at the surface and 5.2-5.5 at

depth.

The above amelioration of soil acidity was obvious. Liming was also done on the

property, covering an overall area of 250ha. One year after liming the 250ha area,

dairying production increased 110% from the previous year. The sustainability and high

yields of clover and rye grass, appeared to be at least largely responsible for this increase Chapter 7: DISCUSSION AND MANAGEMENT 178 in dairying production. Until liming, these pastures had not been highly productive since deep drainage was put in place (-20 years before - see Chapter 2). It is likely that the rise

in pH also improved calcium levels in the milk and nutrient uptake by grasses, as well as reducing the toxicity of free aluminium in the soils. Further liming trials were to begin in

September 1994, over a larger area, and with tonnages of 5 tonnes/ha and 12 tonnes/ha

(P. Morris, dairy farmer, pers. comm., 1994).

Whether liming improved the severity of acid drainage from the property is not known;

However studies were, at the time of writing, underway to try to understand acid

drainage dynamics on the floodplain and the influence of liming was having on levels of

oxidation products in the acid drainage.

Lime had also been applied to 200ha of the floodplain on the northern side of the

Shoalhaven River -4km south-west from the study area (see Figure 2.3). This land is

was owned by Shoalhaven Starches Pty Ltd. Hydrated lime was applied to the

floodplain through irrigation, mixed in with the company's liquid waste. For 3 years

prior to early 1994, 80 tonnes per week of lime was applied in 2.5Ml of liquid waste to

the 200ha (0.4 tonnes/ha - hydrated lime). pH of the irrigated effluent was -10 during

this 3 year period. After early 1994 the tonnage of hydrated lime used was halved to 0.2

tonnes/ha, due to high costs. pH of the effluent from early 1994 was maintained as close

as possible to 9 and only falls below 9 for 10% of the time (A. Murphy, Shoalhaven

Starches Environmental Manager, pers. comm., 1994).

On the 200ha irrigated with hydrated lime, pH of the upper 0.5m of the soil profile

increased from 3.2-4.2 before initial liming to 6-7 by August, 1994 (-3.5 years). More

interestingly, drain water pH was 5-6, in the past 2 years in and adjacent to the lime area,

where in the last 2 years other drains located as close as 0.5krn from the limed area had

drain water pH's of 3-4, suggesting a link between liming and less acidic drain water (A.

Murphy, Shoalhaven Starches Environmental Manager, pers. comm., 1994). This Chapter 7: DISCUSSION AND MANAGEMENT 179 liming work on 2 areas of the the floodplain is a positive indication of how the acid sulphate soils did respond to liming, with probable implications to improved water quality of the acid drainage.

However, work in this thesis and elsewhere (White et al., 1993) has been orientated

towards understanding watertable dynamics in relation to the production of acid drainage,

including and the possibility of managing watertable changes as a means of managing

acid drainage (Willett and Bowman, 1990). To most accurately understand certain

attributes of acid drainage, monitoring parameters must be specific and carried out on a

very regular and systematic timescale such as has been established in White eta!. (1993).

Opening floodgates at a time of unusually heavy rainfall at Rocky Mouth Creek, near

Woodburn, northern NSW, has seen pasture quality improve drastically. Drain water

quality improved to the extent where cows had started to drink the water, and fish were

noticed in the drains where they had not been seen for years. The partial transformation

of the floodplain back to swamps indicated by 0.2m of water covering the pastures had

resulted in the water succulent, natural swamp grasses (e.g. water couch) returning to

where they once thrived (Bush, 1994). Anecdotal evidence from local dairy farmers with

a long term association with the study area suggest pasture quality was noticeably greater

than present before the introduction of extensive deep drainage (P. Morris, dairy farmer,

pers. comm., 1994) implemented from 1968 (see Chapter 2).

Overseas, in some areas used for agricultural purposes where acid sulphate soils had

developed, productivity has decreased to the extent where continued production was not

economically viable. It has been common practise to return these areas to wetlands by

eliminating all drainage works, at the expense of total loss of potential agricultural land.

However, in some of these areas (e.g. Malaysia), blocking all drains and allowing the

watertable to rise above the acid sulphate layer caused productivity to rise above the

levels that had been achieved before acid sulphate soils had developed (Dent, 1986). Chapter 7: DISCUSSION AND MANAGEMENT 180

When watertable levels are partly or fully returned to natural positions, natural, and sometimes agricultural vegetation growth increases (Dent, 1986, 1993; Dent and Pons,

1993). This is an indication of improved water quality from areas of acid sulphate soils, that can also be assumed to indicate more favourable conditions for the existence and

survival of aquatic life in contact with the acid drainage. Raising the watertable where

acid sulphate soils are found is likely to be the best means of reducing acid drainage.

However, management practices must take into consideration the concerns of landholders

in changing the physical environments of floodplains. In northern NSW and in the lower

Shoalhaven, there is little doubt that flood mitigation and drainage works have allowed

more grazing days per year than before flood mitigation (NSW Fisheries and Agriculture,

1989). Water covering the floodplain on a semi-permanent basis could be detrimental to

the practicability and safety of managing a dairy farm. Thus a fine line must be drawn

between raising the watertable to the maximum in order to most efficiently reduce acid

drainage, and not allowing the watertable to rise so far that agricultural practices become

unsustainable. There may well be a moderate rise in the watertable which will improve

agricultural activity without making the land too dificult to work. The present lower

levels are likely to be disadvantaging farmers by making the soils more drought-prone;

they are certainly reducing the viability of natural vegetation, and possibly of pasture

grasses.

7.2.3 Proposals for Remediation Strategies

Initially, the remediation works to manage acid drainage for the study area were planned

to be the conversion of deep trench drains into shallow swale drains. It was opportune

that these remediation works were to go ahead soon after this monitoring program was to

begin. Ideally, the design for such a large scale drainage conversion would follow

significant amounts of preliminary work such as detailed analysis ground surface runoff

patterns and soil porosity. The proposed remediation offered the potential for before and

after comparisons. Chapter 7: DISCUSSION AND MANAGEMENT 1 8 I

As mentioned earlier the owners of the site (Australian Army) decided not to proceed with drain conversions at present. This remediation work may still go ahead at some time in the future, and all monitoring from this thesis would be beneficial in devising any final drainage conversion plan. However, in light of a growing list of examples becoming apparent during the completion of this work, whereby watertables have been raised by simpler alterations to the drainage networks already in place, the extensive works originally envisaged may be unnecessary. Less drastic alterations could reduce risk of further disturbance of pyrite that could occur as deep trench drains were turned into shallow swale drains. Disturbance of pyrite in such an exercise in the study area would require very careful planning, since soil analysis here found alluvial deposits covering the acid sulphate layer to be very shallow (often no more than 0.2m thick).

Hence, the material to fill trenches could not be taken from the upper soil layers of the floodplain but would have to be imported.

Shoalhaven City Council had immediate plans of trialing increasing watertables via changing the operation of drains in those areas. One option to reduce the impact of acid drainage on aquatic life in Broughton Creek is to leave the floodgates semi-permanently open, allowing more saline creek water up the drains to ameliorate oxidation products in the drain. Water quality analysis of a main drain and a mole drain in Chapter 4 showed where even minor flushing of the main drain only occurred, water quality in the that drain significantly improved (due to a leaky floodgate). However, while flushing the drains by opening the floodgates would reduce the impact of recurrent discharge in particular, it is not considered a means of significantly improving the overall acid drainage problem. It

was shown in Chapters 4, 5 and 6 that the acid drainage which appeared to be having by far the biggest impact on aquatic life in Broughton Creek, was occurring during flooding and for extended periods immediately after flooding. The vast majority of acid drainage

which entered Broughton Creek was moved from within the floodplain into the drains Chapter 7: DISCUSSION AND MANAGEMENT 182 and thence Broughton Creek during high intensity rainfall periods. This means the most efficient way to minimise the acid drainage that enters Broughton Creek is to minimise oxidation within the floodplain. The aim must be to limit the development of acid sulphate soils, and consequently the amount and level oxidation products from the floodplain which are in a position to be potentially transported into the creek after high intensity rainfall. Raising the watertable will most efficiently reduce oxidation.

Therefore, the best management plan to achieve a reduction in the severity of the water

quality of acid drainage for the study area would involve raising the watertable, and this

can be done with the existing drainage network in the drains.

Inside floodgates along Broughton Creek are 0.05m wide x 0.03m deep slots which

were moulded into the concrete. These slots were designed for the fitting of boards

which would act to cross the drain. The depth of the water in the drain would then

become a function of the height of the fitted board (wood or metal), and not, as at

present, a function of the low tide level in the creek. This is a potentially simple means

of controlling drain water depth, and therefore, watertable position (groundwater height).

If blocking the drains is shown to be practicable, the next step in this process is to

determine what height the boards should be to accurately control watertable position. To

raise the watertable in order to decrease oxidation of the soil is a simple concept. It was

shown in Chapter 4 that the bore with the highest mean watertable above high tide level

(Bs 17) had the lowest mean and standard deviation pH levels. However, while any raise

in the watertable should reduce oxidation, the precise improvement in water quality is

difficult to predict. It was shown in Walker (1972) and Chapter 4 (section 4.6) here, that

the rate and magnitude of watertable and pH changes in floodplain soils are part of a

rapidly varying system. Important inputs to the floodplain, such as water, vary so much

with time that the soils may never be in a state of equilibrium as regards to soil moisture

and solute concentration. It should not be forgotten that, certainly, the soils cannot be

properly characterised by single values for watertable position and pH (or for - iron and

aluminium). Chapter 7: DISCUSSION AND MANAGEMENT 183

In the study area, when the watertable fell into the zone of abundant jarosite 0.7m below the ground surface (-0.4m AHD), iron and then aluminium levels increased rapidly and pH remained very low. It is suggested the majority of acid drainage that enters

Broughton Creek is generated below this depth, within approximately the lower 30% of the oxidised acid sulphate soil profiles in the backswamps. If the watertable can be kept considerably above this level, the consequent improvement in acid drainage severity may be such that the saline creek water can almost competely ameliorate any acid drainage entering the estuary. Based on decreased acid drainage production (associated with

Figure 4.5) above the zone of abundant jarosite (by up 40%) and vastly decreased (by up to 60%) acid drainage production within the zone of abundant jarosite, if the watertable was to rise -30%, it is extrapolated that the resulting decrease in the severity of acid drainage produced may be up to 60%.

For such a change in watertable position to take place, the depth of the drains would not need to be changed so that the bottom of the drains was -0.8m AHD (0.4m higher than at the time of writing). What would have a similar effect would be to raise the minimum drain water depth in order to decrease the average depth to the watertable. The minimum drain water depth at the time of writing was the low tide level. .The minimum drain water height could be raised by 0.4m above the present minimum level by placing boards

across the drains (built to specified heights), inside the floodgates. Hence, the idea of

placing boards across the drains is a potential way in which drain water depth and

therefore, depth to groundwater could be trialled quickly. Problems would arise in such

an exercise such as obtaining a good seal with the weirs and what influence a raise in the

watertable would have on flood water removal. These problems would be worthy of

further research, with preference of including other bodies such as the Public Works

Department. An engineering input would be required for answering problems such as

incresing flood risk and other suggestions of raising the drain water depth with the

involvement of engineers would be very useful. Chapter 7: DISCUSSION AND MANAGEMENT 184

Working on a percentage system, the altered flood risk (decreased drainage capability) to the floodplain would be increased by approximately 33%. In the present situation a 1: 4 year flood (1.3m AHO) drains to 0.2-0.4m AHO in 5-6 days. It is therefore estimated in the revised flood risk situation that a 1:4 year flood would drain to 0.2-0.4m AHO in

6.6-8 days.

Further discussion of the drainage specifications on the Shoalhaven floodplain surrounding Broughton Creek is considered necessary to re-affirm the need for drainage related remediation work to be done in order to decrease the acid drainage hazard to

Broughton Creek, while also helping to explain the severity of the acid drainage already described. As discussed in Chapter 3, levels of TP A from within the floodplain were not considered exceedingly high and were lower than for most other known areas in

Australia. However, the severity of oxidation products in acid drainage (shown in

chapter 4) were high and at least comparable to those for other areas in Australia where

severe impacts on aquatic life had taken place (Sammut et al., in press). The

concentration of pyrite in the study area, therefore, does not appear to be the sole cause

of the severity of the acid drainage. The deep drainage of this floodplain on the northern

side of the Shoalhaven River was probably the major cause, because it exposes a very

large volume of pyritic soil to oxidation. Drainage in the study area was deeper than for

other areas in Australia, meaning that a greater depth of pyrite can be oxidised, resulting

in a larger proportion of drainage water being leached through oxidised (acidic) soil. The

shallow occurrence of jarosite throughout the backswamps exacerbates this problem on

the Shoalhaven floodplain, and is cause for concern.

7 .3 Restatement of Aims * The extent and characteristics of acid sulphate soils throughout the northern side of

the lower Shoalhaven floodplain were investigated, with extra attention paid to

backswamp soils where estuarine sediments were very close to the ground surface. Chapter 7: DISCUSSION AND MANAGEMENT 185

* The relationships between rainfall, fluctuating watertables and the quality of

groundwater were investigated, and the relationships were found to be strong and

consistent.

* Conditions required to produce acid drainage from the study area into the drains and

from the drains into receiving waters of Broughton Creek were - low watertables as a

result of dry weather, leading to sulphide oxidation. Water then leached out into deep

drains, causing high levels of acidity, aluminium and iron. This polluted water is

flushed into Broughton Creek and thence into the Shoalhaven estuary, when

significant rainfall flushes oxidation products from the drains, and also frequently at

low tides even during dry weather.

* The resultant variations in water quality in Broughton Creek during a minor flood

event caused clarification of the creek, and associated low pH and high metal levels.

Fish and prawns abandoned the affected stretches.

* Management options with the aim of reducing acidic drainage discharges into

Broughton Creek include liming of soil and watertable management. Raising the

existing level of drain water at the floodgate could reduce the severity of acid drainage

produced in the groundwater by up to 60%. REFERENCES 186 REFERENCES

Acid Sulphate Soils Circular (1993) Draft circular to councils - acid sulphate soils. Department of Planning, Northern Regional Office. NSW Government Offices, 49 Victoria Street, Grafton, 2460. Alabaster, J.S. and Lloyd, R. (1980) Water Quality Criteriafor Freshwater Fish. (2nd ed.). Food and Agriculture Organisation of the United Nations. Butterworths, London. Anderson, J. (1992) Australia's Acid Drain. Angry Dolphins, March/April. ANZECC (1992) Australian Water Quality Guidelines for Fresh and Marine Waters. Australian and New Zealand Environment and Conservation Council - National Water Quality Management Strategy, Melbourne. Arakel, A.V. and Hongrun, T. (1992) Heavy metal geochemistry and dispersion pattern in coastal sediments, soil, and water of Kedron Brook Floodplain area, Brisbane, Australia. Environmental Geology and Water Science, 20 (3): 219-231. Bannerman, S. and Hazelton, P. (eds.) (1991) Introductory Notes on Mine Wastes geochemistry and Acid Mine Drainage. In: Soil Technology-Applied Soil Science, p. 173-188. Barton, G.B. (1980) Historical Sketch of New South Wales (2nd ed.). Lansdowne Press Sydney, 176 South Creek Road, Dee Why West, NSW, Australia, 2099. Bayley, (1975) Shoalhaven. History of the Shire of the Shoalhaven (2nd ed.). South Coast Printers, Port Kembla, NSW. Beamish, R.J., Lockhart, W.L., Van Loon, J.C. and Harvey, H.H. (1975) Long-term acidification of a lake and resulting effects on fishes. Ambia, 4: 98-102. Belperio, A.P. (1979) Negative evidence of Mid-Holocene high sea level along the coastal plain of the Great Barrier Reef Coastal Province. Marine Geology, 32: Ml­ M9. Berner, R.A. (1970) - Sedimentary pyrite formation. American Journal of Science, 268: 1-23. Bishop, K.A. (1980) Fish kills in relation to physical and chemical changes in Magela Creek (East Alligator River System, Northern Territory) at the beginning of the Tropical Wet Season. Australian Zoology, 20: 485-499. Bloomfield, C. and Coulter, J.K. (1973) Genesis and Management of Acid Sulphate Soils. Advanced Agronomy, 25: 265-326. Bowman, G.M. (1993) Case studies of acid sulphate soils. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p.95-114. REFERENCES 187

Brown, T.E., Morley, A.W., Sanderson, N.T. and Tait, R.D. (1983) Report of a large fish kill from natual acid water conditions in Australia. Journal of Fish Biology, 22: 335-360. Brinkman, R. ( 1982) Social and economic aspects of the reclamation of acid sulphate soil areas. In: H. Dost and N. van Breeman, (eds.), Proceedings of the Bankok symposium on acid sulphate soils, ILRI publication 31, Wageningen, the Netherlands. p. 12-20. Brinkman, R. and Pons, L.J. (1973) Recognition, classification, and mapping of acid sulphate soils. In: H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 2, ILRI publication 18, Wageningen, the Netherlands, p. 169- 203. Brown, T.E., Morley, A.W., Sanderson, N.T. and Tait, R.D. (1983) Report of a large fish kill resulting from natural acid water conditions in Australia. Journal of Fish Biology, 22: 335-350. Buckler, D.R., Mehrle, P.M., Cleveland, L. and Dwyer, F.J. (1987) Influence of pH on the toxicity of aluminium and other inorganic contaminants to east coast Striped Bass. Water, Air and Soil Pollution, 35 : 97-106. Bush, R. (ed.) (1994) A newsletter about acid sulphate soils. ASSAY, Wollongbar Agricultural Institute, NSW, No. 5, April. Callinan, R.B., Fraser, G.C. and Melville, M.D. (1992) Seasonally recurrent fish mortalities and ulcerative disease outbrakes associated with acid sulphate soils in Australian estuaries. In: Fourth International Symposium of Acid Sulphate Soils, Ho Chin Minh City, Vietnam, March 2-6, 1992. The working group on acid sulphate soils of the International Society of Soil Science. Calvert, D.V. and Ford, H.W. (1973) Chemical properties of acid sulphate soils recently reclaimed from Florida marshland. Soil Science Society of America Proceedings, 37: 367-371. Chappell, J. and Thom, B.G. (1986) Coastal morphodynamics in north Australia: review and prospect. Australian Geographical Studies, 24: 110-127. Child, J. (1965) Australian Sea Shells. Periwinkle Press. pp. 80. Child, J. and Currey, J. (1972) Shells and the Seashore. Landowne Press. pp. 78. Coleman, N. (1990) What Shell is That? Landowne Press. pp. 298. Coulter, J.K. (1973) The management of acid sulphate and pseudo-acid sulphate soils for agriculture and other uses. In : H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 2, ILRI publication 18, Wageningen, the Netherlands, p. 255-269. Creagh, C. (1991/92) Preventing acid spills from farmland. ECOS, 70: 12-16. Creagh, C. (1993) Working together with acid sulphate soils. ECOS, 77: 25-29. REFERENCES 188

Cruz, J.A.M. (1969) About the possibility of iron absorption by fishes and its pathological action. Anna/es De Limnologie, 2: 187-193. Cumming, R.A. (1992) Report of the Lower Shoal haven Water Quality Working Party. Environment Protection Authority, South Coast Office, 84 Crown Street, Wollongong, 2500, 31st March, pp. 1-8. Daye, P.O. and Garside, E.T. (1976) Histopathologic changes in surficial tissues of brook trout, Salve Ii nus fontinalis (Mitchill), exposed to acute and chronic levels of pH. Canadian Journal of Zoology, 54: 2140-2155. Dent, D. (1986) Acid Sulphate Soils: A baseline for research and developmentt. ILRI publication No. 39, Wageningen, pp. 204. Dent, D. (1993) Bottom-Up and Top-Down Development of Acid Sulphate Soils. Catena, 20: 419-425. Dent, D. and Bowman, G. (1993) Definition and Quantitative Assessment of the Sulphate Hazard for Planning and Environmental Management. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p. 94-115. Dent, D. and Pons, L. (1993) Acid and Muddy Thoughts. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p. 1-18. Driscoll, C.T., Baker, J.P., Bisgoni, J.J. and Schofield, C.L. (1980) Effect of aluminium speciation on fish in dilute acidified waters. Nature, 284: 161-164. Easton, C. (1989) The trouble with the Tweed. Fishing World, March, p 58-59. Environews (1993) Acid Sulphate Drainage: Shoalhaven. Environment Protection Authority - South Coast Office, 84 Crown Street Wollongong, 2500, ENVl-water, April. Fitzpatrick, R.W., Fritsch, E. and Self, P.O. (1993) Australia's Unique Saline Acid Sulphate Soils Associated with Dryland Salinity. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p. 41-56. Fraser, G.C., Callinan, R.B. and Calder, L.M. (1992) Aphanomyces species associated with red spot disease, an ulcerative skin disease of estuarine fish from eastern Australia. Journal of Fish Diseases, 15: 173-181. Freda, J. and McDonald, D.G. (1988) Physiological correlates of interspecific variation in acid tolerance in fish. Journal of Experimental Biology, 136: 243-258. Fromm, P.O. (1980) A review of some physiological and toxiological responses of freshwater fish to acid stress. Environmental Biology of Fish, 5: 79-93. Galloway, R.W. (1982) Distribution and Physiographic Patterns of Australian Mangroves. In: B.F. Clough (ed.) Mangrove Ecosystems in Australia. ANU Press, Canberra, p. 276-286. REFERENCES 189

Green, D. (1993) Rivers of Death. Fishing World, March, p. 38-43. Greenberg, A.E., Clesceri, L.S. and Eaton, A.O. (eds.) (1992) Standard methods for the examination of water and wastewater. (18th ed.) American Public Health Association, 1015 Fifteen Street, NW Washington, DC 20005. Gutteridge Haskins and Davey (1993) Environmental Imapct Statement (r2476) - for Proposed Recycling Papers Plant, at Shoalhaven Mill, Bomaderry. Railway Square, 39 Regent Street, NSW, 2000. Hazelton, P.A. (1992) Soil Landscapes of the Kiama 1:JOO000 sheet map. Department of Conservation and Land Management (incorporating the soil conservation service of NSW), Sydney. Johanssen, N., Kihlstrom, J.E. and Wahlberg, A. (1973) low pH values shown to affect developing eggs (Brachydanio rerioi) Ambia, 2(1-2): 42-43 Kanapathy, K. (1973) Reclamation and improvement of acid sulphate soils in West Malaysia. p. 383-389. In: H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 2, ILRI publication 18, Wageningen, the Netherlands. Konston, C.J.M., Brinkman, R. and Andriesse, W. (1986) A field laboratory method to determine total potential and actual acidity in acid sulphate soils. p. 106-134. In: H. Dost (ed.) Selected papers of the Dakar Symposium on Acid Sulphate Soils. ILRI publication, No. 44, Wageningen, the Netherlands. Kwain, W. and Rose, G.A. (1985) Growth of brook trout (Salvelinus fontinalus) subject to sudden reductions in pH during their early life history. Tansaction of the American Fish Society, 114: 564-470. Landford-Smith, T. and Thom, B.G. (1969) New South Wales coastal morphology. Journal of Geological Science of Australia, 16: 572-580. Langdon, J.S. (1988) Investigations offish kills - 1. History and causes, 2. Investigat01y approach. Postgraduate Communication in Vetinary Science, Uni. Sydney, Fish Diseases Course notes, May, 1988. Leadbitter, D. (1993a) Multiple benefit management of estuarine floodplains in NSW: a fishing industry perspective. 33rd Annual Flood Mitigation Conference, Taree, NSW, p. 25-28, May. Leadbitter, D. (1993b) The Acid Test: Basic Concerns of the Fishing Industry about Coastal Floodplain Management in NSW. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p. 62-70. Leivastad, H. and Muniz, L.P. (1976) Fish kill at low pH in a Norwegian River. Nature, 259: 391-392. Lilley, J.H., Phillips, M.J. and Tonguthai, K. (1992) A review of Epizootic Ulcerative Syndrome (EUS) in Asia. Aquatic Animal Health Institute and Network of Aquaculture Centres in Asia-Pacific, Bankok, Thailand, pp. 73. REFERENCES 190

Lin, C. and Melville, M.D. (1992a) Mangrove soil: a potential contamination source to estuarine ecosytems of Australia. Wetlands (Australia), 11: 68-75. Lin, C. and Melville, M.D. (1993b) Control of soil acidification by fluvial sedimentation in an estauarine floodplain, eastern Australia. In: C.R. Fielding (ed.). Current Research in Fluvial Sedimentology. Sedimentaty Geology, Special Issue, 85 (in press). Lines-Kelly, R. (1992) Acid Sulphate Soils - soil information for north coast farmers. Soil Sense leaflet, Agdex 550, Wollongbar Agricultural Institute. Mathews, C.T. and Robins, R.G. (1974) Aqueous oxidation of iron disulphide by molecular oxygen. Australian Chemistly and Engineering, 6: 19-24. McCahon, C.P., Brown, A.F., Poulton, M.J. and Pascoe, D. (1989) Effects of acid, aluminium and lime additions on fish and invertabrates in a chronically acid Welsh stream. Water, Air and Soil Pollution, 45: 345-359. McCormick, J.H. and Jensen, K.M. and Anderson, L.E. (1989) Chronic effects of low pH and elevated aluminium on survival maturation, spawning and embryo­ development of the fathead minnow in soft water. Water, Soil and Air Pollution, 43: 293-307. McDonald, D.G. (1983) The effects of hydrogen upon the gills of freshwater fish. Canadian Journal of Zoology, 61: 691-703. McK.ibben, M.A. and Barnes, H.L. ( 1986) Oxidation of pyrite in low temperature acid solutions: rate laws and surface textures. Geochim. Cosmochim, Acta, 50: 1509- 1520. Melville, M.D. (1984) Headlands and offshore islands as controlling factors during late Quaternary barrier formation in the Forster-Tuncurry area, NSW, Australia. Sedimentary Geology, 39: 243-271. Melville, M.D., White, I. and Willett, LR. (1991) Problems of acid sulphate soils and water degradation in Holocene pyritic systems. In: G. Brierley and J. Chappell (eds.) µplied Quaternary Studies. ANU, Canberra, p. 99-122. Melville, M.D., White, I. and Lin, C. (1993) The Origins of Acid Sulphate Soils. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24- 25 June, Coolangatta, p. 19-25. Merriner, J. and Vaughan, D. (1987) Ecosystem and fisheries implications of ulcerative mycosis. In: Proc. Workshop on Fishery Diseases for the Albemarle-Pamlico Estuarine Study. Gray J. ed. UNC Water Resources Institute. Miller, S., Jeffery, J., Wong, J. and Goldstone, A. (1991) In-pit identification and management of acid forming waste rock at the Golden Cross Mine, New Zealand. Cyprus Gold (New Zealand) Limited. Mount, DJ. (1973) Chronic effects of low pH on fathead minnow survival, growth and reproduction. Water Research, 7: 987-993. REFERENCES 1 9 1

Mulvey, P. (1990) Groundwater Monitoring - A New Approach. New Zealand Hydrology Society Conference, November. Mulvey, P. (1992) Identifying and Managing Pyritic Clays for Development. Soil Science Society of Australia Workshop for Acid Sulphate Soils, Nowra, 28th November, p. 1-10. Mulvey, P. (1993) Pollution, Prevention and Management of Sulphidic Clays and Sands. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p. 116-129. Naylor, S. (1993) Guidelines for the assessment and management of coastal land developments in areas of acid sulphate soils. Environment Protection Authority, NSW Government Offices, P.O. Box 498, Grafton, 2460. Neilsen, P.G. (1993) Acid Sulphate Soils - A Sugar Industry Viewpoint. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p. 57-61. Noller, B.N. and Cusbert, P.J. (1985) Mobilisation of aluminium from a tropical floodplain and its role in natural fish kills: A Conceptual Model. Office of the Supervising Scientist, Jabiru, Northern Territory, Australia, 5796, p. 700-702. Norrgren, L., Wicklund, G. and Malmborg, 0. (1991) Accumulation and effects of aluminium in the minnow (Phoxinus phoxinus L.) at different pH levels. Journal of Fish Biology. 39: 833-847. Norwood, T. (1975) Studies on Acid Sulphate Soils of the Lower Shoal haven River Floodplain. University of Wollonong. Unpublished honours thesis. NSW Agriculture and Fisheries (1989) Review of land and water management impacts onfisheries and agricultural resources in the lower Mac/eay. Working Party Report. North Coast Agriculture Institute, Wollongbar, NSW. December, 1989, pp. 18. NSW Fisheries Data (1994) Commercial fish catches from the Shoalhaven estuary for fiscal years 1984-1993. Fisheries Research Institute, Cronulla, NSW. Pearce, M. (1990) Epizootic Ulcerative Syndrome.Technical Report, December 1987- September 1989. Northern Territory Department of Primary Industry and Fisheries. Fisheries Report No. 22, Darwin. Poelman, J.N.B. ( 1973) Soil material rich in pyrite in non-coastal areas. In: H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 2, ILRI publication 18, Wageningen, the Netherlands, p. 197-207 Polard, D.A. (1976) Estuaries must be protected. Australian Fisheries, 35:6-10. Pons, L.J. (1973) Outlines of the genesis, characteristics, classification, and improvement of acid sulphate soils. In: H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 2, ILRI publication 18, Wageningen, the Netherlands, p. 3-27. REFERENCES 192

Pons, L.J., van Breeman, N. and Driessen, P. (1982) Coastal sedimentary environments influencing the development of potential soil acidity. In: Acid Sulphate Weathering. Soil Science Society of America, special publication 10, Madison, Wisconson, p. 1-18. Powter, DJ. (1993) Bio-geochemical constraints upon thefate and recycling of heavy metals in sediments and groundwater. Unpublished honours thesis, University of Sydney. Public Works Department (1990) Lower Shoalhaven Flood Study Report. No. PWD 87049, April. Raffell, D.A. (1992) Report of the city health surveyor - Shoalhaven River Water Quality Working Party Committee Meeting -Tuesday, 31st March, 1992. Shoalhaven City Council. Rickard, D.T. (1973) Sedimentary iron sulphate formation. In: H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 1, ILRI publication 18, Wageningen, the Netherlands, p. 28-65. Ritsema, CJ. and Groenenberg, J.E. (1993) Pyrite oxidation, carbonate weathering, and gypsum formation in a drained potential acid sulphate soil. Soil Science Society of America Journal, 57: 968-976. Roy, P.S. (1984) New South Wales estuaries: Their origin and evolution. In: B.G. Thom (ed.) Coastal Geomorphology in Australia, Academic Press, pp. 99-120. Roy, P.S., Thom, B.G. and Wright, L.D. (1980) Holocene sequences on an embayed high energy coast: an evolutionary model. Sedimentary Geology, 26: 1-9. Sammut, J., Callinan, R.B. and Fraser, G. C. (1993) The Impact of Acidified Water on Freshwater and Estuarine Fish Populations in Acid Sulphate Soil Environments. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p. 26-40. Sammut, J., Melville, M.D., Callinan, R.B. and Fraser, G.C. (in press) Estuarine acidification: the impacts on aquatic biota of draining acid sulphate soils. In W.D. Erskine and M.C. Thom (eds.), Human Impacts of River Systems, Australian Geographical Studies. Shepard, M.J. (1974) Progradation of Holocene sand barriers in NSW. Search, 5 (5): 210-211. Simpson, H.J. and Pedini, M. (1985) Brackishwater aquaculture in the tropics: The Problem of Acid Sulphate Soils. Fisheries Circular, No. 791: Food and Agriculture Organisation of the United Nations, Rome, August, pp. 32. Singer, P.C. and Stumm, W. (1970) Acid mine drainage: the rate determining step. Science, 167: 1121-1123. State of Environment Report (1992) Shoo/haven City Council, pp. 59-61. REFERENCES 193

Stone, Y.N. (1993) A State Perspective on Planning for Acid Sulphate Soils. In: R. Bush (ed.) Proceedings, First National Conference on Acid Sulphate Soils, 24-25 June, Coolangatta, p. 84-93. Stumm, W. and Morgan, J.J. (1970) Aquatic Chemisf1y. Wiley Interscience, New York. Thom, B.G., Bowman, G.M., Gillespie, R., Temple, R. and Barbetti, M. (1981) Progradation histories of sand barriers in NSW. Search, 12 (9): 323-325. Thom, B.G. and Chappell, J. (1975) Holocene sea levels relative to Australia. Search, 6 (3): 90-91. Tweed Shire Council (1992) Landuse guidelines for acid sulphate soils - guidelines for development, 23rd September, pp. 1-12. van Breeman, N. (1973) Soil forming processing in acid sulphate soils. In: H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 2, ILRI publication 18, Wageningen, the Netherlands, p.66-130. van Breeman, N. ( 1982) Genesis, morphology and classification of acid sulphate soils in coastal plains. In: Acid Sulphate Weathering. Soil Science Society of America, special publication 10, Madison, Wisconson, p.95-108. van der Kevie, W. (1973) Physiography, classification and mapping of acid sulphate soils. In: H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 2, ILRI publication 18, Wageningen, the Netherlands, 204-222. van Holst, A.F. and Westerveld, G.J.W. (1973) Corrosion of concrete foundations in (potential) acid sulphate soils and subsoils in the Netherlands. In: H. Dost (ed.) Proceedings of the Wageningen symposium on Acid sulphate soils. Vol. 2, ILRI publication 18, Wageningen, the Netherlands. Veness, R. (1990) Acid Sulphate Soils. Soil Note 22190, Soil Conservation Service of New South Wales. Virgona, J.L. (1992) Environmental factors influencing the prevalence of cutaneous ulcerative disease (red spot) in sea mullet, Mugil cephalus L., in the Clarence River, NSW, Australia. Journal of Fish Diseases, 15: 363-378. Walker, P.H. (1960) Soil investigations in the Alumy Creek-Great Marlow area, Grafton, NSW, CS/RO Australia. Division of Soils. Report No. 6/60. Walker, P.H. (1972) Seasonal and stratigraphic controls in the coastal floodplain soils. Australian Journal of Soil Research, 10: 127-142. Wendelaar Bonga, S.E. and Dederen, L.H. (1986) Effects of acidified water on fish. Endeavour. New Series, 10: 198-202. White, I., Melville, M.D., Wilson, B.P., Price, C.B and Willet, LR. (1993) Understanding Acid Sulphate Soils in Canelands. In: R. Bush (ed.) Proceedings,

First National Conference 011 Acid Sulphate Soils, 24-25 June, Coolangatta, p. 130- 148. REFERENCES 194

Willett, LR., Crockford, R.H. and Milnes, A.R. (1992a) Transformations of Iron, Manganese and Aluminium During Oxidation of a Sulfidic Material From an Acid Sulphate Soil. Catena Supplement, 21: 287-302. Willett, LR. and Bowman, G.M. (1990) Acid Sulphate soil conditions near flood mitigation drains on the lower Macleay River. Report prepared for Kempsy Shire Council, CSIRO Division of Soils, Canberra. Willett, LR., Melville, M.D. and White, L (1992b) Acid drainwaters from potential acid sulphate soils and their impact on estuarine ecosystems. In the 4th International Symposium on Acid Sulphate Soils. Ho Chi Minh City, Vietnam, March 2-6, pp. 418-425. Willett, LR. and Walker, P.H. (1982) Soil morphology and distribution of iron and sulphate fractions in a coastal floodplain toposequence. Australian Journal of Soil Research, 20: 283-294. Wright, L.D. ( 1970) The influence of sediment availability on patterns of beach ridge development in the vicinity of the Shoalhaven River Delta, New South Wales. Australian Geographer, 11: 327-335. Wright, L.D. (1977) Morphodynamics of a wave dominated river mouth. Proceedings of the 15th International Coastal Engineering Conference, Honolulu, 1721-1737. Young, R.W., Bryant, E.A., Price, D.M., Wirth, L.M. and Pease, M.I. (1993) Theoretical constraints and chronological evidence of Holocene coastal development in central and southern New South Wales, Australia. Geom01phology, 7: 317-329. APPENDIX

APPENDICES APPENDIX

APPENDIX A - WATER QUALITY SAMPLING

Sampling Frame

Site Selections/Program Structure

The Jasper's Brush acid sulphate soil - water quality monitoring program was initially set up within the Army's 203 ha property (Figure 3.3). The monitoring program was set up to take watertable-depth and water quality measurments from a series of boreholes and drains. The study area was visited, and aerial photographs and topographic maps were used, to select a subcatchment within it. This subcatchment had a main drain through it, and boreholes were located across the catchment perpendicular to the drain (see Chapter

3 and 4).

The drain selected for monitoring (transect drain) was the drain thought to be the most influential contributing towards lowering the watertable and therefore, pyrite oxidation from within the study area. It was the deepest passing through the study area.

Boreholes were placed on both sides and perpendicular to this drain near to a bridge which provided easy access. Another reason for extending the line of bores out from the bridge was that the ground surface topography had very little relief, especially on the eastern side of the drain. Sampling of most bores on as flat an area as possible meant that any change in watertable levels observed away from the drain were more likely to be the result of influence of the drain other than factors such as permeability differences or surface runoff.

Bore holes were cored to I.Om lengths using a mobile drill rig provided and operated by

Mr Roy Laurie from the Department of Agriculture, NSW. To prevent collapsing of the bore and contamination of any samples, each bore was lined with 0.05m diameter PVC pipe and capped. The entire length of each pipe was slotted at approximately 70° with a hacksaw to allow groundwater seepage at all depths. Boreholes were placed approximately 5m from both sides of the drain and progressively spaced further apart APPENDIX away from the drain. The reason for this was to monitor as large an area of the floodplain as possible while concentrating the monitoring relatively closely to the drain.

A total of twelve bores were dug. Three were located in a line on the western side of the drain, with one of these placed adjacent to a palaeochannel. Eight bores were located on the same line on the eastern side on the drain. On the eastern side, the furthest bore

(Bsl7) was placed 400m from the drain. One of these bores was placed in a palaeochannel (Bs16) and another adjacent to a low lying swamp northeast of the drain

(Bs 18).

Eleven of the twelve bores dug were used solely for watertable and pH measurements.

One larger core was dug, lined with 0.15m diameter slotted PVC pipe and capped. The bottom of the pipe was lined with geo-fabric to prevent sediment entering the bore water.

This bore was dug to approximately 1.4m and was not only used for watertable and pH measurements but also for groundwater sampling; a Submersible Data Logger (SDL) was also deployed in it. This bore was the third bore on the eastern side of the drain

(Bs12), and was located approximately 35m away from the drain.

Initially three water quality sampling locations were chosen - the bore with the SDL and two drains. The first drain sampling site was located in the drain described above

(transect drain) in line with the bore transect. The transect drain sampling site was

located here so that groundwater fluctuations referred to came from adjacent locations to

this drain sampling site. The second drain sampling site was located in a small (mole)

drain on the eastern side of the study area which fed into a larger (main) drain of similar

dimensions to the first drain location. Drain location two (road drain) was chosen as an

example of a mole drain. Another reason for sampling this drain was that investigatory

sampling at its junction with a larger drain by the EPA and Shoalhaven City Council

showed abnormal acidic and extremely elevated aluminium concentrations in the water.

The road drain was located just outside the study area boundaries so that monitoring APPENDIX could continue at the same site when remediation took place involving drains within the

study area (see Figure 3.3 for locations).

Samples were also taken to analyse water quality just inside the floodgates of the transect

drain in this study and of the large drain leading from the feeder drain (Figure 3.3).

Sampling at the floodgates in the later part of the monitoring program, when it became

clear that remediations works would not proceed (see Chapter 1).

Surveying

All bores and the ground surface between them and drain sampling sites were surveyed

to Australian Height Datum (m AHO) using a dumpy level. The initial spot height was

obtained using the PWD 1967 Flood Mitigation map. This provided an initial spot height

located on top of the floodgate which at the end of the main drain (gate drain - see

Chapter 3, Figure 3.3). Bore (m AHO) heights were taken level with the top of the

bores. On routine drain monitoring, height measurements were taken from a fixed

position. The first drain (m AHO) level was taken to the bottom of the overhead bridge

and the second to the top of an adjacent post. The distance between the bottom of the

drains to the fixed measuring positions was subtracted from each field measurement to

calculate water levels in each drain to (m AHO).

Sampling

Groundwater Measuring Device

A device was designed to measure watertable and pH in the bores. The device was made

from a l.Sm length of 0.035m x 0.005m wood and l.7m length of clear 0.015m

diameter plastic tube. Both sides of the entire length of the wood were marked at O.Olm

intervals. One end of the tube was placed level with the bottom of the wood. The tube

was attached to the wood by wrapping electrical tape around the wood and tube at two

locations along the wood. This device remained in its original condition throughout the

eight month monitoring period. APPENDIX

Watertable Measurement Procedure

Watertable was measured by placing the bottom of the instrument at the top of the bore.

The operator inhaled gently as the instrument was slowly placed down the bore, until the instant when suction of the water could be felt and/or heard. The watertable level was read off the instrument against the top of the PVC, usually after some fine adjustment suction with the bottom of the instrument at the top of the water level. This process took approximately 15 seconds (depending on watertable depth) with estimated ±0.005m accuracy.

Groundwater Sample Collection

The instrument was used to extract samples to measure pH by suction of the clear tube

until water was seen to reach the top of the wood. To transfer the sample, the thumb

was placed over the top of the tube and removed after the bottom of the instrument was

placed in the PVC cap from each bore analysed. Using the cap from each bore prevented

contamination from samples in previous bores. Contamination was further minimised by

flushing the instrument with water from the bore about to be sampled before a sample

was placed in a PVC cap. Samples taken from the larger bore for water quality analysis

were obtained by filling the 250ml nutrient (for chloride and sulphate) and acid washed

(for iron and aluminium) sample bottles provide by the Environment Protection Authority

(EPA). All water quality measurements and samples were taken from O.lm below the

watertable level to increase consistency.

Drain and Creek Water Sample Collection

Drain and creek samples were taken from surface samples. Acid drainage is less dense

than more saline creek waters for example. Therefore, drain and creek sample results

may not be totally representative for the water quality severity throughout all depths of

the drain and creek, but are reprsentative for the acid drainage in the drain as leached

from the groundwater, and in the creek as released by the drains. All groundwater, drain APPENDIX water and creek water samples were stored in an esky when taken in the field and placed in a refrigerator immediately upon return.

pH Probe Used

Once placed in a PVC cap, samples were measured for pH. The Scan 2 pH (Eutech

Cybernetics) meter was used and was found to be a very efficient field and laboratory pH

instrument to ±0.1 pH unit accuracy. It held its calibration for roughly a month and field

measurements only took around 15 seconds to stabilise. The Scan 2 pH meter was

initially compared to the more expensive and more prncise (0.01 pH unit) Hana 8014 pH

meter. Both meters were calibrated against standard buffers of pH 4 and 7 before and

after use. The Hana 8014 meter rarely held its calibration for longer than a week and

was difficult to calibrate accurately. The Hana 8014 meter was considered too sensitive

to give accurate field measurements. Slight movements of its probe in field samples

made it almost impossible to obtain a reading of greater than ±0.15 pH unit accuracy.

The Scan 2 pH meter was pocket sized, could be calibrated in less than one minute and

was generally considered to be a far more reliable and accurate instrument to use than the

Hana 8014 pH meter.

Analysis Methodology

Bore and drain water samples were analysed by the EPA's, Lidcombe chemical

laboratories for soluble chloride, sulphate, iron and aluminium. Creek samples were

analysed for soluble and total iron and aluminium. Water samples were tested for iron

and aluminium as these two metals are generally considered common by-products of acid

sulphate soils and the most likely elements to be detrimental to survival and life cycles of

estuarine aquatic life forms (Melville et al., 1993; Sammut et al., 1993). Soluble chloride

and sulphate (nutrients) were analysed to help determine the role of differing sulphide

oxidation rates in different parts of the study area. APPENDIX

Chloride and Sulphate

This method used by the EPA laboratory - Lidcombe, was as per: Greenberg et al.

(Standard Methods for the examination of water and wastewater, 1992, p. 4.1-4.5 - for full description).

Chloride and Sulphate were determined by ion chromatography; with chemical suppresion of eluent conductivity. Samples were filtered with a membrane filter to remove particles >0.2µm.

Iron and Aluminium

This method used by the EPA laboratory - Lidcombe, was as per: Greenberg et al.

(1992, p. 3.2-3.17 - for full description).

Soluble iron and aluminium was determined by filtering the sample through a pre­ washed ungridded 0.40-0.45µm pore-diameter membrane filter (polycarbonate or cellulose acetate), the filtrate acidified and analysed directly by atomic absorption spectrometry.

"Total metals" includes all metals, inorganically or organically bound, both dissolved and particulate. Samples are digested with with cone. nitric acid before determination of total metals, the the following procedure as per soluble metals.

Submerged Data Logger (SDL) Use

Water quality aspects were also considered with the use of Submersible Data Loggers

(SDL's) built by Yeo-Kai Electronics. The SDL's used recorded pH, dissolved oxygen

(mg/Lor% saturation), temperature, turbidity, salinity and conductivity. SDL's were used as they could be deployed remotely and the parameters analysed at selected intervals per hour. During field monitoring in this analysis, SDL's were secured with locks and chains in the sampling bore and the first sampling drain site (attached to an overhead APPENDIX

pipe). In the latter part of the program SOL's were deployed inside and outside two

floodgates of the two main drains analysed. Here the SOL's were attached to fence

posts. Where an SOL was deployed outside a floodgate a lm x lm right angle metal ann

was constructed to swing the instrument out from the floodgate wall to prevent possible

damage if the vertically attached floodgates opened after rain.

SOL's were checked for accurate calibration before and after every field deployment.

The SOL deployment periods and sampling intervals varied depending mainly on field

sites. It was found the battery and memory of the SDL1s would adequately cope with

deployment of three weeks at a time with a sampling interval of 2/hr. A sampling

interval of 2/hr was considered sufficient for this purpose since the sites were in a bore

and top of a drain where any variations over time would be slow. Security at these sites

was good, allowing deployment of up to three weeks at a time. However, these

locations were very seriously affected by acid drainage with pH commonly 3 or less and

it was found the pH probe became saturated, requiring expensive maintenance after three

week periods of use at a time.

The sampling interval chosen at the floodgates was 3/hr in order to sample frequently

enough to identify water quality changes due to factors such as tide changes. SDL's

were deployed at the floodgates for up to two weeks.

Aerial photos

Next page APPENDIX

(1949) ( 1979) (1981) area - Jasper's B./Berry Jasper's Brush Berry/Broughton Ck.

1: 100,000 sheet - 9028 Kiama 9028 Kiama 9028 Kiama film - SUY 562 Nowra NSW 2759 MBC 1309 run - 2 1 62/63 print numbers - 63/64 05/07 41/43/45 altitude - 15,000' 2468m 3810m focal length - 153.000mm 151.45mm 152.02mm approx. scale - 1:30,000 1: 16,000 1:25,000

(1986) (1993) area - Jasper's Brush Broughton Ck./Numbaa Is.

1: 100,000 sheet - 9028Kiama 9028Kiama film - NSW 2526 NSW 4106 run - 63 9/10 print numbers - 42/44 71172173, 182/183 altitude - 3828 A.S.L. 4084m focal length - 153.lOmm 151.45mm approx. scale - 1:25,000 1:25,000 APPENDIX

APPENDIX B - SOIL ANALYSIS

Sampling Frame

Initial soil samples were obtained from the twelve cores taken in establishing the bores used in the monitoring program. These samples provided some variation within the soils in a relatively small area. To achieve a broader picture of the acid sulphate soil distribution on the Jasper's Brush floodplain additional soil samples were collected along the levees lining Broughton Creek, at the toe of these levees and across the main floodplain. In total 45 sites were sampled (see Figure 3.2).

Collection of samples

The cored profiles were described in the field. For subsequent laboratory analysis, the lm cores of were cut into three lengths and wrapped in black plastic.

Soil profiles not cored were dug using screw augers. Two screw augers of lengths lm and 2.5m were used. Care was taken not to push to auger to prevent mixing of the sample. Again each profile was described in the field. Also, six samples were collected down the augured profiles which were up to 2.5m deep. Samples were always made sure to include soils from each of the A, A2, mottled jarosite, jarosite and unoxidised sediments where possible. Where no jarosite or unoxidised sediments were found, the subsoil sampling continued to the watertable. Where soil coherence permitted, auguring was continued for up to one metre below the watertable depth to check for the presence of jarosite and unoxidised sediments. Samples from augured profiles were placed in air­ tight plastic bags.

Augured and cored samples were immediately placed in a portable freezer in the field to minimise bacterial activity. These samples were transferred into another freezer for

storage in the University of WoIIongong Geography laboratory. APPENDIX

Soil Preparation

For, Total Potential Acidity (TPA) and grain size analysis, a sample of frozen soil was placed in a aluminium moisture tin and oven dried at 100°C. The approximate amount of soil placed in the tins varied according to the amount required in the analysis. Smaller samples of approximately 5gms dry weight for TPA analysis were left to dry for 24

hours. Larger samples, for grain size analysis were left in the oven for up to three days

to ensue complete drying.

pH

All soil pH measurements were made on oven dried soil finer than 2mm. Forty grams of

air dried, <2mm soil were mixed in a beaker with 40ml of freshly distilled water to form

a 1:5, soil:water slurry. The slurry was stirred briskly with a glass rod for thirty seconds

and allowed to stand for one hour after which it was again stirred briskly. The pH

reading was then taken by inserting the electrode of the Scan 2 pH meter freshly

calibrated. Once the initial reading was made the slurry was again stirred briskly and a

second reading taken. If both readings were the same this value was taken as the pH.

Where there was a difference in the values, further readings were taken until a constant

reading was obtained.

To avoid contamination, the glass rod and electrode was cleaned with distilled water after

use with each sample.

Total Potential Acidity (TP A)

Twenty five millilitres of lM KCl were added by dispenser to 5gms of oven dry soil in a

conical flask (250ml flask for samples with minimal oxidisable material, 500ml flask for

maximum samples). These samples were mixed with a glass rod.

Twenty millilitres of 30% H102 was initially added to each flask, swirled and placed on

a hot plate at a very low temperature setting. Despite this procedure in accordance with APPENDIX

Dent and Bowman (1993) stating care needs to be taken to avoid excessive frothing during initial oxidation of the sample in the previous step, it was found additional precautions were necessary to prevent excessive frothing. Frothing was found only to be controlled when 5ml of 30% H20 2 was added and the further 15ml added 10 minutes later. Further excessive frothing was controlled by placing the samples on the hot plate set as low as possible overnight to complete the oxidation.

On the following day complete oxidation was tested with a few drops of peroxide. The cooled sample was filtered in a Buchner funnel and the filtrate transfered to a 250ml beaker. The sample was made up to approximately lOOml with distilled water and pH measured. Distilled water was used instead of deionised water due to a lack of deionised water availability and a Scan 2 pH meter was placed into continually stirred titrant solution in place of a autotitrator as prescribed by Dent and Bowman (1993). The titrant was titrated to pH 5.5.

TPA (mole/kg) =(volume of titrant[ml]) x titrant concentration (mol/1)/5

Particle Size

Fifty grams of oven dried soil was treated with lOOml of 6% w/v hydrogen peroxide, to oxidise the organic matter, and allowed to stand overnight. A further 50ml of hydrogen peroxide was added and the suspension heated gently to ensure oxidation was complete.

After cooling, the suspension was shaken manually for two periods of ten minutes each, separated by enough time for a brisk stir with a glass rod. Twenty five millilitres of 5% calgon (sodium Polymetaphosphate) solution had been added prior to the shaking to assist in the dispersion of the particles.

The coarse sand was removed by sieving (0.2mm mesh) while suspension of fine sand,

silt and clay was made up to l litre in a measuring cylinder. The suspension was stirred

with the paddle for one minute and then the hydrometer readings taken at 4 min/50 sec APPENDIX and hourly intervals. After adjustments of minus lgm per litre for calgon, and addition or subtraction of 0.3ppm above or below 19°C for temperature the weights of sand, silt and clay were expressed as a percentage of the soil sample taken.

Colour

A Munsell soil colour chart was used to test soil colour. Samples were tested in the laboratory. Care was taken in not allowing any samples to be exposed to air for longer

than possible from the field until testing to prevent drying and therefore, distortion of

field soil colours.

Topcon

The photogrammetric process of reconstruction of the situation that applied when the

photos were taken from the survey aircraft is often lengthy and difficult. There are three

steps in this reconstruction~

1) Interior orientation in which the situation inside the aerial camera is reconstructed.

This involves the setting of the correct focal length for the camera, the positioning of the

film in relation to the central axis of the lens system, and compensation for errors

introduced into the photographic image by the camera lens.

2) Relative orientation in which the operator obtains a stereo model by manipulating both

photographs using a specialised procedure until each photo is in the correct relative

relationship with its partner as applied when the photos were exposed. The unit that

results from this orientation is the stero model.

3) Absolute orientation in which the stereo model resulting from the relative orientation

is scaled, rotated and shifted in space so that eventually the positions of the 2

photographs at the moments of exposure becomes unknown, along with the tips and tilts

resulting from an unstable camera platform. Ground control points, that is points with APPENDIX known x/y/z coordinates, are needed to perform the absolute orientation m all photogrammetric applications.

Ground control points were taken; using the Berry, 1988, 9028-3-N topographic map for ground control point coordinates and the PWD, 1967 map for the elevation of those same points to O.Olm accuracy. A total of 8 ground control points were obtained. The accuracy of the stereo map produced was ±0.7m. APPENDIX

APPENDIX C - Groundwater/Drain Acid Drainage Dynamics Data Rainfall record

date rainfall date rainfall date rainfall date rainfall date rainfall 17/2 28 14/4 0 9/6 0 4/8 1 29/9 0 18/2 2 15/4 0 10/6 0 5/8 11 30/9 0 19/2 0 16/4 0 11/6 0 6/8 0 1/10 8 20/2 15 17/4 0 12/6 0 718 0 2110 0 21/2 0 18/4 0 13/6 0 8/8 0 3/10 4.5 2212 0 19/4 0 14/6 0 9/8 0 4/10 2 23/2 0 20/4 0 15/6 0 10/8 0 5/10 0 24/2 0 21/4 0 16/6 0 11/8 0 6/10 0 25/2 2 22/4 0 17/6 0 1218 0 7110 0 26/2 0 23/4 0 18/6 0 13/8 0 8/10 0 27/2 1.5 24/4 0 19/6 0 14/8 0 9/10 0 28/2 0 25/4 0 20/6 0 15/8 0 10/10 0 1/3 0 26/4 0 21/6 0 16/8 0 11/10 0 2/3 0 27/4 0 22/6 0 17/8 0 12/10 0 3/3 0 28/4 0 23/6 0 18/8 0 4/3 0 29/4 2.5 24/6 0 19/8 0 5/3 0 30/4 5.5 25/6 0 20/8 0 6/3 0 1/5 0 25/6 0 21 /8 0 7/3 0 215 0 27/6 0 22/8 0 8/3 20 3/5 0 28/6 6 23/8 0 9/3 10.5 4/5 0 29/6 5 24/8 0 10/3 1.5 5/5 0 30/6 0 25/8 5 11/3 17.5 6/5 0 117 0 26/8 4.5 12/3 7.5 715 0 217 0 27/8 0 13/3 0 8/5 0 317 0 28/8 7 14/3 0 9/5 0 417 0 29/8 0 15/3 5 10/5 4.5 517 2.5 30/8 11 .5 16/3 0 11/5 0 617 16 31/8 1.5 17/3 12 1215 0 717 10.5 1/9 0 18/3 1.5 13/4 0 817 0 219 0 19/3 18.5 14/5 0 917 15 3/9 0 20/3 2 15/5 0 1017 0 4/9 0.5 21/3 2 16/5 0 1117 0 5/9 0 22/3 0 17/5 0 1217 6/9 0 23/3 0 18/5 0 1317 0 719 0 24/3 0 19/5 0 1417 0 8/9 0 25/3 3 20/5 0 1517 0 9/9 11 26/3 8.5 21/5 10.5 1617 0 10/9 5 27/3 0 2215 0 1717 0 11/9 0 28/3 0 23/5 0 1817 0 12/9 56 29/3 0 24/5 0 1917 0 13/9 70.5 30/3 0 25/5 0 2017 0 14/9 6.5 31/3 0 26/5 0 2117 0 15/9 0 1/4 0 27/5 0 2217 0 16/9 1.5 2/4 0 28/5 0 2317 0 17/9 0 3/4 0 29/5 0 2417 0 18/9 0 4/4 0 30/5 0 2517 4 19/9 0 5/4 0 31/5 0 2617 3 20/9 0 6/4 0 1/6 1 2717 0 21/9 0 714 0 216 0 2817 0 22/9 0 8/4 0 3/6 16 2917 4 23/9 0 9/4 0 4/6 0 3017 0 24/9 0 10/4 0 5/6 0 3117 0 25/9 0 11/4 0 6/6 0 1/8 0 26/9 0 12/4 0 716 0 2/8 0 27/9 0 13/4 0 8/6 0 3/8 0 28/9 0

Rainfall record for the study area 17/2/93-12/10/93 - see Figure 3.3 for site location APPENDIX

Watertable

Dates Bs7 8s8 Bs9 Bs10 Bs11 Bs12 Bs13 Bs14 Bs15 Bs16 Bs17 Bs18 transect d. gated. road d. Control 17/2193 -0.60 -54 -5 4 2 1 -19 -35 -31 2 -62 -3 152 80 111 23/2193 -61 -48 -59 -50 -17 -14 -24 -37 -15 -27 -63 -6 148 80 110 26/2193 -71 -55 -65 -63 -47 -43 -44 -52 -45 -37 -72 -36 144 81 112 3/8/93 -73 -59 -65 -17 -41 -38 -4 7 -56 -38 -24 -74 -10 149 78 105 3/12193 -67 -56 -60 -54 -33 -26 -26 -44 -30 -22 -67 -7 151 80 104 15/3/93 -72 -57 -63 -58 -31 -30 -36 -32 -38 -26 -69 -7 150 80 109 19/3/93 -39 -29 -41 2 2 0 -1 -10 0 4 -44 -1 156 89 112 24/3/93 -4 7 -40 -54 -5 2 -5 -3 -12 -27 -2 -4 -57 -2 153 83 111 4/2193 -56 -45 -56 -59 -36 -29 -27 -41 -19 -19 -59 -7 151 99 129 4/5/93 -48 -49 -56 -61 -42 -33 -37 -40 -24 -22 -59 -9 150 89 114 4/8/93 -62 -53 -61 -65 -51 -42 -42 -50 -33 -20 -64 -10 148 90 118 :;:::::::::;::::::::::::=:::::::·: 15/4/93 -71 -60 -66 -68 -58 -49 -53 -59 -42 -43 -71 -13 143 90 115 20/4/93 -73 -66 -70 -72 -61 -53 -57 -64 -48 -43 -69 -39 143 85 111 27/4/93 -79 -68 -75 -78 -77 -61 -62 -69 -56 -53 -69 -52 139 85 111 -230 6/5/93 -88 -74 -79 -89 -82 -75 -72 -79 -61 -59 -71 -57 131 84 119 -221 14/5/93 -90 -79 -79 -87 -81 -79 -74 -86 -63 -60 -69 -59 137 87 118 -223 24/5/93 -93 -88 -86 -87 -84 -80 -77 -91 -65 -63 -73 -72 132 88 116 -228 29/5/93 -98 -91 -89 -89 -90 -83 -85 -94 -68 -68 -76 -73 128 80 105 -223 6/2/93 -92 -95 -75 -71 -80 -84 -73 -92 -63 -53 -68 -50 134 84 119 -223 6/10/93 -94 -95 -77 -75 -81 -76 -73 -83 -59 -58 -73 -65 133 88 128 -221 16/6/93 -103 -99 -71 -73 -86 -84 -80 -92 -65 -68 -81 -76 126 87 130 -240 2216/93 -105 -101 -85 -86 -87 -89 -88 -98 -72 -74 -88 -81 120 88 118 -246 30/6/93 -111 -108 -92 -89 -90 -91 -90 -100 -72 -70 -90 -67 129 81 118 -244 7/9/93 -80 -90 -68 -57 -47 -47 -52 -63 -40 -3 -56 -8 143 83 107 -240 15/7/93 -82 -78 -68 -58 -53 -42 -60 -55 -37 -25 -60 -25 143 98 125 -238 23/7/93 -87 -79 -78 -68 -56 -50 -53 -63 -45 -37 -67 -40 142 84 144 -230 27/7/93 -86 -79 -76 -67 -55 -48 -52 -62 -42 -30 -66 -35 144 88 119 -240 8/8/93 -81 -73 -74 -62 -50 -52 -48 -55 -33 -28 -65 -32 142 90 121 -249 17/8/93 -91 -80 -79 -70 -61 -56 -59 -65 -48 -48 -78 -42 137 86 115 -243 24/8/93 -96 -82 -78 -74 -73 -60 -70 -67 -56 -56 -83 -57 135 88 109 -250 7/9/93 -92 -86 -80 -72 -64 -50 -59 -58 -46 -49 -82 -42 140 85 119 -235 14/9/93 5 20 18 18 17 14 8 0 13 13 -15 12 213 157 197 -154 16/9/93 -14 5 3 4 4 3 -3 -11 4 8 -29 4 190 126 173 -134 19/9/93 -36 -25 -49 0 0 0 -7 -15 0 4 -36 0 156 97 126 -136 21 /9/93 -43 -36 -56 -40 -1 -6 -20 -36 -1 0 -45 -2 156 88 114 -138 25/9/93 -50 -43 -59 -60 -39 -30 -34 -43 -32 -18 -60 -3 148 80 119 -151 29/9/93 -57 -4 7 -61 -63 -50 -37 -42 -50 -29 -29 -64 -14 148 85 112 -175 3/10/93 -57 -37 -60 -62 -43 -32 -38 -48 -28 -25 -61 -67 166 86 112 -170 7/10/93 -57 -43 -60 -57 -28 -20 -30 -0 .4 -14 -13 -60 -10 150 98 147 -180 12/10/93 -62 -50 -65 -67 -57 -48 -52 -59 -40 -44 -74 -27 147 90 118 -185

Depth to watertable for all bores and drain water depths APPENDIX pH

Dates Bs7 Bs8 Bs9 Bs10 Bs11 Bs12 Bs13 Bs14 Bs15 Bs16 Bs17 Bs18 transect d. gated. road d. 17/2193 5 5.7 5.4 4.6 5.2 4.9 4.9 3.9 4.5 4.5 5.1 4.2 3.2 3.3 3.3 23/2193 3.4 3.8 4.4 4.1 4.3 3.4 3.9 3.8 4.1 4.6 4.1 3.6 3.1 3.1 3 26/2193 3.4 3.8 4.1 4.1 3.8 3.3 3. 7 3.7 3.8 4.1 3.8 3.4 2.9 3 2.9 3/8/93 3.8 4.8 4.4 4.1 4.4 3.8 3.8 4 4.1 4.4 3.8 3. 7 3.3 3.3 3.3 3/12/93 3.5 4.5 3.9 3.9 4.2 3.8 3. 7 3.6 3.6 4.5 3.9 3. 7 3.2 3.3 3.3 15/3/93 3.6 3.9 4.1 3.9 4.2 3.9 3.6 3.6 3.6 4.4 4 3.6 3.1 3.1 3.3 19/3/93 4.7 5.1 5.3 4.7 4.8 5.1 4.9 4 4.3 4.8 5.2 4.1 3.7 3.4 3.4 24/3/93 3.6 4.1 4.2 4.1 4.1 3.9 3.8 4.5 3.9 5 5.1 4. 7 3.2 3.3 3.3 4/2193 2.7 3.4 3.5 3.7 3.5 3.2 3.2 3.5 3.1 3.2 3.9 2.9 2.8 3.3 2.7 4/5/93 3 3.4 3.6 3.6 3.4 3.2 3.1 3.4 3 3.2 3.6 3 3 3.5 2.9 4/8/93 3 3.4 3.6 3.6 3.5 3.5 3.3 3.3 3.2 3.4 3.6 3.3 2.9 3.3 3 15/4/93 3 3.2 3.4 3.2 3.5 3.2 3.4 3.2 3.2 3.6 3.6 3 3.1 3.4 3 20/4/93 3.2 3.3 3.5 3.4 3.6 3.3 3.3 3.4 3.1 3.4 3.6 3 3 3.4 2.9 27/4/93 3.1 3.3 3.3 3.3 3.6 3.3 3.6 3.2 2.9 3.5 3.4 3 2.9 3.2 2.9 6/5/93 3 3.1 3.1 3.3 3.1 2.9 3.1 2.9 3.3 3.3 3.3 3 2.8 3.3 2.8 14/5/93 3.2 3 3.2 3.1 3.3 2.8 3.2 3 2.9 3.2 3.5 3 2.8 3.4 2.8 24/5/93 3 3.2 3.4 3.2 3.3 2.9 3.2 3.2 3 3.2 3.5 3 2.8 3.5 2.8 29/5/93 3.1 3.2 3.6 3.2 3.2 3 3.3 3.2 3 3.2 3.5 3 2.8 3.3 3 6/2193 3.3 3.1 3.5 3.1 3.1 2.8 3 3.2 2.9 3.2 3.2 2.9 2.8 3.2 2.8 6/10/93 3.1 3.1 3.5 3 3.2 2.9 3. 1 3.3 2.8 3.6 3.4 3 2.8 3 2.9 16/6/93 3 3 3.2 3.1 3.2 2.8 3.1 3.5 2.9 3.1 3.5 3 2.8 2.9 2.9 2216/93 3.1 3.1 3.6 3.4 3.4 3 3.2 3.5 2.9 2.9 3.3 3.2 2.8 2.9 2.7 30/6/93 3.3 3.2 3.5 3.5 3.5 3 3.2 3.2 2.8 2.8 3.2 3.1 3.1 3.2 2.9 7/9/93 3.3 3.7 3.6 3.4 3.7 3.2 3.4 3.2 3.2 3.8 3.6 3.3 3.2 3.2 3.5 1517/93 3.3 3.5 3.5 3.4 3.4 3.2 3.3 3.2 3 3.5 3.4 3.3 3.1 3.2 3.3 2317/93 3 3.1 3.4 3 3.4 3 3.2 3.2 2.9 3.2 3.4 2.9 2.8 2.9 2.7 2717/93 3.1 3 3.2 3.1 3.2 3.1 3.2 3.2 2.9 3.1 3.1 3.3 2.9 2.9 2.7 8/8/93 3.1 3.2 3.3 3.2 3.4 3.2 3.3 3.2 3.1 3.3 3.3 3. 1 2.9 2.9 2.8 17/8/93 3.3 3.3 3.5 3.3 3.5 3.2 3.5 3.4 4 3.3 3.3 3.1 3 2.9 2.9 24/8/93 3.2 3.3 3.3 3.1 3.3 3 3.4 3.4 2.9 3.3 3.3 2.9 3 2.8 2.9 7/9/93 3.3 3.4 3.6 3.3 3.4 3.2 3.3 3.4 3 3.4 3.1 3 3 3.3 2.7 14/9/93 5.5 5.5 4. 7 4.3 5.1 5.5 5.5 5.5 5.5 5.2 5.1 4.4 4.3 4 3.8 16/9/93 3.3 3.5 3.5 3.4 3.6 3.2 3.5 4.8 2.9 3.7 4 3.2 4.1 3.9 3.9 19/9/93 2.9 3.4 4 3.8 3.8 3.4 3.5 3.9 3.1 3.6 4.3 3.1 3.4 3.2 3.1 21 /9/93 3.7 4.1 4.2 5 5.3 4.4 4.2 4.2 3.6 4.1 4.1 3.5 3.6 3.3 3.3 25/9/93 2.9 3 3.5 3.3 3.6 3.3 3.4 3.4 3 4 4 3 3 3 2.7 29/9/93 3 3.6 3.9 3.6 3.9 3.7 3.7 3.9 3.9 3.9 4.2 3.5 3.1 3.3 3.1 3/10/93 2.7 3.1 3.4 3.3 3.5 3.2 3.2 3.2 3 3.7 3.7 2.9 3.3 3.2 2.8 7/10/93 2.7 3 3.3 3.3 3.2 3.3 3.4 3.4 3 3.6 3.4 2.8 2.9 2.9 2.7 12/10/93 2.8 3.1 3.4 3.3 3.4 3.1 3.4 3.4 3.2 3.5 3.6 2.8 3 3.1 2.5

pH for all bores and drain sites APPENDIX

Chloride and Sulphate

Dates ...... bore...... transect...... d. road...... d. ....Inside...... F1 .....Inside...... F2...... bore...... transect...... d. road...... d...... Inside...... F1 .....Inside...... F2 ...... ~!:i.~~r.l~.~ ...... ~.':l.!P.!:!~.~~ ...... 17/2193 28 320 43 30 560 360 23/2193 55 530 170 220 970 1700 26/2193 60 640 180 250 990 1700 3/8/93 44 705 150 130 945 1450 3/12193 45 630 120 125 975 1100 15/3/93 37 300 130 130 1100 1200 19/3/93 21 70 89 33 160 750 24/3/93 41 97 120 140 400 150 4/2193 64 170 130 260 730 1100 4/5/93 80 170 140 420 740 1100 4/8/93 84 190 160 470 750 1500 15/4/93 110 230 170 740 850 1700 20/4/93 120 320 190 850 870 2000 27/4/93 140 490 230 1000 920 2500 5/6/93 180 210 230 1400 240 2500 14/5/93 180 850 230 1600 960 2400 24/5/93 210 760 210 1700 1100 2300 29/5/93 230 830 210 2000 1100 2300 6/2193 230 790 180 1900 1100 1800 6/10/93 230 1000 240 2000 1100 2500 16/6/93 250 2000 240 1900 1100 1900 2216/93 280 3100 230 2100 1100 2100 30/6/93 300 6400 230 2200 1200 2100 7/9/93 150 1500 76 900 410 450 1517/93 88 2000 180 300 570 1200 2317/93 2800 820 2717/93 2800 870 8/8/93 2600 9400 4400 820 1100 850 17/8/93 3300 11000 6400 1100 1300 1000 24/8/93 24 3500 270 11000 8900 76 1100 2300 1300 1100 7/9/93 2700 4900 2800 1000 1300 920 14/9/93 300 300 830 100 100 300 16/9/93 64 120 64 160 19/9/93 24 110 56 160 200 66 210 420 90 210 21/9/93 29 190 36 350 250 110 350 580 150 110 25/9/93 32 250 120 490 510 91 390 770 340 260 29/9/93 770 500 370 530 3/10/93 38 360 120 1300 1300 95 550 900 1300 540 7/10/93 1000 700 38 490 500 12/10/93 47 430 180 1900 1900 130 700 1500 600 500 APPENDIX

Iron and Aluminium

Dates ...... bore...... transect...... d...... road...... d...... Inside...... F1...... Ins...... ide...... F2...... bore...... transect...... d...... road d...... Ins.....i...... de F1...... Insi....de...... F2 ...... iron ...... aluminium...... 17/2193 0.4 6.2 3.8 0.9 30.1 9.6 23/2193 18.2 4.8 93 52.3 10.6 89.2 26/2193 5.5 15.7 78.7 12.7 48 92.1 3/8/93 1.7 8.8 61 .7 6.9 45 .9 74.4 3/12193 71 .6 2.1 11 .8 68.4 7.2 47.4 15/3/93 2.8 16.6 65 .2 6.3 49.5 75 .1 19/3/93 1.3 3.4 22 0.2 6 44.3 24/3/93 4.1 8 50 6.1 17.9 47.4 4/2193 12.1 16.9 77.8 9.8 33.1 51.1 4/5/93 31 .1 19.9 86 15.6 31 .6 52.2 4/8/93 30.9 17.9 66.1 18.2 32.8 80.5 15/4/93 54 16 66 22 34 83 20/4/93 72 16 75 28 34 93 27/4/93 85 14 220 31 37 97 5/6/93 90 5 230 37 15 90 14/5/93 192 15 186 43 42 96 24/5/93 208 18 189 44 47 82 29/5/93 229 19 172 45 45 79 6/2193 223 14 136 48 39 81 6/10/93 265 17 292 100 48 96 16/6/93 320 15 190 93 52 97 2216/93 322 12 194 87 41 96 30/6/93 340 6 195 81 22 103 7/9/93 33 3 8 58 12 13 1517/93 198 5 82 49 30 71 2317/93 10.4 42 2717/93 10.8 48 8/8/93 8.4 0.1 1.8 48 0.8 21 17/8/93 11 .6 0.2 0.8 53 0.2 12 24/8/93 148 13.4 180 0.2 0.7 104 60 117 0.1 1.2 7/9/93 24 0.1 7.9 57 0.04 26 14/9/93 0.3 7.8 2 2 9 16/9/93 0.4 2.2 3 9 19/9/93 7.8 4.9 18 0.1 4 8 22 18 5 27 21/9/93 0.8 3.6 0.1 1.8 4 13 3 12 25/9/93 2.7 5.9 48 0.7 0.5 6 32 65 17 13 29/9/93 1.1 4.4 19 33 3/10/93 2.4 9.5 47 1.4 0.8 7 37 79 17 7/10/93 1.2 4.3 20 27 12110/93 2.1 9.1 45 1.6 2.8 8 54 45 19 23 APPENDIX

APPENDIX D - Broughton Creek Water Quality Data

Chloride

......

Mean St. dev. 16/9/93 100 110 63 120 100 70 Mean 110 105 66 .5 S.t dev. 14.1 7.1 4.9 19/9/93 4000 160 100 4200 160 99 Mean 4100 160 99 .5 St. dev. 14 1.4 0.0 0.7 21/9/93 3900 580 130 120 3900 600 150 120 Mean 3900 590 140 120 St. dev. 0.0 14.1 14.1 0.0 22/9/93 1700 690 170 180 180 160 100 1700 700 230 180 190 160 130 Mean 1700 695 200 180 185 160 115 St. dev. 0.0 7.1 42.4 0.0 7.1 0.0 21 .2 25/9/93 3600 2000 130 3700 2100 120 Mean 3650 2050 125 St. dev. 70.7 70.7 7.1 29/9/93 5700 3000 1800 1300 600 470 380 5600 3000 1900 1400 620 490 400 Mean 5650 3000 1850 1350 610 480 390 St. dev. 70.7 0.0 70 .7 70.7 14.1 14.1 14.1 3/10/93 7000 4900 2000 720

Mean St. dev. 7/10/93 5900 3200 180

Mean St. dev. 12/10/93 6500 4400 1900 420

Chloride (ppm) APPENDIX

Sulphate

...... ~) .~!.?.!}~.~. .~P.~ .~r.~ .?..~ ...... 9.:?...... ~.: ~...... §. :§...... ?. :.~ ...... ~ :. ~...... ~:.§...... 1 ..~ . :§...... 14/9/93 73 61

Mean St. dev. 16/9/93 20 39 12 25 35 14 Mean 22.5 37.a 13 .0 S.t dev. 3.5 2.8 1.4 19/9/93 56a 67 29 550 66 31 Mean 555.a 66 .5 3a .o St. dev. 7.1 0.7 1.4 21/9/93 53a 0a 11a 24 52a 75 11 a 3a Mean 525.0 77.5 11a.a 27 .a St. dev. 7.1 3.5 a.a 4.2 22/9/93 24a 11 a 84 0a 69 54 21 25a 11 a 64 75 71 5a 21 Mean 245.a 11a.a 74 .a 77.5 7a .a 52.a 21 .a St. dev. 7.1 o.a 14.1 3.5 1.4 2.8 a.a 25/9/93 340 32a 27 37a 3aa 30 Mean 355.a 310.a 28.5 St. dev. 21 .2 14.1 2.1 29/9/93 73a 46a 2aa 19a 130 84 61 72a 48a 19a 190 140 84 1oa Mean 725.a 47a.a 195.a 19a.o 135.a 84.0 8a .5 St.dev. 7.1 14.1 7.1 a.o 7.1 0.0 27 .6 3/10/93 92a 63a 330 11 a

Mean St. dev. 7/10/93 78a 43a 38

Mean St. dev. 12/1 a/93 830 650 3aO 68

Sulphate (ppm) APPENDIX

Soluble Iron

...... 9 .i.?.! .?. .~~.~ .. ~J?.~.~'.. ~.?.~ ...... 0.2 4.5 6.8 7.4 8.1 9.8 11 .5 U•••••• ••••••••u••• •• •• ••••••••• • • • •••••••••oooao oo oooo ooo oo • •• •• ••••• •• ••• ••• • •••• • ••• • • • ••• • •••••• ••••• •• .O • ••••••• •••••••••••••• • •• ••••••••••• •• ••• •••• ••• ••••••• • • • • • ••••• •••••• •• •"' 14/9/93 0.2 0.5

Mean St. dev. 16/9/93 0.1 0.5 0.3 0.1 0.4 0.3 Mean 0.10 0.45 0.30 St. dev. 0.00 0.07 0.00 19/9/93 0.07 0.2 0.07 0.05 0.1 0.2 Mean 0.06 0.15 0.14 St. dev. 0.01 0.07 0.09 21/9/93 0.08 0.3 0.5 0.08 0.07 0.2 0.4 0.1 Mean 0.08 0.25 0.45 0.09 St. dev. 0.01 0.07 0.07 0.01 22/9/93 0.05 0.08 0.3 0.3 0.1 0.05 0.3 0.08 0.08 0.3 0.2 0.1 0.07 0.4 Mean 0.07 0.08 0.30 0.25 0.10 0.06 0.35 St. dev. 0.02 0.00 0.00 0.07 0.00 0.01 0.07 25/9/93 0.05 0.06 0.7 0.03 0.05 0.3 Mean 0.04 0.06 0.50 St. dev. 0.01 0.01 0.28 29/9/93 0.04 0.07 0.07 0.07 0.09 0.08 0.2 0.04 0.06 0.07 0.09 0.11 0.09 0.2 Mean 0.04 0.07 0.07 0.08 0.10 0.09 0.20 St. dev. 0.00 0.01 0.00 0.01 0.01 0.01 0.00 3/10/93 0.02 0.04 0.4 0.08 0.02 0.04 0.3 0.09 Mean 0.02 0.04 0.35 0.09 St. dev. 0.00 0.00 0.07 0.01 7/10/93 0.02 0.03 0.1 0.02 0.05 0.1 Mean 0.02 0.04 0.10 St. dev. 0.00 0.01 0.00 12/10/93 0.04 0.02 0.06 0.4 0.02 0.02 0.06 0.5 Mean 0.03 0.02 0.06 0.45 St. dev. 0.01 0.00 0.00 0.07

Soluble iron (ppm) APPENDIX

Toatal Iron

...... 9 !.?.!.~!:!9.~ .. ~J?.~.~ f.~.~!:'.) ...... 0.2...... 4...... 5 ...... 6.....8...... 7.4...... 8.1...... 9.8...... 11...... 5 ...... 14/9/93 3.7 2.9

Mean St. dev. 16/9/93 1.4 1.6 0.8 1.4 1.2 0.9 Mean 1.40 1.40 0.85 St. dev 0.00 0.28 0.07 19/9/93 0.6 0.8 0.7 0.6 0.7 0.7 Mean 0.60 0.75 0.70 St. dev. 0.00 0.07 0.00 21/9/93 0.3 0.8 0.8 0.7 0.3 0.8 0.8 0.8 Mean 0.30 0.80 0.80 0.75 St. dev. 0.00 0.00 0.00 0.07 22/9/93 0.4 0.3 0.6 0.7 0.2 0.2 0.6 0.3 0.3 0.6 0.9 0.3 0.4 0.6 Mean 0.35 0.30 0.60 0.80 0.25 0.30 0.60 St. dev. 0.07 0.00 0.00 0.14 0.07 0.1 4 0.00 25/9/93 0.2 0.3 0.8 0.2 0.2 0.7 Mean 0.20 0.25 0.75 St. dev. 0.00 0.07 0.07 29/9/93 0.2 0.2 0.2 0.2 0.3 0.5 0.6 0.2 0.2 0.3 0.2 0.5 0.5 0.6 Mean 0.20 0.20 0.25 0.20 0.40 0.50 0.60 St. dev. 0.00 0.00 0.07 0.00 0.14 0.00 0.00 3/10/93 0.3 0.2 0.5 0.7 0.3 0.3 0.5 0.8 Mean 0.30 0.25 0.50 0.75 St. dev. 0.00 0.07 0.00 0.07 7/10/930.1 0.2 0.8 0.3 0.2 0.8 Mean 0.20 0.20 0.80 St. dev. 0.14 0.00 0.00 12110/93 0.2 0.3 0.3 1 0.1 0.2 0.4 0.9 Mean 0.15 0.25 0.35 0.95 St. dev. 0.07 0.07 0.07 0.07

Total iron (ppm) APPENDIX

Soluble Aluminium

...... ~.i.~!.?.~9.~ .. ~P.~.~r.~.?.~ ...... 0.2...... 4.5 ...... 6.8...... 7.4 8.1...... 9.8...... 11.5...... 14/9/93 0.2 0.5 0.6 Mean 0.2 St. dev.

16/9/93 0.1 0.2 0.2 0.1 0.07 0.3 Mean 0.10 0.14 0.25 St. dev. 0.00 0.09 0.07 19/9/93 0.1 0.4 0.1 0.08 0.3 0.1 Mean 0.09 0.35 0.10 St. dev. 0.01 0.07 0.00 21/9/93 0.1 0.6 3.2 0.1 0.1 0.5 3 0.1 Mean 0.10 0.55 3.10 0.10 St. dev. 0.00 0.07 0.14 0.00 2219/93 0.1 0.1 0.7 0.5 0.1 0.06 0.1 0.1 0.3 0.8 0.7 0.1 0.09 0.08 Mean 0.10 0.20 0.75 0.60 0.10 0.08 0.09 St. dev. 0.00 0.14 0.07 0.14 0.00 0.02 0.01 25/9/93 0.02 0.02 0.1 0.03 0.02 0.1 Mean 0.03 0.02 0.10 St. dev. 0.01 0.00 0.00 29/9/93 0.02 0.02 0.07 0.02 0.02 0.01 0.01 0.01 0.02 0.02 0.02 0.03 0.04 0.02 Mean 0.02 0.02 0.05 0.02 0.03 0.03 0.02 St. dev. 0.01 0.00 0.04 0.00 0.01 0.02 0.01 3/10/93 0.03 0.02 0.06 0.08 0.05 0.06 0.07 0.01 Mean 0.04 0.04 0.07 0.05 St. dev. 0.01 0.03 0.01 0.05 7/10/93 0.02 0.02 0.1 0.02 0.02 0.07 Mean 0.02 0.02 0.09 St. dev. 0.00 0.00 0.02 12/10/93 0.02 0.04 0.04 0.12 0.02 0.02 0.06 0.13 Mean 0.02 0.03 0.05 0.13 St. dev. 0.00 0.01 0.01 0.01

Soluble aluminium (ppm) APPENDIX

Total Aluminium

...... ~!.~!.?.~~-~ .. ~J?.~.1!:~.?~ ...... 0.2 4.5 6.8 7.4 8.1 9.8 11.5 ooooooo•••ooo o ooooo • •••••••••••••••••oooo o ••oooo oooooo• oo•o ooooooo•• o o oooooooooo ooo o oo ooooooooo ooooo o •o o o oo oooo o o••• • •••••••o•ooooooo oooo• • •••••••••••••oooo o o oo•u o oo ooo•oonooooooouooooo o ooo•oo 14/9/93 3.1 3.3 0.4

Mean St. dev. 16/9/93 2 2 0.4 1.5 2 0.3 Mean 1.75 2.00 0.35 S.t dev. 0.35 0.00 0.07 19/9/93 0.3 1 0.2 0.5 Mean 0.25 1.00 0.75 St. dev. 0.07 0.00 0.35 21/9/93 0.2 1.3 3.1 1 0.3 1.4 3.3 0.8 Mean 0.25 1.35 3.20 0.90 St. dev. 0.07 0.07 0.14 0.14 22/9/93 0.2 0.3 1. 1 0.5 0.3 0.3 0.3 1 1.3 0.8 0.6 0.4 Mean 0.25 0.30 1.00 1.20 0.90 0.55 0.35 St. dev. 0.07 0.00 0.00 0.14 0.14 0.07 0.07 25/9/93 0.4 0.3 0.4 0.4 Mean 0.40 0.35 St. dev. 0.00 0.07 29/9/93 0.1 0.1 0.2 0.3 0.3 0.5 0.1 0.1 0.1 0.1 0.3 0.4 0.6 0.2 Mean 0.10 0.10 0.15 0.30 0.35 0.55 0.15 St. dev. 0.00 0.00 0.07 0.00 0.07 0.07 0.07 3/10/93 0.1 0.1 0.4 0.05 0.1 0.1 0.4 0.06 Mean o.1 O O.1 O 0.40 0.06 St. dev. 0.00 0.00 0.00 0.01 7/10/93 0.1 0.2 0.2 0.3 1.3 Mean 0.15 0.25 1.15 St. dev. 0.07 0.07 0.21 12/10/93 0.2 0.09 0.5 0.1 0.1 0.07 0.4 0.08 Mean 0.15 0.08 0.45 0.09 St. dev. 0.07 0.01 0.07 0.01

Total aluminium (ppm) APPENDIX

Calculations for total drain discharge into Broughton Creek for 14th-16th

September, 1993 (from Chapter 6)

* Discharge for the transect drain

* Average discharge - for all (3) floodgate flaps;

= 1,445 l/sec

= 1,445 x 60 x 60 l/hr

= 5,202,000 l/hr

*Total discharge (14th-16th September); =5,202 ,000 (l/hr) x 50.5 (hrs) = 2.62x1os 1

but for 13.5 hrs out of 50.5 hrs (27%) water was assumed as not flowing out;

* Revised total discharge;

= 5,202,000 (l/hr) x 37 (hrs)

= l.92xl08 l

* Total discharge for 1 floodgate flap;

= l.92xI08 (l) + 3

= 64,158,000 I/flap

* Discharge for all drains draining into Broughton Creek * Total discharge for all floodgates (18) and therefore 38 floodgate flaps for 14th-16th

September, 1993;

= 64,158,000 (l/flap) x 38 (flaps)

= 2.43x109 l

* Total volume of acid drainage discharged into Broughton Creek as a

percentage of the creek's low tide capacity

*Broughton Creek volume on low tides; APPENDIX = 11,500 (m - length measured) x 52.5 (m - average width) x 3 (m - average

depth)

= 1,181,250 m3 = l.81xI09 l * Percentage volume of acid drainage in Broughton creek;

= 2.43x109 (l) + l.8lxI09 (l)

= 1.34

* Therefore, total discharge for all floodgates between 14th-16th September, 1993 produced enough acid drainage to fill Broughton Creek on a low tide 1.34 times ( 134% capacity) APPENDIX

APPENDIX E - Diatom Analysis

vso-; n::vbif - ··.· -- --· -- -··· -- !-- .. ------. ·-· - - .~- - . ------·- - ___ :______...:... __ - . -- .

~~ ; . ·------. - · --~: • I • . . - . . -- --·- - - ·· --- ·- ·- ___ [.,_, ·- ·· ···--·-· --···-··------·· --·------·-·------·\ - II .\- +- I,.,. II - •..

- + -

• • 1 ~;~~~~-~-~:=~- 1 -=--- -=-+-H-1--~1----_-- --~-~-- -- - 0 _:~ ~--=~~~: ~~~=si·~~-r~:·CL~~ _,~,=====:+±· ======---- ~ }=_-_--___-__ =-~ ~- +- .._ ~ --~ -~---- · ------..._.. Ii I -:-as -·· · ------.- ·-·-- -·- I -- - ·---- .. ·--·---·--- -- · ·------· -- · ---~ - <:) J ._._ -- - ... ~~~~?~!~.?~~o~u~!~~s~o~~~~~~-=-~.s-_-~,-. ~JjL__ ~___ ~;·=L------_- __- _-_-__-_- . ~... --~-- --- ~ - ---~-· - - - ~ =~- - ~-~~~ ~ - - : - 1......

·· ---l----- I . -I ~' \------1 -· - --- 1--- ··- - l.·- ···-1-. ... \------'- ·------· -- · -- - --· c::i Ci ' <:) ~ c _: ___../. ------~-:· ~ ---=------~--~~~- -~--~~~ ~ :__-_ _:~ -: - :- . - -:~-~-~ - - - ~~--~- ~~ ~ ~-~~~ ---==== ~--~~-~=~--- ~=:=:z __ ~ - 0\AT<1MS I.owe , R .1. .. 1974 Lowe. R l... 1?74

..\dlll•nCl'll'S d('/iC•(Ulll 1\chn11nU1es t:"nti:\h1 :\cbn11n1ht•s huurlluna Mc ,.\chm1.01b1.•s bu11~u1c.u lnd1rrcrcnt Lakes and romh ln1l1fkrcnt Achuncbes lan<"f'L'l•l.n huhff~n~nl Snriu 1md Slru1m'f \nrillkl'\'111 \' \11"\"tiftll\IOU:S /\choaac.hr-s m1aui1uunM AmrhirJeura .1d:ah1 Amphora cotll.'J1t•form1.-.: Mcsohalollous AmJ'lhor.a hobacaa Indifferent lm11H\"rl:'nt . ~·untml1nc Amt'lhora 0111111.s ''*"· •Hin" Auliscus cada1us 8ncdh1n:a rancloxa Mcsohalolio1a and Eurvhalohous Mcsohnlo~ · M\•,ohulohou!I. l.'urvhaltnou5 I' . u Calone-1sl'lre\U n*l1'1:t'f:llmtt126-s C:imM1o:nna C"'TJlbrlliform1s ill *ft;'l'f'f:!lm"' 35- 16 Ch11rtoceros r•drcan.s ~m~l~ft ca JS Ccin1to11eu .11rcus lnd1Cft'r~nt to Hui Srinnri!.S und Streum Fd C.hP~roceros d\'ciP1eos f"li!lflil~ltrl 3S-l6 Cbaetocero.1 al' l'li:Jlll!tl!Uf 3S-26 Coceoneis dimmut:i Indifferent to Hal L:tkC3; , Ponds and Rh~ lndiffrrcnt., Coccont:IS Pl•ct"ntul• Indifferent iJi.1f'(l~'tfl :! > Indifferent lnd1fferC"nl . 1."unt111hnl' fc 4 Coccont'1s scuri:-Uum Euhulohous ~lanne ifli*-~llU~~JI Mcsohuloh· Euhulobous Mb 4 ·) Coscwodiscus asreromrhalus ~mll~lt ca. J5 CoSC1nodi.scus i.":1ru ~j:fr.Jf"t ca. JS Coscmod1scvs (jne::nu:s 4 . J Cose1nod1scus nodul1fer 4. J Co.scu1oducus oculusir1d1.s ca. 35 CycJoteUa menellblJlJana ..::! CycfOleUa mene'!biaiana-2 ~0--2 C>'CotttJa !ln:u::1 Mesobalobous JS-26 Mesoh::ilobous. euntinlinous 3 . 1 C}'clOleU• Sl\1orum J C}'tloteUa ment>~h1n.iMna ili.J!< li'lDni!l'.tl!l C>mbeJJa Da\.1cu.CUorm.Js Indifferent Indifferent lndiCfercnt C>mbeUa mi.auta ~*~'.ti! < 2 C)mbeU:i rum1da ili.J!dDJa \.'Ilt. ruppoaics CymbeJJ.a wm.ncosa lndi.fferent Indifferent Indifferent. ~urvhali.nous Dialomu elon,i?21um '-'Dr minor Diatoma h1emaJe Halobobous DiMtoma '-'UUlllllre lodlfferent Indifferent Indifferent Dim~o.llnimm:1 /ulwm iil7'1:t'fi.!ll11t! 35-26 Dimerouamm.a b~"D.liaum iliJ!Josu:s .itr.::1nuJ:11.:1. i1ul Mer1d100 C1rCUJare ili.*liI'.t!J < 2 J.ad1fferent Indifferent N.:1\1CUJ• ~Ph tlJ)htOUS Nai.1cul• d1cepbaJa i;!tJ!lJa,1c:.il• Pde2J"W% fo. mi.::ior Me:soh:ikbou:s .Na'",cub pupuJa ~a\.'lcu.la sallnar\lm·I Mesoh::i.lobous Ni1vtcufa sthnarum ·1 :i-JaVJcu/a ~ae.c..a Nawcvla rr:.pu.awau Indifferent and El Lakes and Ponds NaV1cuta viridu/a ~iczsdia acumioa.i:a Nin::scl:tia addt>cia NicucJua .ampb1b1a lndtffuent Indifferent lod1ffcrent SiC13Cb1a ampbitna-2 Ni,Z5Cb1a ai>rcuJau Niczsr:hia diss.irnua Indifferent Lakes and Ponds Indifferent Indifferent NiczscbJa fasacu/aca Nin:scbJ.11 (ilform1i MesohWobous !1Jd1fforen1 !'-Jiizscbui /ru3fDJum H:tlopbdou' to Indifferent :tnd uppurcntlY Eur)'halobous hHhHerent F·B N'ilzscbut /rusiuJum ·1 iOJDni!l'.tlt 20-2 Nicz:scbua .iv:1nuJ.ata i ii*~'.l'{'fill!lil:30-12 ~itzschu1 Haoczscbiana Indifferent! :'-.'iczsch1a hua(ancoi Mesobttlobous to Halophilous iiilfhilllobou ~ '' .')·,nedra fiJformu S\nedr<1 t;ibuJau;i Srnedra ulna [ndtfkrent. lnd1ffl:rem lnd1(fcrcnt T at-eJJana (eoe!lr.:ua ilalophobous Lakcs a.nd Ponds llitlohobou Halophobous Fa TabeJfan• fJoccuJou H 11lophobous Ponds llalohobou llalorohohous Th21lu!110:1.1nt'.'ma n11~ch101d-.·:J !1~i'M1'i~ft l ~j~~ C:t. 351 l5 :?6 Thula.ss10s1rn nordenstJold1J \'l.i'FltlMI« c'-35 Tr.:1cb~henia .austr:1.lu iii*l~Pl'.'fl!lr.l!!!JS-26