6-rr -qb
sediment and Phosphorus Bioturbation by carp (Cyprínus carpio L.) in Irrigation Drains near Griffith, New South Wales
Shaun Meredith, B.Sc. (Hons)
Department of ZoologY UniversitY of Adelaide in conjunction with CSIRO Division of Water Resources' Griffith' NSW
Submitted in fulflrtment of the requirements for the degree of Master of Science'
March 1996 "If ttre correct stocking densities are maintained, coÍlmon carp should prove to be an effective, cheap and long-tenn answer to submerged weed control in small shallow lakes and ponds. Achieving this level of control may' however, result in some cha¡acteristic changes to the environment. The most common feature is the distinctive green colouration of the water...."
Seagrave (1988) "Aquatic Weed Control" The Dorset Press, England Addendum
p.56 Results for ANOVA on sedimentary phosphorus dataarctabulated below:
Source d.f. F-ratio P Landuse 2 4.596 0.013 Length of Upstream Drainage (LUSDR) 3 3.491 0.020 Sampling Date 1 18.519 <0.001 Landuse x LUSDR 6 0.448 0.844 Landuse x Sampling Date 2 0.026 0.974 LUSDR x Sampling Date 3 0.344 0.794 Landuse x LUSDR x Date 6 0.069 o.999
p. 67 The small holes in the walls of the core sampler presented in Figure 3.1 are to enable water from above the core sample to escape without disturbing the sediment. I
Table of Contents
t
IY
Iþclaration v vt
vu List of Tables......
List of vul
Chapter 1: Introduction...... 1 1 1.1 Background...... ) 1.2 The Issue: Eutrophication....-...... -. 4 1.3 Carp in the Murray-Darling Basin...-.... 6 L.4 Carp Feeding Behaviour 1.5 Resuspension of Sediment and Phosphorus by Carp' I 9 1.6 Measurement of Phosphorus...... I.7 Study Area...... 10 1.8 Inigation Channels.. 11 t3 1.9 Project Aims......
Chapter 2: Variabitity in the Abundance and Distribution of Carp in the Mirrool ¡ñ^tt¡ll 17 2.1 Introduction T7 t7 2.1.L Background...... 2.1.2 Objectives 20 2.2 Methods... 20 20 2.2.1 Site Selection...... 2.2.2 Estimation of Fish Abundance 2l 2.2.3 Data AnaIysis...... 23 25 2.3 Results..... 25 2.3.1 Carp Entry into the Minool Catchment... 2.3.2 Increasing Carp Abundance Late in the Irrigation Season.. 27 2.3.3 Spatial Distribution of Carp-. 28 2.4 Discussion 29 2.4.1 Temporal Variaúon in Carp Abundance 29 2.4.2 Spatial Distribution of Carp.- 33 2.4.3 Conclusions...... 34 u
Chapter 3: Spatiotemporal Distribution of Sedimentary Phosphorus in the Mirrool Catchment...... -...... """' ¿t8 3.1 Inuoduction 48 3.1.1 Background...... 48 3.1.2 Objectives 51 3.2 Methods... 52 3.2.1 Site Selection...... 52 3.2.2 Sampling Procedue. 53 3.2.3 Sediment and Data Analysis... 54 3.3 Results..... 56 56 3.3. 1 Total Phosphorus...... 3.3.2 Organic Matter...... 57 3.3.3 Trace Element Composition.... -...-.... 58 3.3.4'Water Velocity... 58 3.4 Discussion 60 3.4.1 Landuse... 60 3.4.2 Length of Upstream Drainage-- 63 3.4.3 Temporal Variation (Sampling Date)...... 65 3.4.4 Conclusions...... 65
Chapter 4: Sediment and Phosphorus Resuspension by Carp"""" 81 4.1 Introduction 81 4.1.1 Background...... 81 4.L.2 Objectives 83 4.2 Methods... 83 4.2.1 Experimental Design. 83 4.2.2 Sample Analysis... 85 4.2.3 Data Analysis...... 87 4.3 Results..... 88 4.3.t Sediment.. 88 4.3.2'Water Quality..... 89 4.4 Discussion 9T 4.4.I Suspended Sediment and Turbidi 91 4.4.2 Total and Filterable Reactive Phosphorus.. 93 4.4.3 hon-Strip Desorbable Phosphorus...... -...... 95 4.4.4 Experiment Duration. 97 4.4.5 Conclusions...... 99
Chapter 5: Discussion...... 106 106 5. 1 Introduction...... 5.2 Sediment and Phosphorus Resuspension by Ca¡p.... r07 ro7 5.2.1 Quantity of Resuspended Sediment. 5.2.2 Retention of Resuspended Sediment in the Water Column.... 109 110 5.2.3 Phosphorus Content of Sediment...... - -... -.-.. lll
5.2.4 Sediment and Phosphorus Resuspension by Carp: A Model..' 110 5.3 Resuspension of Sediment and Phosphorus by Carp in the 110 Mirrool Carchment 5.3. 1 Quantity of Resuspended Sediment...... 111 5.3.2 Retention of Resuspended Sediment in ttre'Water Column..... rt3 5.3.3 Phosphorus Content of Sp¿lirnenf tt4 5.3.4 Conclusions...... TL4 5.4 Conclusions: Sediment and Phosphorus Resus¡rension by Carp...... "' 116 5.5 Future V/ork...... 116
Referenccs. 124 lv
Abstract: Cary Glpriruts cørpio L.) a¡e abundant in many natural and constructed waters in ttre Murray-Darling Basin. This introduced fish has been implicated in the demise of aquatic plants and native fish, bank slumping, incteasing orbidity, and more recently, increasing water column phosphorus concentrations. This study aims to assess the contribution of the benthic feeding behavioru of carp to phosphorus and sediment resuspension in the irrigation drainage network of the Mirool catchment near Griffith, New South V/ales.
An observation survey (Chapter 2) r,evealed carp Ìvere abundant in the drainage network during the irrigation season, but not so during the off-season. The inc¡ease in carp numbers ûuing the inigation season was shown to be due to upstreÍrm migfation from more pennanent $'aters downstrea¡n, entry through irrigation supply lvater, and to a lesser e*æoi to the reconnection of overwintering siæs \ilithin the drainage network. I-arge numbers of juvenile carp were also observed taæ in the irrigation season' indicating successful recruitment of carp within the drainage network. Based on this informaúon, a model of the movement of carp to and from the drainage network is presented. When abundant in the drainage network, the distribution of carp was concentrated at the intersection of srnaller lateral drains with the faster-flowing, deeper Main Drain "J". Ïlis disribution was not found to be related to differences in the physical attributes of sites srudied, but to the diversity of habitat at the junction of lateral drafurs with the Main Drain.
Exa¡nination of the temporal and spatial distribution of sedimentary phosphorus (Chapter 3) revealed sediments in drains receiving \ilater from a predominantly uban catchment contained higher concentrations of total phosphorus than those receiving riceþasture runoff. Sedimentary total phosphorus was also found to be greatest at the upstream end of lateral drains, a¡rd least at the downstream end. Similarly, phosphorus concentrations in the sediments were greatest prior to the commencement of the irrigation season. The distribution of sedimentary total phosphonrs in the Mirrool catchment was linked to spatial and temporal differences in runoff water quality and velocity, and to spatial differences in the geochemical and organic composition of sediments.
A pond experfunent was conducted (Chapter 4) to further examine factors affecting water quatity resulting from carp feeding behaviour. The variable effects of carp on turbidity, ùrp"nOø sediment, total phosphorus and ISDP were attributed to the interaction of carp .o¿ ttt" phosphorus content and particle size disributions of two different sediments used. The implications of these resuls on both past and future studies on the impact of carp are discussed-
Finally (Chapter 5), information on the spatial and æmporal distribuúo¡ of carp and r.ai-*t"ry total phosphorus in the drainage network is combined with information attained during the pond experiment to assess the role of carp in sediment and phosphorus resuspension in the Minool catchment. It is concluded ttrat the distribution of carp is such ìi il that concentration of sediment arid phosphorus r€suspended is likely to be inhibited" however, the export of resuspended phosphorus is enhanced. { v
This work contains no mâterial which has been accepted for the awa¡d of any other degree or diploma in any university or other ærtiary institution and, to tlre best of my lnowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text
I give consent to this copy of my thesis, when deposited in the University Library, being available for loan and photocopytng.
Signed: Date: 7) l'( ,(? vl
Acknowledgments
I gratefully acknowledge the invaluable guidance I received from both of my supervisors, Dr. Jane Roberts, and Assoc.Prrof. Keittr V/alker. There \ilere many difñculties associated with joint supervision, especially when supervisors are separated by the best part of the Murray-Darling Basin and I thank them both for their considerable effort in maintaining a working envi¡onrnent that allowed this work to happen.In preparing this thesis,I received only valuable conmrents and constructive criticism from both Keith and Jane, so I sincerely thank them both fø their efforts, and panicularly for ttre insight they have given me into this snrdy, and into the study of ecology in general. Thanþou both very much.
I would also like to thank Dr. Peær Fairweather for answering each of the several hundred questions I have asked him regarding statistical analysis, and for his comments on drafts of this thesis. Thanþou also to Dr. Da¡ren Baldwin for his help and patience in guiding an ecology student through the world of phosphorus chemistry. Thanþou.
For their comments and help with matters technical, I thank Geoff 'r€al work' McCorkelle for guiding a city boy through GrifFrth's 'Irrigation Wonderland', Andrew Palmer for not being afraid ro get his hands dirty, Alan Chick fu helping to set things up and empty bottles of wine, Brendan Ebner for his constant supply t¡f tpw literaturc and bad humour, Carl Pender for help electronically and with my chess game, and Jacqui Olley for her help in Canberra with sample preparation and analysis. Special thanks go to the chem lab, in particular Sharyn Foster and Peær Thompson for chunking through the large number of samples and not making a profit All of these people helped prevent this becoming a four year study, something for which I a¡n eternally grateful. I would also like to thuk every member of the staff I haven't mentioned from CSIRO in Griffith. I'm sure I have asked everyone out there at least one question during this study, so I thank you all for your help.
On the personal front,I thank my Mum and my Dad for theirphonecalls every Sunday as I was serving dinner, forproviding the help in moving to Grifñth, and for their encourageûrent and will for me to succee{ something which has been a constant driving force for me. Thanþou. Thanks also to Deb Crealy for dealing with my grumpiness, stress, and late night vigils, and also for helping me when I was nronetarily and vehicularly challenged- And to the people with whom I have lived, especially Andrew Cremasco and Peter Edwa¡ds, I ttrankyou. I lnow it wasn't easy. To Brad Power for his supply of 'refrreshments', and to all other nrembers of the mighty Galahs hockey team (here we go, here we go, two in a row) and Leagues Club Cricket teams fc their sporting relief, thankyou. To the recently deceased Brown Hornet, a car that got me from A to B more often than not,I say thankyou (with special thanks to the guy who bought it from me). To Glenn Borlace for constant pick-nre-ups and reality checks, and for lening me beat him at chess, and to Jim Woolcock for gin and inspiration, thankyou both. And finally to Kahlua, my dog. Thankyou for barking at the phone when I was on it, and just for being so cute. 'We'll go for lots of walks now this is over. vll
List of Tables
Table 1.1: Major crops in irrigation areas of the Riverina...... """"' 1t
Table 2.1: Total carp observed at each site throughout the study perid...... """"' 28
Table 3.1: Factors affecting sedimentary phosphorus concentration 49 Table 3.2: SIMPER analysis of similarity within landuse groups...... 59 Table 3.3: SIMPER analysis of dissimilarity between landuse groups...... 60
Table 4.1: Total phosphorus and particle size distributions of sediments used in the pond experiment...... -... 88 Table4.2: Two-way model I repeated measnres ANOVA for suspended sediment, turbidity and total phosphorus- 90 Table 4.3: Single degree of freedom polynomial contrasts for suspended sediment, turbidity and total phosphorus... -. - -...... 9l Ylrl
List of Figures tsigure 1.1: l'he original paradigm t4 Figure 1.2: Irrigation areas in the Mirrool Caæhment 15 Figure 1.3: The Mirrool irrigation catchment r6
Figure 2.1: 'Sill' at the intersection of laæral drains and Main Drain "I' 36 Figure 2.2: 'Sill' at the intersection of laæral drains and Main Drain "I' 36 Figure 2.3: Permanent sites for carp obsenration study 37 Figure 2.4: Average disunce of sites in which caq, were observed ftom the most downstream siæ throughout the study period...... 38 Figure 2.5: Carp jumping a sill at the inærsection of site 23 andMain Drain "I'...... 39 Figrre 2.6: Carp being washed over a sill at site 2...... 39 Figure 2.7: Total number of carp observed and water depth throughout the study period...... q Figure 2.8: Size class of observed fish throughout the study perid...... 47 Figure 2.9: Toal number of carp observed in lateral a¡rd Main Drain sites throughout the study period,...... 42 Figure 2.10: Total number of carp in 25m sections of sites throughout the study period.. 43 Figure 2.11: Multi-Dimensional Scaling (MDS) representation of obsen ation sites cha¡acterised according to carp abundance 4 Figwe2.L2: Average \rater temperature of sites throughout study perid...... 45 Figure 2.13: Sources of temporal variation in carp abundance in the drainage network.... 46 Figure 2.14: Water temperatues in a lateral drain (site 19) and in the adjacent Main Drain "J" (site 26)...... 47
Figure 3.1: Sediment corer...... 67 Figure 3.2: Sedimentary total phosphorus: landuse..... 68 Figrre 3.3: Sedimentary total phosphorus: length of upstream drainage... 69 Figure 3.4: Sedimentary total phosphorus: sampling date... 70 Figure 3.5: Organic rnatter: lengttr of upstream drainage.... 7L Figure 3.6: Organic matter: landuse... 72 Figure 3.7: Organic matter: sampling date...... 73 Figure 3.8: Multi-Dirnensional Scaling (MDS) representation of sediment XRF data cha¡acterised by landuse.... 74 Figure 3.9: Multi-Dimensional Scaling (ltDS) representation of sediment XRF data characterised by length of upstream drainage... 75 Figure 3.10: Water velocity: length of upstrearn drainage.... 76 Figure 3.11: Water velocity: sampling date...... 77 Figure 3.12: Sedimentary CaO concentrations in r¡rban and rice/pasnue subcatchments...... 78 lX
Figure 3.13: Sedimentary SO¡ concentrations in r¡¡ban and riceþasture subcatchments...... 79 Figure 3.14: Relationship between vyater velocity and sedimentary total phosphonrs...... E0
Figrre 4.1: Experimental ponds.. 101 Figure 4.2: Suspended sediment in experimental t¡eaments...... LOz Figure 4.3: Turbidity in experimental treaments... 103 Figure 4.4: Total phosphorus in experimental treaments 104 Figure 4.5: kon-strip desorbable phosphcus in experimental treaün€nts.... 105
Figure 5.1: Model of the factors affecting s€diment and phosphorus resuspension by carp.. 119 Figrue 5.2: Gradients of carp aburdance andphysicorctremical characteristics in lateral dr¿ins r20 Chapter 1: ¡.IEG Introduction
1,.1, Background
This study is one component of a National Resoruce Management Srategy (NRMS) project (no. M3105 "Role of Irrigation Drains in Nurient Scavenging") established to investigate possible methods for reducing nutrient tra¡sport from irrigation drains to
Australian inland rivers. A preliminary study for the larger project focussing on the
'interception' of nutrients by aquatic plants (Bowmer et al. 1992) found phosphorus
measurements were confounded by the presence of carp (Cyprinus carpio L.). As a
result, it was decided to further examine the role of carp in sediment and phosphorus
resuspension, which forms the basis of this study.
Numerous studies have attributed rising suspended sediment and phosphorus
concentrations to the benthic feeding behaviour of carp (section 1.3). Carp are
abundant in irrigation drains throughout the Murray-Darling Basin, and are therefore
potentially important sources of phosphorus in i:rigation runoff. Further, irrigation
d¡ains a¡e substantial contributors to total phosphorus loads in inland rivers
(Gutteridge et al. 1992), thus carp may play a significant role in eutrophication of these
systems. This was the original paradigm around which this study was based, and is
summa¡ised in Figure 1.1. 2
L.2 The Issue: Eutrophication
Blooms of toxic blue-green cyanobacteria, such as that in the Darling River in 1991' are symptomatic of eutrophication in Australian inland freshwater. Associated with
(Mason these blooms and their decay are a suite of detrimental effects such as anoxia
1981; G.Haris 1995), high concentrations of metal ions in bottom waters @owling
1994;G.Ha:ris 1995), water discolouration, taste and odour problems (Moss 1988;
Bowling L994: Codd et al. L994; Oliver Lg94), stock deaths (Francis 1878)' fish kills
(Moss 1988; Bowling 1994; G.Ha¡ris 1995), reduced aesthetic and recreational appeal
(Wood 1975; Oliver lgg4), and skin initations and kidney damage in humans
(Falconer et al.1983).
Phosphorus is recognised as the principal nutrient limiting algal and cyanobacterial
growth in most freshwater systems (Johnston 1995; Morse et al.1993). Phosphorus
loading to rivers is generally categorised as originating from either point or diffuse
sources (e.g. Gutteri dge et aI. 1992; Donnelly et al. 1994). Point soulces, such as
serwage treatment plants, can make a significant contribution to phosphorus loads in
many catchmens (e.g. Morse et al.1993; V/ilson and Jones 1995). In the Murray-
Darling Basin however, diffuse sources (e.g. erosion, agdcultural fertilisers) are
becoming recognised as the major contributors @onnelly et al.1994). According to
one estimate, diffuse sources contribute beveen 27Vo (in a dry year) and837o (n a
wet year) of the total phosphorus load to rivers (Gutteridge et al. L992). Both point
and diffuse sources of phosphorus are, however, considered extemal to the water
body. Past research has paid relatively little attention to in-channel sources of
phosphorus, or ro in-channel processes affecting phosphorus bioavailability. 3
Sediments can act as both a sink and a source of phosphorus in freshwater systems.
Many sediments have a large capacity to adsorb phosphorus from overlying water through both rapid and slow kinetic reactions (van der 7'ee et al. t987; Froelich 1988;
Oliver 1993; Donnelly et aI.1994). Rapid reactions occur over time-scales of minutes to days and involve attachment of phosphorus to surfaces of clay minerals, and to iron and aluminium oxides (van der 7¡,e et al. L987; Oliver 1993). Slow reactions require
solid state diffusion of phosphorus into the sediment particle matrix and occur over
time-scales of months to years (Froelich 1988; Oliver 1993). During each of these
processes, phosphate is effectively removed from the water column and held in
scdiments where it is less available to algae (Taylor ancl Kr¡nishi l97l;DePinto et al.
1991; Krogstad and Lovstad I99I; Lijklema et al. 1993)'
The adsorption process, in particula¡ the rapid rate reaction, is reversible (van der 7*e
et at. L987;Lopez and Morgui 7993; Oliver 1993). Desorption of phosphorus from
sediments increases the available pool of phosphorus in the water column (Oliver
1993) and is influenced by the complex interaction of a variety of physico-chemical
factors (refer to Table 3.1). Although sediments can therefore act as a source of
phosphorus to the water column, the fluxes of phosphorus from sediment are generally
(Gachter small, often measured in units of mg P released per m2 of sediment per day
and Meyer ¡gg3). Gehrke and Harris (1994) recognised the potential for much larger
fluxes of phosphorus through bioturbation of sediments by catp, Cyprinus carpioL- 4
1.3 Carp In the Murray'Darling Basin
Three genetically distinct strains of carp were identified in Australia by Shearer and
Mulley (1978). The 'Prospect' and 'Yanco' strains were thought to have remained relatively contained, while the 'Boola¡ra' strain expanded its distribution and
abundance throughout the Murray-Darling Basin (Shearer and Mulley t978; Brown
1996). Innoduced to a fish farm in Gippsland, Victoria in 1961 (V/eatherly and Lake
lg67),the 'Boolarra' srrain is now the greatest single fish species biomass in many of
Australia's major rivers (Gehrke et aI. 1995). In addition to natural waters, carp afe
also the most abundant fish in irrigation areas throughout New South V/ales and
Victoria (M. Fuchs, electrof,rsher, pers. coûrm. 7995; L. Jaeckel, Senior Technical
Officer, Rural Water Corporation, pers. comm. 1994). The success of carp in all of
these systems has been anributed to their tolerance of a wide range of environmental
conditions, their high fecundity, and their ability to feed in turbid water (Cadwallader
and Backhouse 1983; Merrick and Schmida 1984; Brown 1996).
Carp are widely considered responsible for degradation of aquatic ecosystems.
Although the evidence is fragmented, and sometimes contradictory, carp have been
implicated in:
o the destn¡ction of aquatic macrophytes. Although gut content analyses of carp have
revealed the presence of plant material, it is unlikely plants form a major part of the
diet of carp (Crivelli 1983; Fletcher et aL 1985). The destruction of aquatic
macrophytes by carp is thought to be principally due to uprooting resulting from
benthivory a¡ound the plant base (Hume et aI.1983; Brown L996) and is thus 5
dependent on the strength of the root system, or 'robustness' of individual plant
species (Crivelli 1983; Roberts et a|.1995).
increasing turbidity. There is conjecture in the literature over the effect of carp on
nubidity. Carp have been associated with increased turbidity in experiments (e.g.
Qin and Threlketd 1990; Cline et aI. 7994; Gatlo and Drenner 1995; Roberts ¿r ¿1.
1995) and recorded observations (Cahn 1929; Meijer et al. L990;Bowmer et al.
1992;Eagle 1994: Killen l994;Tlvelkeld 1994), however other authors found no
correlation (Crivelli 1983; Hume et a|.1983; Fletcher et aI.1985). This is
discussed further in Chapter 4. a the demise of native fish stocks. The destruction of aquatic plants and increased
turbidity associated with carp are thought to adversely affcct naúve fish
@owerman L975; Hume et al. 1983; Fletcher 1986). The reduction of aquatic
macrophytes reduces available spawning sites required by species such as Murray
cod (Maccullochclla peeli) andgolden perch (Macquaría ambígua) (Bowerman
1975; Fletcher 1986). Increased turbidity reduces the effrciency of visual feeding
@owerman L975; Hume et al.1983), and could thus affect native fish such as
Murray cod, golden perch, trout cod (Maccullochella macquariensís) and silver
perch (Bidyanus bidyanus). Furthermore, carp can act as a vector for the parasitic
anchor wonn (I-ernaea qprínacea), which is capable of infecting a nmge of native
frsh (Merrick and Schmida 1984; Brown 1996). The mouthpÍìrt anatomy of carp,
however, indicates they are not likely to prey directly on other frsh (Sibbing et al.
1986), and differeqces in the spawning time and location of carp and most native
fish (possible exceptions being gudgeon and rainbow fish species) reduces direct
competition (Reynolds 1983; Brown 1996). 6
to reduce the o reducing benthic invertebrate biomass. Carp have been shown
(Richardson ef al' l99O; Wilcox biomass of benthic invertebratcs due to predation
andHornbachlggl;Clineetal.1994:TatraietaI.1994).
carp is thought to erosion of channel banks. The benthic feeding behaviour of
and Harris undermine channel banks, eventually causing their collapse @rown
pers' 1994;L.Jaekel, Senior Technical Officer, Rural Water Corporation'
that fluctuations in comm.1994; Brown 1996). There is, however' some evidence
of bank erosion waterregime chafacteristic of river regulation are a major source
(Thoms and V/alker 1992).
a soufce (Lamara a increasing nutrient loads. Carp have been shown to be both
a¡1d Drenner 1995) and 197S;Brabrand et al.1990: Qin and Threlkeld 1990; Gallo
for nutrients in the water column' a sink @oers et aI- 1990: Robens et al.1995)
This is also discussed funher in chapter 4'
Task Force) and Despite recent activities (e.g. establishment of a National Carp
Carp, 1994;'The Carp resolutions made at workshops (¿.8. 'The Forum on European
the eradication of carp' Summit,, 1995) in the Murray-Darling Basin being directed at lemain nxmy of the issues regarding their effect on the aquatic environment
unresolved.
!.4 Carp Feeding Behaviour
(Hume et 1983; Lammens and Carp feed on both pelagic and benthic food items al'
depends on visual Hoogenboezem 1991). Feeding from the water column, however, 7
detection of prey (Jobling 1995) and is therefore not likely to be effective in turbid waters such as the lowland rivers of the Murray-Darling Basin. Benthivory is therefore ttre likely optimal feeding mode for carp.
Carp benttrivor|, termed 'mumbling' by Cahn (1929), consists of three phases' The description presented below was derived from information presented in Sibbing er ø1.
(1986) and Sibbing (1988):
1. Sediment intake: The buccal cavity is compressed and the mouth opened nea¡ the
sediment water interface. The rapid expansion of the buccal cavity through
muscula¡ contraction generates a vacuum which draws sediment and/or food items
in through thc mouth.
2. Food item detection: Following intake of sediment into the buccal cavity, food
items are detected by size and/or taste. Size selection requires the branchial sieve to
separate the larger food items from sediments. Although the mechanism of taste
selection is not known, tastebuds inside the buccopharyrx provide ttre sensory
basis.
3. Response. If potentially harmful items are detected, or no food items are found in
the ingested material, the spit response is evoked. This involves a rapid contraction
of the buccal cavity and expulsion of ingested material through the mouth. If food
items a¡e detected, the material is sorted in the pharyngeal cavity and inedible
sediment is expelled through either the opercula or mouth. 8
1.5 Resuspension of Sediment and Phosphorus by Carp
Resuspension of sediment and associated porewater provides conditions conducive to
blue-green algal blooms due to increased nutrient levels and turbidity (Bowling1994;
Sherman et at. 1994). V/hilst sediment resuspension is considered important in many
systenrs, it is seen as largely an abiotic process resulting from wave and wind action
(e.g. Blom et aI. 1994; Padisak and Dokulil 1994).The contribution of benthivorous
fish to sediment resuspension has been recognised by relatively few authors (e.9.
Lamarra 1975; Brabrand et a\.1.990: Meijer et aI.1990). In theirreview of the
contribution of carp to blue-green algal blooms, Gehrke and Harris (1994) conclude
that carp are likely to contribute more to water column nutrient loads than other fish in
the Murray-Darling Basin because of their abundance and benthic feeding behaviour.
They identified three pathways contributing phosphorus: excretion, maclophyte
uprooting, and resuspension of sediment due to benthivory. This study proposes a
fourth pathway, that of incidental resuspension due to the movements of carp, as it is
likely to be a significant source of sediment resuspension in the shallow waters of an
irrigation drainage net'work.
Sediment resuspension can contribute to the bioavailable phosphorus fraction in the
water column in two ways:
1. Porewater phosphorus is soluble, and can contain 20 times the orthophosphate
concentration of overlying water @ckerrot and Pettersson 1993). If disturbed
into the \ryater column, most of this fraction is immediately available for algal
growth. 9
is available 2. T1'rcloosely bound, or labile, component of particulate phosphorus
for algal gro,wth (Sharpley et aI.l98I; Oliver et a\.7993)' Resuspension of
where it sediment can therefore place available phosphorus into the photic zone
can be used by algae.
These pathways \ryere not examined separately in the cunent study.
L.6 Measurement of PhosPhorus to All phosphorus is potentially bioavailable @onnelly et al' 1994). However, in order
instantaneous understand algal response to phosphorus inputs, it is necessary to have
correlations measgres of bioavailable phosphorus. This has been demonstrated through
with algal gowth (Oliver et al. L993). Techniques for the meastrement of bioavailable
yet be phosphorus ate, however, still being developed and a standa¡d method is to
prepared agreed upon. A method based on adsorption of phosphates onto specially
(Sharpley er a/. iron strips and subsequent acid digestion is becoming widely accepted
1981; van derTæe et aI. L987; Olive¡ et a\.7993). However many authors employ
subtly different techniques, with a range of reagent concentrations and analytical
techniques (see Sharpley et a\.1981; Oliver et aI. L993)'
The absence of a standard method for measuring bioavailable phosphorus combined
carp' with the need for comparison with other studies of phosphorus bioturbation by
required this study to focus rnainly on traditional phosphorus measures. Total and
filterable reactive phosphorus therefore form the basis of phosphorus measurement
throughout this study. It was necessary' however, to include Some measure of r0 phosphorus available for algal growth. The iron-strip desorbable phosphorus (ISDP)
merhod used in Chapter 4 of this study is a variation on that used by Sharpley er aI.
(1981), van der 7-ee et at. (L987) and Oliver et al. (1993) as it involves a sonification
step to remove particulate matter adhered to ttre iron strip prior to acid digestion. This
method is currently undergoing evaluation at the University of Canberra and CSIRO
Division of Water Resources.
L.7 Study Area
The Mum¡mbidgee Inigation Area (MIA) is located within the Murray-Darling Basin,
and incorporates the towns of Griffith, Leeton and Narrandera in southern New South
'Wales, Australia. The MIA consists of the Yanco and Mirrool Irrigation Areas and the
Tabbita, Wah V/ah and Benerembah Irrigation Disricts (Fig. 1.2). The catchment has a
semi-a¡id climate, receiving on average 396mm of rainfall per yer¡r, and has an average
January and July minimum and maximum tempefature of t5.4 - 30.9'C and 3.5 -
ls.2"Crespectively (unpubl. data held at CSIRO, Griffith, 1995).
The study area (henceforth referred to as the Mirrool catchment) lies within the
Mirrool Inigation Area, which contains 783 km of drainage cha¡nel receiving nrn-off
from urban and ru¡al land near Griffrttr @.Power, Senior'Water Administrator,
Mumlmbidgee Irrigation, pers. comm. 1995). Water from the smaller lateral drains
ultimately reaches the main drainage channel, known as "Main Drain 'J"', which ntns
through the centre of the Inigation Area and into Mirrool Creek approximately 12km
west of Griffith. Mi¡rool Creek flows into Willow Dam, and eventually Barren Box
Swamp, a natural depression of 3200ha serving as a storage and supplier of water for ll
the Wah Wah lnigation District (Frg. 1.3) (Lachlan Catchment Management
Conrmittee 1993).
inputs from The drainage network of the Mi:rool catchment receives a diverse range of
crops (fable 1.1), pastures, supply channels and urban inputs from Griffrth and
surrounding villages.
Table 1.1: Major crops in Irrigation Areas of the Riverina (from Bowmer et aI. t994)
Crop Area (ha) rice 133,000 winter cereals >100,000 vegetables 9000 soybeans 7500 citrus 7400 grapes 5000 ma]ø;e 4900 sunflowers* 1200 stonefruit 900 * indicates no significant crops in Mirrool catchment
1.8 IrrigationChannels
(supply Irrigation channels can be divided into those which supply the a¡ea with water
the a¡ea channels), and those which carry drainage, runoff and excess water away from
(drains). The focus of this study is on irrigation drains'
'.. :
Drain morphology within the Mirrool catchment varies greatly. Drain width ranges
pers' from 3 to 16.5m, and bank height from 0.5 to 4.1m (N.Ward, M.Sc. student,
comm. 1995). The va¡iable number of inputs to d¡ains coupled with temporal variation t2
in in rainfall and irrigation run-off results in discharges from 0.14 to lz4glvn-day-l
Main Drain "J" and water velocity ranging from 4-95 - 73.5km aay-t IDLWC data'
season. unpubt.). Further, some sections of drain remain dry throughout the irrigation
in faster flowing Such variation results in a range of substates from hard-packed clays
and ponded areas' d¡ains to fine silt sediments several centimetres deep in slow flowing
provides a This variability, coupled with the changing natufe of input water quality, diverse range of habitats for carp in the drainage network'
River at the On average, 420,000ML of water is diverted from the Mum¡mbidgee (B'Power' Berembed Weir into the Mirrool catchment during an irrigation season
Suppty Senior'Water Adminisuator, Mumrmbidgee lrrigation, pers.comm.1995).
water enters the drainage system in two ways:
either 1. supply water is diverted onto farmland and used for inigation, the excess
running overland into d¡ains, or (in the case of tile drainage) draining into
underground sumps and being pumped into the drainage network.
being 2. excess supply water is diverted directly into the drainage system without
used for agriculture through structures called escapes'
Escape water serves to both reduce pressure on the supply system and to dilute
and pollutants such as herbicides, pesticides and salts. This improves water quality
allows reuse of water downstream in the V/ah Wah Inigation District'
Both supply and drainage channels are conventionally viewed as transporters of water,
thus little attention has been given to their ecology. This is reflected by inadequate
rwater quality data' accr¡rate mapping of the drainage system, and limited historical r3
L.9 Project Aims
inland rivers Inigation has been shown to be a significant source of total phosphorus to
load in some areas in the Murray-Darling Basin, contributing up to 237o of the total
(Gutteridge et al. L992). The major objective of this study was to examine
source of phosphorus resuspension of sedimentary phosphorus by carp as a possible exported from irrigation a¡eas.
of sedimentary In the drainage network of the Mirrool catchment, the resuspension
and phosphorus by ca¡p can be expressed simply as a funcúon of the density
governing the relationship distribution of carp in the drainage network, and the factors
aims were selected between carp and sediment resuspension. With this in mind, three
as the basis for the study. These are:
distribution of carp in the 1 To describe and interpret the spatio-temporal
drainage network of the Mirrool catchment,
of 2. To describe and explain variations in the spatio-temporal distribution
sedimentary total phosphorus in the drainage network of the Mirrool
catchment, and
quality' 3. To examine the effects of the interaction of carp and sediment on water Figure 1.1: The original Paradigm
Feeding Resuspension of Increased P in in Carp Behaviour Sediment & P Irrigation Drains Inland Waters
È 15
Figure 1.2: Irrigation Areas in the Mirrool Catchment
H L A N REGION IRRIGATION DISTRICTS IRRIGATION AREAS L A C 1 Wah Wah 8 Yanco 2 TabbiÞ 9 Mirool -¡____lla 5 Benerembah 10 Coleambally 4 Wakool 11 Tullakool - 5 Denibooa Booligal 6 Denimein I 7 Beniquin 2 I I ¡ - - rl ,--f----.rr¡¡ I t- I RIVER lr I Balranald þGÉE Coleambally ¡ I I hAUßFUMB MURRUMBIDGEE REGION a -¡-ll ------r-t-" t MURRAY s
,?E G/ON NSW
Victoria Echuca N Figure 1.3: The Mirrool Irrigation Area r
\ TA68.7A /.D. "* '? ?h /. a /.4 a aa
a a
R/ Lêaray o î,tl
o\ t7
Chapter 2z Variability in the Abundance and Distribution of Carp in the Mirrool Catchment
2.1 Introduction
2.1.t Background
Water levels in the drainage network of the Mi:rool Catchment follow an annual cycle largely dependent on the amount of water diverted to the area for irrigation. During the down-phase of this cycle, or'off-season', when water is not being delivered to the irrigation area (typically June - Sept.), \¡/ater may drop below a minimum level required by
part carp. This is panicularly thc case in lateral drains, many of which are dry for at least of the off-season. Alternately, during the irrigation season, when water is present in the supply system (typically Oct-May), water levels in Main Drain "J" average approximately
56cm depth (unpubl. data; measu¡ed at Yoogali gauge), and most lateral drains are flowing.
Personal observations and catch information from local electrofishers, suggesß this water level variability has a pronounced effect on the temporal distibution and abundance of carp. Observations in Main Drain "J" during the off-season of 1994, when water levels were low and visibility high, indicated very few carp were present. During the peak of the subsequent irrigation season however, professional electrofîshers removed 3-4 tonnes of
30+cm carp fromMain Drain "J" in 7-8 hours approximately once every fortnight 18
(M.Fuchs, electrofisher pers. comm. 1995). Such a short-term fluctuation in adult carp numbers indicates large numbers of carp enter the drainage network during the irrigation season. It follows that temporal va¡iation in carp abundance within the drainage network of the Mirrool catchment is largely dependent on the entry of carp from external sources.
Discussions with landholders and electrofishers suggested three likely pathways for the entry of large numbers of carP:
1. Upstream migration. Carp seek warmer, deeper water during winter months (Johnsen
and Hasler Lg77).Ba:ren Box Swamp, Willow Dam and Mirrool Creek, located
downstream of the Mirrool catchment (see Fig 1.3), provide such environments. Carp
mey enter the drainage network from these more pe.rrnanent waters moving upstream
through Main Drain "J".
2. Entry through escapes. Carp are present in supply channels (Peß. obs.). Escapes (see
section 1.7 for definition) are not screened, thus in periods of excess supply, carp may
enter the drainage network in escape water.
3. Over-wintering sites. Due to either permanent water supply or channel morphology,
ponds of water deep enough to maintain carp populations remain in some drains
during the off-season. Many of these ponds reconnect with the drainage network when
the irrigation season begins, allowing carp to access the rest of the habitable drainage
network. r9
influenced by Once in the drainage network, the spatial distribution of carp is likely
example, stone physical barriers and physico-chemical properties of the water column. For
to as 'sills') are or concrete structures protruding above the water (henceforth referred
"1" (e'g' Figs 2'1 and present at the intersection of many lateral d¡ains with Main Drain
water entering 2.2). Although originally constructed to reduce the scouring effects of
Mumrmbidgee Main Drain "J" from lateral drains (B.Power, Senior Water Administrator, forcarp' thus Irrigation, pers. comnì. lgg6),some sills may provide impermeable bariers of food limiting ttreir distribution. Other physical cha¡acteristics, such as the distribution
presence/absence of items (stemberger and Lazorcheck 1994; Uiblein 1995), and the
et 1994) have vegetation (I-eslie and Timmins 1994) and overhead cover (Mikheev al'
parameters such as pH been shown to affect frsh distribution. Similarly, water quality
(Blaber Virgl and McPhail 7994; @inder and Morgan 1995), depth et aI.1994; (gtu. 1995) Scheidegger and Bain 1995), salinity (Dew and Hecht lgg4),temPerature
fish distribution- and dissolved oxygen (Vandamme et aI. t994) have all been linked to
thus the spatial Variabitity of these factors is high in irrigation drains (¿.g. Ha:ris on 1994)'
distribution of carp was expected to reflect this variability.
in the drainage Variability in sediment physicochemical cha¡acteristics and watervelocity
as that by network (see chapter 3) means that the effects of sediment resuspension, such
factors influencing carp, will vary on both spatial and temporal scales. Determination of
to determine their tfre distribution of cary in the Mirrool catchment is therefore necessary
contribution to phosphorus exports from the irrigation drainage network' 20
2.I.2 Objectives
into the 1. To determine the relative contributions of recognised modes of entry for carp
Minool catchment drainage network.
Z. To determine the spatial disribution of carp within the drainage network during an
irrigation season.
2.2 Methods
2.2.1 Site Selection
Twenty-six sites (Fig 2.3), eachT5m in length, were chosen to represent four major
criteria:
1. Distance from Main Drain "J". Half of the sites were chosen within or immediately
the adjacent to the Main Drain ('Main Drain sites'), the remainder separated from
Main Drain by between 400m and 5625m of channel ('lateral sites').
Z. presence of sills and escapes. Seventeen of the twenty-six sites contained both escapes
and sills.
3. Distribution throughout the catchment. Selected sites spanned a range of 10-75km of
channel benveen the most upsu.eam and the most downstream sites'
4. Drainage landuse. Due to farming management practices, different crops produce
different run-off water qualities (see chapter 3) which could affect the distribution of 2t
carp. Sites were therefore selected in citrus, stonefruit, vegetable, rice, pasture and
urban catchments.
2.2.2 Estimation of Fish Abundance
The shallow waters within the drainage network allowed visual estimation of fish abundance from channel ba¡ks. Carp abundance tevas estimated at approximately four- weekly intervals beginning on2017/94. Additional observations were made on4/8194 and
ZOl4lgS during periods of perceived rapid changes in fish numbers. Water temperature and depth, fish size, turbidity and the presence of snags can affect the observation of frsh
(Northcote and Wilkie 1963;Ba¡ker 1988; Jowett 1990; Tierney and Jowett 1990; Hayes and Baird 1gg4), and were therefore recorded. Other factors recorded were time of day, weather, water velocity (three categories; fast, medium, slow), pH and conductivity. Sites were also divided into ttree 25m sections, and carp presence was recorded in each. An example of data sheets taken into the field is presented in Appendix 1.
Initial pilot observations (June 1994) were used to trial and refine data collection methods.
Because this provided an incomplete, and in some cases inconsistent, data set, it was not included in statistical analysis, but does appeü on some of the g¡aphs presented as a sampling at -5 weeks where appropriate.
It was originally planned to calibrate observation estimates with actual ca¡p numbers determined by netting. After consultation with New South Wales Inland Fisheries 22
end of (Narrandera), it was decided that seining to a fyke net anchored at the downstream
total carp abundance in a a site was likely to be the most effective. method of determining
iS inability to caæh all section of drainage channel. Trials of this procedure demonstrated
velocities, and fish because nets could not be anchored to the substrate in high water
channel bank when because it was not possible to adequately follow contours of the
people for seining. Netting was also found to be expensive in time, requiring two probability of approximately 45min per site. These concerns coupled with the high
(and site) characteristics damaging netted fish (Jones Lgg3)and of altering substrate hence
solution' during the seining process resulted in netting being rejected as a possible
esdmatçs, ElecUohshing was also cxamined as a method for calibrating observation
equipment. however it was discarded because it was not possible to attain appropriate
possible' Calibration of observation estimates of carp abundance was thelefore not
observation' The To compensate for this, a measure of 'confidence' was recorded for each
to be applied intention was to use this measure as the basis for a compensatory coefflcient
to raw data to produce a more accurate estimate of carp abundance. 'Confidence'
plesent at a site' represented an objective assessment of the likelihood of observing carp
presenÐ to 10 (alt carp and was ranked between 1 (very little chance of observing any carp
car¡) present were observed). Several combinations of factors (including 'confidence',
study period, obsen¿ed at each sampling, carp observed at each site over the entife
of these variance of carp observed) were trialed as possible coefficients' Application 23
meaningful resuls. The coefficients to raw observation data did not, however, produce
presence/absence of carp, numbcr of corp observed at each site is depencient on both the
not possible to and the probability of observing any carp present- It was therefore
channel using only a determine the number of fish present in a section of drainage
where 'confidence' measure in an environment such as the Mi¡rool catchment" determinants of the presence or absence of carp are largely unknown.
the planned analyses' Other limitations of the observation technique disqualified some of
period, however it For example, carp behaviour was recorded throughout the study
influenced the behaviour became apparent that the pfesence of the observer in some cases
therefore not possible' of fish. Analysis of carp behaviour within the drainage network was
sedimenS Analysis of the effect of carp on turbidity was also disqualified. Carp resuspend
sediments (section 1'5)' through both benthivorous feeding behaviour and movement near Turbidity was It was intended to compare turbidity data from with and without carp.
the channel, thus however a major factor preventing the observation of carp in drainage
analysis was confounded.
2.2.3 Data AnalYsis
catchment were The contributions of recognised modes of entry for carp into the Mirrool
assessed using recorded observations. t4
Differences in the distribution of carp between Main Drain and lateral sites was
determined ¡sing the Mann-Whitney U test. Sites which were not 'habitable' were
excluded from analysis. For the purposes of this study, 'habitable' sites a¡e defined as
were those with at least 10cm water depth, as this was the minimum level in which carp
observed throughout the study. Sites within Main Drain "J" (sites 24,25 and26) were also
excluded from this analysis due to consistently low 'confidence' of observations.
V/ithin site (25m secrion) differences in carp abundance were analysed using Kruskal-
Wallis non-parametric test. Only included in this analysis were sites in which carp were
observed.
SySTAT for'Windows version 5.02 was used for all statistical analyses mentioned above.
physico-chemical attributes of sites (water width, water depth, pH, conductivity, water
temperarure) were examined with Multi-Dimensional Scaling (NDS).Due to limitations
imposed by the statistical package (PRIMER version 4.0), only 250 of the total338
observations could be analysed. All observations from sites within Main Drain "J" were
excluded due to consistently low 'conf,rdence' estimates. Observations with missing data
due to lack of water in drains, or equipment malfunction were also excluded. Eighteen
randomly selected observations were similarly removed from analysis. 25
of a I25xL25 Data were standardised and divided into two groups, to allow calculation
Bray-ctrrtis similarity matrix, the maximum size allowed by PRIMER version 4.0. These
and 'late' goups were formed according to observation date; 'early' Q\nD4 - 17llll94)
(l5t12lg4 - 3tlslgs)in the irrigation season. similarity mafices for each were compared using the RELATE progam within PRIMER.
Data from each similarity matrix were compressed to two axes using the NMDS
The five atgorithm. Each observation was classified according to carp abundance'
analysis of categories (no carp, l-5,6-20,2t-50 and 50+ carp) underwent one-way
related to similarities (ANOSIM) to determine if physical cha¡acteristics of drains were
carp abundance.
2.3 Results
2.3.1, Carp Entry into the Minool Catchment
network, If upstream migration was a significant source of carp to the irrigation drainage
sites carp would f,ust appear in thefabitaUfe inrósi'äownstream sites rather than other ( .''
throughout the network. The average distance of habitable sites from the most
the average downstream site remained relatively constant throughout the study, however
season distance of sites in which carp were observed gradually increased as the irrigation
was a progressed (Fig 2.a).These observations therefore suggest that upstream migration
significant mode of entry for carp into the irrigation network. 26
Determination of the relative importance of carp entry through escapes was complicated because the assumption that sills provided a ba¡rier preventing carp from entering lateral drains was found to be invalid in many circumstances. A series of 185 'jumping' events by juvenile carp (<150mm total length) were recorded in an 80 minute observation period at site 23 on|l2l95 (unpubl. data). Although success rate was low (5.4Vo), it appeared fish were attempting to access waters upstream of the sill (Fig. 2.5). This, coupled with an isolated observation on l5/I2/94 of amore mature carp (approx. 30cm SL) jumping in excess of 1.2m above water level from the base of a sill in the Main Drain, suggests that it is not only possible for carp to gain access to water upstream of sills, but there may also be some behavioural stimulus that elicits jumping behaviour.
Regardless, some situations did occur during the observation period where the only likely
mode of entry of carp into a d¡ain was via escape water. For example, carp were first
observed at site 5 late in the irrigation season (7/4195). Throughout the irrigation season,
water levels were insufficient to allow carp movement between this site and Main Drain
"I'. An escape immediately downstream of the site provided the ponded water in which
carp were observed. The only likely source of these carp was therefore through the
escape.
Similarly, at site 2, movement of carp over the sill from Main Drain "J" to the lateral drain
was unlikely as it required a horizontal jump of approximately 4m. Two carp were 27
observed upsrream of this sill on L9/L0/94 when the escape (approx. 400m upstream) was flowing. Both fish were washed over the sill into the Main Drain (Fig. 2.6)' again indicating that ca¡p enter the drainage network through escapes.
Over-wintering sites were identified prior to reconnection of sites with the remainder of
the drainage nenvork. Three caq) were observed at site 22 dunngthe initial incomplete
sampling onZlílgl.Insufficient water levels and a large concrete structure sepaxated this
site from Main Drain "J", and escapes were not present. Barring the unlikely
anthropogenic addition of carp, these fish must therefore have remained in the channel
throughout the 1994 winter, demonstrating the existence of over-wintering sites inthe
Mirrool catchment.
Each of the three recognised modes of entry were therefore shown to be possible sources
of fish into the drainage network of the Mirrool catchment.
2.3.2 Increasing Carp Abundance Late in the Irrigation Season
The numbers of carp observed increased rapidly during the initial stages of sampling (June
- July 1994; weeks -5 to 0) corresponding to increased \vater depth in Main Drain "J".
Carp numbers increased markedly in March-April 1995 (weeks 38 to 40), before
i decreasing rapidly by May 1995 (week a5) Fig 2.7). Much of the large increase in carp ""'
numbers towards the end of the sampling period was due to an increase in the smallest size
class (<150mm) of fish (Fig.2.8). 28
2.3.3 Spatial Distribution of Carp
the status The total number of carp observed at each site over the entire study period, and
2'1' of each site as either a Main Drain or lateral site is presented in Table
Tabte 2.1: Totat carp observed at each site throughout the study period
Site Number CarP Observed (M)ain Drain or site 20 520 M 19 348 M 23 111 M 18 73 M T7 54 L 2l 35 L l1 18 M )) 16 L 25 15 M 16 11 L 15 7 L 4 5 M 12 5 L 5 4 L 6 4 L 8 J M 2 ') M 7 2 M 13 2 L
1 0 M 3 0 M 9 0 L 10 0 L t4 0 L 24 0 M 26 0 M TOTAL 1235 29
lateral sites (Mann-Whitney Significantly more carp were observed in Main Drain than in
U = 8750; P < 0.001) (Fig 2.9).
were significant (Kruskal- Within site differences in carp abundance be¡veen 25m sections
in downstream thirds Watlis test statisti c =34.49,P < 0.001). More calp were observed than in both upstream and middte thirds (Fig' 2'10)'
not found to be similarity matrices from 'early' and 'late' in the irrigation season were
The results of significantly different (Global RHO = -0.034, significance level =72.67o).
sets of physicechemical data are the MDS (99 iterations, minimum stress = 0.02) for both
not separate any presented with respect to carp abundance in Figure 2.11' ANOSM did
characteristics of sites of the carp abundance categories on the basis of physico-chemical
late data (Global R = - for both 'early' (Gtobal R = -0.176, signif,tcance level =99'9Vo) a¡d
0. 106, signifrcance level = 97 .97o)-
2.4 Discussion
2.4.1 Temporal Variation in Carp Abundance
of total Limitations of the observation technique used in this study preclude estimation
the increases in carp carp abundance in the Mi:rool catchment. Large scale Íends, such as
weeks -5 to 0) and numbers at the onset of the irrigation season (June to August 1994;
in carp later in March to April 1995 (weeks 33 to 40) and also the large reduction
however apparent' numbers between April and May 1995 (weeks 40 and 45), were 30
Observations suggest that upstream mipgation, escapes and over-wintering sites a¡e all sources contibuting to the influx of carp at the beginning of the irrigation season.
However, only one site was identified as an over-wintering location, and other
are observations throughout the catchment failed to identify others. Over-wintering sites therefore not likely to make a signifrcant contribution to the influx of carp at the beginning of the irrigation season.
Two other possible modes of carp entry into the drainage network were identified during
the course of this studY:
1. Anthropogenic introduction. Carp have been usecl as a bait fish by anglers (J-Harris
1995). However, carp account for approximately 99Vo of all frsh in the Mirrool
catchment (M.Fuchs, electrofrsher' pers. comm. 1995) and are not thought to be
piscivorous (Weatherly and Lake 1967; Lammens and Hoogenboezem 1991). The use
is of carp as bait therefore seems an unlikely source of anthropogenic introduction. It
possible that anth¡opogenic introduction may occur in some catchments to increase
food fish stocks, or to reduce unwanted vegetation. However, the large number of
carp already presenr in the drains also reduces the likeiihood of this possibility.
2. Recruitment. Female carp can produce between 13,500 and 3,000,000 eggs in one
spawning season (Cadwallader and Backhouse 1983), thus the recruiünent ofjuvenile
fish has the potential to greatly increase carp numbers. Carp require water
temperatures of 17-25oC to spawn (Merrick and Schmida 1984; Brown 1996)' 3r
Backhouse although threshold temperature may be as low as 14oC (Cadwallader and
1983). Spawning usually occlrrs in shallow (<0.5m depth) waters' and demersal,
(Cadwallader adhesive eggs anach to substrates provided by aquatic plants and rocks
at and Back*rouse 1983; Merrick and Schmida 1984). Average water temperatures
and sites used in this study were conducive to spawning in the months of September
and October in1994 (weeks 8 and 13), and later in the irrigation season in February
<0.5m April 1995 (weeks 29 and¿O; Fig. 2.12). Similarly, average water depth was
throughout the study period (Fig.2.7), and was therefore conducive to spawning'
Furthermore, aquatic plants and/or rocky substrates required by carp as a spawning
habitat are present in d¡ains throughout the network'
The drainage network therefore provides a habitat ideally suited to carp reproduction.
This, combined with personal observations of ca¡p spawning behaviour on26l9/94' and
(weeks and 40; the large number of juvenile (<150mm) carp observed in Aprit 1995 38
this Fig. 2.8), suggests that recruitrnent within the drainage network is occurring, and that is the likely cause of the large increase in carp numbers observed late in the irrigation season.
In contrast to the influx of carp at the beginning of the irrigation season, a large decrease in carp numbers occurred beween April and May 1995 (weeks 40 and 45).It was
to a apparent in the off-season of 1995, as in 1994, water levels in most drains decreased 32
which carp exit level insufficient for carp. In contrast to the modes of entry, pathways by
identified: the drainage network m¡st therefore exist. Two possibilities were
drainage network 1. Downstream migration. The same pathway by which carp enter the
more peÍnanent through upstream migration may also be used by carp to move to the
waters of Mirool creek, willow dam and Ba:renbox swamp.
2. Mortality. Carp mortality results from both anthfopogenic activity and natural both processes in the Mirrool catchment. These include; frshing (carp are frshed
herbicide (acrolein) commercially and for individual consumption); natural causes; and
do not, used to control unwanted vegetation in drains. These causes of mortality
can however, have an increased effect near the end of an inigation season' and
and May thereforc not explain the observed reduction in carp numbers between April
an 1995. Altemately, receding water levels characteristic of the end of irrigation
mortality would season may have isolated some fish in ponded water. An increase in
likely result by either stranding carp when drains d¡ied, or increasing their
susceptibility to predation by waterbirds such as corrnorants and pelicans'
on the Temporal variation in carp abundance in the Mirrool catchment is largely dependent
modes of entry and eút enury and exit of fish at various times during the year. The likely
discussed above are summarised in Figure 2'13' 33
2.4.2 Spatial Distribution of Carp
Results from both MDS and ANOSIM indicated carp abundance was not related to the physicechemical characteristics of the sites in which they were observed. The greater number of fish in Main Drain sites than in lateral sites is therefore the likely result of the position of sites in relation to Main Drain "J".
'Water within Main Drain "J" is generally deeper and more turbid that that within lateral
drains (pers. obs.). Main Drain "J" \ryaters may therefore provide a refuge for carp from
perceived predators, such as waterbirds, humans and (possibly) foxes. Observations made
during the sampling period of a tendency for carp in sites adjacent to Main Drain "J" to
move quickly downstream when disturbed, suppofi this explanation. Carp are also capable
of feeding using visual stimuli (Lammens and Hoogenboezem 7991; Sibbing 1991) and the
rwater efficiency of this feeding mode is likely to be enhanced in the less turbid of lateral
drains. The junction of Main Drain "J" and lateral drains therefore provides environments
conducive to both predator evasion and feeding.
Additionally, carp are reported to favour slower flowing waters (Brown 1996)' however
faster flowing waters facilitate greater diffusion of oxygen ttrrough the gills (Moss 1988).
The junction of relatively slow flowing lateral drains with the faster flowing water of Main
Drain "J" provide a habitat in which both behavioural preferences can be satisfied- 34
32oC (Cadwallader Carp are also reported to prefer water temperatures between 15 and and Backhouse 1983; Merrick and Schmicla 1984) with an 'optimum'preferred
"J" and adjacent temperature of 25oC (Cadwallader and Backhouse 1983). Main Drain
period, with the lateral drain water temperatures differed slightly throughout the study
move between areas latter gener alry 2-3oc\ilarmer (e.g. Fig. z.r4). The ability ro readily
the junction of of d,ifferent temperatures may also explain the apparent preferences for
Main Drain "J" and lateral drains.
ideally suited The behavioural preferences of carp reported in the literature are therefore
drains. This' coupled to the habitat provided by the junction of Main Drain "J" with lateral
third of sites (i¿' with the significantly grearer number of carp observed in the downstream
of physico- closest to their junction with Main Drain "J"), suggests that the variability
drains is the likely chemical cha¡acteristics at the junction of Main Drain "J" with lateral
cause of the larger number of carp observed at Main Drain sites.
2.4.3 Conclusions
(July - August) The increasing numbers of carp at ths beginning of the irrigation season
carp numbers at and later in the season (March - April) coupled with a large reduction in
temporal the end of an irrigation season (April - May) were the major causes of high
entry variability in this study. The observed initial increase in carp numbers was due to the
waters' entry of carp into the catchment via upstream migration from more perrnanent
through escapes, and to a lesser extent from reconnection of permanent over-wintering 35
increase in carp numbers late in the sites already present in the catchment. The observed fish' many of which irrigation season was primarily due to an increase in young-of-the-year
eallier in the irrigation were the likely result of spawning behaviour observed in d¡ains
the irrigation season is likely due season. The large reduction in carp numbers at the end of mortality resulting from the to downstream migration of carp to more pennanent waters,
predation by waterbirds on ca4) stranding of carp as water levels fall, and from increased
''', ' '' I ,, isolatedinshallowwater. '-' ,ii..i i .i ,,.1
intersection of lateral drains Spatially, carp distribution appears concentrated around the
velocity and temperature at with Main Drain "J". The variability of water depth, turbidity,
preferences of carp rhese intcrsections provides a habitat conducive to the behaviotlral
reported in the literature. 36
asills' and Mnin Drain Figures 2.1 anel 2"2: at the interseetion of l¿-tteral ttrains "J"
I ll'"
il
38
from most Figure 2.4: [verage distance of sites in which carp were observed downstream site throughout the study period (with standard error bars)
E o ! CD 6000 qtE Lo cCD 5000 oo= oE 4000 E o L 3000 @ CD o-o 2000 t-o oqt o () 1 000 (úc ct, o o (¡o qt g o 20 30 40 50 @ 10 Weeks Slnce SamPllng EÞgan 39 t Ðrâin Figure 2.5: CarP jumPing Ívsill at the intersection of'site 23 and Main "J"
..-*." *ff- * .âc.v.#i.;'
. "'I
Figtrre 2.6: Carp being lvashcd t)vcr {ì sil! at site 2 40
Figure 2.7zTotal number of carp observed and water depth throughout the studY Per¡od
400 No. of Observed
300 Average\r, Site Depth (run) a a-\ 200 ? V t o 100 J
o -5 5152535 45 Weeks Slnce Sampllng Began 4t
Figure 2.8: Size class of observed fish throughout the study period
300
Do 2c/0 (D dt o-o o 6 O o 1 oo zö Nl >450mm E 3OO-4.50mm I 150-300mm <150mm o E .6 O 2 1 I fS 17 21 26 29 93 38 ¡¡¡¡ ¡5 Weeks Since SamPling EÞgance 42
Figure 2.9:Totalnumber of carp observed in lateral and Main Drain sites throughout the studY Period
400
300 f,o o o, o-o o 200 o6 o zct 100
Nl Maln Draln sltes o I Lateral sltes o 2 4 I 1317212625 3{t38æÆ Weeks Slnce Sampllng Began 43
Figure 2.10: Total number of carp in 25m sections of sites throughout the study perÍod
800
700
ô00 Þo og ø, 500 o-o o 400 od bo 300 zö 200
100
0 Downstream Middle UPstream 25m Sectlon 4
Figure 2.11: Multi-Dimensional Scaling (MDS) representation of observation sites characterised according to carp abundance
2
a 1 a a c\l a a "a A o å¡" o 6 "." å AA TL aA af o a a a A AB a a & A e ¡A A e a A 8¿
-1 -4 -3 -2 -1 0 1 2 3 4 Factor (1)
(early' Lower case in irrigation season = (late' Upper case = in irrigation season
A,a = no carp observed at site B,b = 1-5 carp observed at site Crc = 6-20 carp observed at site D,d = 21-50 carp observed at site Ere = 50+ carp observed at site 45
Figure 2.12: Average water temperature of observation sites (with standard error bars)
40
30 o t-o f d (D o- 20 E t-o ot- d 3 10
o o 2 4 I 1317212629 333840 46 Weeks Since Sampling Began Figure 2.132 Sources of temporal variation in carp abundance in the drainage network
Recruitment Upstream
Downstream Carp in Drainage Entry Through Escapes Network Increased Motality due to Receding Water Iævels
Over-wintering Sites Mortality due to fishing, natural causes, acrolein use, and Predation
AprilMay Sept/Oct 5 Irrigation Season o\ 47
Figure Z.1,4z'Vlater temperatures in lateral drain (site 19) and in adjacent Main Drain "J" (site 26) l
ì
I 1
ì
I &
I
I
I
I 630 A (D P\/ ) 6 8zo E o I v\ (D / I 310qt
Slte 2ô 0 o 9182736 45 Weeks Slnce SamPllng EÞgan 48
Chapter 3: Spatio-temporal Distribution of Sedimentary Phosphorus in the Mirrool Catchment
3.1 Introduction
3.1.1 Background
The phosphorus content of sediments is detennined by the complex interaction of a large number of sediment and water characteristics. These are summarised in Table 3-1.
In the Mirrool catchment, a suite of these cha¡acteristics may be determined by the managenrent practices imposed by different landuses. For example, cropspecific applications of fertilisers and other chemicals can affect sedimentary phosphorus by direct input of phosphorus, and indirectly by alærations of sediment sorptive capacity induced by iron, sulphur and other elemen¡s. $imil¿¡ty, the volume, velocity and chemistry of drainage water at any point depend upon catchment area" so that location along the drain is a fr¡rther source of spatial variation.
Small-scale æmporal variæion (months to years) in phosphonrs exports from lotic waters is primarily a result of stomr events (Chittleborough 1983; Maher 1Ð3; Smalls and Preece
1993; Donnelly et al.l994; Ha¡ris 1995). For example, Cullen (1995) demonstrated that
6lfto ofthe annual total phosphorus exported from a small carchment occurred tn l%o of the time. Water velocity and turbulence following heavy rainfall cause resuspension and 49
Table 3.1: Factors Affecting Sedimentary Phosphon¡s Concentration
Factor Process affectin g SedimentarY Reference Concentration 1975 Geochemical Variability of geochemical composition Holford & Maningty et al. I98l composition þarticularty Fe, Al, Mn, Ca, CO¡) affects Sharpley of sediment the numberof phosphorus adsorption Bostrom et aI.1982 and water sites, and the attraction of phosphorus to Logan 1982 these sites. Goltemran 1984 Enell & Lofgren 1988 Shaw&Prepas 1990 Driscoll et aI. L993 Fox 1993 Olila & Reddy 1993 Popovich 1993
Redox Reducing conditions facilitate the release Mortimer 1942 potential of Fe boundphosphorus from sediment to Holdren & Arrrstrong 1980 the water column. Golterman 1984 Shaw & Prepas 1990 Redox also affects the storage and release Gachter & Meyer 1993 of phosphorus from bacteria in sediment Lijklema 1993 by a variety of comPlex PathwaYs. Ohlaet al.1995 Baldwin & Mitchelt 1996
pH pHhas avariety of effects sedimentary Bostrom et al.1982 phosphorus dependent on geochemical Golterman 1984 composition of sediments. Generally, alærs Enell & Lofgren 1988 charges on sediment particles, thus Driscoll et aI.L993 affecting phosphorus Kleeberg & Schlungbaum 1993 adsorptiory'desorption. Lijklema 1993
External Phosphonrs concentration in the water Taylor & Kunishi 1971 loading column drives the equilibrium phosphorus Logan 1982 Golterman 1984 þhosphorus concentration of sedimenl concentration Olila & Reddy 1993 in water Portielje & Lijklema 1993 column)
Organic Is a source of phosphorus in sediments. Hartet aI.1976 content of Also, humic substances coat s€dinrent Enell & Lofgren 1988 1993 sediments particles neutalising charges on clay Eckerrot & Pettersson minerals, thus decreasing available Popovich 1993 phosphonrs adsorption siæs. See also 'Mineralisation of organic matter'. 50
Pettersson 1993 Mineralisation Mineralisation dePleæs oxygen in Eckerrot & & Sctrlungbaum 1993 of organic s€diment, thus affecting redox potential. Kleeberg 1993 rnattcr See 'Redox potontial'. Lijklema Slomp et al. t993
1993 Bacterial Effect on sedimentarY PhosPhorus 1S Davelaar & Prarie 1993 abundance and dependent on type ofbacteria redox de Montigny Pettersson 1993 activity condiúons and geochemical composition Eckerrot & 1993 of sedirnents. Gachter & Meyer Bacteria can transfer phosphorus directly Baldwin & Mirchell 1996 from sediment organic matter to the water column, catalyse iron-hydroxide reduction, and produce refractory PhosPhonrs compounds.
& Armstrong 1980 Sediment Alærs the concentration gradient between Holdren et al.1982 distr¡rbance sedi¡nent and water column, thus affecting Bostrom 1988 (e.9. the flux of phosphonrs between the t'wo Enell & Iofgren bioturbation, compaftrnents gas ebullition, turbulence)
Sediment Pa¡ticle size is generally inversely Jins 1959 1968 particle size proportional to surface area' and therefore Hartner affects the availability of phosphorus Stone & English 1Ð3 adsorption sites.
Amrst¡ong 1980 Temperature Increasin g temperature increases bacterial Holdren & 1993 activity. See 'Bacterial abundance and Eckerrot & Pettersson activity'.
Sulphide Sulphide binds to Fe, thus decreasing Ca¡aco etaI.1993 et al.1993 concentration available sites for phosphorus adsorption. Driscoll
1993 Sediment Sediment deposition alters the Lijklema deposition rate concentration gradient benryeen sediment and water column, thus affecting flux between the two comPonents.
Nitrate Can act to increase redox potential, thus Bostrom et al.1982 concentration decreasing phosphonrs flux from sediment' orcan enhance microbial mineralisation of organic matter, decreasing redox and thus increasing phosphonrs flux from sediment 5r mobilisation of particulate phosphonrs from bottr the catchment and in-channel sedirnents
(Cullen 1986; Pickup 1986). In the Mirrool catchment, as in natural systems, the major
sor¡rce of temporal variation is likely to be lvater velocity. Again stonn events are
important, whilst seasonal and daily demands for water by irrigators increase flow
variability.
Due to the diversity of landuses, rnanagement practices and water velocities, it was
therefore anticipated that sedimentary total phosphorus concentrations within the Mirrool
catchment would be highly va¡iable, both spatially and æmporally.
3.1.2 Objectives,
Objective 1: To determine the spatial and temporal distribution of sedimentary total
phosphorus in sub-catchments of the MiÍool catchmenl
Objective 2:To identify predictors (i¿.landuse, length of upstnearn drainage) of
sedimentary total phosphorus levels in the drainage network, allowing
extrapolations to areas that were not sampled. 52
3.2 Methods
3.2.L Site Selection
rice, citn¡s, The major cropping landuses in ttre Mirrool catchment are winter cereals,
grouped into three categories that sha¡ed Sôpes, pasture and vegetables. These were regimes) and/or similar management practices (e.g. fertiliser applications and waæring
receive geogfaphic proximity. Pe¡manent mixed plantings of citn¡s trees a¡rd gape vines
category. Alttrough similar waæring regimes, and were grouped as a "citrusÁ¡ines" landuse
to farrring methods for rice and pasturre are quite different, many rice bays are cultivated
supply gfanngs6ck wittr pasture during the off season. These crops were therefore
was "urban", combinedin a "rice/pÀsture" landuse category. The third landuse category
including d¡ains that receive run-off from the city of Griffith.
ground level' The landuse composition of suÞcatchments was deærmined by inspection at
70Vo of Sub-catchments \vere assigned to a landuse category if they contained a minimum
than/O%o oî' the landuses identified in that category. SuÞcatchments containing less
irdividual landuses identifred were omined.
of the The length of upstream drainage at any point wittrin a sub-carchment is indicative
of 1, 2, 4-5 area of land draining into the system above that poinr Four discrete categories
across and 7-g kilometres of upstream channel provided the only replicable combinæion
"bottom" of all landuse cæegories. The option of sampling fr,om the "top", "middle" and
subcatchments tvas disregarded as it often misrepresented the catchment a¡ea above 53
loads flowing sampling poinS, possibly affecting watef velocity and Otal phosphonrs down the sysæm.
(n distance Fourreplicate sites were identified for each combination of landuse = 3) and
48 sample siæs class of upstream drainage (n = 4) in an orthogonal design comprising from 12 different sub-catchments.
3.2.2 Sampling Procedure
(Frg' 3'1)' Cores Sediment was sampled using a perspex sediment corer of 75rrm diameter
that might easily be comprised only the topmost 5cm of sediment, to represent the zone resuspended by carp.
and again Sites were sampted fi¡st in June 1994 before the irrigation season commenced,
were taken fr'om in December, dgring the irrigation season. In addition, sediment sarrples
the V/arburn Rdft{ain a fr¡rther 17 siæs at lkm intervals along Main Dfain "J", between
,,J,, not be re- Drain and the l.¿wrence Rd/lv[ain Dr¿in ''J'' intersecúons. These sites could
Dr¿in "J" at that sampled in December due to prohibitive water depth and velocity in Main
lme
collected) Temperature and pH (sampled at mid-water column above the sediment to b
of the were measured using a YEW model PH5l pocket pH metef. Conductivity
Other overlyrng \ilater was collected with an EC-TDScan 4 (range 0 - 19'9 mscml)' v nreasurements included \ilater column depth and width, percentage vegetation cover and turbidity.
3.2.3 Sediment and Sample Site Analysis
Sediments were analysed for total phosphorus, organic matter and face element content.
All samples \ilere oven dried at 105oC for 24 houts, then gtound to a ma,ximum particle
size of 2mm. For total phosphorus, ground sediment (0.5 t 0.005g) was digested with hot
sulphuric acid and selenium catalyst (3.6m1). Sarnples were then rehydrated to 75ml total
volume and thoroughly mixed. The supernatant of digested material underwent
molyMenum/antimony colourimetric analysis to determine total phosphorus (Tecator FIA
method ASTN 23185).
Samples from categories with significantly different sedimentary total phosphorus
concentrations were also analysed for organic matter content, estimaæd by the ash-free
dry weight (AFDW) of samples ashed at 550oC for 4 hou¡s in a muffle furnace, following
Aloi (1990).
Watervelocity was estimated by timing a floating orange over a minimum distance o12m
three times at each site. Velocity was calculated by multiplying the three-run average by
0.85 to account for channel roughness (Gordon et ø1. 1992). This method was used due to
the low sensitivity a¡rd adverse effects of high suspended sediment loads on a propeller-
driven flow meter which required continual cleaning and was not time-effective. 55
CaO, Fe2O3'þO' Sediment trace elementcontent (expressed in oxidised fomU Al2O3,
Mgo, Mn3o4, Na2o, P2o5, So3, Sio2, Tio/ was determined by X.Ray Fluorescence
could be processed, 28 sarrples spectromeûry CXRF). As only a limited nr¡mber of samples
fu¡tlrer ground in a were selected from the June sampling. FoTXRF analysis, samples were
(0'3S + was mixed tungsten mill and dried overnight at 105'C. Ground sample 0'005g)
4O0oC for 10 minutes with 1.8759 of flux and 5rnl UNq. This mixnne lvas oven d¡ied at
pelletised' before being placed in a furnace at l050oQ for 20 minuæs and finally
were Total phosphorus, organic matter and watervelocity data from the 48 selected sites
analysedwere all analysed using model l, 3-way analysis of va¡iance (ANOVA). F'actors
SYSTAT for fixed factors, being landuse, length of upstneam drainage and sampling date'
and watef Windows version 5.02 was used O analyse all total phosphorus, organic matter
velocity data.
data XRF data were analysed using multi-dimensional scaling (MDS). Standa¡dised
were exltfessed as underwent 4ttr root transformation befqe simila¡ities be¡peen samples
using ttre NMDS a Bray-Curtis similarity maUix. Data were compressed to two axes
algorithm. One-way analysis of simila¡ities (ANOSM) and similarity percentages
(SIMPER) analyses were also employed. All )(f,F data were analysed with Plyrnouth
Routines in Multiva¡iate Ecological Resea¡ch (PRIMER) version 4'0' 56
3.3 Results
3.3.1 Total Phosphorus
Cochran's test showed raw total phosphorus data to be heteroscedastic (C1*r") = 0.31@;
transformation (C1."r") Cç,u w.osl = 0.1907; P < 0.01), but only marginally so after log =
for by setting cr to 0.04 0.192L; C1t,u ua.osl = 0.1907; P = 0.048). This was compensated
for interpretation of ANOVA results (see Underwood 1981)'
Three-way ANOVA revealed significant differences in sedimcntary total phosphorus Ð( concentrations due to landuse (P = 0.013), length
sampling daæ (P < 0.001), but with no significant
sedimentary total phosphorus concentrations in
(mean 0.520mg.g-tDVy', SE = 0.049) to be greater than rice/pasture sub-catchments =
(rnean 0.335mg.g-tDVy', SE = 0.024) (p = 0.002). Citn¡Vvines sub-catchments =
riceþasture or 0.0.4gmg.g-t DW, SE = 0.036) were not significantly different from either
urban sub-catchments (Fig 3.2). Sites wittr 1 km of upstream drainage contained
significantly greater sedimentary total phosphorus (mean = 0.503mg.gt DW, SE = 0.059)
2 than those with 7-9 kn (mean = 0.319mg.g-t DV/, SE = 0.033) (P = 0.018). Sites with
and 4-5 lon of upsEeam drainage were not significantly different from any other category
(Fig 3.3). Sedirnents sampled in June (mean = 0.491mg.gt DV/, SE = 0.030 ) had greater 57 sedimentary total phosphorus concentrations than those sampled in December (mean =
0.349mg,rlDlV, SE = 0.032) (Frg 3.4).
3.3.2 Organic Content
Because samples analysed for organic rnattef content were selected according to the observed differences in sedimentary total phosphonrs, three t-tests were used to analyse the d¿ta.
The F-ratio æst comparing sites with 1 and 7km of upstream drainage showed data to be homoscedastic (F1c+.m, s,sl= 7.15, F"d"= z.Aq. Sediments from sites with 1km of upstreart drainage had significantly grcater fimounts of organic matter (mean = 7-0omg.g-r of sediment DW, SE = 0.37) than those \ilith 7km of upstream drainage (mean = 4.64g-kgr of sedimenrDW, SE = 0.53) (P=0.005)(Fig. 3.5). Data from ricelpasnue and urban catchments was also homoscedastic (F,r+.os 4'82,F"¡"= t'62)' Sarnples from '5,s= rice/pasture catchments contained significantly gfeater anrounts of organic matter (nrear¡ =
7.03g.kg-1 of sediment DW, SE = 0.48) than those from urban siæs (mean = 5.13g-kg'1 of sedimenr DW, SE =0.74) (P=0.041)(Fig. 3.6). The F-raúo test showed data from the two sampling dates also to be hornoscedastic (F1o+.os,r,al= 4.36,F".¡"= 1.70). No
significant difference in sedimentary organic content was found benreen the sampling
dates (June sampling nrean = 5.70g.kgr of sedirnent DW, SE = 0.63; December sarrrpling
mean = 6.35g.kgr of sedimentD'W, SE = 0.51)(P=0.433XFi8.3.7). 58
3.3.3 Trace Element Content
the basis MDS of XRF data (pp iterations, minimum stress = 0.09) separated samples on
(Fig ANOSM of landuse (Fig 3.S) but not length of upstrearn drainage 3'9)' One-way of pairwise comparisons showed significant differences in the trace element composition
(P and rice/pasture sediments from riceþasnre vs citn¡sÁ¡ines subcatchrnents = 0.001),
}\'ere found be¡veen vs urban sub-catchments (P < 0.001). No significant differences
length citruvvines and urban suÞcarchments or ben¡'een any of the upstream drainage
were categories. SIMPER analysis showed the major sources of average similarity
AlzO¡ and consistent for each parwise comparison of landuse categories, being SiO2,
dissimilarity were also consistent Fe2O3 Clable 3.2). Tlrcthree major sources of average
for all pairwise comparisons, being cao, So¡ and Sioz (table 3.3).
3.3.4 'Water VelocitY
0'1907; P > Raw watervelocity data were homoscedastic (Ctor"t =0.L667; Cç,a a.a.osl =
differences 0.05) and were thus not transformed. Three-way ANOVA revealed signifrcant
(P No due to length of upstream drainage (P < 0.001) and sampling date = 0'013)'
water velocity to signifrcant differences due to landuse were found. Tukey's test showed
SE 0'026 be greater at sites u¡ith 7-9 1on of upstream drainage (mean = 0.160m-sec-t, = )
SE 0.014, P < than with both 1 and2kn of upsüìeam drainage (mean = 0.029rnsec-t, =
and no significant 0.001; and mean = 0.042m.sect, SE = 0.019, P = 0.001 respectivelY)
water velocities (rnean difference between any other pairwise comparison (Fig. 3.10). June 59
lower than those in December (mean = = g.g5grnsec", SE = 0.011) were significantly
0.108nsec-t, SE = 0.019) (Frg 3.11).
phosphonrs showed a A Pearson correlation of watervelocity to sedimentary total
significant negative correlation (Pearsonr = -0.398, P < 0.001).
groups Tabte 3.2: SIMPER analysis of similarity within landuse
Urban Rice/Pasture Citrudvine *cotttr. +cdttr llcr¡nul R¡¡rk rcmù. llsr¡nul R¡nk #ctmrul (%) (7o) (%) (%) (%, (s.) 2t.9r 2t.91 sio2 I 23.08 23.08 I 22.87 22.87 | 14.59 37.6 2 14.18 36.æ AIzOc 2 15.22 3E.30 2 10.82 48.28 3 11.19 47.28 FezO¡ 3 12.r0 50.39 3 8.66 55.94 KzO 4 8.83 59.22 5 8.63 56.91 5 7.86 63.80 Mgo 5 8.15 67.37 6 8.09 65.00 6 10.65 75.65 4 9.21 73.00 CaO 6 7;14 75.11 4 7.15 82.79 7 6.99 79.99 T¡O2 7 7.45 82.57 7 5.31 88.10 8 6.00 85.99 NazO 8 5.38 87.95 8 4.29 92.39 9 5.92 91.91 PzOs 9 4.r8 92.t3 9 4.t3 96.53 10 4.6t 96.52 SO¡ l0 4.01 96.r4 l0 100.0 11 3.48 1m.0 Mn3Oa ll 3.86 100.0 11 3.47 elemear ro tconr. = indivió¡¡l cqrtrihnion of of oxidiscd clc¡ncn¡o ovøell låq¡mul = cr¡nul¡rive com¡itxnion 60
landuse groups Table 3.3: SIMPER analysis of dissimilarity between
RiceFasture vs RicelPasture vs Urlnn vs
*cqrtr. Rånk +conts. lkr¡nul #crrnul (9o) (%\ 19.45 19.45 I 29.58 29.58 I u.v ztt.y I CaO 37.58 45.32 2 20.81 45.r5 2 18.13 SOg 2 15.74 v.97 3 10.53 48.11 sio2 3 9.22 fl.v 3 9.82 8 5.n ffi.37 7 1.87 55.98 FezO¡ 4 8.82 63.36 69.38 4 9.74 65.72 AlzO¡ 5 8.28 7r.& 4 9.01 5 8.16 77.y 5 9.8 74.81 NazO 6 7.10 78.74 6 8.31 83.12 Mgo 7 5.96 84.70 7 5.91 83.45 6 6.67 90.r2 8 5.78 88.90 PzOs I 4.36 89.06 l0 3.38 93.50 l0 3.4 92.y MnrO¿ 9 3.94 93.01 1l 2.78 95.t2 Kzo r0 3.50 !)6.51 ll 3.VI 96.57 4.88 100.0 11 3.49 100.0 9 3.43 100.0 9 of ele¡nerto gror¡p of oxidised cleme¡rt o overall similadtY llo¡mul = cr¡nrul¡¡ive codrihfion
3.4 Discussion
3.4.L Landuse
were found in urban suþ. Higher concentrations of sedimentary Otal phosphorus
of water velocity data showed no catchments than in riceþasture subcarchmens. Analysis
account for obse.¡ed differences in difference due to landuse, thus water velocity does not
are therefore likely due to the landuse drainage sedimentary phosphorus. These differences
and/or the phosphonts variety of inputs into drains associated with different landuses,
sorption capacity of the sedimens'
likely to be lower than other Phosphorus inputs into riceþasture subcatchments are
no additional phosphorus through landuses in the catchment. Rice crops generally receive 61
fertilisation, as nitr,ogen is the major nutrient limiting growth (Heenan and Sykes 1984).
Pastures do receive fertiliser phosphorus, but again, the application rate is generally lower than for many other crops (Harrison 1994). Alærnaæly, r¡rban subcatchments deliver relatively high levels of phosphorus to drainage u,ater (Lambert L993;Dowrelly et al.
L994). Practices in the Minoot catchment such as the dumping of lawn clippings into the drainage systern, the use of deærgents and lawn and garden fertilisers, and road run-off possibly combine to produce high levels of phosphorus in run-off lvater.
Although direct comparison of inputs from urban and riceþastu¡e suÞcatchments is not possible in this study, it is likety that greater phosphorus loads enter the drainage channels of urhan suþcatchments. Adsorption of this phosphorus onto sediments would explain the observed differences in sedimentary total phosphorus berween urban and riceþasture sut> catchments.
Of perhaps gxeater importance however, is the adsorbtive/desorbtive capacity of sediment, which is determined largely by the trace element composition of sediments (Shaw and
Prepas 1990; Olila and Reddy L993). XRF revealed that compounds contributing most to trace element dissimilarity benveen urban and riceþastr¡re sediments lvere calcium oxide
(24.3Vo) and sulphite (2O.8Vo), bottr of which are in greater levels in urban subcaæhments
(Figs 3.12 and 3.13).
Calcium is among a group of elernents, including i¡on, aluminium and manganese, responsible for the transformation of phosphorus from the aqueous to the sedimentary 62
1990; Olila and Reddy L993; Rutænberg phase @nell and Lofgren 1988; Shaw and Prepas
sedinrents and the 1993). Phosphate bonds with these mçtals, resulting in attachrnent to
Reddy 1993)' Such possible formation of minerals @nell and Lofgren 1988; Olila and
phase (Olila phosphorus becornes insolube, and is therefore imrnobilis€d in the sediment and Reddy 1993) increasing sedimentary total phosphonrs concentrations'
phosphorus There is debate in the literature about the role of sulphtu in sediment
(e'8' FeSO¿, CaSO4) is dynamics. The microbial reduction of sulphate compounds
such as calcium' i¡on, considered an important mechanism in the mobilisation of metals
their reaction with aluminium and manganese (Myers and Nealson 1994). This facilitates
capacity of phosphate, and so has the potential to increase the phosphcrus sorption
(Boers et aI.1993; My€rs sediments and the concentrarion of insoluble metal phosphates
(¿.8'HzS, FeS) are thought to inhibit and Nealson lgg4).Alternately, sulphide compounds
(Caraco 1993)' This may be the adsorptive capacity of sediments for phosphorus et al'
attachment sites' the explained by the preferential binding of sulphu to phosphorus
the oxidation of displacement of phosphorus att¿ched to sediment by sulphur, and/or
Freshwater Research sulphur to sulphate (D.Baldwin, resea¡ch scientist, Murray-Darling
and sulphide centre, p€rs. comm. 195). It is, however, not possible to detemrine sulphaæ
to sulphide during concentrations in XRF samples due to the transformation of all sulphur
in the rnodiFrcation of sample preparation. conclusions regarding the role of sulphu
ascertained in this study' sedimentary total phosphorus concentrations can therefore not be 63
The cause of greater concentrations of calcium and sulphur in urban sediments is unknown. Possible explanations include the greaær application of fertilisers (which contain- ,'I ¿o both elements in varying concentrations) and rypsum (CaSO4), or a natural deficiency of calcium and sulphur in ttre heavy soils required for rice. Whatever the reason, the greater levels of calcium (and perhaps sulphate sulphur) in urban sediments allows for greater adsorption of phosphorus frcm overlying llraters. This, coupled v¡ith higherphosphonts concentrations in urban input water, rnay erylain the differences in urban and riceþasture sedimentary total phosphorus in the Mirrool catchmenL
3.4.2 I-ength of Upstream Drainage
No consistent differences wet€ observed in trace element concentration of sediments with respect to length of upstream drainage. The maæhing of significant differences in
sed.imentary total phosphorus to watervelocity (lkm upsneam drainage mean sedimentary
total phosphorus = 0.503mg.g-t DV/, mean watervelociqr = 0.029m.sec-t;7-9lan
upstream drainage mean sedimentary toal phosphorus= 0.319mg.9t DVy', mean water
velocity = 0.160¡nsec¡¡ implicares \ilatervelocity as the rnajor modifier of sedimentary
total phosphorus with respect to length of upstream drainage.
High water velocities are inimical to many plants and animals (Nowell and Jumars 1984;
Begon et al.l99O: Smith 1992; Walker et al. t992). Phosphorus is present in all
organisms, and the decomposition of organic material provides a direct sor¡rce of
phosphorus to sediments. Decomposition also provides oxidants which facilitaæ the
adsorption and precipitation of phosphorus into ttre sediment phase (Ruttenberg 1993: æ
i\\.,r' excluding ttre biotic component of the Myers and NealsonLgg4).'Watervelocities ,-) . i.,.'t" ..., _."!.' .,," ; 1,': phosphorus likely to cause reduced concentrations of phosphonrs in ll cycle arç therefore ' if. \ t..t r.,' the sediment- This point is illustrated by the significantly higher levels of organic matter found in sites with t hn of upstreâm drainage in comparison with siæs with 7Im of upstream drainage.
Water velocity also govems the particle size of sediments. Sediments beneath higher velocities contain largerparticles than those beneath slow flowing \tater due to the removal and transport of srnaller particles downstream (Begon et al. L990; Smith 1992).
Smaller particles have greater surface areas, thus their ability to adsorb phosphorus from overlying wateris enhanced (Oliver 1993; Stone and English 1993; Lick 1994). Sedimens beneath faster flowing \ñ,aters a¡e therefore likely to have reduced adsorptive capacities, and thus lower total phosphorus concentrations than those beneath lower water velocities.
A combination of biotic exclusion and increased sediment particle size as a result of increase water velocity at the downstream end of an irrigation drain provides a likely explanaúon for the observed differences in sedimentary toal phosphonrs. However, the conelation between \patervelocity and sedimentary total phosphorus explains only
approximately l5Vo of the variability @earson / = 0.151)(Fig 3.14), suggesting that
although water velocity affects sedimentary phosphorus concentration, much of the
variability is attributable o the physicochemical properties of water passing over
sediments and the complex processes affecting the sorptive capacities of sedirnents. 65
3.4.3 Temporat Variation (Sampling Date)
As with the length of upstrearn drainage, significant differences in sedimentary total phosphorus coincide wittr signifrcant differences in wuer velocity (June sarnpling nrean sedimentary total phosphonrs = 0.491mg.g-r DV/, mean u,atef velocity = 0.058m.sec-r;
December sampling rnean sedimentary total phosphorus = 0.349mg.g-t DW, mean lvater
3.4-2.), water velocity = 0.l08m.sec"¡. For r€asons mentioned above (sections 3.4.1 and velocity is responsible for temporal variation in total phosphonrs concentration of
sediÍlents, however the physico'chemical properties of both the sediment and water
not þg column a¡e also likely to play a majorrole. Samples fr,om both sampling dates could
analysed using XRF due to time and budget constraints, thus it is not possible to conrnent
on the effects of physico-chemical changes in sediment during the irrigation season and
their possible effects on sedimentary total phosphonrs.
3.4.4 Conclusions
Spatially, the distribution of sedimenøry total phosphorus in the Mirool catchment is
influenced by run-off water quality as a result of different landuse, geochemical
composition of the sediments and water velocity. These factors combine O produce
greater concentrations of phosphorus in sediments located at the upstream end of
irrigation drains, and in u¡ban sub-catchments by comparison wittr rice/pasture sub-
catchments. 6
Temporally, differences in nrn-off wat€r quality may arise from timing of fertiliser applications, sowing and harvests, and this wor¡ld likely have an effect on the adsorption of phosphonrs to sediments. This could not be exanined due to time and budgetary constraints. Significant differences in waær velocity correspond to differences in sedimentary total phosphorus at differcnt umpling dates. This, combined with the
phosphorus, significant negative corelation of lvater velocity and sedimentary total implies thatphosphorus levels in the sediments of the Mirrool catchment are likely to be least d¡ring tlre peak of the irrigation season when the a¡nount of water passing through
the catchment is greatest. Figure 3.l: Sediment corer
I
')
9S0
.l o á m ;
Ít o Aû
o J F E È 50
30m ?sm 30m
I
I 68
Figure 32: Sedimentary total phosphorus: landuse (with standard error bars)
600 ì c] CD o 500 o> f 400 t-o .C o- o.D È-c. 300 õ o l- 200 6 c (D 100 E õo CD 0 ricelpasture citrus/vines urban
Landuse 69
Figure 33: Sedimentary total phosphorus: length of upstream drainage (with standard error bars)
ôoo 3o o 500 ol o 400 o= E. q,o- o TL 300
cú o t- 200 6L c o 100 E p (D c/) o 1km zkrn 4-5km 7-9km Length of Upstream Dralnage 70
Figure 3.4: Sedimentary totat phosphorus: sampling date (with standard error bars)
600 ?o o o 400
CDf o .C, 300 g)o- o .c. fL 6 200 t-o g6 oc 100 E õ(D CD 0
July '94 Dec'94 Sampllng Date 7L
Figure 35: Organic matter: length of upstream drainage - (with standard error bars)
I
ìo 7 oc E 6 E o CÞ 5 o CD J 4 o co 3 c o o 2 o =.o6 ot- 1 0 1km 7-9km Length of UPstream Dralnage 72
Figure 3.6: Organic matter: landuse (with standard error bars)
I
ìo 7 c @ E 6 õo ct, 5 o CD J 4 CD c 3 +ro oc o () 2 c CÚ CD o 1 0 ricelpasture urban Landuse 73
Figure 3.7: Organic matter: sampling date (with standard error bars)
7
=o 6 c @ E 5 õo cf) o 4 .E o 3 (Dc c oo 2 o E 6 o 1 ol- 0 July '94 Dec'94 Sampllng Date 74
Figure 3.8: MultÍ-Dimensional Scaling (MDS) representation of sediment XRF datå characterised by landuse
2
*
1 + + c! + o * c, ct LL t * * o t I + I I ¡l t * urban * cltruVvlne -1 t ilce/pasture -2 -1 o1 2 3 Factor (1) 75
Figure 3.9: Multi-Dime¡uional Scaling (MDS) representation of sediment XRF dâta characterised by length of upstream drainage
2
+
1 + (\¡ + + oL + () + o o + f + o t + * I + o *r o 7-9km tu + 4-5km o * 2km -1 ¡ 1km -2 -1 o1 2 3 Factor (1) 76
Figure 3.10: Water velocÍty: length of upstream drainage (with standard error bars)
o20
o.15 C) (D cn E
() o. 1 o õo
L (D 6 = o.05
o.o0 1km zt Figure 3.11: Water velocity: sampling date (with standard error bars) o.15 () (D qt o. 1 o E õ õo (D P ct o.o5 = o.o0 July '94 Dec'94 Sampllng Date 78 Figure 3.12: CaO concentrations in urban and rice/pasture sub'catchments 4 o o = 3 q) oc E E o CD 2 o oc oc o 1 o6 C) o ricelpasture urban Landuse 79 Figure 3.13: SO¡ concentrations in urban and rice/pasture sub-catchments o.5 o o.4 àJ o c Eo Þ o.g o ct) o o,2 Eo c oo I 0.1 CD 0.0 ricelpasture urban Landuse 80 Figure 3.14: Relationship between water vetocity and sedimentary total phosphorus o.5 I 0.4 () g,o o € o.g O o o 'e 9oz-9 .l (D ¡,O a 6 oa a O = o.1 "I Chapter 4z sediment and Phosphorus Resuspension by Carp 4.L Introduction 4.L.1 Background cycle in Many chemical compounds in aquatic systems spend at least part of their sediment resuspension have sediments. Changes in the rate or nafl¡rc of these cycles due to et aI. L995; Svendsen er been documented for phosphates (e.g. olita et at. t995; Pedersen Ford and al. L99il),heavy metals (Blom andToet 1993;Balls er at' 1994;Bloesch 1995; hydrocarbons Ryan 1995), polychlorinated biphenyls (Ko and Baker 1995), and aromatic literature' and (Literatlry et al. L994: Ko and Baker 1995). Mafine examples dominate the action and storm the few fieshwater examples focus on abiotic prccesses such as wave events (e.g.Licket al.1994; Svendsen et al' 1995)' generally Although dependent on a variety of factors (refer to Table 3'1), sediments (flart et al' 1976; contain orders-of-magnitude greater phosphorus than overlying water is therefore Donnelly et al. 1994). Resuspension of sediment by biota, or bioturbation, in the water column recognised as a potentially significant modifier of phosphorus levels (tloldren and Armstrong 1980; Lijklema et aI. L993; Clavero et al' t994)' 82 The bulk of the literature on bionrbation examines bunowing benthic macroinvertebnates such as polychaetes (Hyllebcrg and Henriksen 1980; Aller and Yingst 1985; Clavero ¿r a1.1992,1994), dipteran larvae (Gallepp et al.1978; Karnp-Neilsen ef al.1982) and oligochaeres (Kamp-Neils€n ¿f al. L9ï2;Matisoff et aI. L985). In these studies, most of the phosphorus flux has been attributed to porewater exchanges acrloss concentration gradients associated with burrows. Total phosphorus flux is therefore very small, often measrued in pmol L-r or mg P dayr. In contrast, carp resuspend unconsolidated sediment into the water column during feeding behaviour (see section l.SXCline et at.1994; Threlkeld t994), thus their capacity to affect phosphorus flux across the sedimentlwater interface is far greaær than macroinvertebrates. This is recognised by Gehrke and Haris (1994) and Threlkeld (1994), who view biotrubation of sediments by carp as a significant source of water column nutrients. Previous experiments and recorded observations focussing on sediment bioturbation by cúp (e.g. L,amarra 1975;Hurne et at.1983; Meijer et al.l99O; Qin and Threlkeld 190; Cline el al. L994; Threlkeld 1994; Roberts et al.1995) have produced a variety of sometimes conflicting results. The manipulated or observed variable in these studies is carp size and/or density, wittr little (if any) description of sediment characæristics. Pa¡ticle size and phosphorus concentration variability of sediments in these studies offers an explanation for the reported variability in results. 83 from With regard to phosphorus measurement, the bioavailable component resulting the lack of bioturbation has not been measured in previous s$dies. This is likely due to case appropriaæly developed æchniques at the timc of experimentation' or' in ttre of the macroinvertebrate studies, immeasr¡rable flt¡xes of bioavailable phosphorus across for sediment-water inærface. Wittr the deveþment of a relatively new technique concentrations estimating the bioavailable phosphorus fraction, and the high phosphorus 1995), such expected to result from carp activity in these ponds (see Roberts et al' phosphonrs' û,"asurenrent is possible. Therefore, in addition to total and filterable reactive Phosphorus ttris study aims to examine the effects of carp on Iron Strip Desorbable (ISDP) as an estimate of bioavailable phosphorus (see section 1.6). 4.I.2 Objective Objective 1: To determine the effects of the interaction of carp and rwo different orbidity sediments from irrigation drains of the MiÍool catchment suspended sediment, andphosphorus loads in the rüater column. 4.2 Methods 4.2.1 Experimental Design The experiment took place in 12 in-ground, plastic-lined ponds on site at the CSIRO 4m x 3m x Division of Water Resources in Cnifflrth, NSr$/. Ponds measured approximately (1995)' lm depth (Frg 4.1) and were the same ponds used by Roberts et al. u and 'low' levels of Sediments from the irrigation drainage network containing 'high' produce four treaünents' phosphorus were crossed with the presence/absence of carp to (2 x2) Treatments were triplicated and randomly assigned to ponds in an orttrogonal design. identified as containing 'high' Sediments were collected on 26t5lg5from d¡ains previously maintain the vertical and 'low' levels of sedimentary Otal phosphonrs. Ca¡e was taken to x 345mm x profile of sediments as they were shovelled in6 mys measuring 295mm for sedimentary total 50mm deep. Trays loaded with sedirnent were weighed, sampled ponds' Sixteen trays phosphorus and particle size analysis, and then placed into empty tray was used for wcre placed in cach pond in an evenly spaced 4x4 gnð' One extra of carp' Due to analysis of redox potential of sediments imnediately pfior to the addition could not bg problems with equiprnent and reagents however, acc¡rate measurements anoxic. taken though observation and odour indicated that sediments \ñ'ere supply u'ater to a Ponds were filled with approximately gzþLof sand-filtered irrigation "J" measured depth of 75-80cm, coresponding to the maximum depth of Main Drain which ponds duing the lggLl1irrigation season. Filling was completed on 2615195, after were allowed to settle until the initiat wat€r column salnpling on29l5l95' Michael Fuchs' a Carp were collected from the irrigation drainage network by Mr professional electrofisher, on Igtllg| and placed in6 a holding dam on site' Following 85 removal from the dam by seine netting,3 carp (350-420'mm SL) were placed in each of the 6 designated 'carp present' üeatments at 13:30h on216195. 4.2.2 Sample AnalYsis Sedinrents used in the experiment were analysed for particle size and total phosphonrs. For particle size analysis, 50.09 of air-dried and cn¡shed sample was placed in lL of 0.57o sodium hexametaphosphate and hydromeær readings urene taken after 5 min and 7 -75hto determine fine sand (0.2 - 0.02mm), silt (0.02 - 0.002mm) and clay (<0.002mm) fractions. (0.2 - Samples were then filæred through a 200¡rm mesh to determine the coarse sand 2mm) fraction. Replicaæ samples urere oven dried at 105oC to determine dry weight. The coarse and fine sand fractions were combined as 'sa¡td' for daø analyses' Total phosphonrs deærmination of sediments is described in se¡tion 3.2'3' Integrated \ñ/ater column samples were taken for all lvater analyses. An open-ended clear perspex tube was lowered into the ponds until it lvas a few centimetres above the pond floor. A rubber bung sealed the top of the tube which was then drawn out of the water until the open end of the tube was just below the waær surface. A simila¡ bung was then ptaced in the underwater opening of the perspex tube and the intact \vater column sample was removed and mixed by inverting the tube three tinres. Sarnptes were then transferred into acid-washed glassware and transported to the laboratory for processing' 86 One sample was collected from each pond every 24hrs between the completion of pond equilibration (29t5195) and the addition of carp (U6195).Previous experiments in the ponds (Roberts et al. t995) found that the effects of carp addition became evident in the fimt Z hours, so the sampling regime rvas constn¡cted a¡ound an approximately logarithmic time scale: samples were collected 1, 2,4,8,12, 18, 24,36,48,72,96,I2O, 168,2æ, and 456h after the addition of carp. 'Water samples were analysed fu suspended sediment, turbidity, total phosphorus and filterable reactive phosphorus (FRP). Samples collected at 0, 8, 48 and 120h after carp addition were also analysed for ISDP. Suspended sediment was deærrrined as the difference in dry weight of a Wharnans GF/C filter paper after filtration of a known volurne (Arnerican Pr¡blic Health Association 1989). Turbidity was measu¡ed with aHach 21004 u¡rbidimeter. Total lvaterphosphorus lvrls determined by hot sulphuric acid digestion and molybdenum/antimony colorimetric analysis (Tecator FIA method 23|85).FRP was defrned as the concentration of orthophosphate (by molyHenuny'antimony colourimetric analysis) in the sample after 0.45pm filtation. The detection limits for watercolumn total phosphorus andFRP were 0.03mg.Ir and 0.01mg.1-1 respectively. t7 (approx' 13 x 70mm) ISDP for each sample was determined by placing 6 iron-oxide strips hor¡rs. water samples and 30mL of sample into a polypropylene tube and shaking for 24 to remove adhering were then discarded and strips removed and sonified for 10 seconds fr'om the particles before being renrrned to ttre sarrrple vial. Phosphorus was extracted hour for 6 hours' Strips strips by cold digestion in 0.1M H2SO4, shaken for 1 minute every were disca¡ded and digest acid was analysed for orthophosphate using 1. was 2.5¡rg.L antimony/molybdate colourimetric analysis. The detection limit for ISDP 1'6)' This method is c¡rrently being assessed by Jacobs (in prep.)(see also section 4.2.3 Data AnalYsis were Total phosphorus concentrations of the 'high' and 'low' phosphorus sediments particle size data were analysed with the Kruskal-\il/allis non-pararnetric test. Sediment and clay f¡actions' arcsine transformed and analysed with separaæ f-tests of the sand, silt of particle Homoscedasticity of all size fractions was analysed with F-tests, and results size comparison were subjected to Bonferroni correction. wittt suspended sedimenr, tqrbidiry and total phosphøus data were analysed separately of carp model I repeated measrres ANOVA with two crossed factors þresence/absence C was used to and higflow sedimentary total phosphorus concentration)' Cochran's sediment dete¡mine homoscedasticity of all repeated urcasu¡es analyses. For suspended greatest variance and turbidity data it was necessary to rcmove the sampling time with tlre and since be¡x,een replicates in order to acheive homoscedasticity. ISDP data at 0 lÐh 88 carp addition lve¡e analysed separately with Kruskal-\Yallis tests, and results were subject to Bonferroni adjusnnent. 4.3 Results 4.3.I Sediments Sedimentary total phosphorus and particle size data fr,om all sediment sanples is presented in Table 4.1. The selected 'high' phosphorus sediments contained significantly greater sedimentary total phosphorus than 'low'phosphorus sediments (P = 0.004). Particle size (F.-¿ data were arcsine transformed- Sand, silt and clay data were all homoscedastic = 7.42, F"it, = 3.88, F"n, = 1.73, F1t,3,U,05(z)) = 15.4). 'High'phosphorus sediments contained signifrcantly greater silt than 'low' phosphoms sediments (P = 0.000), however 'low' phosphorus sediments had greaterclay content (P = 0.004). No significant difference was found in the sand fraction (P = 0.463). Tabte 4.1: Total phosphorus and particle size distributiorrs of sediments r¡sed in pond exPeriments "Totat osand tsilt ocl"y Sediment Phæphorus % shigh' ólowt r= min. - mzu(. range âvoÍâgo of 6 samples = âvgrâge of 4 samples " = standard error = 89 4.3.2 Water Quality Suspended sediments data (Fig. 4.2) werc made homoscedastic after 4th root transformation and removal of samples taken 18h afær the addition of carp (see section 4.2.3) (Cra"r= 0.1176, Cp,eo, q¿.or)= 0.1371). Trubidity data (Fig. 4.3) were made homoscedastic after 4th root transformation and ¡emoval of samples taken 48h afrer the addition of carp (see section a'2'3)(C<-t"l= 0'1370, CB,to,q4'ot)= 0'1371)' Repeated n¡gasures analyses of suspended sediments and turbidity data were run with and without ttre omitted data sets and no differences in the significance of results were observed- Total phosphonrs data (Fig. a.a) were homoscedastic following 4th root transformation (C1".r"1= 0. 1250, C1r,eo, aa.ott= 0.137 1)- Results from all repeaæd measrres analyses, including probabilities, are presented in Table 4.2. Suspended sediments and turbidity data showed signiñcant differences in all comparisons both be¡ween and wittrin subjects, including all inæractions. Total phosphorus data showed significant difference due to the presence/absence of carp, but no difference due to either sediment or the lcarp x sediment] interaction factor. Within subject comparisons showed significant differences due to tirne and [time x carp] interacúon, but not due to the [time x sediment] or [time x sediment x cafp] tenns. Results from single degree of freedom polynomial contrast analyses, including probabilities, are p¡esented in Table 4.3. All water quality rneasures were significant with 90 P 0'017; respect 19 time forthe third order (cubic) contrast (suspended sediment = nrbidity P = 0.005; total phosphorus P < 0.001). FRp concenmdons were below the detectable limit (0.01mg.Ur) for all sarrrples. ISDP data (Fig. 4.5) for all treaunens at 0 houn after carp adötion were not significantly gfeater different (p = 0.180), but the 'high P + car¡r' treatment contained signifrcantly (P levels of ISDp than the other treaments at 120 hours after carp addition = 0.002). Table 4.2: Two-way model I repeated measures ANOVA for suspended sedimentst turbidity and total PhæPhorus Source Suspended Turbidity Total Phoryhorus F-¡atio dJ. Þob. ¿f. Prob. F-ratio dJ' P¡ob' *0.(m -F-¡atio I,E +0.0m I,E Between cåfP 230.æ I,E 119.03 .0.0(x I,E +0.001 t.?Ã 1,8 0.306 Subjects sediment 16.16 I,t 30.2ß .0.qN I,E +0.001 0.04 1,8 0.845 carp x sed 16.27 1,8 23.18 +0.0æ *0.0ü) 303.14 13.104 +0.0m Tt/ithin Ume 26.O2 t4,ll2 53.6 l3,lg *0.000 r0.m 13,104 *0.0m 9.96 l3,lß Subjects time x carp 39.E9 t4,ll2 6.ß r0.030 r0.(m t.0t l3,lü 0.391 time x sed 2.t2 t4,ttz 9.69 l3,l(x +().021 {).0ü) l.l1 13,1(X 0.364 time x sed x 3.05 t4,lt2 9.36 l3,l(X cafp t = significant result (a-{.05) 91 sediment' Table 4.3: Single degree of freedom polynomial contrasts for suspended turbiditY and total PhæPhorus (d.f. were ln8 for all contrasts) Total Phosphorus Order Source Suspended Turbidity Sediments F-ratio P¡ob. F-ratio Prcb. F-ratio kob. *0.000 1010.4 {.m0 time t37.94 {).000 280.7r 1st *0.030 r0.000 352.58 *0.000 6.97 0iæ¡r) time x carp 2v.26 .0.037 {).000 L.22 o.302 time x sed 6.n 36.87 *0.001 L.2t 0.303 tirnexsedxcarP 5.26 0.051 31.07 1.00 0.346 67E.6E {).000 2nd time 4.52 0.066 0.330 n.50 {).001 (quadratic) time x carP 0.28 0.6t2 r.0E 0.095 L.97 0.r95 time x sed 3.50 0.098 3.59 0.31E 0.5E8 timexsedxcarP 4.55 0.ffi5 4.74 0.061 *0.0r7 *0.005 482.55 {).m0 3rd time 8.99 t4.6 *0.005 19.r7 *0.002 (orbic) time x carP 7.t5 {).028 r438 *0.026 0.57 o.473 time x sed 2.63 o.r4 7.& *0.022 0.76 0.410 tirnexsedxcarP 2.65 0.r42 8.t2 * = significant ¡esult (a{.05) 4.4 Discussion 4.4.1 Suspended Sediment and Turbidity sediment and The presence of carp in experimental ponds increased both suspended (Qin Threlkeld nrbidity. This is in concordance with other manipulative experirrrcnts and 1995) and recorded 1990; Cline et aI.1994: Gallo and Drenner 195; Roberts et al' it contradicts the results observations (Cahn 1929;Meijer et al.1990; Threlkeld 1994),yet (1983) Reynolds (1987)' of Hume et aI. (1983), Fleæher et ø1. (1985), Crivelli and different Explanation of this conflict is dernonstrated by ttre incorporation of ¡ro ær¡n' x sedfunent]' in sediments in the cruïent experiment The significant interaction [carp that sediment rcsuspension by both suspended sedirnent and turbidity analyses is evidence 92 carp is not only dependent on carp activity, but also on the nanue of the sediment. Va¡iable sediment characteristics may thc¡pforc explain the different results gairied by the above studies. The retention of resuspended sediment in a lentic $'ater column can be approximated by Stokes'law (Linsley et a\.1988) and is therefore largely dependent on sediment particle greater size (Lick 1982;Ongley et aI.1982). 'High'phosphorus sediments comprised a (Table silt fraction, and a smaller clay fraction than 'low'phosphorus sediments 4.1). Similar rates of resuspension of both sediments would therefore result in greater suspended sediment in the lvater column of 'low'phosphonrs sediment treaErents, as was observed- No scdiment particle sizo analyses are presented in any of the previous studies of carp bionlrbation, thus although variation in this factor alone may be the source of conflicting results, insufficient data is presented to confrrm this. Va¡iation in carp feeding activity is also likely to affect sediment resuspension. Lammens and Hoogenboezem (1991) and Sibbing (1991) suggest food t¡pe (e'g' chironomids, molluscs) and availability (ie. density, size distibution, visibility, depth in sediment) affect carp feeding behaviour. Dfferent oral processing behavioun are required for different food types (Sibbing 1991), altering the effrciency of feeding, and thus sedimentresuspension rates. Similarly, food availability affects both oral processing and food foraging behaviour (I-ammens and Hoogenboe zpmlggL;Sibbing 1991) arxi may therefore affect sediment resuspension rates. There is, however, no infomration in the 93 literatr¡re quantifying the effects of a va¡iable bioÉc component of sediment on biotr¡rbation by carp. Thus although different rates of sediment resuspension arB likely to occur in biologicalty rich and depauperaæ environments, the nature of this relationship remains the subject for future study. Conflicting results in the literature regarding ttre affect of carp on suspended sediment loads and turbidity are therefore the likely product of variability in the physico+hemical and biological properties of sediments. It is not possible to accurately extrapolate the results of these studies until more infomration on the sediments used becomes available, and further study is underøken to determine the effects of a variable biotic component of sediment on calp feeding behaviour and sediment resuspension rates. 4.4.2 Total and Filterable Reactive Phosphorus As with suspended sediment and n¡rbidity, the presence of carp in experimental trea¡nens significantly increased r¡¡ater column total phosphorus concentrations. Unlike suspended sediment and tubidity data however, no differences in water column total phosphorus concentration were found due to sedirnent, or the [sediment x carP] factors. Simila¡ u/ater column total phosphorus concentrations in 'high' and 'lo\P' sedimentary phosphorus treaûments is explicable by the greater concentration of suspended sediment in the 'low' phosphorus treatÍrents. Although comprising a lower phosphorus concentration, this increased mass of sediment has produced simila¡ n/ater column total phosphorus concentrations to the smaller mass of 'high' phosphøus sediment. Sedimentary total 94 phosphorus concentration is therefore not necessa¡ily indicative of water colurnn total phosphonrs concentration following bioturbaúon. Facors likely to affect the concentration of suspended sediment in the water column (Íe. particle size, food type and density), are therefore also detemrinants of total phosphorus concentrations. The lack of detection of any FRP is consisænt with experiments conducted in the same ponds by Roberts et aI. (1995). Previous rnea$nes of irrigation supply $'ater, such as that used to fi]1 ponds in this experiment, have revealed deæctable levels of FRP in the range of 0.025-0.46mg Lt (unpubl. data). Sand filtration may be responsible forremoving FRP from this water prior to it entering the ponds. In 'carp absent' treatments the flux of phosphorus from sediments to the watercolumn is unlikely to prcrduce detectable levels of FRP and they would be expected to rernain low throughout the experiment, as lvas observed. The lack of FRP in 'carp present' Eeatments, however, contradicts the results of Lamarra (1975), who attributed an increase in water column phosphorus concentration to carp excretion. Fish excrete soluble phosphorus (Gehrke andHarris 1994) which would be detectable in ttre FRP fraction. Excretion in this experiment is therefore either insufficient to affect water column phosphorus concentrations, orexcretedphosphonrs is being removed from the water column via adsorption. Soluble phosphorus generally has a high affilnity for suspended sediments (Oliver 1993; Oliver et at. L993), and may adsorb to some plastics, such as that used to line the experimental ponds (Dr. R. Oliver, Murray Darling 95 for Freshwater Research Centre, pers. cornm.). Both processes offer possible explanations fate the undetectabte FRp concentrations, hotvgvgr it is not possible to determine the of the soluble phosphorus fraction in ttris experiment water The principal mechanism by which benthivorous fish and sediment interact to affect column phosphorus concentrations is not evident. Lnma¡ra (1975) and Brabrand ¿r ¿I. (1990) identify excretion as the tikely major contributø o observed differences in phosphorus loadings, Gallo and Drenner (1995) recognise both excretion and resuspension of phosphorus loaded sediment as possible sources, Boers et al. (1991) propose that fish in water act as a sink for nutrients, as do Roberts et al. (1995), who found no differences column phosphorus concentration attibutable to the presence of carp. As with conflicting evidence of the effect of carp on suspended s€dfunent and turbidity, much of ttris variability in results is likely due to physico-chemical and biological cha¡acteristics of sediments used in experiments. This, combined with evidence suggesting ttre trophic state of a waterbody affects the relationship between \ilater column phosphonrs concentrations and carp (Riemann 1985; Gallo and Drenner 1995), indicates that a simple cause and effect model of total phosphorus resuspension by carp is not ¿rcceptable' 4.4.3 Iron Strip Desorbable Phosphorus Contrary to total phosphorus analysis,ISDP data separaæd 'carp present' treaünents produced according 19 sedimentary phosphorus concentration. 'High P + carp' treaEnents 96 afær the addition significantly higher ISDP concentrations than all other treaEnents lÐh of carp. (SRP) and labile The ISDP technique nìeasures both soluble reactive phosphorus et al' 1993)' phosphorus weakly adsorbed to particles (van der z.ee et al.1987; Oliver therefore the difference FRp results indicate there is very little sRP in the water column, the labile phosphonts benveen the 'high P + carp' and the other trea¡nents is due to the 'high' and 'low' component of suspended sediment. Much of the difference between and more bio- phosphorus sediments used in this experiment is therefore due to a labile, Resuspension of the available form of phosphorus associated with the particulaæ fraction. water ,high' phosphorus sedimentis thus more likely to stimulate algal gfowth in the column than the 'low'phosphorus sediment carp feeding previous studies of phosphorus enrichment in the \ilater colurnn as a result of (¿'8' FRP) to approximate activity use measules of dissolved fomrs of phosphorus SRP, C||ne ¿r øl' 1994)'[\e the bioavailable fraction (e.g.Lamarral97S;Brabrand et at. L99A, not curent experiment demonstrates that soluble phosphorus concentrations are particularly tn¡e in necessarily indicative of bioavailable phosphonrs. This is likely to be water6ies with high suspended sediment loads such as those typicalty found throughout of carp to the Murray-Darling Basin. Future work aimed at assessing the contribution a rlore reliable algal blooms associated with europhication should therefore included estimate of bioavailable phosphonrs, such as the ISDP technique' 97 4.4.4 Experiment Duration total Single degree of freedom potynomial contrasts for suspended sediment, turbidity and phosphorus are all signifrcant at the third order with respect to time. Plots of these $'ater quallty paraû¡gters show an initial large, rapid increase following the addition of carp, followed by a more gradual reduction continuing through to the final sarrpling 19 days later (Figs 4.2,4.3 and 4.4). Many similar experiments examining the effecS of carp in artificial ponds or Ûlesoco$ns (e.9. have produced similar shaped curves for a variety of water quality parameters Lamara 1975 for total phosphorus and chlorophyll a; Cline et aI. t994 for turbidity and dissolved oxygen; Roberts et at.1995 for turbidity and suspended sediment). Lamara (1925) proposed two reasons for the gfadual reduction of water column phosphonrs following a rapid initial increase: 1. a decline in carp feeding rate following over- exploitation of the food supply, and 2. increasing sedirnentation of phosphorus due to algal uptake. In an experiment designed to test this, he concluded that the latær explanation deærmined the shape of the phosphorus plot in the pfesence of carp. This experiment required carp to be placed in either clea¡ or opaque plastic bags, the laner treatment excluding sunlight so as to inhibit algal growttr. Carp are reported to be rnost active at night (Cadwallader and Baclúrouse 1983), therefore the va¡iable photoperiod imposed by the experimental trearnents is likely to affect feeding behaviour. The conclusion reached from this experiment is therefore possibly the result of alærations in carp behaviou¡ due to (1975) experimental design. In addition to this, the explanation offered by Lamarra does 98 not account for similarrelationships found for suspended sediment and n¡rbidity by Cline et øt. (1994), Roberts et al. (L995) and the cturent experiment. The coincidence of similar shaped ploa for suspended sediment, turbidity and total phosphorus suggest ttrat ttre rapid inctease and subsequent gradual dec¡ease of these prirameters is due to some form of physical stining, and is therefore linked to carp activity. In the scope of the current experiment, however, it is notpossible to deærrrine if this is a result of initiat over-exploitation of food supply, or to soule other behavior¡ral trait of carp. Furthermore, it is not possible to detennine if such behaviour is particular to experiments in small enclosures, or if it also occurs in larger natural systems. Regardless of the reason, this temporally variable relationship between carp and water quality has implications for the interpretation of previous experiments and observations. In addition to variabilþ imposed by different sediment cha¡acæristics, the duration of exposure of carp to sediments in an experirnental situation, and possibly in more natu¡al environments, will tikely have an effect on lvat€r quality.Experiments must therefore account for this temporal variability by either justifiably defining the end point of an experiment, or using time series data analysis techniques. Neither have generally occune4 with authors comparing data from one sampling time'before' andone sampling time 'after' the addition of carp, or using averaged data from pre- and post-carp addition (e.9. Qin and Threlkeld 1990; Cline et al. 1994; Roberts et al. 1995). Failure to account for the æmporal va¡iation in the relationship benneen carp and water quatity in experimental 99 on the effects of ponds is therefore another possible explanation for conflicting rcports bioturbation bY carP. 4.4.4 Conclusions prodgced higher suspended The interaction of carp and sediments used in this experiment than sediment loads, turbidity and total phosphorus water column concentrations some similar experiments treatfnents where carp were absent These results concuf with and observations, yet contradict the results of others' ¡s s¡amins Unlike previous experiments, the curent study used two different sediments (íe' their differential effect on water quatity in the presence of carp. Physicochemical the sediment particle size) and biological (i¿. food type and availability) characteristics of Furthermore' the were identified as variants of water quality following carp bionubation' and total relationship be¡veen the presence of carp and suspended sediment, turbidity the conflicting phosphorus was found to vary with time.It was therefore concluded that and/or results presented in past studies a¡e the result of va¡iable sediment cha¡acteristics, timecourses of exPeriments- 1' furttrer study In order to overcome these limitations in the future, it is suggesæd that: and biological be undertaken to exarnine the relationship between the physicochemical information be characteristics of sediment and rates of resuspension by carp,2' more used in presented on the physicechemical and biological char¿cteristics of sediments 100 experiments, and 3. datafrom experiments should be analysed using time series analysis æohniques to account for temporal variations in the relationship benryeen carp bionrbation and water quality. FRp measurements in atl trearnents were below ttre deæctable limit (0.01mg.Ur). ISDP P + measr¡rements showed greater concentrations of bioavailable phosphorus in the 'high carp' treaünent than in all other treatrnents 120h after the addition of carp. Combining the these resuls indicates soluble phosphorus can not be used to accurately estimate effecs of carp bioturbation on \rater quality, as has been done in previous experimens. It was concluded that techniques such as the iron-srip method should be used in fun¡re expedments to assess the contribution of carp to algal gfowth resulting from nutrient enrichment of the water column. \' ill l!,t Figure 4.1: Experimental Ponds L tB';' tvz Figure 4.2: Suspended sediment in experimental treatments 250 { 3 200 o E o, C 150 (D E Eo CD Eo 100 1Jc o JCD LoP-C CD 50 LoP+C HI P-C --+ HI P+C 400 500 9 1 00 o 1oo 200 300 Time slnce carp added (hrs) r03 Figure 4.3: Turbidity in experimental treatments 200 F----{ 150 i , a I t-- z { 1 00 =E -o¡- t-'= 50 LoP-C . LOP+C --þ"-":"':"':f -Hi P-c Hl P+O 0 500 1 00 0 100 200 300 400 Tlme slnce carp added (hrs) I I i I I 104 Figure 4.4: T otzl phosphons in experinrental treatments 150 3 o 1 oo gt f oL .c. gto. o .c, fL 6 50 t-o \ LoP-C LoP+C --...... ,---.- -Ht P-O HI P+C 0 -1 00 o 100 200 300 400 500 Tlme slnce carp added (hrs) 105 Figure 45: Iron-strip desorbable phosphorus in experimental treatments 16 3 o = tt :t ot- 1 o E, gto- Eo o- þ -o E 6 5 ----- _.r..1 -=il- - õ ----::: -9 + LoP-C LoP+C HI P-C 0 H¡ P+C o 20 40 60 80 100 120 Tlme slnce carp added (hrs) r06 Chapter 5: Discussion 5.1 Introduction Carp are potentially important in-channel conüibutors of phosphorus to the watercolumn through their benthic feeding behaviour. The major aim of this study was to assess this contribution in the irrigation drains nearGriffith, N€w South Wales. The resuspension of sediment and phosphonrs by carp has previously been viewed as a simple consequence of benthic feeding behaviour. In this context, attempts to quantify the effecs of carp bioturbation have produced conflicting results, nnst likely reflecting the variety of physical, chemical and biological condiúons imposed by different locations and experimental designs (section 4.4). Arequirement of any assessment of the role of carp must therefore examine the physico-chemical va¡iants of sediment and phosphorus bionrbation in the study area. Spatial and temporal va¡iation in both carp abundance (Chapter 2) and sedimentary phosphorus concentration (Chapær 3) in the Mirn¡ol catchment were examined as they were considered rnost likely to be the majordeærminants of phosphorus bioturbation by carp. Further, an examination of the interaction of carp and sediment lvas conducted (Chapter 4) to betær understand this ¡elationship and its effects on the amount of sediment and phosphorus resuspended by carp feeding behaviour. TTre results of each of these studies are summarised in section 5.3. to7 model of the This chapter builds on the conclusions presented in Chapter 4 to construct a with variants of sedinrent and phosphorus resuspension by carp' This is combined to information on the abundance and distribution of carp and sediment cha¡acteristics sediment and describe and evaluate, so far as possible, the contribution of carp to phosphonrs resuspension and phosphorus ery)ort from the Mirrool catchnrcnl 5.2 Sediment and Phosphorus Resuspension by Carp quantity of The quantity of phosphorus contributed by carp activity depends on the reæntion of sediment resuspended, the phosphorus content of the sediment, and the resuspended sediment in the lvater column. These factors a¡e elaborated below' 5.2.1 Quantity of Resuspended Sediment the Carp abundance and biomass. In otherpublished studies of sediment resuspension, 100 (King number of carp varies from 1 (Clivelti 1983; Cline et at. 1994) to more ttran t up to 4400kg ha 1995), and density varies from less than lkg har @etch er et al' 1985) relationship (Cline et at. 1994). However, relativeþ few studies have examined the (1995) found greater between the quantity of suspended sediment and carp biomass. King (l9X)) and nrrbidity in treatments with higher carp biomass, and both Meijer et al. and Breukelaar et al. (L994) found a linea¡ relationship between benthivorous fish biomass berween fish size suspended sediment. Breukelaar et at. (1994) also found no correlation of fish was (in the range 250-500mm) and suspended sediment, indicating that the number r08 the main determinant of suspended sediment load. Fletcher et al. (1985) found no correlation between carp biomass and turbidity in Australian lvaters, but in that study, both lentic and lotic environments \ilere included and biomass $/as low at several siæs Oess than I lkg ha at one site). They concluded that va¡iations in übidity between sites were due primarily to hydrological factors, however this does not exclude the possibility that carp biomass is implicated. In general, the balance of evidence suggests that the quantity of resuspended sediment is affected by both abundance and biomass of carp. Feeding behaviour. Juvenile carp feed alnrost exclusively on plankton (Jobling 1995; Brown 1996) so are not likely to greatly affect sedimentresuspension. Later, ontogenetic changes lead to greater dependence on benthivory. For example, thete is a loss of UV sensitivity and hence ability to visually detect prey (Jobling 1995), although mature carp retain some ability to feed on pelagic prey (Lammens and Hoogenboezeml99l; Sibbing 191). High turbidity can be expected to reduce the effectiveness of visual feeding (Jobling 1995) and so encourage benthivory and sediment resuspension. Further, the nature and abundance of the food supply may encourage a dietary shift (Jobling 1995) so that sediment resuspension is geatest in environments with a rich benthic fauna (e.9. chironomids, gastropods) and depauperate pelagrc fauna (e.g. cladocerans, calanoid copepods). 109 Presence of unconsolidated sedimenL Carp feeding involves the intake and expulsion of sediment (section 1.3), Sediment resuspension will therefore clearly be greaær over unconsolidated sedfunent than rocþ or hard-packed clay substrata 'Water 5.2.2 Retention of Resuspended Sediment in the Column Particte size distribution of unconsotidated sediment. In lenúc systems, the settling velocity of suspended sediment is approximated by Stokes' law (Linsley et ø1. t988) and is ttrerefore largely dependent on particle size (Lick 1982; Ongley et al.1982; see section 4.4.1). Va¡iation in particle size distribuúon due to $,ater velocity (Linsley et al. 1988) or flocculation Marshall and Holmes 1979; Eisma 1993; Lick 1Ð4) will alter particle settling velocity, and thereby affect the retention of suspended sediment in the rilater column (Lick 1994). Turbulence. Turbulence generally increas€s the retention time of suspended sedfunent (Linsþ et al.1988: Eisma 1993). In lentic systems, n¡rbulence is generated by wind, surface tension and themlal instability (Linsley et ø1. 1988), but in lotic systems the effects of tubulence inc¡ease with water velocity (Pickup 1986; Eisma l993;Zteglet et aI.1994)- The reæntion time of resuspended sediment in the rvater column is therefore likely to be gr:ætþr in lotic than in lentic systeus. lr0 5.2.3 Phosphorus Content of Sediment Sedimentary phosphonrs concentration is the product of a complex interaction of a variety of envi¡onmental facors (refer to Table 3.1). Regardless of its derivation, the concentration of sedimentary phosphorus will directly affect rvater column phosphorus concentrations after carp bioturbation. Of particular interest is the algal available fraction, which is likely to be an important detemrinant of the impact of carp biotr¡rbation on algal blooms. 5.2.4 Sediment and Phosphorus Resuspension by Carp: a Model The facors affecting sediment and phosphorus resuspension by carp a¡e combined into a model, as shown in Figrue 5.1. 5.3 Resuspension of Sediment and Phosphorus by Carp in the Mirrool Catchment As itproved impossible ¡9 esúmaæ total carp abundance in the drainage netlvork (se¡tion 2.2.2),the contribution of carp to total phosphorus resuspension and export cannot be estimated in absoluæ terms. Here, the relative contribution of carp is considered, given information on temporal and spatial variations in carp abundance (Chapær 2) and sedfunent characteristics (Chapter 3). 111 5.3.1 Quantity of Resuspended Sediment governed by the annual The temporal abundance of carp in the Mirool carchrnent is network coincided with irrigation cycle (section 2.3.1). The influx of carp to the drainage and observed inoeasing water levels in drains at the beginning of the irrigation season' yvater end of the season (FLg'2'7)' carp numbers decreased rapidly as levels fell nea¡ ttre drains vrith Main Drain "J" Spatialty, carp were concentrated at the intersection of lateral phosphorus by (section 2.3.3).On this ba.sis, the temporal resuspension of sedimentary sediment and carp is tikely to be greaæst druing the inigation season' while spæially, of phosphorus resuspension is dependent on the physico-chemical cha¡acteristics "J"' sediments at the intenection of lateral drains with Main Drain season remained The size distribution of carp observed over the 1994t95 irrigation juveniles (<150mm) (Fig' 2'8)' relatively constant until March, when there was an influ< of were unlikely to have a However, as juveniles were likely to be planktivorous' they significant effect on sediment resuspension' was variable' Turbidity in ttre drainage network during the 1994195 irigation season generally higher rurgrng from 10-420 NTU (Meredith, unpubl. data). However, the (pen' obs') would n¡bidity and deeper water in Main Drain "J" tha¡lin lateral drains Dfain "J"' probabty inhibit visual feeding, in turn promoting benthic feeding in Main rr2 (section 2'2'2), and the Unfortunately, the influence of the observer on carp behaviour if carp were limited visibility in Main Drain "J" meant ttrat it was not possible to determine junction lateral drains with the feeding. However, visibility was generally gfeater at the of likely to Main Drain, where carp wefe most abundant. Visual feeding by carp is therefore be possible at these siæs- The diet of carp is dependent on the availability of food iæms in the environrnent abunda¡rce of (I-ammens and Hoogenboe z.em lpl).Sampting to determine the type and it is difficult to these food items is therefore difficulr Furthermqe, in lotic environments, a large estimaæ the abundance and disribution of invertebrates which constitute because proportion of carp diet (Sibbing 1988, 1991; Lammens and Hoogenboezem 1991) (e'g' homogeneity of the influence of a wide variety of physicechemical characteristics and water and availability of substrates, sediment particle size, light penetration, Hild¡ew 1993)' temperature, dissolved oxygen and velocity; Minshalt t984;Lancaster and comment Without knowing benthic invertebrate distribution, it is therefore not possible to sediment and on the effect of food type and abundance on the contribution of carp to phosphorus resuspension and export from the Mirrool catchment. periods sedirnent Unconsolidated sediment was found in all lateral drains during both of within Main sampling for total phosphorus analysis (Chapter 3). In contrast, the substrate \tater velocity Drain ',J,, was hard-packed clay, except for the littoral fringe where reduced 1993) facilitated due to channel bank friction and the presence of water plants @isma u3 sediment deposition. Unconsolidated sediment was therefore present in all siæs where carp were observed in the Mirroot catchmenl 5.3.2 Retention of Resuspended Sediment in the Water Column Sediment particte size in the Mirrool catchment was not measr¡red in ttris study. However, high \ilater velocity inc¡ease benthic sediment particle size through sediment disturbance and transportation of smaller particles downstream (Linsley et al. t988). Increasing $'ater velocity from the upstream to downstream end of lateral d¡ains (section 3.3-4) therefore indicates that average benthic sediment particle size increases wittr downstrea¡n distance. On ttris basis, sediment resuspended by ca{p at the upstream end of a lateral dr¿in will be retained in the \ñ,ater column longer than that resuspended nearer the downstrean end. Turbulence is also likely to increase with distance from the upsUeam end of lateral drains due to increasing watervelocþ @isma 1993).In conEast to particle size however, increasing trubulence would enhance the reæntion of suspended sediment in ttrc lvater column. The confounding effect of water velocity on sediment particle size and turbulence ûreans there is not a simple, linear relationship between retention of suspended sediment in the water column and upstream drainage. tt4 However, the proximity of sites in lateral drains where carp are most abundant to Main f)rain "J" msa¡¡s ttrat any resuspended sediment is likely to enter the Main Drain. Ha¡d packed clay substraæ in Main Drain "J" indicates minimal deposition, and thus continuotrs transport, of suspended sediÍpnt. Carp in the Mirrool catchment a¡e therefore most abundant in a position that facilitates the export of suspended sediment from the irrigation drainage network. 5.3.3 Phosphorus Content of Sediment The distributions of sedimentary total phosphorus and carp in the Mirrool catchment a¡e inversely related- Temporally, sedimentary total phosphorus concentrations were greatest prior to the commencement of the irrigation season (section 3.3.1), when carp abundances were lowest (section 2.3.1). Spatially, sedimentary total phosphorus concentrations were greatest at the n1gst upstream sites in lateral drains (section 3.3.1), again where carp abundance was lowest (section 2.3.3).The sediment beingresuspended by carp in the Mirrool catchment is therefore generally low in phosphorus. However, the distribution of carp in relation to water velocity likely enhances their effect on export of resuspended sediment, and therefore phosphorus from the irrigation drainage network. 5.3.4 Conclusions The distribution of carp and sedimentary total phosphorus in the Mirrool catchment is related, causally or otherwise, to water velocity. This relationship deærmines the effects of benthic feeding behaviour on \ilater column concentrations of suspended sediment and il5 phosphonrs, and on the export of resuspended sediment and phosphorus from the irrigation drainage network. V/ater velocity inqeases with lateral drain length a¡rd is therefore greatest at the intersection of laæral drains with Main Drain "J". A simila¡ gradient is expected to exist for both turbulence and sediment particle size. The distributions of both carp and sedimentary phosphorus however, follow an inverse gradient, being greatest at the upstream end of laæral drains, and least at the inærsc¡tion of lateral drains with M¿in Drain "J" (Fig. 5.2). Scdiment bionubation by carp is therefore expected to be greatest at thç intersection of lateral drains with Main Drain "J", where sedimentary phosphorus concentrations are lowest and particle sizes greatest. The effect of carp benttric feeding behaviotu on water column suspended sediment and phosphorus concentration is therefore minimis€d- Conversely, the effect of carp on the export of resuspended sediment and phosphonrs from ttre Mirrool catchrrrcnt is ma¡rimised due to gleater water velocity and turbulence in a¡eas with the greatest benthic feeding behaviour. The absoluæ effects of carp cannot, however, be quantified due to an inability to accurately estimaæ otal carp abundance in the Mirool catchmenl The quesúon of whether carp are significant contributon to the suspended sediment and phosphonrs loads exported from irrigation drains therefore remains unanswered. 116 5.4 Conclusions: Sediment and Phosphorus Resuspension bY CarP 1975; Bowmer Carp have been associated with increasing suspended s€diment @owennan phosphorus (Gehrke et al. L992; Brown andHa¡ris t994;Eagle 1994;Killen t994) and Basin' and Harris lÐ4;Hindma¡sh lgg4)concentrations throughout the Murray-Darling exarrined" thus The process of sediment resuspension by carp has not previousþ been the feeding previous studies a¡e based on a simplistic cause and effect relationship between behaviour of carp and sediment resuspension (see Fig' 1'1)' concentrations This study shows the effect of carp on suspended sediment and phosphorus and water to be dependent on not only carp abundance, but also a variety of sediment that the column cha¡acteristics (Figure 5.1). The complexity of this relationship means impact of carp can only be discussed in a context relevant to the physico-chemical char¿cteristics of the study catchment 5.5 Future Work phosphorus resuspension The model presented to describe factors affecting sediment and Basin. conclusions by ca¡p can be applied o waterbodies throughout the Munay-Darling need for an regarding the absolute effect of carp bioturbation ale, however,limited by the in carP accurate estimation of carp abundance. The large scale temporal variations t17 the catchment disqualifies abundance and the patchy spaúal distribution of carp in Mirool measurements (¿.8. capture- the use of standa¡d æchniçes that provide static abundance could be focussed mark-recapture). Instead, frequent small-scale measrÚes of abundance and low potential for sediment on channel sections identified in ttris study as having high carp density' Electrofrshing and phosphorus bioturbation by carp, and/or high and low against collecting juvenile could be used as it is accurate and nondestnrctive, and its bias experiments in these carp would not greatly affectbioturbation estimates. Manipulative on a 'per-carp' basis channel sections to determine sediment and phosphorus resuspension estimaæ the contribution of could be combined with abundance frgures to nþre accurately catchment' cafp to suspended sediment and phosphonrs loads in the Mirroot (see section 1'1), the export with regard to the NRMS project of which this study is a part natural and anthropogenic of phosphorus from irrigation drains is dependent on a fange of application' Opsoil variants including carp, land managenrcnt practices (¿'g' fertiliser (¿'g' and stonn destabilisation by ploughing), drain managenrent practices dredging) in the Mirool catchment' events. During the study p€rid, several large storms occurr€d increased markedly in both Suspended sediment, and therefore phosphorus, concentrations and inc¡eased lvater lateral drains and Main Drain "J" as a result of greater overland flow events velocity.In relatively small,lotic sysæms (e.g. Cj:ieeks and other tributaries)' storm loads, contributing have been shown to be the major con¡ibutors to annual phosphonrs 1995)' The above large amounts of phosphorus over a short time period (e.g' Cullen The variable observations suggested a similar contibution in the Mirool catchment' ll8 impact of such large scale, rapid inpus of phosphorus from irrigation drains to receiving waters, in comparison to smaller scale continuous inPuts (such as that fr'om carp bioturbation), must be considerod when deærmining nutrient rnanagement strategies in inigation drains. Figure 5.1: Model of factors affecting sediment and phosp orus resuspension by carp Increased carp abundance/biomass Rich benthic and depauperate pelagic fauna Increased turbulence (increased water velocity) Ontogenetic shift from sediment planktivory to benthivory Reduced consolidation High turbidity/suspended Reduced sediment particle Increased benthic sediment concentration size (hi clay, low smd) feeding activity Increased volume of sediment Increased retention of susPended Increased sedimentary PhosPhorus (see table 3.1) resuspended by carP sediment in the water column concentration Increased Phosphorus Concentration in the water column \o Figure 5.2: Gradients of carp abundance and physico'chemical characteristics in lateral drains Water Velocity, Turbulencer Sediment Particle Size Carp Abundance' Total PhosPhorus ol.J tzl 122 Appendix 1: Carp observation data sheet Site 1: Ceccato Rd / Main Draln "J" intersection 'Weather: Date: T"rme: V/aærVelocity: Hi Med Low Turbidity: Hi Med Low V/aterDepth (ave cm): S/aterWidth (ave cm): Carp Present Y N Confidence: ll0 Behavioural table: insert no. of observed Behaviour type Upstream 25m Middle 25m Downstream 25m Cruising upstreaût Cnrising downstrea¡n Loafing Feeding Other Size: <15Omm: 150-30Omm: 300-45Omm: >45Omm: Sediment samples taken?: Y N Are sills: Underwater ExPosed nla Other Comments: EZt I?A References Allen, R.J. 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