Environmental Condition of Rivers and Streams in the Mitchell, Tambo and Nicholson Catchments

ENVIRONMENT REPORT

ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

ENVIRONMENT REPORT

ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Freshwater Sciences EPA Victoria 40 City Road, Southbank Victoria 3006 AUSTRALIA

Key contributor: Stephen Perriss

Publication 858 ISBN 0 7306 7620 X

ABSTRACT

This report provides an assessment of the environmental condition of rivers and streams in the Mitchell, Tambo and Nicholson catchments. Together, these river systems form the eastern part of the Gippsland Lakes catchment. Since European settlement, forests in these catchments have been cleared for agriculture, urban development and mining of gold and other metals. In general, the impacts from these activities have been less severe than in the catchments of the Latrobe, Thomson and Avon river systems, which form the western part of the Gippsland Lakes catchment.

The environmental condition of the rivers and streams in the Mitchell, Tambo and Nicholson catchments was assessed against the draft State environment protection policy (Waters of Victoria) (SEPP WoV) biological objectives. Habitat condition and water quality measures were used to explain why sites may be degraded. The environmental condition of sites largely reflected landuse in the catchment.

In the Mitchell catchment – where agriculture and human settlement are largely concentrated in the lowlands – water quality, habitat condition and biological scores were markedly lower compared to sites in the upper catchment. Diminished riparian zones and poor water quality are identified as issues that may help to explain low scores for the draft SEPP WoV biological objectives in the lower reaches of the Mitchell River and its tributaries.

A gradient between upland and lowland sites was less apparent in the Tambo River where much of the catchment in the upper to mid reaches has been cleared for agriculture. Poor riparian zones, elevated salinities and a lack of in-stream habitat for aquatic life are issues in these reaches of the Tambo River and two of its tributaries, Little River and Swifts Creek. These were reflected in low scores for the draft SEPP biological objectives and habitat condition ratings.

In the Nicholson catchment, habitat condition ratings and scores for the draft SEPP biological objectives were generally good. However, Morgans Creek, a small tributary of the Nicholson River, was found to be degraded. This report highlights a number of streams in the Mitchell, Tambo and Nicholson catchments which, like Morgans Creek, are intermittently flowing, particularly in drought years. These stream types are difficult to assess against the draft SEPP (WoV) objectives, which are designed for perennial rivers.

Initiatives are now being implemented to restore the quality and quantity of streamside vegetation and in-stream habitat in these catchments. If support for these programs is to be maintained, their effectiveness needs to be demonstrated. A review of current investment in program monitoring and assessment could be considered, as this feedback is essential for demonstrating the value of programs, improving current programs and adapting to new challenges.

LIST OF ACRONYMS

AUSRIVAS Australian Rivers Assessment System

AWT Australian Water Technologies

CMA Catchment Management Authority

DNRE Department of Natural Resources and Environment

EGCMA East Gippsland Catchment Management Authority

EPA Environment Protection Authority Victoria

EPT Ephemeroptera, Plecoptera, Trichoptera

ISC Index of Stream Condition

NRHP National River Health Program

RBA Rapid Biological Assessment

RHA Rapid Habitat Assessment

SEPP State environment protection policy

SIGNAL Stream Invertebrate Grade Number Average Level

USEPA United States Environmental Protection Agency

VWQMN Victorian Water Quality Monitoring Network

WoV Waters of Victoria

ACKNOWLEDGEMENTS

Stephen Perriss prepared the text, figures and tables for this report and also carried out data manipulations and calculation of biological indices. Lisa Dixon provided extensive editing and review of the various drafts. David Robinson also provided editorial comments.

EPA acknowledges the financial support of the Commonwealth under the NRHP, for the collection of the biological information that forms the primary basis for the assessment of environmental condition.

iii

TABLE OF CONTENTS

ABSTRACT ...... I

LIST OF ACRONYMS ...... II

ACKNOWLEDGEMENTS...... III

1 INTRODUCTION ...... 1

1.1 THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS: FEATURES AND HISTORY...... 1 1.2 SCOPE...... 2 1.3 DATA SOURCES ...... 2 2. ASSESSING ENVIRONMENTAL CONDITION...... 4

2.1 ENVIRONMENTAL QUALITY OBJECTIVES...... 4 2.2 WATER QUALITY...... 5 2.3 BIOLOGICAL QUALITY ...... 7 2.4 HABITAT CONDITION ...... 11 3. BIOLOGICAL REGIONS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHME NTS ...... 12

3.1 HIGHLANDS (REGION 1)...... 12 3.2 FORESTS B (REGION 3) ...... 13 3.4 CLEARED HILLS AND COASTAL PLAINS (REGION 4)...... 13 4. MITCHELL RIVER CATCHMENT ...... 15

4.1 STUDY AREA...... 15 4.2 HISTORY OF CATCHMENT LANDUSE...... 15 4.3 WATER QUALITY CHARACTERISATION AND ASSESSMENT...... 16 4.4 BIOLOGICAL ASSESSMENT...... 19 4.6 MITCHELL CATCHMENT SUMMARY...... 27 5. TAMBO AND NICHOLSON RIVER CATCHMENTS...... 28

5.1 STUDY AREA...... 28 5.2 HISTORY OF CATCHMENT LANDUSE...... 28 5.3 WATER QUALITY CHARACTERISATION AND ASSESSMENT ...... 29 5.4 BIOLOGICAL ASSESSMENT...... 33 5.5 TAMBO AND NICHOLSON CATCHMENT SUMMARY ...... 42 6. OVERVIEW OF THE CATCHMENTS ...... 44

6.1 INTRODUCTION ...... 44 6.2 HIGHLANDS...... 45 6.3 UPPER CATCHMENTS (FORESTS B)...... 45 6.4 LOWLAND REACHES (CLEARED HILLS AND COASTAL PLAINS) ...... 46 6.5 MAIN FACTORS INFLUENCING ENVIRONMENTAL CONDITION...... 47 7. MANAGEMENT INITIATIVES IN THE REGION ...... 49

7.1 CATCHMENT AND WATERWAYS MANAGEMENT ...... 49 8. CONCLUSIONS...... 51

8.1 HABITAT DEGRADATION ...... 51 8.2 WATER QUALITY...... 51

8.3 MONITORING AND ASSESSMENT ...... 51 9. REFERENCES AND FURTHER READING ...... 53

APPENDIX 1: BIOLOGICAL INDICATORS AND REGIONS ...... 57

1.1 USING MACROINVERTEBRATES AS BIOLOGICAL INDICATORS...... 57 1.2 DEVELOPING THE BIOLOGICAL REGIONS...... 58 1.3 AUSRIVAS ...... 58

TABLES

TABLE 1: DRAFT STATE ENVIRONME NT PROTECTION POLICY (WATERS OF VICTORIA) IN-STREAM WATER QUALITY INDICATORS AND OBJECTIVES AS THEY APPLY TO THE MITCHELL, TAMBO AND NICHOLSON CAT CHMENTS...... 6

TABLE 2: DRAFT BIOLOGICAL OBJECTIVES AND HABITAT CONDITION CATEGORIES FOR EACH BIOLOGICAL REGION IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS...... 9

TABLE 3: WATER QUALITY RESULTS FOR BIOLOGICAL SITES IN THE MITCHELL CATCHMENT...... 17

TABLE 4: WATER QUALITY RESULTS FROM VWQMN SITES IN THE MITCHELL CATCHMENT BETWEEN 1996 AND 1999...... 18

TABLE 5: TRENDS IN WATER QUALITY IN THE MITCHELL CATCHMENT, 1975 TO 1999...... 19

TABLE 6: RESULTS FOR DRAFT BIOLOGICAL OBJECTIVES, ISC AND RHA FOR SITES IN THE MITCHELL CATCHMENT. ..21

TABLE 7: AUSRIVAS AND SIGNAL SCORES FOR MITCHELL RIVER DOWNSTREAM OF WENTWORTH RIVER (WYG)...... 24

TABLE 8: WATER QUALITY RESULTS FOR BIOLOGICAL SITES IN THE TAMBO AND NICHOLSON CATCHMENTS...... 30

TABLE 9: WATER QUALITY RESULTS FROM VWQMN SITES IN THE TAMBO AND NICHOLSON CATCHMENTS BETWEEN 1996 AND 1999...... 32

TABLE 10: TRENDS IN WATER QUALITY IN THE TAMBO AND NICHOLSON CATCHME NTS, 1975 TO 1999...... 33

TABLE 11: RESULTS FOR DRAFT BIOLOGICAL OBJECTIVES, ISC AND RHA FOR SITES IN THE TAMBO AND NICHOLSON CATCHMENTS...... 35

TABLE 12: SIGNAL SCO RES AND NUMBER OF KEY FAMILIES FOR TIMBARRA RIVER AT TIMBARRA PLAINS...... 38

TABLE 1: EXAMPLE AUSRIVAS O/E FAMILY SCORE CATEGORIES...... 59

FIGURES

FIGURE 1: LOCATION OF THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS IN VICTORIA...... 3

FIGURE 2: BIOLOGICAL REGIONS OF VICTORIA...... 8

FIGURE 3: TIMBARRA RIVER AT TIMBARRA PLAINS...... 12

FIGURES 4 AND 5: WONNANGATTA RIVER AT WATERFORD (LEFT) AND TAMBO RIVER AT PRETTY FLAT CREEK (RIGHT)...... 13

FIGURES 6 AND 7: MITCHELL RIVER AT LAMBERTS FLAT (LEFT) AND NICHOLSON RIVER UPSTREAM OF MORGANS CREEK (RIGHT)...... 14

FIGURE 8: LOCATION OF VWQMN SITES AND BIOLOGICAL REGIONS IN THE MITCHELL CATCHMENT...... 18

FIGURE 9: AUSRIVAS AND SIGNAL RATINGS FOR SITES IN THE MITCHELL CATCHMENT...... 22

FIGURES 10 AND 11: FLAGGY CREEK (LEFT) SHOWING CATTLE ACCESS TO THE CREEK UPSTREAM OF THE SAMPLING SITE. THERE IS NO SIGNIFICANT RIPARIAN ZONE AND THE STREAM BANKS ARE BADLY ERODED. TOMS CREEK (RIGHT) SHOWING PLACEMENT OF BOULDERS TO REINFORCE ERODING STREAM BANKS AND REPLANTING OF NATIVE RIPARIAN VEGETATION BY LANDCARE. CATTLE ARE GRAZED IN THE CATCHMENT OF THIS CREEK BUT FENCING PREVENTS THE M DIRECTLY ACCESSING THE WATER...... 27

FIGURE 12: TAMBO RIVER AT BRUTHEN SHOWING LARGE DEPOSITS OF SAND ON THE RIVERBED...... 29

FIGURE 13: LOCATION OF VWQMN SITES AND BIOLOGICAL REGIONS IN THE TAMBO AND NICHOLSON CATCHMENTS...... 31

FIGURE 14: AUSRIVAS AND SIGNAL RATINGS FOR SITES IN THE TAMBO AND NICHOLSON CATCHMENTS...... 37

FIGURES 15 AND 16: SWIFTS CREEK (ISC REACH 19) AND LITTLE RIVER (ISC REACH 18)...... 40

FIGURE 17: NICHOLSON RIVER UPSTREAM OF MORGAN’S CREEK (XYL) SHOWING GOOD RIPARIAN ZONE DOMINATED BY NATIVE VEGETATION...... 41

FIGURE 18: TAMBO RIVER AT STEPHENSON ROAD (XYN) SHOWING LOW FLOW STATUS AND LIMITED RIPARIAN ZONE...... 42

ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

1 INTRODUCTION

1.1 The Mitchell, Tambo and Nicholson Catchments: Features and History

The Mitchell and Tambo river catchments are located in the Gippsland region of Victoria (Figure 1) and form part of the catchment area of the Gippsland Lakes. These lakes are ecosystems of international significance and are listed under the Ramsar Convention on Wetlands. Lake Wellington is the westernmost of the lakes, connecting to Lake Victoria via McLennan’s Strait. Lake Victoria flows into Lake King, which connects to Bass Strait at Lakes Entrance. Both the Mitchell and Tambo rivers discharge to Lake King, which supports extensive beds of sea grass, aquatic macrophytes and a rich marine benthic fauna. Lake Victoria and Lake King are more influenced by marine waters than Lake Wellington, but freshwater inputs into Lake Wellington from the Latrobe, Thomson and Avon rivers significantly influence the water quality of the lakes system as a whole, particularly the western end of Lake Victoria (EPA 1996).

The East Gippsland Catchment Management Authority (EGCMA) region extends eastward from the Mitchell, Tambo and Nicholson catchments to the New South Wales border and also includes the Victorian portion of the Snowy River catchment. The region has undergone extensive changes since European settlement in the 1830s but is still one of the least impacted regions in Victoria, largely as a result of relatively low population levels. Agriculture is an important part of the East Gippsland economy. Farmland covers approximately 419,300 hectares of the 2.13 million hectares in the region. Most of the income generated is derived from crops but livestock is also a substantial component. Forestry is a significant sector of the regional economy and East Gippsland accounts for a substantial proportion of Victoria’s hardwood timber production. Approximately 1.26 million hectares of the East Gippsland region are in State Forest although only 35 to 40 per cent of this area is available for harvesting.

The region is also an important location for commercial and recreational fishing. Fisheries in the Gippsland Lakes account for 2.5 per cent of the total Victorian catch. Evidence from a 1995 survey of recreational fishers (Conron and Coutin 1995) suggested that fish catches in the Gippsland Lakes have significantly declined since the early 1980s. With large areas of native forests, rivers and lakes, and long stretches of coastline, East Gippsland is a popular tourist destination. Recreation and tourism are significant contributors to the regional economy, emphasising the importance of protecting and enhancing the region’s environmental values.

Since European colonisation of the region, nutrient exports and loads have increased and water quality has generally deteriorated in the Lakes. The natural flow regimes of the major river systems have been significantly altered as a result of dam construction and other water-harvesting activities. One of the most visible signs of deterioration is the occurrence of major algal bloom outbreaks recorded at regular intervals since 1974. Blooms of Nodularia spumigenia (a toxic, nitrogen-fixing blue-green alga) frequently occur, mostly in wet years when nutrient inputs from the Lakes’ catchments are greatest as a result of increased agricultural run-off. There is a rising level of community concern about the environmental health of the Gippsland Lakes. As a result, the water

Environment Report 1 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

quality, hydrology and catchment landuse of the region has been the subject of greater attention in recent times (see Harris et al. 1998).

A number of studies have attempted to quantify the contribution of nutrient loads from the various river systems to the Gippsland Lakes (EPA 1986, Grayson et al. 2001, Longmore 1989). These studies have shown that the Latrobe, Macalister and Thomson rivers are by far the major contributors of nutrient loads to the Lakes. The loads from these rivers are twice that of the Mitchell, Nicholson and Tambo rivers combined (Grayson et al. 2001), and the impact of these inputs is greatest under high flow events (Robinson 1995). All of the nutrient inputs from the Latrobe, Macalister and Thomson rivers enter Lake Wellington. The Mitchell and Tambo rivers are significant sources of inorganic nitrogen to the nitrogen-limited Lake King (EPA 1986, Longmore 1989). Biogeochemical modelling suggests that reductions of 50 to 70 per cent in current loads from the rivers entering the Gippsland Lakes would be required to reduce the intensity of algal blooms (Grayson et al. 2001).

1.2 Scope

This report provides an assessment of the environmental condition of rivers and streams in the Mitchell, Tambo and Nicholson catchments. The main focus of the study considered the impacts of broad catchment-wide issues. The effects of specific point source discharges and urban areas are not addressed. The assessment is based largely on biological indicators, these being the best indicators of overall condition, but also incorporates water and habitat quality assessments.

1.3 Data Sources

The information presented in this report incorporates a number of data sources, but relies predominantly on biological monitoring undertaken by EPA between 1990 and 1999 as part of the National River Health Program (Davies 1994) and State-wide biological monitoring programs. Other main sources of information include the Index of Stream Condition assessment (Victorian Water Resources Data Warehouse) and water quality data collected for the Victorian Water Quality Monitoring Network (1977 to present).

EPA Victoria 2 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figure 1: Location of the Mitchell, Tambo and Nicholson catchments in Victoria.

Environment Report 3 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

2. ASSESSING ENVIRONMENTAL CONDITION

Monitoring and assessment of environmental condition provides essential feedback on the state of our river systems. This feedback enables managers to develop and refine management programs, and to direct resources and activities to where they are needed most.

Traditionally, assessment programs have relied upon physical and chemical indicators of water quality. EPA Victoria has moved in recent years towards a more holistic approach to environmental assessment in rivers and streams, incorporating biological indicators of ecosystem health.

When using physical and chemical indicators alone, the underlying assumption has been that if these are met, then the aquatic environment can be considered to be in good health. However, the problems with using physical and chemical indicators alone include:

· interactions between contaminants, which may affect biota, are not taken into account;

· the types of measurements, as spot measurements in time, do not reflect the full variability of water quality. Intermittent inputs and flood events are often missed;

· appropriate parameters may not be measured; and

· a reliance on physical and chemical data does not allow for assessment of other factors that affect distribution of biota, such as inadequate physical habitat, water volume or introduced species.

The use of biological indicators largely overcomes these problems and provides a means for directly assessing the health of an ecosystem. Importantly, the impacts of factors other than water quality, such as habitat degradation and altered flows, can also be detected using biological indicators.

2.1 Environmental Quality Objectives

SEPPs set a statutory framework for the protection of agreed beneficial uses and values of Victoria’s water environments. One of the key beneficial uses is the protection of aquatic ecosystems. Other beneficial uses include water supply for domestic, industrial and agricultural uses, and recreational use of surface waters.

Each beneficial use of water has its own quality requirements. SEPPs protect beneficial uses by establishing environmental quality objectives for key indicators. These objectives are based upon what is achievable in the context of natural background levels and constraints placed by human landuses and activities within a catchment. Objectives are set to maintain the quality of a healthy ecosystem or, in the case of degraded systems, are more usually set as targets to bring about a significant improvement in the condition of a water body over time.

EPA Victoria 4 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

In Victoria, all surface waters are covered by the SEPP Waters of Victoria (WoV) (Government of Victoria 1988), which sets the strategic framework and environmental quality objectives for the protection of all surface waters within Victoria. Within the framework of the SEPP WoV, schedules are developed for specific water bodies and catchments in Victoria. For indicators of environmental condition not covered by specific schedules, the objectives in the principal policy SEPP WoV apply, which is the case for the Mitchell, Tambo and Nicholson catchments.

The SEPP WoV is currently under review (EPA publication 795). Building on the knowledge gained in the last decade, quantitative objectives that better reflect environmental quality, including biological objectives, have been developed as a part of the review process and are used in this condition assessment.

2.2 Water Quality

The key physical and chemical indicators considered in this report are nutrients (phosphorus and nitrogen), turbidity, salinity, pH, temperature and dissolved oxygen. The draft SEPP WoV has been used as the basis for the assessment of physical and chemical indicators of water quality (Table 1).

Water quality assessments are based on data from a number of sources. The first is EPA site data, from water samples taken and field parameters measured at the time of biological sampling. There are, however, limitations in the use of these data in that they only represent two points in time and trends cannot be described, nor can it be clearly stated whether water quality meets established objectives. These data can only be used to give an indication of the conditions in which the biota were living at the time of collection, and to help explain differences in community composition. Site-based water quality data are, in effect, water quality snap-shots of the catchments. These snap-shots can be used to graphically display longitudinal patterns in chemical gradients along the rivers, but should be interpreted cautiously due to the small number of samples and because the snap- shot samples are spread out over a period of weeks.

There are a number of reports and databases that assess or provide long-term water quality data throughout the Mitchell, Tambo and Nicholson catchments. The major sources used are annual reporting from the VWQMN (AWT 1999) and trend analysis based on sites with a minimum of 10 years data (Smith and Nathan 1999). The information from these sources is used in conjunction with the water quality data collected during the biological sampling to complement and strengthen our understanding of environmental quality in the rivers and streams throughout the three catchments.

Environment Report 5 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Table 1: Draft state environment protection policy (Waters of Victoria) in-stream water quality indicators and objectives as they apply to the Mitchell, Tambo and Nicholson catchments.

WoV Segment Dissolved oxygen Turbidity Electrical pH Total nitrogen Total phosphorus saturation (%) (NTU) conductivity (µg/l) (µg/l) 25th percentile (µS/cm) 25th/75th 75th percentile 75th percentile /maximum 75th percentile 75th percentile percentiles Mountain reaches

in the Mitchell,

Tambo and 95/110 5 100 6.4/7.7 150 20 Nicholson

Highlands catchments

Upland reaches in the Mitchell, Tambo and 90/110 5 100 6.4/7.7 350 25 Nicholson

Forests B catchments

Lowland reaches

in the Mitchell, Tambo and 85/110 10 500 6.4/7.7 600 40

Plains Nicholson

and Coastal catchments Cleared Hills

EPA Victoria 6 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

2.3 Biological Quality

During the last decade, EPA has developed biological monitoring methods in recognition of the shortcomings of using only physical and chemical objectives for the protection of aquatic ecosystems. These incorporate indicators and draft objectives to supplement existing water quality objectives in environmental policies.

The SEPP Schedule F7 for the Yarra River (Government of Victoria 1999) was the first to include quantitative biological objectives for aquatic macroinvertebrates as well as the presence of certain species of fish. Draft biological objectives have been developed and are being considered for the revised SEPP WoV (Table 2). If adopted, these draft objectives will apply to all Victorian surface water streams that do not have specific catchment-based objectives in place.

Given that it is not practical to develop objectives for all ecosystem components and processes, EPA selected aquatic macroinvertebrates as the most appropriate component for developing biological objectives (see Appendix 1.1). A fundamental feature of the draft objectives is that they are based on biological regions. This was needed due to the obvious differences between, for example, an alpine stream and a stream in the Wimmera. Biota in different regions are distinctive and require their own regionally-based objectives. This approach is similar to that used to develop water quality objectives in catchment-based policies in which segments are defined, usually based upon landuse. In this case, the regions have been defined by the biota (Figure 2) and are further described in Chapter 3 and Appendix 1.2.

The draft biological objectives represent goals for the restoration of some streams and minimum maintenance standards for others. Some streams of very high quality will easily meet the draft objectives and, in these cases, maintenance of background condition is required.

Seven indices of river condition are used to assess the environmental condition of the rivers and streams in the Mitchell, Tambo and Nicholson catchments. They are AUSRIVAS (AUStralian RIVers Assessment System), SIGNAL (Stream Invertebrate Grade Number Average Level), Key Families, Number of Families, EPT (Ephemeroptera + Plecoptera + Trichoptera) Index, the ISC (Index of Stream Condition (ISC), and the USEPA Rapid Habitat Assessment (RHA) Protocol.

Of these indices, five specifically assess the status of the aquatic macroinvertebrate community (AUSRIVAS, SIGNAL, Key Families, Number of Families and EPT), one is specific to stream habitat values (RHA), and the other (ISC) is a general overview incorporating five components of stream condition. The latter two indices (RHA and ISC) are mainly used to assist the interpretation of the biological assessments.

Draft objectives for ecological health, within each biological region, are generally provided for each of four macroinvertebrate community indices (AUSRIVAS, SIGNAL, Number of Families, and EPT). These indices can be broadly grouped into three categories – a measure of diversity (Number of Families), biotic indices (SIGNAL and EPT) and measures of community structure (AUSRIVAS). Where AUSRIVAS results are not available, the Key

Environment Report 7 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Families indicator is used. Draft objectives are provided for both riffle and edge habitats as different invertebrate communities occur in each habitat and both habitats may not occur at all sites.

The draft biological objectives cover a broad range of sizes and stream types, and some anomalies are expected to occur. It is possible, for example, that one habitat will pass while the other habitat fails to meet all objectives. When this discrepancy between habitats occurs, then the overall site assessment is usually based on the worst outcome; that is, an environmentally conservative approach is followed. If a site does not meet one or more of the draft biological objectives, the judgement or opinion of qualified stream ecologists is needed to determine whether the stream is anomalous within its assigned region or is truly failing to meet objectives. In some cases, this could highlight the need for further sampling of the site to clarify the assessment.

Assessment against the draft biological objectives requires that:

· the Rapid Bioassessment Protocol (RBA) (EPA 1998) has been used to collect the data;

· edge and/or riffle habitat data are used;

· samples are collected from two seasons (spring and autumn) within one year, and combined for assessment; and

· presence or absence of all invertebrate families is recorded.

Biological Regions Highlands For ests A For ests B Clear ed Hills and Coastal Plains Murra y and Western Plains Unclassified

0 50 100 150 200 Kilometers

Figure 2: Biological Regions of Victoria.

EPA Victoria 8 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Table 2: Draft biological objectives and habitat condition categories for each Biological Region in the Mitchell, Tambo and Nicholson catchments.

Indicator Highlands Forests B Cleared Hills and Coastal Plains (Region 1) (Region 3) (Region 4) (edge/riffle) (edge/riffle) (edge/riffle) AUSRIVAS N/A Band A Band A SIGNAL 6.2/5.8 5.8/6.0 5.5/5.5 Number of Families 13/22 24/23 26/23 EPT Index score 4/10 9/10 N/A Key Families (Combined habitats) 18 N/A N/A

ISC/RHA Condition Excellent Good Marginal Poor Very Poor Rating ISC score 42-50 35-41 26-34 20-25 0-19 RHA score >150 140-150 130-140 120-130 <120 N/A = not applicable

AUSRIVAS

AUSRIVAS is a classification and predictive modelling technique based upon the River InVertebrate Prediction And Classification System (RIVPACS), originally developed in Britain (Wright 1995). AUSRIVAS was developed under the Federal Government’s National River Health Program as a means to assess the condition of rivers and streams across Australia. The models predict the aquatic macroinvertebrate families expected to occur at a site in the absence of environmental stressors, such as water pollutants or habitat degradation. By comparing the totalled probabilities of predicted families and the number of families actually found, a ratio can be calculated for each test site. This ratio is expressed as the observed number of families/expected number of families (the O/E index). The O/E scores are used to place a site into a band or category that summarises its ecological health. The derivation of AUSRIVAS scores and the banding categories are given in Appendix 1.3.

Regional models have been developed for all biological regions except the Highlands Region. As a consequence, there is no draft AUSRIVAS objective for the Highlands Region. In this case, the site is assessed against the alternative draft Key Families objective.

In this report, unless otherwise noted, collections from two seasons (spring/autumn) are combined for assessment. Where multiple visits to a site have occurred, only the most recent sampling data are used. If data from two seasons is not available for a site then a single season assessment is presented.

Key Families

This method focuses mainly on the loss of taxa indicative of good habitat and water quality. The families that are selected are those that are typically found in the streams of the region. For example, families such as Coloburiscidae and Austroperlidae occur in cool, forested streams typical of the upland and mountain areas of

Environment Report 9 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

the State. Other families, such as Calamoceratidae, Coenagrionidae and Hydrophilidae become more common in the warmer streams of the foothills and lowlands. Not all of the families can be expected to occur in every stream throughout each region. The Key Families include taxa that are representative of all major habitats expected in each region and are commonly collected when present.

SIGNAL

The SIGNAL index (Chessman 1995), is an arithmetic average of pollution sensitivity values assigned at the family level for aquatic macroinvertebrate taxa. It was developed for south-eastern Australian streams and is more sensitive to organic pollution than to habitat degradation. Sensitivity values range from one to 10 with lower values representing pollution-tolerant families. Some macroinvertebrate families were not assigned scores in Chessman (1995) but have subsequently been allocated sensitivity ratings (B. Chessman, pers. Comm.).

Number of Families

The number of aquatic macroinvertebrate families collected using RBA provides a general indication of the health of a site. Generally, a healthy site will support a large number of families, whereas the presence of stressors will eliminate some families. The number of families of invertebrates found at a site will vary over time and also across a catchment. This is a simple index of health and is used in conjunction with other biotic indices.

EPT Index

Species from the insect orders of the Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies) are considered to be some of the most sensitive to pollution and disturbance. High numbers of families from these orders at a site are considered to indicate a healthy stream.

Index of Stream Condition – ISC

The ISC is a general indicator of the environmental condition of rivers and streams. It integrates information from five sub-indices (Victorian Water Resources Data Warehouse):

1. Hydrology – flow volume and seasonality of flow

2. Physical Form – stream bank and bed condition, presence of and access to physical habitat

3. Streamside Zone – quality and quantity of streamside vegetation

4. Water Quality – nutrient concentration (total P), turbidity, electrical conductivity and pH

5. Aquatic Life – diversity of macroinvertebrates

The final ISC score is a weighted mean of the five sub-indices and ranges from zero to 50 with higher scores (greater than 35) indicating good stream condition (see Table 2).

EPA Victoria 10 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

The data for the Hydrology, Water Quality and Aquatic Life sub-indices were collated by the DNRE from the Victorian Hydrographic Network, the VWQMN and the NRHP, respectively. In some cases, data for the Water Quality and Aquatic Life sub-indices were not available and were estimated by EPA. The East Gippsland CMA collected physical form and streamside zone data during site visits in 1999.

Rapid Habitat Assessment – RHA

Rapid Habitat Assessment (Barbour et al. 1999) classifies a stream’s habitat condition based upon the variety and quality of the substrate, channel morphology, bank structure and riparian vegetation. Ten parameters are evaluated visually and rated on a numerical scale of zero to 20, giving a possible range of scores from zero to 200. Scores greater than 140 are considered to indicate good to very good habitat conditions (Table 2). RHA data were collected as part of the National River Health Program.

2.4 Habitat condition

In the past, water quality has been a major focus of attention. Recently, however, the physical degradation of waterways and poor in-stream and riparian habitats are receiving increased recognition. Maintenance of a stream’s habitat features is a key component of river health. Even with good water quality and flows, a healthy aquatic ecosystem cannot be supported if suitable habitat is not present.

While quantitative environmental quality objectives for habitat have yet to be developed, the importance of habitat is emphasised in the draft SEPP WoV management objectives, which feature strongly in the policy’s attainment measures. In this report, general qualitative or semi-quantitative assessments of habitat condition have been used.

Habitat quality assessments are based on the USEPA RHA Protocol and the ISC (Table 2).

Environment Report 11 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

3. BIOLOGICAL REGIONS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

3.1 Highlands (Region 1)

As the name suggests, the Highlands Biological Region is restricted to the high country of Victoria, with streams often on steep slopes, generally above 1,000m and subject to high rainfall. The vegetation tends to be native forest, woodland and grassland. Riparian shading varies from moderate to low cover, depending on whether streams flow through forested or grassland areas respectively. The streams tend to be small (compared to other biological regions). They also have the lowest water temperatures, and very low alkalinity, turbidity and salinity. The stream habitat is generally characterised by the presence of riffles and limited edge habitat, with coarse substrate and low macrophyte cover and diversity. An example of a site in this region is the Timbarra River at Timbarra Plains in the Tambo catchment (Figure 3).

Figure 3: Timbarra River at Timbarra Plains.

EPA Victoria 12 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

3.2 Forests B (Region 3)

The Forests B Region incorporates the Otway Ranges and the foothills both north and south of the Great Dividing Range, forming a discontinuous region supporting tall open forests. The region generally covers an area lower in altitude than the Highlands Region (Figure 2). Stream slopes are less steep and rainfall is moderate to high. A greater degree of clearing for forestry, grazing and some intensive agriculture occurs in this region compared with the Highlands Region. This results in a lower level of riparian shading. Streams are generally larger, with more than double the catchment area of streams in the Highlands Region. Alkalinity of the cool waters typical of this region is slightly elevated relative to the Highlands Region, but still remains low along with turbidity and salinity. Stream habitat is characterised by the presence of riffles and edges, with very coarse substrate and high macrophyte diversity and cover. Figures 4 and 5 show examples of this type of river from the Mitchell and Tambo catchments.

Figures 4 and 5: Wonnangatta River at Waterford (left) and Tambo River at Pretty Flat Creek (right).

3.4 Cleared Hills and Coastal Plains (Region 4)

The urban area of Melbourne divides this region, which is characterised by coastal plains in the south, and inland plains and low foothills in the north and east. Streams flow through an undulating landscape of low altitude with little gradient and relatively low rainfall. The region has been substantially cleared for intensive agriculture (including dryland pasture and some irrigated pasture), resulting in poor riparian shading. Warm stream waters with high alkalinity, and low to moderate turbidity and salinity, characterise the region. The edge habitat is more developed and extensive runs and riffles are less common. The substrate tends to be composed of moderate to fine particles, and there is a very high diversity and moderate cover of macrophytes. Figures 6 and 7 show examples of rivers in this region from the Mitchell and Nicholson catchments.

Environment Report 13 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figures 6 and 7: Mitchell River at Lamberts Flat (left) and Nicholson River upstream of Morgans Creek (right).

EPA Victoria 14 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

4. MITCHELL RIVER CA TCHMENT

4.1 Study Area

The Mitchell River catchment extends from the eastern highlands of the Alpine National Park in the north to Lake Victoria in the south. The total area of the catchment (5,500km2) represents 26 per cent of the catchment area of the Gippsland Lakes, and the mean annual flow of 960,000ML represents 28 per cent of the total discharge. Elevations in the eastern highlands are generally 1,200m above sea level and higher, rising to 1,868m at Mount Hotham in the north of the catchment. The Mitchell River rises in the Barry Mountains between Mounts’ Howitt and Hotham. In its headwaters, the Mitchell River is known as the Wonnangatta River. Tributaries of the Wonnangatta River include the Wongungarra and Dargo rivers. Downstream of its junction with the Wentworth River at Tabberabbera (Figure 8), the river is known as the Mitchell River, which flows through a narrow gorge to emerge in undulating plains at Glenaladale. The river then winds through alluvial flats, the major rural town of Bairnsdale and drains into Lake King.

The climate varies between the north and the south of the catchment, with the north being generally cooler and wetter than the alluvial and coastal plains in the south. For example, average annual rainfall ranges from 1,200 to 1,600mm in the high country of the Dargo Plains but decreases to 702mm at Bairnsdale. Approximately 75 per cent of average annual stream flows occur in winter and spring, partly as a result of snowmelt from the upper catchment.

Much of the Mitchell River catchment is based on the conglomerate, pebbly sandstone, sandstone and siltstone of the Early Carboniferous Period (about 350 million years ago). Consequently, the beds of streams in this catchment are generally very stony. An exception is Clifton Creek, which derives its sediment from older Ordovician (510 to 435 million years ago) rock and is composed of much finer sediment.

In April 1990, the Mitchell River suffered one of its largest recorded floods. The effects were most strongly felt in tributaries including the Crooked and Wonnangatta rivers, whose stream banks were badly eroded. Extensive floodplain stripping also occurred in these tributaries (Erskine et al. 1990).

4.2 History of Catchment Landuse

European settlement in the Mitchell catchment dates back to the 1840s, when areas of the southern plains were first used for grazing, vegetable growing and dairying. However, the mountainous country of the north was largely undeveloped at this time. Although gold was discovered in the Mitchell catchment in the mid-nineteenth century, gold mining was relatively short-lived. During this time, land was cleared in the catchments of the Crooked and Wongungarra rivers, although the forest regenerated after mining finished. Many miners remained in the region to farm land in the plains of the Mitchell, Dargo and Wentworth rivers. By the 1880s, maize, wheat, potatoes,

Environment Report 15 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

hops and other crops were all being grown in the catchment. The building of a rail link with Melbourne led to an increase in dairy and vegetable production to supply the Melbourne market. Further expansion occurred to meet needs during World War II.

The north of the catchment is still largely forested, with the exception of areas that have been cleared for grazing in the lower reaches of the Dargo River. The foothills to the south of the eastern highlands are sparsely populated but used extensively for timber production. The timber industry developed initially to supply needs for building and fencing during the settlement period of the nineteenth century but then expanded to meet wartime and post- war construction requirements. Since the 1970s, however, the timber industry in Gippsland has been in decline.

The forests of the Mitchell catchment are also a significant recreation resource. The north-west of the catchment encompasses part of the Alpine National Park while the mid to upper reaches of the Mitchell River are set aside in the Mitchell River National Park. The Wonnangatta and Mitchell Rivers are classed as Heritage Rivers under the Heritage Rivers Act 1992 due to their high conservation values, relative intactness and relatively natural flow regimes.

The south of the catchment is more populated and includes the towns of Bairnsdale and Paynesville. The alluvial plains in the south of the catchment are extensively used for dairying, grain growing, grazing and vegetable production.

4.3 Water Quality Characterisation and Assessment

The draft SEPP WoV water quality objectives for the Mitchell, Tambo and Nicholson catchments are given in Table 1. Water quality results for turbidity, dissolved oxygen, salinity (electrical conductivity), pH, total nitrogen (TN) and total phosphorus (TP) for biological sites are presented in Table 3. These EPA site data provide an indication of possible non-compliance with draft objectives (see 2.2).

EPA Victoria 16 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Table 3: Water quality results for biological sites in the Mitchell catchment.

Site Site Biological Total N Total P Turbidity EC25 Code Region (mg/l) (mg/l) (NTU) (mS/cm) Upland reaches of the Mitchell River and tributaries Wonnangatta River at Moroka WYB 3 0.11 0.016 1.8 40

Wonnangatta River at Crooked River WYC 3 0.09 0.015 1.1 48

Wonnangatta River at Waterford WYL 3 0.18 0.018 1.5 69

Mitchell River downstream of WYG 3 0.10 0.011 0.8 59 Wentworth River Wongungarra River at Crooked River WYD 3 0.16 0.315 1.4 52

Wentworth River at Jones Road WYF 3 0.16 0.013 2.8 61

Dargo River downstream of Wallace WYE 3 0.21 0.026 1.2 48 Creek Dargo River at Dargo WYM 3 0.17 0.012 1.9 62

Dargo River at Lower Dargo Road WYN 3 0.19 0.015 1.4 72

Cobbannah Creek at Dargo Road WYS 3 0.24 0.017 9.1 141

Cleared Hills and Coastal Plains

Mitchell River at Lamberts Flat WYR 4 0.14 0.016 0.9 70

Mitchell River at Perry’s Crossing WYI 4 0.14 0.012 1.1 88

Mitchell River downstream of Lindenow WYA 4 0.11 0.115 1.4 65

Mitchell River at Soldier’s Road WYQ 4 0.34 0.018 2.8 112

Iguana Creek at Dargo Road WYK 4 0.64 0.033 12.8 608

Flaggy Creek at Wy Yung-Calulu Road WYO 4 0.42 0.015 3.0 3904

Boggy (Prospect) Creek at Counihans WYP 4 1.11 0.098 6.8 1528 Bridge Clifton Creek WYH 4 0.42 0.017 29.7 1090

Toms Creek at Bengworden WYJ 4 3.19 0.180 16.9 2025

Red indicates a value greater than the 75th percentile draft SEPP objective.

In addition to the water quality data collected during the biological surveys, there are three VWQMN sites in the Mitchell catchment. These results were assessed against the draft SEPP objectives on the basis of average

Environment Report 17 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

monthly values between 1996 and 1999. The location of these sites and the draft SEPP segments they fall within are presented in Figure 8.

Figure 8: Location of VWQMN sites and biological regions in the Mitchell catchment.

Table 4: Water quality results from VWQMN sites in the Mitchell catchment between 1996 and 1999.

Site name Site number TN TP EC Turbidity

(mg/l) (mg/l) (mS/cm) (NTU)

Mitchell River at 224203 0.252 0.023 84 3 Glenaladale

Wonnangatta River at 224206 0.268 0.025 55 3 Crooked River

Dargo River at Lower 224213 0.271 0.028 78 2 Dargo Road

Values that exceeded the draft SEPP objectives are highlighted in red.

EPA Victoria 18 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Generally, the VWQMN sites met the draft SEPP objectives. The exception was Dargo River at Lower Dargo Road (224213) where the 75th percentile value for total phosphorus was just above the draft objective.

Trends in water quality of VWQMN sites in the Mitchell catchment are presented in Table 5. Analysis was based on sites with a minimum of 10 years data (Smith and Nathan 1999). The analysis did not find a significant increase in total nitrogen or total phosphorus levels at any of the three sites. In fact, there was a trend of decreasing total nitrogen levels at Mitchell River at Glenaladale (224203) and Wonnangatta River at Crooked River (224206).

Table 5: Trends in water quality in the Mitchell catchment, 1975 to 1999.

Site name Site pH Turbidity Electrical Total Total Conductivity Nitrogen Phosphorus number (NTU) (mS/cm) (mg/l) (mg/l)

Mitchell River at 224203 Change (units 0.000 0.00 0.0 -0.013 0.0 per year) Glenaladale

Significance **** **** NS **** ****

Wonnangatta 224206 Change (units 0.000 0.00 0.0 -0.011 0.0 per year) River at Crooked River Significance * NS **** **** NS

Dargo River at 224213 Change (units 0.000 0.00 0.0 - - per year) Lower Dargo Road Significance **** NS ****

Source: Smith and Nathan 1999

4.4 Biological Assessment

The seven indices described in section 2.3 have been used to make an assessment of the environmental condition of the health of the Mitchell River catchment. The draft SEPP biological objectives for each region and the habitat condition categories are shown in Table 2. The results for the Mitchell catchment sites are given in Table 6.

For the convenience of discussion, the Mitchell catchment sites have been divided into two groups that broadly correspond to the topography and type of landuse present. The grouping reflects the boundaries of the biological regions.

Environment Report 19 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

1. Upland reaches of the Mitchell River and tributaries (Forests B) (10 sites)

2. Cleared hills and coastal plains (9 sites)

The rivers and streams in the Mitchell River catchment that are considered to be in good ecological condition are found predominantly in the upper catchment. Most of the creeks in the lower catchment suffer from habitat and water quality degradation. This is evident in Figure 9, which shows the AUSRIVAS and SIGNAL results for each site. The AUSRIVAS and SIGNAL results are discussed in relation to the draft SEPP WoV objectives.

A number of creeks in the Mitchell catchment, such as Toms and Iguana creeks, are intermittent. Neither creek was flowing when sampled in autumn 1998 although they were both flowing the following spring. These stream types are poorly represented in the reference site data set used to derive the draft objectives. Therefore, the results presented here give an indication of the health of these streams but further investigation using the risk- assessment approach would be necessary to make an accurate assessment.

EPA Victoria 20 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Table 6: Results for draft biological objectives, ISC and RHA for sites in the Mitchell catchment.

Site Site Biol. AUSRIVAS SIGNAL Number of Families EPT families ISC Reach ISC Score RHA Code Region Edge Riffle Edge Riffle Edge Riffle Edge Riffle

Upland reaches of the Mitchell River and tributaries

Wonnangatta River at Moroka WYB 3 1.05 (A) 1.14 (X) 6.2 6.6 34 41 14 21 12 45 166# Wonnangatta River at Crooked River WYC 3 0.99 (A) 0.96 (A) 5.8 6.4 32 31 9 13 11 33* 132 Wonnangatta River at Waterford WYL 3 1.05 (A) 1.04 (A) 5.8 6.5 36 38 12 17 9 36*+ 162 Mitchell River downstream of Wentworth River WYG 3 0.93 (A) 1.07 (A) 5.8 5.7 34 34 9 14 7 37* 155 Wongungarra River at Crooked River WYD 3 1.07 (A) 0.94 (A) 6.3 6.6 33 29 12 17 30 42* 144# Wentworth River at Jones Road WYF 3 1.13 (A) 1.06 (A) 6.2 6.9 33 39 15 20 25 44* 173# Dargo River downstream of Wallace Creek WYE 3 1.08 (A) 0.88 (A) 6.1 6.6 35 31 14 16 27 44* 153# Dargo River at Dargo WYM 3 1.14 (X) 0.96 (A) 5.9 6.1 38 30 12 12 26 36 115 Dargo River at Lower Dargo Road WYN 3 1.14 (X) 0.98 (A) 5.9 6.0 33 34 10 13 26 36 142 Cobbannah Creek at Dargo Road WYS 3 0.57 (C) N/A 5.2 N/A 26 N/A 3 N/A 23 24* 164

Cleared Hills and Coastal Plains

Mitchell River at Lamberts Flat WYR 4 1.17 (X) N/A 5.6 N/A 38 N/A 11 N/A 7 37* 148 Mitchell River at Perry’s Crossing WYI 4 1.00 (A) 1.01 (A) 5.3 6.0 28 24 7 10 6 27 119 Mitchell River downstream of Lindenow WYA 4 0.93 (A) N/A 5.6 N/A 24 N/A 8 N/A 5 25*+ 136# Mitchell River at Soldier’s Road WYQ 4 0.87 (A) N/A 5.5 N/A 26 N/A 6 N/A 5 25*+ 113 Iguana Creek at Dargo Road WYK 4 1.04 (A) N/A 5.4 N/A 40 N/A 5 N/A 22 38* 99 Flaggy Creek at Wy Yung-Calulu Road WYO 4 0.68 (B) N/A 5.1 N/A 23 N/A 1 N/A - N/E 86 Boggy (Prospect) Creek at Counihans Bridge WYP 4 1.03 (A) N/A 5.5 N/A 35 N/A 6 N/A 19 34* 107 Clifton Creek WYH 4 0.83 (B) N/A 5.8 N/A 23 N/A 5 N/A 16 N/E 120 Toms Creek at Bengworden WYJ 4 0.68 (B) N/A 4.9 N/A 21 N/A 1 N/A 1 38* 121 Draft SEPP Biological Objectives MEETS THE OBJECTIVE DOES NOT MEET THE OBJECTIVE *at least one sub-index score not directly available. Sub-index score/s estimated on the basis of other sub-index scores (pro rata). +at least one sub-index score estimated by EPA. #results of RHA scores from 1994-6 were standardised to a maximum total of 200. ISC/RHA rating: Excellent Good Marginal Poor Very Poor N/A = habitat not available N/E = reach not evaluated for ISC

Environment Report 21 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figure 9: AUSRIVAS and SIGNAL ratings for sites in the Mitchell catchment.

EPA Victoria 22 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Upland Reaches Of The Mitchell River And Tributaries (Forests B)

Waterways within this region include the Wonnangatta River, Dargo River, Crooked River, Wentworth River, Cobbannah Creek and the upper section of the Mitchell River. Ten biological monitoring sites were sampled in this region (Table 6 and Figure 9). Streams in this region are for the most part in a relatively natural state. There are no impoundments and, while water is extracted from some streams for domestic and irrigation use, flows are largely natural. There are some cleared areas, for example around the township of Dargo in the catchment of the Dargo River, but the region is largely forested. Consequently, streams in this region would be expected to be in relatively good condition.

Eight reaches of the Wonnangatta River were assessed using the ISC. Assessments ranged from ‘marginal’ to ‘excellent’. Low sub-index scores for streamside zone (caused by discontinuous riparian cover with little regeneration of native vegetation) were the primary factors contributing to lower ISC scores. While the three uppermost ISC reaches of the Wonnangatta River lie in the Alpine National Park, they scored relatively poorly for the ISC streamside zone sub-index. This patchiness of riparian vegetation is probably a reflection of the fact that land in this section of the Wonnangatta Valley was historically cleared for cattle grazing. A number of noxious weeds including blackberry have become established in the valley and are probably preventing the regeneration of native vegetation.

Wonnangatta River at Moroka (WYB) met the draft SEPP WoV objectives for both AUSRIVAS and SIGNAL (Table 6). Forty-one taxa were collected in the riffle sample and 34 in the edge sample. These results indicate that both water quality and habitat for aquatic macroinvertebrates are excellent within this reach of the river. Wonnangatta River at Crooked River (WYC) rated as ‘marginal’ against ISC with poor streamside zone and eroded banks identified as the main concerns. RHA also scored this site relatively poorly, chiefly due to poor riparian zone, low bank stability and marginal in-stream habitat. However, this does not appear to have impacted the biota with AUSRIVAS and SIGNAL scores meeting the draft SEPP objectives.

Tributaries of the Wonnangatta River include the Moroka, Wongungarra and Dargo rivers. The greater proportion of the Moroka River flows through the south-eastern portion of the Alpine National Park and is rated as ‘excellent’ by ISC. Water quality and biological data were not collected for this river but it is likely that both would support the ISC assessment. The Wongungarra River was also rated as ‘excellent’ by ISC. Wongungarra River at Crooked River (WYD) was sampled in spring 1995 and autumn 1996 and met the draft SEPP objectives for both AUSRIVAS and SIGNAL (Table 6).

Although the upper reaches of the Dargo River are within the Alpine National Park, some land in the lower sections has been cleared for grazing. This was reflected in the lower ISC score for the downstream reach (ISC reach 26) compared with upstream (ISC reach 27). Once again, the reason for the lower rating was a relatively poor sub-index score for streamside zone. Other sub-indices including water quality and aquatic life scored well. Dargo River at Dargo (WYM) and Dargo River at Lower Dargo Road (WYN) were sampled in autumn and spring of

Environment Report 23 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

1998 and both met the draft SEPP objectives for AUSRIVAS. The edge sample for WYM was rated ‘above reference’. This means that more predicted macroinvertebrate families were collected at this site than would be expected if it were reference quality. This can be interpreted as indicating that this site is a ‘hotspot’ of biodiversity or may be mildly organically enriched. Total nitrogen and phosphorus values (Table 3) were not particularly high, although these results are based on just two sampling occasions. Further investigation would be required to determine whether this ‘above reference level’ AUSRIVAS score is indicative of mild enrichment or whether this site is a biodiversity hotspot. Macroinvertebrate samples were also collected at Dargo River downstream of Wallace Creek (WYE). This site met all the draft SEPP biological objectives (Table 6).

Wentworth River at Jones Road (WYF) met all the draft SEPP biological objectives. ISC scored this reach as ‘excellent’ but the downstream reach of Wentworth River (ISC reach 24) had a relatively narrow streamside zone in some sections and low streambed stability. Nevertheless this reach still fell within the ‘good’ category for ISC. The Mitchell River downstream of the confluence with Wentworth River (WYG) also scored well for AUSRIVAS and ISC. However, SIGNAL scores for the riffle habitat did not meet the draft SEPP objectives. Several years of sampling shows that this site frequently does not meet the draft SEPP objectives for SIGNAL (Table 7). This site is just upstream of the Mitchell River National Park and cattle grazing occurs in close proximity to the river. It is possible that the surrounding landuse is impacting the macroinvertebrate community here, leading to low SIGNAL scores.

Table 7: AUSRIVAS and SIGNAL scores for Mitchell River downstream of Wentworth River (WYG).

Date AUSRIVAS band SIGNAL score AUSRIVAS band SIGNAL score (edge) (edge) (riffle) (riffle) 1994-5 A 5.5 A 6.1 1995 X 5.6 A 5.8 1995-6 X 5.9 A 5.8 1997 A 5.8 A 5.7 Draft SEPP WoV Biological Objectives: MEETS THE OBJECTIVE DOES NOT MEET THE OBJECTIVE

Cobbannah Creek drains the foothills in the west of the catchment and was assessed as being in ‘poor’ condition by ISC. The physical form sub-index scored particularly poorly. There was little in-stream habitat for aquatic life, and bed instability and moderate bank erosion were also noted. The streamside zone of this creek was assessed as being moderately to heavily impacted. Biological sampling of Cobbannah Creek at Dargo Road (WYS) also indicated clear impact. AUSRIVAS and SIGNAL scores for the available edge habitat were well below the draft SEPP objectives. This is a relatively turbid creek with low dissolved oxygen levels (5.44 mg/l in autumn 1999 and 3.35 mg/l in spring 1999) and a predominance of fine sediments. Such conditions do not favour diverse macroinvertebrate communities, particularly sensitive forms, and, together with the lack of suitable habitat, are likely to be responsible for the low AUSRIVAS and SIGNAL scores.

EPA Victoria 24 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Cleared Hills and Coastal Plains (Region 4)

Riffles are less common in the Cleared Hills and Coastal Plains region. However, the edge habitat tends to be more extensive due to the presence of backwaters and other areas of relatively low flow. Nine biological monitoring sites were sampled in this region (which includes the lower reaches of the Mitchell River and Clifton and Toms creeks). Extensive clearing for agriculture has occurred in this region, and it is also more heavily populated, including the towns of Bairnsdale and Paynesville.

Mitchell River at Lamberts Flat (WYR) was sampled for macroinvertebrates in 1999. AUSRIVAS scored the site as ‘above reference’ and the SIGNAL score also met the draft SEPP WoV objective for this region. This site is just downstream of the Mitchell River National Park and although grazing land surrounds this site, there is still significant riparian zone. Total nitrogen and phosphorus values for this site were not high (Table 3), and it is possible that the ‘above reference’ AUSRIVAS score indicates a potential biodiversity ‘hotspot’.

Downstream of Lamberts Flat, ISC scores for the Mitchell River were ‘marginal’ or ‘poor’, largely as a result of poor streamside zones. In many areas, riparian zones have been cleared or replaced by exotic vegetation such as willows, and there is little evidence of regeneration of the natural riparian zone. Mitchell River at Perry’s Crossing (WYI) met all draft SEPP biological objectives except for the SIGNAL score for the edge sample.

The Mitchell River downstream of Lindenow (WYA) was sampled between spring 1994 and autumn 1996. Nutrient samples taken at the same time as macroinvertebrate sampling showed evidence of phosphorus enrichment (Table 3). AUSRIVAS and SIGNAL scores for the available edge habitat met the draft SEPP objectives (Table 6) although the Number of Families did not. The AUSRIVAS and SIGNAL scores may seem surprising given the poor ISC rating and surrounding landuse (cropping and grazing), but they both suggest that the site is relatively healthy given the nature of the dominant landuse. Mitchell River at Soldier’s Road (WYQ) met all the draft SEPP biological objectives.

A number of tributaries, of which Iguana, Boggy (Prospect) and Clifton creeks are the most significant, enter the Mitchell River in this region. Although the AUSRIVAS score and Number of Families for the available edge habitat at Iguana Creek at Dargo Road (WYK) met the draft SEPP objectives, the SIGNAL score did not (Table 6). The sweep sample yielded 40 macroinvertebrate taxa, the most for any edge sample in the Mitchell catchment. However, only five of these were members of the relatively sensitive Ephemeroptera, Plecoptera and Trichoptera (EPT) orders of insects. This is a slow-flowing, turbid creek with relatively low levels of dissolved oxygen. Consequently, the more sensitive macroinvertebrate taxa are unlikely to occur. RHA scored this site very poorly, largely as a result of a poor riparian zone and low bank stability. Water quality was also poor.

Boggy Creek at Counihan’s Bridge (WYP) met all the draft SEPP biological objectives. However, habitat quality was poor. ISC scored this reach as ‘marginal’ and the RHA score was in the ‘very poor’ category. The streambed and banks of this creek were assessed as relatively unstable and the streamside zone was poor. Water quality was also poor. Phosphorus, nitrogen and salinity levels were high and dissolved oxygen levels were low (Table 3).

Environment Report 25 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

The latter suggests that organic pollution is occurring. Anaerobic sediment odours were observed at this site, indicating high levels of organic matter in the sediments. Further investigation would be necessary to identify the source of this organic matter.

At Clifton Creek (WYH), edge habitat samples were collected in autumn and spring of 1997. While the SIGNAL score met the draft SEPP objective, AUSRIVAS and Number of Families did not. This combination of scores and the relatively low RHA score indicates that habitat quality rather than water quality is an issue at this site. Flaggy Creek at Wy Yung-Calulu Road (WYO) was sampled in 1998. This creek failed to meet any of the draft SEPP biological objectives and also recorded the highest salinity value for any site in the Mitchell catchment (Table 3). The average EC value of 3904 mS/cm at 25°C is approximately eight times the draft SEPP objective for this region (500mS/cm) and would significantly impact on the aquatic macroinvertebrate community. RHA scores were also low for this site, reflecting poor in-stream habitat, riparian zone and badly eroding streambanks (see Figure 10). Cattle are allowed direct access to this creek just upstream of the sampling site and this has contributed to stream bank erosion.

Two reaches of Toms Creek, which drains the south-west of the Mitchell catchment and flows directly to Lake Victoria, were assessed for ISC. The lower reach was found to be in good condition but the upper reach was rated as ‘marginal’, chiefly due to limited bank and bed stability, a lack of physical habitat for aquatic life and poor streamside zone. Toms Creek was sampled in 1998 at Bengworden (WYJ). Although this site lies in the lower ISC reach of this creek, it rated poorly for both AUSRIVAS and SIGNAL and failed to meet any of the draft SEPP objectives. Only 21 taxa were collected at this site, and only one was a member of the more pollution-sensitive EPT orders of macroinvertebrates. While this site was an isolated pool in autumn 1998, total nitrogen and phosphorus were still high in spring 1998 when the creek was flowing. Turbidity and salinity levels were also high. Dissolved oxygen levels were low in both spring and autumn 1998 indicating high levels of organic loading. The land surrounding and upstream of this site is intensively grazed and seems the most likely source of this high organic loading.

Both Toms and Flaggy creeks are degraded lowland creeks in areas of grazing land. The grazing of stock in streamside zones damages natural riparian vegetation and prevents its regeneration. This leads to increased erosion, so that nutrient-rich run-off reaches the waterways. Where stock are allowed to enter waterways, the stream channel can be damaged and turbidity increased, while animal wastes lead to reduced water quality and the possibility of algal blooms as a result of nutrient enrichment.

EPA Victoria 26 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figures 10 and 11: Flaggy Creek (left) showing cattle access to the creek upstream of the sampling site. There is no significant riparian zone and the stream banks are badly eroded. Toms Creek (right) showing placement of boulders to reinforce eroding stream banks and replanting of native riparian vegetation by Landcare. Cattle are grazed in the catchment of this creek but fencing prevents them directly accessing the water.

4.6 Mitchell Catchment Summary

Water quality in the upland reaches and tributaries of the Mitchell catchment was generally good and this was reflected in biological, RHA and ISC assessments. A clear exception was Cobbannah Creek where the poor environmental condition was clearly reflected in the low ISC, AUSRIVAS and SIGNAL scores.

Sites in the lower catchment were clearly more impacted, as might be expected since the majority of human settlement and agriculture occurs here. Only three sites, Mitchell River at Lamberts Flat, Mitchell River at Soldiers Road and Boggy Creek met all the draft SEPP biological objectives. Water quality was also poorer in this region. Although water quality in the Mitchell River itself was reasonable, a number of smaller streams such as Iguana Creek, Clifton Creek, Toms Creek, Flaggy Creek and Boggy Creek had elevated salinities, turbidity and/or nutrient- enriched waters. ISC scores also indicated deterioration in environmental condition from upland areas of the catchment. In many of the waterways in the lower catchment, the riparian zone has been removed or is dominated by weeds such as willow and blackberry. Clearing of the natural riparian vegetation contributed to low ISC scores in lower reaches of the Mitchell River while many of the smaller creeks are also badly eroded and provide poor habitat for aquatic fauna. Large woody debris has frequently been removed, leaving little habitat for aquatic life. In some sections, cattle are allowed direct access to the streambed. Trampling of the banks and channel causes increased turbidity and bank and bed erosion, as well as preventing natural regeneration of the riparian zone.

Environment Report 27 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

5. TAMBO AND NICHOLSON RIVER CATCHMENTS

5.1 Study Area

The Tambo River Basin includes the two easternmost rivers that flow into the Gippsland Lakes - the Tambo and Nicholson river systems. The total catchment area is 4,300km2, which represents 20 per cent of the catchment area of the Gippsland Lakes.

The source of the Tambo River is in the Bowen Mountains (part of the Great Dividing Range) in the north of the catchment. From here, the river flows south through dissected mountain ranges to meet Swifts Creek and Haunted Stream, which drain the west of the catchment. The river then swings to the east and is joined by the Timbarra River, which drains the north-east of the catchment. After its confluence with the Timbarra River, the Tambo River flows south-west through undulating hills and flat alluvial and coastal plains, finally discharging to Lake King (Figure 1).

The Nicholson River rises on Mount Baldhead in the west of the catchment and flows south through lowland forest and alluvial plains to Lake King. In 1982, a dam was built on the Nicholson River at Deptford to supply water to Lakes Entrance.

The climate of the Tambo River Basin varies between the north and south, with the north being generally colder and wetter. For example, average annual rainfall in the north is approximately 1,000mm. At Bruthen in the south, the average rainfall is 763mm, which decreases to 734mm at Lakes Entrance. The winter flow in the Tambo River is approximately 2.5 times the summer flow. The Nicholson River exhibits a similar pattern of seasonal flow and the two rivers combined contribute about 8 per cent of the total river flow into the Gippsland Lakes.

The parent rock of much of the Tambo River Basin is comprised of sediments laid down during deep marine conditions in the Ordovician period (510 to 435 million years ago). The Tambo and Nicholson rivers derive most of their sediments from these rocks, resulting in a river substrate of sand and clay with relatively few cobbles.

5.2 History of Catchment Landuse

Much of the open country in the Tambo River Basin was developed for grazing in the 1840s. Agriculture expanded to cope with the gold rush in the 1850s. After the rush, many of the miners stayed on to farm the land. During this period, large-scale clearing of native vegetation from the banks of the Tambo River and its tributaries occurred. Willows were planted in many areas to help combat stream bank erosion. The increased rate of erosion in the upper catchment of the Tambo River and sediment mobilised by gold mining resulted in the formation and transportation of a ‘sand slug’ approximately 1km in length, which resides on the river bed and floodplain of the Tambo River between Bruthen and Tambo Upper (see Figure 12). The sand slug at Bruthen is actively degrading as a result of mechanical dredging and exhaustion of upstream sediment supply (Erskine et al. 1990).

EPA Victoria 28 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figure 12: Tambo River at Bruthen showing large deposits of sand on the riverbed.

Cattle and sheep farming and grain production are the main industries in the Tambo River Basin today. Stock are grazed along the lower reaches of the Nicholson River and in cleared areas in the central and upper catchment of the Tambo River. Much of the lower catchment of the Tambo River is cleared for production of vegetables, lucerne and maize, and for grazing of dairy and beef cattle. The township of Lakes Entrance is a popular tourist resort and also supports a large fishing industry.

In June 1998, the Tambo River experienced its largest flood recorded in the last century. As a result, large-scale erosion, sedimentation and damage to public and private assets occurred in the Bruthen area. The East Gippsland CMA commissioned a detailed geomorphological investigation (Craigie et al. 2000) to enable the development of appropriate and effective management strategies for the Tambo River and its floodplain areas. This report identified several changes in the hydrology and geomorphology of the river since European settlement. Changes included the clearing and development of the floodplain area, elevated sediment inputs from upstream (largely derived from gold mining activities), the introduction of exotic vegetation such as willows and poplars, the construction of levee banks and erosion control works.

5.3 Water Quality Characterisation And Assessment

The draft SEPP WoV water quality objectives for the Tambo and Nicholson catchments are given in Table 1. Water quality results at biological sites for turbidity, dissolved oxygen, salinity (electrical conductivity), pH, total nitrogen (TN) and total phosphorus (TP) are presented in Table 8. These EPA site data provide an indication of possible non-compliance with objectives (see 2.2).

Environment Report 29 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Table 8: Water quality results for biological sites in the Tambo and Nicholson catchments.

Site Site Biological Total N Total P Turbidity EC25 Code Region (mg/L) (mg/L) (NTU) (mS/cm) Highlands Timbarra River at Timbarra Plains XYW 1 0.22 0.030 2.3 22 Upland reaches of the Tambo River Tambo River upstream of mine XYI 3 0.48 0.061 7.4 127 Tambo River downstream of Straights XYK 3 0.27 0.045 5.2 106 Creek Tambo River at Wilga weir XYJ 3 0.36 0.028 4.4 137 Tambo River at Tongio XYD 3 0.20 0.017 1.3 188 Tambo River at Swifts Creek XYT 3 0.12 0.011 1.5 263 Tambo River near Doctors Flat XZB 3 0.21 0.021 1.9 327 Tambo River downstream of XYA 3 0.21 0.017 1.9 342 Boonibirrah Tambo River at Angora XYE 3 0.20 0.014 1.6 340 Tambo River at Barangarook XYF 3 0.20 0.013 1.2 345 Tambo River at Pretty Flat Creek XYG 3 0.19 0.013 1.5 346 Tambo River at Millers Access Road XYB 3 0.23 0.016 1.8 339 Tambo River downstream of Sa ndy XZA 3 0.22 0.017 1.8 356 Creek junction Tambo River downstream of Barks XYU 3 0.37 0.015 1.4 291 Shed Creek Tambo River downstream of Peters XYV 3 0.26 0.016 1.3 197 Creek Tambo River at Ramrod Creek XYQ 3 0.23 0.015 2.1 145

Tributaries of Upper Tambo River Little River at Ensay South XYC 3 0.42 0.041 1.8 309 Swifts Creek at Swifts Creek XYH 3 0.25 0.032 0.6 745

Timbarra River downstream of XYX 3 0.22 0.016 3.1 65 Wilkinson Creek Haunted Stream at Stirling XYY 3 0.46 0.023 2.4 97 Nicholson River Nicholson River at Deptford XYZ 3 0.27 0.018 2.3 111

Nicholson River at Atkinson Road XYM 4 0.28 0.013 3.1 125 Nicholson River upstream of Morgans XYL 4 0.29 0.010 3.2 139 Creek Morgans Creek at Bellbird Road XYO 4 1.45 0.053 21.0 1155 Lower Tambo Tambo River at Bruthen Bridge XYR 4 0.22 0.014 1.7 157 Tambo River at Stephenson Road XYN 4 0.38 0.023 3.3 280 Red indicates a value greater than the 75th percentile draft SEPP objective.

EPA Victoria 30 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

In addition to the water quality data collected during the biological surveys, there are seven VWQMN sites in the Tambo and Nicholson catchments. These results were assessed against the draft SEPP objectives on the basis of average monthly values between 1996 and 1999, and are presented in Table 9. The location of these sites and the biological regions they fall within are presented in Figure 13.

Figure 13: Location of VWQMN sites and biological regions in the Tambo and Nicholson catchments.

Environment Report 31 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Table 9: Water quality results from VWQMN sites in the Ta mbo and Nicholson catchments between 1996 and 1999.

Site name Site number TN TP EC Turbidity

(mg/l) (mg/l) (mS/cm) (NTU)

Tambo River at Swifts Creek 223202 0.055 0.022 320 4

Nicholson River at Deptford 223204 0.047 0.016 100 3

Tambo River downstream of 223205 0.376 0.021 170 3 Ramrod Creek Timbarra River downstream of 223212 0.385 0.020 61 3 Wilkinson Creek Tambo River downstream of 223213 0.042 0.032 160 8 Duggan Creek Tambo River upstream of Smith 223214 0.454 0.055 200 10 Creek Haunted Stream at Hells Gate 223215 NM NM 95 2

Values that exceeded the draft SEPP objectives are highlighted in red. NM = not measured

Surprisingly, total phosphorus levels were highest at two sites in the upper reaches of the Tambo River (223213 and 223214). The catchment of this section of the Tambo River is in relatively good condition. However, turbidity levels were also markedly higher at these sites indicating that erosion was occurring. Such localised effects require further investigation.

Trends in water quality of VWQMN sites in the Tambo and Nicholson catchments are presented in Table 10. Trend analysis based on sites with a minimum of 10 years’ data (Smith and Nathan 1999) did not find a significant increase in total nitrogen or total phosphorus levels at any of the sites except for a trend for decreasing nitrogen levels of small magnitude at Tambo River downstream of Ramrod Creek (223205).

EPA Victoria 32 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Table 10: Trends in water quality in the Tambo and Nicholson catchments, 1975 to 1999.

Site name Site pH Turbidity Electrical Total Total number Conductivity Nitrogen Phosphorus (NTU) (mS/cm) (mg/l) (mg/l)

Tambo River at 223202 Change (units -0.033 0.00 0.0 -0.005 0.0 Swifts Creek per year) Significance **** NS **** NS NS Nicholson River 223204 Change (units 0.000 0.00 0.0 - - at Deptford per year) Significance **** **** **** Tambo River 223205 Change (units 0.000 0.00 0.0 -0.019 0.0 downstream of per year) Ramrod Creek Significance **** NS **** **** NS Timbarra River 223212 Change (units 0.000 0.00 0.0 - - downstream of per year) Wilkinson Creek Significance * NS NS

Tambo River 223213 Change (units 0.065 0.00 0.0 - - downstream of per year) Duggan Creek Significance **** * **** Source: Smith and Nathan 1999

5.4 Biological Assessment

The seven indices described in section 2.3 were used to make an assessment of the environmental condition of the Tambo and Nicholson catchments. The draft SEPP biological objectives and condition categories for each region are shown in Table 2. The results for the Tambo and Nicholson catchment sites are given in Table 11.

For the convenience of discussion, the Tambo and Nicholson catchments have been divided into five groups that broadly correspond to the topography and type of landuse present.

1. Highlands (1 site)

2. Upland reaches of the Tambo River (15 sites)

3. Tributaries of Upper Tambo River (4 sites)

4. Nicholson River (4 sites)

5. Lowland reaches of the Tambo River (2 sites)

The waterways in the Tambo catchment that are considered to be in good ecological condition are the Timbarra River and Haunted Stream. A number of reaches of the Tambo River and its tributaries suffer from habitat and water quality degradation. This is evident in Figure 14, which shows the AUSRIVAS and SIGNAL results for each site.

Environment Report 33 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

The Nicholson River was found to be in generally good ecological condition, including habitat condition and water quality. In contrast, Morgans Creek, a tributary of the Nicholson River, showed clear evidence of degradation of ecological condition and water quality.

EPA Victoria 34 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Table 11: Results for draft biological objectives, ISC and RHA for sites in the Tambo and Nicholson catchments.

Site Site Biol. Number of Key Families SIGNAL Number of Families EPT families ISC ISC RHA Code Region Reach Score Edge Riffle Edge Riffle Edge Riffle Highlands (B1) Timbarra River at Timbarra Plains XYW 1 21 6.8 7.0 24 24 11 11 16 43* 132

AUSRIVAS Edge Riffle Upland reaches of the Tambo River Tambo River upstream of mine XYI 3 0.68 (B) 0.85 (B) 5.9 6.8 30 34 11 16 12 N/E 164 Tambo River downstream of Straights Creek XYK 3 0.69 (B) 0.78 (B) 6.4 6.5 27 33 14 14 12 N/E 181 Tambo River at Wilga weir XYJ 3 0.90 (A) 0.98 (A) 6.5 6.2 35 37 14 14 12 N/E 176 Tambo River at Tongio XYD 3 0.87 (A) 0.84 (B) 5.7 5.6 30 28 11 11 10 34* 141 Tambo River at Swifts Creek XYT 3 1.03 (A) 0.88 (A) 5.9 5.4 37 32 13 12 9 33 170 Tambo River near Doctors Flat XZB 3 1.01 (A) 0.83 (B) 5.8 5.6 32 25 12 10 9 33 165 Tambo River downstream of Boonibirrah XYA 3 0.94 (A) 0.90 (A) 5.4 5.8 31 27 10 12 9 33 163 Tambo River at Angora XYE 3 0.90 (A) 0.81 (B) 5.3 5.3 29 24 9 9 9 33 136 Tambo River at Barangarook XYF 3 0.94 (A) 0.90 (A) 5.3 5.6 33 26 10 11 9 33 141 Tambo River at Pretty Flat Creek XYG 3 0.99 (A) 0.91 (A) 5.3 5.5 33 27 9 10 9 33 127 Tambo River at Millers Access Road XYB 3 0.94 (A) 0.84 (B) 5.3 5.4 30 24 9 10 8 31*+ 155 Tambo River downstream of Sandy Creek junction XZA 3 1.12 (A) 0.94 (A) 5.4 5.6 36 28 11 11 8 31*+ 145 Tambo River downstream of Barks Shed Creek XYU 3 1.20 (X) 1.11 (A) 5.6 5.9 48 33 13 14 7 36 136 Tambo River downstream of Peters Creek XYV 3 0.90 (A) 0.94 (A) 5.4 5.6 28 29 9 11 6 47* 170# Tambo River at Ramrod Creek XYQ 3 0.86 (B) 0.89 (A) 5.4 N/A 34 N/A 10 N/A 6 47* 118 Tributaries of upper Tambo River Little River at Ensay South XYC 3 0.99 (A) 0.86 (B) 5.7 5.7 39 26 12 10 18 25* 92 Swifts Creek at Swifts Creek XYH 3 0.99 (A) 0.93(A) 5.3 5.5 31 32 7 11 19 25* 103 Timbarra River downstream of Wilkinson Creek XYX 3 1.07 (A) 1.15 (X) 6.1 6.3 35 37 14 18 14 48* 176# Haunted Stream at Stirling XYY 3 0.87 (A) 0.91 (A) 6.3 6.3 31 33 11 15 17 47* 170 Nicholson River Nicholson River at Deptford XYZ 3 0.89 (A) 1.04 (A) 6.0 6.1 37 27 11 13 3 41* 181# Nicholson River at Atkinson Road XYM 4 0.86 (B) 0.93 (A) 5.7 N/A 30 N/A 8 N/A 2 35* 153 Nicholson River upstream of Morgans Creek XYL 4 1.00 (A) O/S 5.9 6.0 37 28 10 12 2 35* 136 Morgans Creek at Bellbird Road XYO 4 0.92 (A) N/A 5.2 N/A 28 N/A 3 N/A - N/E 71 Lowland reaches of the Tambo River Tambo River at Bruthen Bridge XYR 4 1.19 (X) N/A 5.2 N/A 30 N/A 8 N/A 5 30 89 Tambo River at Stephenson Road XYN 4 1.04 (A) N/A 5.2 N/A 30 N/A 6 N/A 4 29* 78 Draft SEPP Biological Objectives MEETS THE OBJECTIVE DOES NOT MEET THE OBJECTIVE *at least one sub-index score not directly available. Sub-index score/s estimated on the basis of other sub-index scores (pro rata). +at least one sub-index score estimated by EPA. Environment Report 35 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

#results of RHA scores from 1994-6 were standardised to a maximum total of 200. ISC/RHA rating: Excellent Good Marginal Poor Very Poor N/A = habitat not available N/E = reach not evaluated for ISC O/S = outside the experience of the model single season – spring

EPA Victoria 36 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figure 14: AUSRIVAS and SIGNAL ratings for sites in the Tambo and Nicholson catchments.

Environment Report 37 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Highlands

The northern section of the Tambo catchment lies in the high country, forming part of the Highlands Biological Region. It is largely protected from human impact, lying for the most part in areas of National Park. Only one site was sampled in this region (between 1994 and 1999 (Table 12)). Timbarra River at Timbarra Plains (XYW) appears to be in good condition, passing all draft SEPP WoV biological objectives. There are no draft SEPP objectives for AUSRIVAS since there is no AUSRIVAS model for this region. However, this site did meet the draft objective for Key Families of aquatic macroinvertebrates, which is used when AUSRIVAS results are not available. ISC assessed this reach of the Timbarra River as ‘excellent’, and while RHA assessed this site as ‘marginal’, this probably reflects the unsuitability of the RHA methodology for small alpine streams. Although nutrient levels were relatively high for this site, human influence is minimal and there appears to be a low level of risk to ecological health.

Table 12: SIGNAL scores and Number of Key Families for Timbarra River at Timbarra Plains.

Date Edge SIGNAL Riffle SIGNAL Number of Key Families 1994-5 7.3 N/A 23 1995 6.7 N/A 22 1995-6 6.5 6.3 23 1999 6.7 7.0 21 Draft SEPP Biological Objectives: MEETS THE OBJECTIVE N/A = habitat not available

Upland Reaches Of The Tambo River

The majority of biological monitoring sites in the Tambo catchment fell into this region, which is part of Biological Region 3 (Forests B). Three sites were sampled for macroinvertebrates in the uppermost reach (ISC reach 12) of the Tambo River. Tambo River upstream of mine (XYI), Tambo River at Wilga Weir (XYJ) and Tambo River downstream of Straights Creek (XYK) were all sampled in 1999. Water quality results (Table 8) indicated that the river was relatively turbid, with elevated nutrient and salinity levels, possibly as a result of low flows in 1999. AUSRIVAS scores for both riffle and edge habitats at Tambo River at Wilga Weir met the draft SEPP WoV objectives (Table 11). However, both habitats at Tambo River upstream of mine and downstream of Straights Creek failed to meet the draft SEPP objectives for AUSRIVAS. SIGNAL, Number of Families and EPT Index scores for edge and riffle habitats at all three sites met the draft SEPP objectives. The sites scored well for RHA, suggesting they were in good condition.

There could be a number of reasons why AUSRIVAS scores were low at Tambo River upstream of mine (XYI) and Tambo River downstream of Straights Creek (XYK). The Tambo River is relatively narrow in this area (one to two metres wide). In addition, these sites were sampled in 1999, a drought year, and flows were relatively low. Consequently, a combination of a relatively uniform channel and low flows may have reduced the amount and

EPA Victoria 38 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

diversity of habitat available for aquatic macroinvertebrates. Tambo River widens out to approximately three metres at Wilga Weir, which may have allowed a more diverse macroinvertebrate community to develop. It is also possible that the regional AUSRIVAS models perform less well at sites such as these that are close to the boundary of two regions.

The four ISC reaches downstream of reach 12 (ISC reaches 8 to 11) rated as ‘marginal’ chiefly due to poor streamside zones which have been invaded by exotic species such as willow. Much of the catchment in this section of the Tambo River has been cleared, mostly for cattle and sheep grazing. Each of the nine biological sites in this section of the Tambo River failed to meet at least one of the draft SEPP objectives. Most site/habitat combinations returned SIGNAL scores that did not meet the draft objectives. Water quality at these sites was generally good with the exception of elevated salinity levels. Salinity levels in these reaches of the Tambo River were consistently high compared to the rest of the catchment.

Tributaries of Upper Tambo River

Swifts Creek joins the Tambo River at the township of Swifts Creek (Figure 13). ISC rated Swifts Creek as ‘poor’, as much of the catchment around the creek is cleared, the riparian zone is highly degraded (Figure 15) and there was very poor in-stream habitat for aquatic life. Swifts Creek at Swifts Creek (XYH) was sampled in 1999. RHA rated this site poorly – it scored a total of 103 out of 200. Stream banks were badly eroded and there was very little riparian zone. Large amounts of fine sediment were also observed. Despite this relatively poor habitat assessment, the site met the draft SEPP objectives for AUSRIVAS. SIGNAL scores, however, were less encouraging and failed to meet the draft SEPP objectives. This combination of scores suggests that while there is sufficient habitat for a reasonably diverse macroinvertebrate community to develop at the sampling site, many of the more sensitive taxa are excluded. For example, in the edge sample for this site, although a total of 31 taxa were recorded from spring and autumn 1999, only seven of these were members of the more sensitive EPT insect orders. Water quality was poor, with elevated total phosphorus and salinity levels.

Little River appears to suffer from similar problems to Swifts Creek. Much of the riparian zone has been removed and there is little evidence of regeneration (Figure 16). The small amount of riparian zone remaining is largely dominated by exotic species such as willows. In-stream habitat for aquatic life is also very poor. ISC rated this river as ‘poor’ and the RHA score for Little River at Ensay South (XYC) was the lowest for any site in this region. Although the AUSRIVAS score for the edge community met the draft SEPP objective, the riffle sample did not. SIGNAL scores did not meet the draft SEPP objectives for either habitat. Total nitrogen and phosphorus values for this site, which is close to the small settlement of Ensay South, were relatively high and salinity values were also elevated (Table 8).

Environment Report 39 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figures 15 and 16: Swifts Creek (ISC reach 19) and Little River (ISC reach 18).

The catchment of Haunted Stream is still largely forested and was rated as ‘excellent’ by ISC. Haunted Stream at Stirling (XYY) met all the draft SEPP biological objectives (Table 2).

The mid and lower sections of the Timbarra River are also in this region. ISC rated the Timbarra River as being in ‘excellent’ condition, except where it flows through small areas of land that have been cleared for grazing around the township of Timbarra. Timbarra River downstream of Wilkinson Creek (XYX) met all the draft SEPP biological objectives. Water quality was also good. This site is downstream of the township of Timbarra and the results suggest the township and grazing land are not significantly impacting downstream river health.

Nicholson River

The uppermost reach (ISC reach 3) of the Nicholson River was rated as ‘good’ by ISC. AUSRIVAS, SIGNAL, Number of Families and EPT Index scores for the Nicholson River at Deptford (XYZ) all met the draft SEPP WoV biological objectives. Water quality was generally good.

Further downstream (ISC reach 2), the Nicholson River upstream of Morgans Creek (XYL) and Nicholson River at Atkinson Road (XYM) were sampled. AUSRIVAS assessments for the edge habitat upstream of Morgans Creek met the draft SEPP objectives but the edge sample at Atkinson Road did not. The edge habitat at Atkinson Road is heavily shaded and there are very few aquatic macrophytes. The relatively low diversity of edge habitat at this site is likely to be responsible for the low AUSRIVAS score. The riffle community at Atkinson Road was only sampled in spring, since the flow level was too low in autumn. Consequently, it could not be assessed against the draft SEPP objectives, which are based on combined seasons’ data. However, the State-wide, single-season AUSRIVAS model assessed the spring riffle sample as ‘reference’ quality. The riffle sample upstream of Morgan’s Creek was found to be ‘outside the experience of the model’. All other draft SEPP biological objectives were met at both sites. This ISC reach was rated as ‘good’. Both biological monitoring sites were surrounded by significant stands of native vegetation and although some land in the immediate catchment is cleared for grazing, this section of the Nicholson River appears to be in relatively good condition.

EPA Victoria 40 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figure 17: Nicholson River upstream of Morgan’s Creek (XYL) showing good riparian zone dominated by native vegetation.

Morgans Creek (XYO), a tributary of the Nicholson River, was sampled in 1998. However, the creek was not flowing in either autumn or spring and was essentially a series of isolated pools. Consequently, it is not surprising that water quality indicators were poor (Table 8). This may help to explain the relatively low SIGNAL score for the available edge habitat at this site, which failed to meet the draft biological objective. This creek was not assessed for ISC but the RHA score was in the ‘very poor’ category. The natural channel of this creek has been significantly altered and there is very little in-stream habitat for aquatic life. The riparian zone was also significantly impacted with an average width of just two metres.

Lowland Reaches Of The Tambo River

Tambo River at Bruthen Bridge (XYR) was sampled in 1997. It met the draft SEPP WoV objective for AUSRIVAS but not SIGNAL for the available edge habitat (Table 11). This site falls within ISC reach number 5, which was assessed, as ‘marginal’. The streamside zone in this reach is very much reduced and there is little in-stream habitat for aquatic life. The AUSRIVAS result suggests the macroinvertebrate community may be relatively healthy although the ‘above reference’ rating may also indicate that the site is subject to mild organic enrichment. Tambo River at Stephenson Road (XYN) also met the draft SEPP objective for AUSRIVAS but not SIGNAL. Although a relatively diverse community of macroinvertebrates was collected in the edge sample at this site, only six of the 30 taxa present were members of the EPT insect orders. This indicates that the site is dominated by relatively tolerant macroinvertebrate taxa. This reach (ISC reach 4) was also assessed by ISC as ‘marginal’ and again the streamside zone was poor, with little evidence of regeneration.

Environment Report 41 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Figure 18: Tambo River at Stephenson Road (XYN) showing low flow status and limited riparian zone.

5.5 Tambo and Nicholson Catchment Summary

There was less distinction between the health of the upper and lower reaches of the Tambo catchment compared to the Mitchell catchment. This reflects the fact that large portions of the central and upper Tambo catchment have been cleared for grazing. The majority of these sites in the upper catchment did not meet at least one of the draft SEPP biological objectives. Many ISC scores were in the ‘poor’ and ‘marginal’ categories. Poor in-stream habitat, reduced riparian zones, the introduction of exotic species such as willows and erosion are major issues in these reaches. Other than the Tambo River itself, areas of particular concern were Swifts Creek and Little River. Elevated nutrient levels were recorded in the uppermost reach of the Tambo River, possibly a natural effect of the high erosion capacity in this section of the river although this requires further investigation. Salinity values were also high in this region. Partly, this may reflect the fact that many of these sites were sampled in 1999, a drought year. While elevated salinities may not be directly responsible for the low SIGNAL scores at many of these sites, a number of macroinvertebrate species are sensitive to elevated salinities (Metzeling et al. 1995) and the elimination of sensitive species will result in reduced biodiversity at these sites.

SIGNAL scores for the lower reaches of the Tambo River indicated impact. ISC and RHA scores were in the ‘poor’ and ‘very poor’ categories. However, AUSRIVAS scores suggested these sites were in relatively good condition. This may seem surprising given the poor habitat scores. However, the reference sites used in the AUSRIVAS models are not necessarily pristine sites but the best available in a particular region and these results indicate that the lower Tambo River is in relatively good condition compared to other rivers in the Cleared Hills and Coastal Plains Biological Region. Water quality in the lower Tambo River was relatively good.

EPA Victoria 42 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

The Nicholson River was found to be in generally good condition when assessed against the habitat, biological and water quality indicators.

Environment Report 43 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

6. OVERVIEW OF THE CATCHMENTS

6.1 Introduction

The primary aim of biological monitoring of rivers and streams is to provide an assessment of ecological condition and to highlight areas which appear to be in poor condition. The approach used focuses on aquatic macroinvertebrates because of their general abundance, ease of collection and the availability of standard assessment methodologies. Other components of the biota, for example, plants, algae, bacteria and fish are all essential for the proper functioning of a healthy ecosystem and ideally one would study them all. However, this is not practical and it is most unlikely that a stressor would affect only one component of an ecosystem in isolation. Usually stress affects all components to some degree, or, if the effect is primarily on one component, change to this component will have a flow on effect to other components. Given this, macroinvertebrates have been chosen as the primary indicator of aquatic ecosystem condition.

To assist in the interpretation of macroinvertebrate data, information is collected on factors that are known to affect the aquatic ecosystem, including physical condition of the stream environment, water quality, catchment condition and landuses. This report uses data from a number of separate studies investigating components or variables that influence the ecology of rivers in the Mitchell, Tambo and Nicholson catchments.

As a number of different types of stress can have similar net effects upon the macroinvertebrate fauna, the data cannot be used to determine causality of change. The following discussion focuses on sites and river reaches which appear to be degraded, and identifies the factors that could be contributing to the degradation. In instances where multiple factors are identified, management actions must address all contributing factors before significant rehabilitation will be achieved. For example, management actions that focus on nutrient problems while neglecting problems with stream habitat and the environmental flow regime will not bring about significant improvement in the health of a stream. Furthermore, stress factors interact and result in possible flow on effects. Attempts to restore woody debris and re-instate old meanders, for instance, may actually reduce a stream’s capacity to carry away flood water and increase the frequency of minor to moderate flooding.

To facilitate the discussion, sites from the three river catchments are grouped as follows:

· Highlands

· Upper Catchments

· Lowland Reaches

EPA Victoria 44 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

6.2 Highlands

There are too few sites in this region to make an overall assessment. However, the remoteness of this area and the fact that much of the region is in the Alpine National Park means that river health should be good to excellent. Potential threats include the ski resorts at Mount Hotham and Dinner Plain, the invasion of pest plants (particularly blackberry) and increased traffic through the area (from snow sports and bushwalking). Cattle grazing, which alters natural vegetation communities in highland areas (Williams 1990) and may introduce invasive pest plants, occurs in some areas in this region. However, more detailed sampling would be required to determine whether grazing in this region significantly impacts on river health.

6.3 Upper Catchments (Forests B)

Human influence in the upper catchments is greater than in the Highlands Region. The majority of biological monitoring sites fell within this region, which includes the upper reaches of the Mitchell and Tambo rivers as well as the Dargo, Wentworth and Little rivers and Swifts Creek. Results varied between the catchments.

This region of the Mitchell catchment appeared to be in good condition overall, with the exception of Cobbannah Creek. The channel and banks of this creek are eroded and there is little in-stream habitat for aquatic life. The presence of woody debris is particularly important in providing stable habitat in streams such as Cobbannah Creek, where the streambed is composed of easily mobilised fine sediment and offers little habitat variety or stability. While woody debris can cause increased flooding and bank erosion, these effects are generally outweighed by its ecological benefit. It is also an important energy source for recovering streams before natural riparian vegetation is re-established. The riparian zone of Cobbannah Creek is discontinuous and has been invaded by exotic species in several areas. Food availability and habitat quality are often lower in reaches where the riparian zone is dominated by exotic species (Read and Barmuta 1999). There is little evidence of regeneration of the natural streamside zone of this creek, although the presence of some areas of natural vegetation indicates regeneration is possible under the right circumstances. Water quality is also poor.

Biological scores for Tambo catchment sites in this region were generally lower than those in the Mitchell catchment. Most sites on the Tambo River itself returned SIGNAL scores below the draft SEPP biological objectives. In contrast, sites on Haunted Stream, Timbarra River and the Nicholson River appeared to be in good condition. These results reflect the fact that while the upper and middle catchment areas of the Mitchell River are in relatively good condition, much of the upper and middle catchments of the Tambo River have been impacted as a consequence of land clearing for cattle and sheep grazing. In addition, increased sedimentation rates and erosion – resulting from historical mining, land-clearing activities and, more recently, the 1998 flood – are likely to be impacting macroinvertebrate communities. Water quality was also poorer in the Tambo catchment. Salinity values, in particular, were higher in the Tambo catchment while some areas, particularly in the upland reaches of the Tambo River, had elevated nutrient levels.

Environment Report 45 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Intensive sampling in the mid to upper reaches of the Tambo River revealed SIGNAL scores consistently below the draft SEPP biological objectives for this region. AUSRIVAS scores were generally higher but there were a number of sites that did not meet the draft SEPP objectives. The removal of native riparian vegetation and a lack of in- stream habitat are important issues in these reaches of the Tambo River. Riparian vegetation plays an important role in stabilising stream banks, reducing the transportation of fine sediment and nutrients bound to particulates into waterways, lowering the water table and providing a source of woody debris for streams. The removal of native vegetation and invasion by exotics such as willows and poplars contributed to the extensive damage to public and private assets caused by the June 1998 flood (Craigie et al. 2000). Willows, in particular, reduce channel flow capacity in rivers causing more water to invade the floodplain.

Introduced species such as willows can also have several consequences for stream ecology. Willows create greater shade than most native species, reducing light levels for in-stream plants, algae and other riparian vegetation. Native trees tend to produce a continuous supply of leaf litter whereas leaf fall from introduced trees is often highly seasonal, resulting in the accumulation of leaves in pool areas and backwaters, and increased dissolved oxygen demand. In addition, introduced trees generally produce lower quality food and large woody debris in comparison to native species (Rutherford et al. 1999).

Other problem areas highlighted are Swifts Creek and Little River. Much of the natural riparian zone of both streams has been removed and in-stream habitat quality is poor. The poor environmental condition of these streams is reflected in their biological assessments, particularly SIGNAL scores, and in habitat condition ratings.

6.4 Lowland Reaches (Cleared Hills and Coastal Plains)

This area includes the lower reaches of the Mitchell, Nicholson and Tambo rivers and has the greatest population density of the three regions. Water quality, habitat condition and biological scores were markedly lower in this area of the Mitchell catchment compared to sites in the upper catchment. This gradient was less apparent in the Tambo River, where much of the catchment in the upper to mid reaches has been cleared for agriculture and has therefore impacted on environmental condition to a similar extent as the lowland reaches.

Degraded streamside zones were the main reason for poor ISC scores in the lower reaches of the Mitchell River. AUSRIVAS scores were generally of reference quality, indicating the health of the Mitchell River was relatively good for a lowland river in this region. Potential problem waterways in the lowland Mitchell catchment include Toms Creek and Flaggy Creek. These creeks failed to meet all the draft SEPP biological objectives and also had low scores for habitat condition and water quality. Toms Creek and Flaggy Creek are badly eroded and degraded, and it is likely that the surrounding agricultural landuse is contributing to poor water quality.

Lowland reaches of the Tambo catchment gave mixed results. The lower reaches of the Tambo River itself were found to be in marginal condition. The main contributing factor was poor streamside zone, which was discontinuous and invaded by exotic species. In contrast, the lower reaches of the Nicholson River appeared to

EPA Victoria 46 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

be in much better condition. generally meeting draft SEPP biological objectives and demonstrating good habitat condition and water quality.

6.5 Main Factors Influencing Environmental Condition

Two main contributing factors to poor ecological condition were identified in the Mitchell, Tambo and Nicholson catchments: habitat degradation and poor water quality. Both factors can have major impacts upon the ecology of a stream.

Habitat Degradation

Catchment and waterway erosion has been accelerated since European settlement. This has resulted in losses to productive capacity (as a result of soil losses), instability of stream channels and banks, and reduced water quality. It was estimated that an average of 38,000 tonnes of suspended solids per year were transported to Lake King from the catchments of the Mitchell, Tambo and Nicholson rivers between 1995 and 1999 (Grayson et al. 2001). A large proportion of the suspended solids arrives in high flow events. For example, 87,300 tonnes of suspended solids were transported to Lake King from these catchments during the June 1998 flood. This suspended material also contains nutrients, which can contribute to algal blooms in the Gippsland Lakes.

The clearing of native vegetation in the catchments of the Gippsland Lakes is one of the most significant factors causing this erosion. While it has been less extensive in this region compared to many other catchments in Victoria, its effect is still measurable. The problem is exacerbated by extreme events such as the flood that occurred in the Tambo catchment in June 1998. The flood resulted in catastrophic erosion, large-scale sedimentation and extensive damage to public and private assets in the Bruthen area (Craigie et al. 2000).

Stream banks are a major source of suspended sediment as a result of soil erosion. Allowing stock access to rivers increases the rate of stream bank erosion. Trampling and grazing by stock also prevents the regeneration of bare areas of stream bank. Weeds such as blackberry have invaded many eroded areas but provide poor protection for stream banks. There is also evidence from the June 1998 flood that introduced trees such as willow and poplar offer less stream bank protection than native trees (Craigie et al. 2000).

Both streamside vegetation and in-stream habitat quantity and quality are poor throughout much of the lower reaches of the Mitchell River and tributaries, and in the mid to upper catchment of the Tambo River and its tributaries. Direct access of stock to rivers and creeks causes local bank instability, reduced water quality and poor habitat conditions. Stock access to the streamside zone should be prevented wherever possible if works to improve the streamside zone are to be successful. Revegetation programs need to have a good understanding of the indigenous vegetation of the affected area and be aware of the importance of all aspects of the natural riparian community. For example, while the re-establishment of larger, slower-growing species is important, fast- growing species such as native grasses can play an important role in stabilising eroded banks. In many cases,

Environment Report 47 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

physical structures will also be needed to stabilise stream banks and allow recolonisation to take place. Further details can be found in A Rehabilitation Manual for Australian Streams (Rutherford et al. 1999).

Water Quality

High nutrient levels combined with low flows can lead to major algal blooms. These have been recorded in both the Nicholson and Tambo rivers, as well as downstream in the Gippsland Lakes.

Horticulture, dairying and urban development are likely causes of nutrient enrichment in lowland reaches. While nutrient inputs from non-point discharges such as agricultural run-off are more difficult to control, reducing sediment movement in the catchment through erosion control measures is an important management strategy. Preventing stock access to waterways and limiting damage to riparian zones will also reduce sediment and nutrient inputs to streams.

EPA Victoria 48 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

7. MANAGEMENT INITI ATIVES IN THE REGION

7.1 Catchment and Waterways Management

The East Gippsland Regional Catchment Strategy (East Gippsland Regional Catchment and Land Protection Board 1997) identified a number of key issues in relation to the region’s waterways, in particular erosion and pest plants. Current management activities to address these issues are summarised below.

Water Erosion and Waterways

In recent years, stream management activities in the lower Mitchell catchment have concentrated on stabilising erosion in tributaries of the Mitchell River, such as Cobblers Creek and Mount Taylor Creek, and along the Mitchell River itself. Stock exclusion fencing and revegetation programs have also been carried out along these tributaries. Willow and poplars have been removed from the lower Mitchell River near Lindenow. Some stabilisation work has also been carried out in this area to alleviate active erosion. In the upper Mitchell catchment, control of bank erosion in the cleared floodplains has been a high priority.

Erosion stabilisation works are also being carried out in the Tambo catchment. Much of this work has aimed at repairing the damage caused by the June 1998 floods. Reducing the sediment load generated from erosion of the Bruthen floodplain is a high priority in this catchment. Natural Heritage Trust funding has been obtained to assist the control of exotic plant species, especially willows, and revegetate streambeds and banks.

Willow control and management has also been a focus of work in reaches of the Tambo River upstream of Bruthen. River stabilisation works have been carried out in smaller tributaries in the vicinity of Swifts Creek, many of which have suffered significant erosion since European settlement.

Erosion control works will also have the effect of reducing the sediment, and therefore nutrient load, to these rivers and ultimately the Gippsland Lakes.

Water Quality

Integrated catchment management is the key to reducing nutrient inputs to waterways in the Mitchell, Tambo and Nicholson catchments and ultimately the Gippsland Lakes. The Gippsland Lakes Management Plan (DCE 1991) and the Nutrient Management Strategy (Victorian Government 1995) are important frameworks for addressing these issues.

Much of the nutrient load to the Gippsland Lakes occurs during storm events, such as the June 1998 floods in the Mitchell and Tambo systems. Erosion and gullying in these catchments are major sediment sources during these events and contribute to poor water quality. The EGCMA is involved in many programs to repair and restore the physical condition of the streams. This will also have beneficial impacts upon water quality.

Environment Report 49 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

River Flow Management

There are no major dams on either the Tambo or Mitchell rivers. A dam exists on the Nicholson River at Deptford, however downstream effects of the change in flow regime and decreased suspended matter load are not known.

EPA Victoria 50 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

8. CONCLUSIONS

8.1 Habitat Degradation

Habitat degradation is a significant issue in the lower Mitchell River, its tributaries and Toms Creek. Streamside vegetation and in-stream habitat quantity and quality is poor in many of these waterways. Streamside vegetation is also poor in the upper to mid reaches of the Tambo River, although in-stream habitat in these reaches is comparatively good. Direct stock access to rivers and creeks promotes local bank instability, reduced water quality and poor habitat conditions. Stock access to waterways needs to be controlled if works to improve the streamside zone are to be successful. Current work programs to improve the quality and quantity of streamside vegetation in degraded areas, control the spread of invasive plant species such as willow and improve in-stream habitat should continue.

8.2 Water Quality

Water quality was good in many areas of the Mitchell, Tambo and Nicholson catchments. Exceptions were the upper to mid reaches of the Tambo River and its tributaries where salinities were elevated. SIGNAL scores generally did not meet the draft SEPP biological objectives in these reaches. This, in combination with relatively good AUSRIVAS and RHA scores, suggests that water quality is the primary issue in this part of the Tambo catchment. Programs to repair and restore the streamside zone in these reaches should also have beneficial impacts upon water quality.

Water quality was also poor in a number of creeks in the lower catchment of the Mitchell River. Some of these creeks were essentially pools when sampled and would be expected to have elevated nutrient and salinity levels as a result of the combined effects of lack of flow and evaporation. Assessing the health of these streams is difficult because intermittent streams are poorly represented in the reference site data set used to derive the draft SEPP biological objectives. There is a need for further study of these stream types and, possibly, the development of a separate AUSRIVAS model for intermittent streams.

8.3 Monitoring and Assessment

A review of current levels of investment in program monitoring and assessment could be considered. The feedback provided by monitoring and assessment is crucial to environmental management. Such feedback is needed to assess the success or failure of management programs, and to direct resources to where they are needed and in the most appropriate manner. The feedback provided will be essential in demonstrating the value of programs, improving current programs and adapting to new challenges.

There is a particular need for the assessment and evaluation of existing rehabilitation and restoration programs. This will demonstrate the success or failure of management programs and enable the direction of resources to

Environment Report 51 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

where they are appropriate and of most value. If community support for these programs is to continue, their effectiveness needs to be demonstrated. The questions that need to be answered are:

· Have the programs to date been effective and appropriate?

· Have the programs achieved what they set out to achieve? For example, how successful has willow removal, meander re-instatement, or attempts to stabilise banks and restrict stock access been?

· Is there a need for further works or new approaches?

· Have the programs resulted in improved habitat and biological communities?

EPA Victoria 52 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

9. REFERENCES AND FURTHER READING

AWT 1999. Victorian Water Quality Monitoring Annual Report: 1998. Report prepared for Department of Natural Resources and Environment by AWT Victoria.

Barbour, M.T., J. Gerritsen, B.D. Snyder, and Stribling, J.B. 1999. Rapid Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates and Fish, Second Edition. EPA 841-B-99- 002. U.S. Environmental Protection Agency; Office of Water; Washington, D.C.

Barmuta, L. A., Chessman, B. C., and Hart, B. T. H. 1997. Interpretation of the Outputs from AUSRIVAS. Land and Water Resources Research and Development Corporation.

Boulton, A.J., and Brock, M.A. 1999. Australian Freshwater Ecology: Process and Management. Gleneales Publishing, Glen Osmond, SA, Australia.

Bunn, S.E., Davies, P. M. and Mosisch, T. D. 1999. Ecosystem measures of river health and their response to riparian and catchment degradation. Freshwater Biology 41: 333-345.

Chessman, B.C. 1995. Rapid assessment of rivers using macroinvertebrates: A procedure based on habitat- specific sampling, family level identification and a biotic index. Australian Journal of Ecology 20: 122-129.

Conron, S. and Coutin, P. 1995. Survey of the Recreational Fishery in the Gippsland Lakes 1995- Progress Report No.1. Victorian Fisheries Research Institute, Queenscliff, Victoria.

Craigie, N., Brizga, S., Clark, S. and Candy, R. 2000. Integrated Hydraulic and Geomorphological Investigations of the Tambo River. Proceedings of IWRA's Xth World Water Congress: http://www.iwra.siu.edu/pdf/Craigie.pdf

Davies, P.E. 1994. River Bioassessment Manual. National River Processes and Management Program, Davies, P.E., Monitoring River Health Initiative.

DCE 1991. Gippsland Lakes Management Plan. Department of Conservation and Environment, Victoria.

East Gippsland Regional Catchment and Land Protection Board (1997). Regional Catchment Strategy. East Gippsland Regional Catchment and Land Protection Board.

EPA 1986. Gippsland Lakes and Rivers. Water quality series data No. WQ7/86. Environment Protection Authority, Victoria.

EPA 1996 Policy impact assessment: Protecting Water Quality in Central Gippsland. Variation of State Environment Protection Policy (Waters of Victoria). Environment Protection Authority, State Government of Victoria, Publication 516.

EPA 1998. Rapid Bioassessment of Victorian Streams: The approach and Methods of the Environment Protection Authority. Environment Protection Authority, Victoria. Publication 604.

Environment Report 53 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

EPA 2001a. Draft State Environment Protection Policy (Waters of Victoria) and Draft Policy Impact Assessment. Environment Protection Authority Victoria, Publication 795.

EPA 2001b. Risk Assessment Approach – Ecosystem Protection. Environment Protection Authority Victoria, Publication 790.

EPA 2001c. Water Quality Objectives for Victorian Streams- Ecosystem Protection. Environment Protection Authority Victoria, Publication 791.

EPA 2001d. Nutrient Objectives for Rivers and Streams – Ecosystem Protection. Environment Protection Authority Victoria, Publication 792.

EPA 2001e. Biological Objectives for Rivers and streams – Ecosystem Protection. Environment Protection Authority Victoria, Publication 793.

Erskine, W.D., Rutherford, I.D. and Tilleard, J.W. 1990 Fluvial geomorphology of tributaries to the Gippsland Lakes, Ian Drummond and Associates Pty Ltd, Wangaratta, Victoria.

Furse, M.T., Moss, D., Wright, J.F., and Armitage, P.D. 1984. The influence of seasonal and taxonomic factors on the ordination and classification of running-water sites in Great Britain (UK) and on the prediction of their macroinvertebrate communities. Freshwater Biology 14: 257-280.

Government of Victoria 1988. State Environment Protection Policy, Waters of Victoria. Victoria Government Gazette, No.S13, Friday 26 February 1988.

Government of Victoria 1999. Variation of the State Environment Protection Policy (Waters of Victoria) - Insertion of Schedule F7. Waters of the Yarra Catchment.

Grayson, R., Tan, K.S., and Wealands, S. (2001) Estimation of sediment and nutrient loads into the Gippsland Lakes. Gippsland Lakes Environmental Study Technical Report. Centre for Environmental Applied Hydrology, University of Melbourne.

Harris, G., Batley, G., Webster, I., Molloy, R., and Fox, D. 1998. CSIRO Gippsland Lakes Audit. Review of water quality and status of the aquatic ecosystems of the Gippsland Lakes. Prepared for the Gippsland Coastal Board.

Hellawell, J.M. 1978. Biological surveillance of rivers. National Environment Research Council and Water Research Ce ntre, Water Research Centre, Stevenage, England.

Hewlett, R. 2000. Classification of Victorian streams: Implications of taxonomic resolution, sample habitat and sample season. MSc Thesis, la Trobe University. Unpublished.

Longmore, A.R. 1989. Nutrient Budget for northern Lake King, Gippsland Lakes, 1987-88. SRS 89/004. Environment Protection Authority, Victoria

EPA Victoria 54 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Marchant, R. 1990. Robustness of classification and ordination techniques applied to macroinvertebrate communities from the Latrobe River, Victoria, Australia. Australian Journal of Marine and Freshwater Research. 41: 493-504

Marchant, L., Doeg, T. and O’Connor, W. 1995. The impact of salinization and sedimentation on aquatic biota. In: Conserving Biodiversity: Threats and Solutions. Bradstock, R.A., Auld, T.D., Keith, D.A., Kingsford, R.T., Lunney, D. and Sivertson, D.P. (eds). Pp 126-136. Surrey Beatty & Sons, Sydney.

Metzeling, L., Doeg, T., and O’Connor, W. 1995. The impact of salinization and sedimentation on aquatic biota. In: Conserving Biodiveristy: Threats and Solutions. Bradstock, R.A., Auld, T.D., Keith, D.A., Kingsford, R.T., Lunney, D., and Sivertson, D.P. 9EDS). Pp 126-136. Surry Beatty & Sons, Sydney.

Newall, P. and Wells, F. 2000. Potential for delineating indicator-defined regions for streams in Victoria, Australia. Journal of the North American Benthological Society, 19, 557-571.

Norris, R.H. and Norris, K.R. 1995. The needs for biological assessment of water quality: Australian perspective. Australian Journal of Ecology, 20: 1-6.

Plafkin, J.L., Barbour, M.T., Porter, K.D., Gross, S.K. and Hughes, R.M. 1989. Rapid bioassessment protocols for use in streams and rivers: benthic macroinvertebrates and fish, Plafkin, J.L., Barbour, M.T., Porter, K.D., Gross, S.K. and Hughes, R.M., U.S. Environmental Protection Agency (EPA/444/4-89-001).

Read, M.G. and Barmuta, L.A. 1999. Comparisons of benthic communities adjacent to riparian native eucalypt and introduced willow vegetation. Freshwater Biology 42: 359-374

Reynoldson, T.B., Norris, R.H., Resh, V.H., Day, K.E. and Rosenberg, D.M. 1997. The reference condition: a comparison of multimetric and multivariate approaches to assess water-quality impairment using benthic macroinvertebrates. Journal of the North American Benthological Society, 16: 833-852.

Robinson, D.P. 1995. Water quality and nutrient status of Lake Wellington. Environment Protection Authority, Victoria. Publication number 460.

Rutherfurd, I.D., Jerie K.E. and Marsh, N. 1999. A Rehabilitation Manual for Australian Streams Volumes 1 and 2. LWRRDC and CRC for Catchment Hydrology [Canberra, Australia] June 1999. Available from Internet: http://www.rivers.gov.au.

Smith, W and Nathan R. 1999. Victorian Water Quality Monitoring Network Trends Analysis – East Gippsland Catchment Management Authority Area. Report to Department of Natural Resources and Environment by Sinclair Knight Merz.

Victorian Government 1995. Nutrient Management Strategy for Victorian Inland Waters – Strategy. State Government of Victoria.

Environment Report 55 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

Wells, F., Metzeling, L., and Newall, P. 2002. Macroinvertebrate regionalisation for use in the management of aquatic ecosystems in Victoria, Australia. Environmental Monitoring & Assessment. 74: 271-294

Williams, R.J. 1990. Cattle grazing within subalpine heathland and grassland communities on the Bogong High Plains: disturbance, regeneration and the shrub-grass balance. Proceedings of the Ecological Society of Australia 16: 255-265

Wright, J.F., Furse, M.T. and Armitage, P.D. 1994. Use of macroinvertebrate communities to detect environmental stress in running waters. In: Water quality and stress indicators in marine and freshwater systems: linking levels of organisation., Eds. Sutcliff, D. W., Freshwater Biological Association, London.

Wright, J. F. 1995. Development and use of a system for predicting the macroinvertebrate fauna in flowing waters. Australian Journal of Ecology 20: 181-197.

EPA Victoria 56 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

APPENDIX 1: BIOLOGICAL INDICATORS AND REGIONS

1.1 Using Macroinvertebrates As Biological Indicators

Ecosystems are generally complex with many component organisms and processes. There are many components of aquatic ecosystems that could potentially be used for the assessment of environmental condition, such as phytoplankton, benthic diatoms, fish, bacteria and invertebrates (Hellawell 1978). Some community process measures have also been proposed, such as stream metabolism (Bunn et al. 1999). The aquatic invertebrate community, however, offers many advantages over other components of the biota, and is the most commonly used component in assessments of environmental health, both in Australia and overseas (Hellawell 1978, Norris and Norris 1995).

Aquatic invertebrates are small animals, generally less than one centimetre long, and include mayfly and dragonfly nymphs, beetles, snails, worms, shrimp and the like. They are very abundant in streams, occurring in all aquatic habitats. They can be found burrowed in mud, in or on woody debris (snags), on the surface of stones in fast flowing riffles and among macrophyte (aquatic plant) beds. As well as being important in their own right, invertebrates are critical to stream ecosystem functioning, both in the processing of energy and as a food supply to yabbies and other invertebrates, fish, platypus, and some birds.

There are now considerable data available on the response of invertebrates to various forms of pollution, to changes in catchment use (for example, agriculture, forestry, and urbanisation), and of their general habitat preferences and ecology. Some types are known to be sensitive to changes in environmental factors such as temperature, dissolved oxygen or nutrient status.

Being of limited mobility, the presence or absence of invertebrate species or families reflects conditions at a site over time, allowing an assessment of intermittent stresses that are often missed in chemical monitoring programs. The presence or absence of specific types of invertebrates is just one way in which information can be obtained about environmental quality. Other information can be obtained from how many different types of animals are found in a stream (biological diversity), the number of animals found in a stream (abundance), and the relationship between all animals present (community structure). Generally, streams with a high level of diversity are in good health. Streams that have low diversity are typically less healthy, often due to the impacts of pollution or loss of suitable habitat. In polluted streams, sensitive species are eliminated and less sensitive species show an increase in numbers.

Most monitoring programs around the world have chosen to use invertebrates, identified to the level of family, and simple presence/absence (or binary data) (eg. Plafkin et al. 1989, Wright et al. 1984). Studies both in Australia (Marchant et al. 1995, Hewlett 2000) and elsewhere (Furse et al. 1984, Plafkin et al. 1989) have shown

Environment Report 57 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

sufficiently high similarity between family and species level patterns and their interpretations, and between quantitative and binary data, particularly when used in broad scale assessments (Marchant 1990).

1.2 Developing the Biological Regions

Around 900 stream sites in Victoria were sampled for macroinvertebrates under the National River Health Program (NRHP), using the Rapid Bioassessment Protocol (RBA) (EPA 1998). Of these, some 200 were designated as ‘reference’ sites for the purpose of building predictive models (Davies 1994). A reference site does not necessarily mean that the site is pristine, but rather is a minimally impacted or best available site (Reynoldson et al. 1997). This is in recognition that most streams in foothill and lowland areas in particular have been greatly modified by human activities and few, if any, unaltered or pristine examples of such streams exist. In developing the draft biological objectives for the SEPP WoV review, all available invertebrate reference site data from edge and riffle habitats (including stream habitat assessments and water quality data) were used.

Stream invertebrate species respond to small-scale influences within a stream as well as large-scale influences. The most obvious large-scale factor is the longitudinal or upstream-downstream dimension as a river runs from its headwaters to the sea. As you move downstream from the headwaters a number of physical features change. There tends to be a decrease in gradient, mean particle size, dissolved oxygen, amount of coarse particulate organic matter, and the degree of channel shading by streamside vegetation. Mean flow and discharge increase the further downstream you travel, the channel becomes more sinuous, the floodplain starts to develop, and turbidity, salinity and temperature tend to increase as well (Boulton and Brock 1999). All of these features are variables with which aquatic biota interact and the mix will influence biota distribution and abundances.

As well as these longitudinal changes there are, over an area as large as Victoria, factors that operate on a regional scale to influence invertebrate distribution. Regional scale factors include climate, geology and topography. In developing biological objectives for rivers and streams in Victoria it was necessary to take account of these longitudinal and regional scale influences. This was achieved by dividing the State into regions with like combinations of longitudinal and regional scale factors. These have been termed biological regions. The regionalisation process involved the classification of reference sites using a combination of statistical (clustering, ordination and multi-linear regression analyses) and qualitative (expert judgement) methods. Regions were delineated primarily on the patterns of invertebrate community assemblage across Victoria. Environmental factors were also used to assist with boundary positioning and the general descriptions of the regions. More detailed description of the regionalisation process and the regions themselves can be found in Newall and Wells (2000) and Wells et al. (2002).

1.3 AUSRIVAS

AUSRIVAS is a classification and predictive modelling technique based upon the River InVertebrate Prediction and Classification System (RIVPACS), originally developed in Britain (Wright 1995). AUSRIVAS was developed under

EPA Victoria 58 ENVIRONMENTAL CONDITION OF RIVERS AND STREAMS IN THE MITCHELL, TAMBO AND NICHOLSON CATCHMENTS

the Federal Government’s National River Health Program (NRHP) as a means to assess the condition of rivers and streams across Australia. The models predict the aquatic macroinvertebrate families expected to occur at a site in the absence of environmental stressors, such as water pollutants or habitat degradation. By comparing the totalled probabilities of predicted families and the number of families actually found, a ratio can be calculated for each test site. This ratio is expressed as the observed number of families/expected number of families (the O/E index).

The value of the O/E index can range from a minimum of zero (none of the expected families were found at the site) to around one (all of the families which were expected were found). It is also possible to derive a score of greater than one, if more families were found at the site than were predicted by the model. A site with a score greater than one may simply result from variation in the capture efficiency of sampling methods, or it may indicate an unexpectedly diverse location, or mild nutrient enrichment stimulating primary and secondary production. The O/E scores derived from the model are assigned to bands (Table 1), which are considered to represent different levels of biological condition (as recommended under the NRHP, Barmuta et al. 1997). The width of the band varies between models but is constant within each model. The band label for the equivalent classifications remains constant across all models, that is, Band A always corresponds to equal to reference site quality.

Table 1: Example AUSRIVAS O/E family score categories

Band Label O/E score Band Name Comments

X >1.15 Richer than reference · more families found than expected · potential biodiversity “hot spot” · possible mild organic enrichment A 0.85-1.14 Reference · index value within range of the central 80% of reference sites B 0.55-0.84 Below reference · fewer families than expected · potential mild to severe impact on water quality, habitat or both, resulting in loss of families C 0.25-0.54 Well below reference · many fewer families than expected · loss of families due to severe to extreme impact on water and/or habitat quality D <0.25 Impoverished · very few families collected · highly degraded · very poor water and/or habitat quality

Environment Report 59