SoE 2006 > Water > 5.1 Freshwater riverine ecosystem health

5.1 Freshwater riverine ecosystem health

Freshwater riverine ecosystems' health has declined in some areas of NSW as a result of drought. However, the NSW water reforms have been designed to improve the status of riverine ecosystems. The Water Management Act 2000 guarantees in legislation the environment's right to water for the first time.

Over the last 100 years, the environmental condition of the majority of NSW rivers has been modified, particularly through vegetation clearing, habitat disturbance, declining water quality, regulation of waterways and water extraction. Water availability and recent climatic conditions are both major determinants of the condition of freshwater riverine systems. Areas where the flow regime is most changed (where river regulation and water use are highest) are generally showing the most signs of ecosystem stress.

Ongoing drought conditions occurring across much of NSW since 2003 have limited water availability. This has contributed to a decline in river health indicators such as macroinvertebrates across many areas of NSW. In the most recent assessments, only 22% of macroinvertebrate sample sites were considered to be in good condition, compared to 56% of sites reported in SoE 2003.

NSW indicators

Introduction

Healthy freshwater riverine ecosystems – comprising rivers and their riparian zones, floodplains and wetlands – are vital for the maintenance of aquatic and terrestrial biodiversity, water quality, and human activities such as aquaculture, fishing, recreation, tourism and swimming.

However, freshwater ecosystems have been greatly modified in most of NSW – with as much as 97% (56,000 kilometres) of river length assessed as being modified in some way (NLWRA 2001). Typical changes include the removal of riverine vegetation; the regulation of rivers; sedimentation from the erosion of land and riverbanks; and the introduction of exotic species. These changes have led to the following problems:

• loss of suitable habitats for native plants and animals, including loss of wetland areas
• changes to flow regimes in rivers, wetlands and floodplains
• changes in water quality
• declining biodiversity.

The condition of freshwater riverine systems can be assessed by measuring the condition of their biological communities. The established method compares macroinvertebrate groups found at the sampled sites with those from reference (less-impacted) streams of a similar type. Details on methods can be obtained from AusRivAS.

Macroinvertebrates (invertebrates visible to the naked eye) are useful indicators of river health because many are sensitive to changes in water flow and quality – fewer species survive at a site as conditions deteriorate. Healthier streams therefore tend to have a greater diversity of macroinvertebrates than unhealthy sites. Also, many species have adaptations for surviving unfavourable periods, and will reappear as conditions improve.

Similarly, the diversity and composition of fish communities can be assessed to indicate the relative health of a river or stream. Data on both types of biotic indicators, macroinvertebrates and fish, is used in this report. For more information on freshwater ecosystem health, see EPA 2000a. Information on the status of wetlands in NSW is presented in Biodiversity 6.6.

Current status and trends

The Sustainable Rivers Audit (coordinated by the Murray-Darling Basin Commission and commenced in 2004) has collected data on fish and aquatic macroinvertebrate diversity as part of its assessment of river health for the Murray–Darling Basin. Information on macroinvertebrates has also been collected for rivers of the mid-North Coast and Hunter Valley by the Department of Natural Resources for the Hunter/Central Rivers Catchment Management Authority; and for metropolitan catchments (the Hawkesbury–Nepean, Shoalhaven and Woronora rivers) by Sydney Catchment Authority (SCA) and Sydney Water Corporation.

River health – macroinvertebrates

Map 5.1 shows macroinvertebrate health scores for each valley in NSW for which data is available. The data shows that generally the upper catchments were similar to reference stream conditions, whereas downstream areas were degraded in both coastal rivers and inland catchments. The exceptions were the Murrumbidgee, where the main channel of the river appears to be in better condition than the upper catchment, and the Macquarie, where there is no consistent pattern in river health. Also notable is the high proportion of normally wet sites (38%), particularly in inland areas, that were dry as a result of the drought.

Map 5.1: Macroinvertebrate condition as an indicator of river health

Sources: DIPNR data 2003; Sustainable Rivers Audit data 2005; Ecowise Environmental Pty Ltd 2004 (SCA data); Sydney Water Corporation data 2005

In 2004–05, assessments for the Hawkesbury–Nepean, Shoalhaven and Woronora rivers highlighted that tributary and upper river sub-catchments were generally healthy, while downstream sub-catchments in main rivers and urban areas tended to be degraded. Reduced flows because of drought conditions appear to have contributed to the condition of these sub-catchments, although loss of habitat, poor quality runoff and discharges are also implicated.

Of those sites that could be sampled in both 2001 and 2004 in the Hawkesbury–Nepean, Woronora and Shoalhaven catchments:

• 34 sites showed no consistent trend in health
• 18 sites were in stable condition
• 11 sites had reduced health
• eight sites had improved health.

Across the State, 22% of sites (108 out of 481) were in reference condition or better when sampled between 2003 and 2005, compared to 56% of sites (557 out of 994) in 2002 (data from SoE 2003). This apparent decline in river health over this period is expected to be mostly due to the record drought between the two sampling periods (see Appendix 1). The fact that over a third of the previously selected, normally wet, sites were dry and could not be sampled in 2004–05 indicates the severity of the drought.

Also, more sites in the metropolitan area, where the drought was less extreme, were in reference condition or better (42%), compared to 17% of sites in other areas of the State.

No data is yet available for the other inland rivers on Map 5.1; however, these rivers are being sampled and assessed as part of the Sustainable Rivers Audit. There is no data for the northern and southern coastal rivers (other than in the Hunter Region and the Hawkesbury–Nepean and Shoalhaven rivers).

River health – fish

The Department of Primary Industries (DPI) has collected data on fish from numerous catchments to produce the fish community integrity index (FCII). The FCII provides a rapid, statewide snapshot of fish community health for use in the water-sharing planning process (see Map 5.2). The FCII is based on two factors: integrity (the expected species of native fish present compared to the fish species actually observed), and nativeness (the proportion of native fish species abundance compared to the total abundance of native and non-native fish).

The terms 'introduced' and 'exotic' are used interchangeably in this report to describe non-native fish. Non-native fish occur widely in NSW rivers, having been either deliberately introduced (as with trout) or allowed to escape from ponds (as with carp). Introduced fish can often thrive and become pests, especially where river conditions have been modified for human use, such as in regulated streams.

Map 5.2: Health of the fish community

Source: DPI data 2006

Based on this index, fish communities appear generally healthy along upper parts of some coastal rivers, and some of the upstream sections of inland rivers and along the Murray. The communities are more degraded along the mid and lower sections of other inland rivers, particularly the Lachlan. This finding has been linked in previous surveys to the extent of regulation for water use (Harris & Gehrke 1997; MDBC 2004a; DPI 2005). Fish surveys regularly find that the worst-affected water bodies are regulated rivers – the installation of weirs and dams to store water for human use often modifies the flow and water quality characteristics in inland waterways, affecting fish communities directly, as well as changing the broader ecological processes that sustain these systems (see Water 5.2). Barriers such as weirs and floodgates also affect fish in coastal streams, while urbanisation and heavily populated coastal areas have further impacts on water quality and fish communities.

Comprehensive surveys of the Barwon–Darling, Murray and Border rivers catchments in 2004–05 for the Sustainable Rivers Audit revealed a high percentage of exotic fish species, comprising 40% of fish biomass in the Border and Darling rivers and 96% of biomass in the upper Murray. For fish numbers rather than biomass, the equivalent proportions are 6–10% exotic fish for the central and lower Murray and Darling, to over 60% for the upper Murray. Apart from the Border Rivers, where most of the native species expected to be present were found (87%), no other catchment had more than half the expected native species. In the Lachlan (a regulated river, see Water 5.2), nearly 40% of individual fish caught during the Sustainable Rivers Audit pilot study in 2002 were exotic species, accounting for six of the 18 species recorded. The Sustainable Rivers Audit will sample the remaining NSW inland catchments in 2005–06 and 2006–07.

Summary

In summary, although some of the State lacks information about the health of aquatic ecosystems, the available macroinvertebrate data indicates that only 22% of sites were not degraded (in reference condition). In addition, the results from fish surveys confirm that 65% of sites sampled had reduced health, compared to their natural (pre-European settlement) condition.

Response to the issue

The major responses to the degraded health of freshwater ecosystems have been to improve the management of river flows and water extraction practices; to install fish passages on barriers to fish movement such as weirs; to develop control measures for carp and other pest species; and to reduce the impacts of different land uses.

The most significant change in NSW in recent years has been the implementation of new water management rules that commenced in 2004 in most of the major inland regulated river systems and included revised environmental flow rules under water-sharing plans (see Water 5.2). It may take some time, however, before the aquatic ecosystems receiving these environmental flows show signs of improved river health. However, there is a risk that environmental flows could become diminished by unlicensed floodplain harvesting in some systems. Programs to improve land management to reduce impacts on the aquatic environment are discussed in Land 4.1.

In 1999, the NSW Government agreed to community environmental values for waterways and endorsed environmental objectives for water quality and river flow for 31 catchments and estuaries in NSW. Some of these objectives were confirmed or updated through Healthy Rivers Commission inquiries. This commission has now been replaced by the Natural Resources Commission (NRC). The environmental objectives have been updated to take account of the revised water quality guidelines (ANZECC & ARMCANZ 2000) that underpin the NRC's standards and targets for water quality.

The protection and rehabilitation of riverine vegetation is another high priority for river health, both for maintaining biodiversity and improving water quality. Riverine vegetation acts as a buffer between the river and adjacent land uses, helps prevent bank erosion, and provides habitat and shade to water bodies. Many rivers, however, have extensively cleared or degraded riparian vegetation, which exposes the waterway to the full impacts from adjacent land uses.

The Government and catchment management bodies are encouraging community groups to rehabilitate riverbanks, because of the ecosystem health and water quality benefits from healthy riverine vegetation. Existing native riverine vegetation is protected under the Native Vegetation Act 2003, and in many rural areas, native vegetation within townships is protected by local government statutes or reservation.

In the Murray–Darling Basin, the Native Fish Strategy 2003–2013 (MDBMC 2003) was released in 2003. It has a long-term goal of rehabilitating native fish communities back to 60% of estimated pre-European populations by the year 2050. It provides a framework for protecting and rehabilitating fish habitat; improving the management of riverine structures (to reduce the impact of cold-water pollution and barriers to fish passage); controlling exotic fish species; protecting threatened native fish species; and better managing fish translocation and stocking.

The construction of fishways or 'fish ladders' to remediate the impact of weirs and dams on the passage of fish is managed in NSW by the DPI, which works with a range of other agencies and stakeholders to improve the movement of fish through the many structures that are barriers to fish passage in NSW. Since 2003, significant research into fish migration and fishway technology has aimed to improve fish passage in a number of regions:

• 12 new fishways in NSW have been constructed since July 2003: four in the Murray system, four in the Macquarie system, and one each in the Murrumbidgee, Lachlan, Hunter and Tuggerah Lakes systems
• the Murray-Darling Basin Commission has commenced a program (Hume to the Sea) for 11 new fishways on the main stem of the River Murray, providing unencumbered passage for fish from the mouth of the river in South Australia to Lake Hume near Albury
• improved management of 58 priority floodgates on the North Coast has opened more than 600 kilometres of waterways to fish passage and more natural flows.

A range of other legislative tools, strategies and policies assist in improving freshwater riverine ecosystem health, such as improving water quality (see Water 5.3), mitigating the impact of cold-water pollution from water storages (see Water 5.3) and protecting aquatic habitat (see Biodiversity 6.6) and aquatic biodiversity (see Biodiversity 6.7).

The statewide natural resource management target for river health is: 'By 2015 there is an improvement in the condition of riverine ecosystems'. The available data may be used as a baseline measure for this target in some parts of NSW, but there is a need for further data on a statewide basis to provide a full picture of progress towards the target. Catchment management authorities (CMAs) will include measures for meeting this target in their catchment action plans.

Future directions

Once drought conditions ease, existing responses should help to prevent further decline in the condition of riverine ecosystems. Although it is too early to determine the long-term effectiveness of providing water for the environment in water-sharing plans (see Water 5.2), especially if dry conditions continue, some positive responses were achieved in 2005–06 despite prolonged drought conditions. Further recovery, including the delivery of additional water for environmental purposes, needs to be implemented to improve wetland health and prevent further degradation of some wetland areas (such as parts of the Macquarie Marshes, the Gwydir wetlands and in the Lowbidgee; see Water 5.2 for water-recovery initiatives).

Investment priorities in catchment action plans need to target the rehabilitation of riverine habitats and wetlands for multiple improvements in riverine health, water quality and biodiversity.

A consistent, comprehensive and ongoing statewide monitoring program is necessary to enable the effectiveness of management strategies to be assessed, and to use the feedback from this assessment to refine future objectives and practices in a process of adaptive management. River health is being monitored to determine both condition and trends but has not yet achieved statewide, consistent coverage. Better coordination and integration to provide for informed resource allocation and management actions will be provided as State agencies and CMAs progressively implement a monitoring strategy for NSW.