Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Jonas Ball, Sinclair Knight Merz Pty Limited, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06750 7
The natural flow regimes of many regulated river systems have been modified because of water extractions and the use of rivers as irrigation and water supply channels. Many of Australia's native flora, fauna and habitats are dependent on natural flow regimes so changes in flow patterns have a significant effect. Aquatic ecosystems in the highly regulated river systems of the Murray-Darling Basin and a number of smaller eastern coastal river systems are likely to be under pressure from modification to natural flow regimes. Environmental water allocations are currently being determined for many regulated river systems and this is further discussed in the Water resources: Key findings.
Increasing salinity of inland waters is a major threat to many aquatic ecosystems. Already aquatic ecosystems in western Victoria and south-west Western Australia are affected by salinity and it is predicted that many wetlands and river systems in the Murray-Darling Basin will be severely affected by increased salinity by 2050. Eighty important wetlands are already affected by salinity and this will rise to 130 by 2050 (NLWRA 2001b).
Cold-water thermal pollution is estimated to affect up to 3000 km of rivers in New South Wales alone and is likely to be occurring in many regulated river systems throughout the nation. Pesticide contamination of groundwater, surface water and sediments has been detected in agricultural areas, although their impact on aquatic ecosystems is not fully understood. Algal blooms are common in many waterways and can have impacts such as reducing dissolved oxygen levels and decreasing light penetration.
Riparian zone habitats (including wetlands) are in poor condition in many areas and are decreasing in others due to the effects of grazing, land clearing, modified flow regimes, salinity, floodplain isolation and the spread of exotic species.
Native fish populations in some river systems are under severe stress from barriers to fish movements, poor water quality, reduction in habitat and competition from exotic species. Six per cent of native fish species are considered threatened. Over 10% of native frog species are considered threatened due to loss of habitat, poor water quality and pesticides. The chytrid fungus has been implicated as a significant cause in the decrease of some frog populations in Australia. Fifty per cent of Australia's inland waterbirds are listed as extinct, vulnerable or near threatened primarily due to wetland and riparian habitat loss. Platypus and some species of freshwater crayfish are considered to be at risk, primarily from loss of habitat. However, there is only limited information on the distribution and condition of these animals.
A national assessment of river 'health' was undertaken using the AusRivAS protocol. At 31% of sites macroinvertebrate communities were significantly impaired, at 8% of sites they were severely impaired and at 1% of sites they were found to be extremely impaired. Generally the degree of impairment was related to land use in the catchment and disturbance of the river system.
The main issues for groundwater-dependent ecosystems include:
- groundwater-dependent ecosystems are poorly understood
- arguably the most significant groundwater-dependent ecosystem is baseflow to rivers. As such, the management of groundwater is fundamental to surface water quality and availability
- the geographic extent and dependence of vegetation on groundwater is not well understood
- environmental water allocation have generally not been determined and so protection mechanisms for groundwater-dependent ecosystems are not in place.
Some of the major management responses to protect and maintain aquatic ecosystems include:
- action plans for the conservation of native frogs and waterbirds
- restocking of native fish and construction of fishways
- national, state and local programs to protect and improve riparian zones and habitats
- additional wetlands listed under the Ramsar Convention and the development of wetland protection policies
- environmental water allocations for surface aquatic ecosystems
- state legislative mechanisms for the protection of riparian zones and threatened aquatic species, and the provision of environmental flows
- the new Commonwealth environmental legislation Environment Protection and Biodiversity Conservation Act 1999 which provides additional protection for threatened aquatic species and Ramsar-listed wetlands from activities on public and private land
- pest management programs.
In many instances there is a lack of conclusive data on the effectiveness of improved environmental management practices on overall aquatic ecosystem health or on individual species or habitats. Increased funding for monitoring the effectiveness of management intervention is urgently needed.
The current pressures on inland aquatic ecosystems are the same as those reported in Australia: State of the Environment 1996 (State of the Environment Advisory Council 1996). Modified river flows, water quality and exotic pests are still the most influential elements of inland aquatic ecosystem health.
As in the 1996 report, there is still a lack of national datasets on the condition of most inland aquatic habitats, flora and fauna. The only national dataset available for this assessment was macroinvertebrate communities measured using the AusRivAS protocol. The AusRivAS protocol is specifically designed to provide an indication of river 'health' and is a useful tool. The AusRivAS assessment and other indicators of condition continue to show that Australia's inland aquatic ecosystems in highly developed agricultural and urban areas are in poor health, with reductions in habitat and biodiversity. Programs to collect these data are being implemented (e.g. National Wetland Inventory) and there should be considerably more data on the condition of aquatic ecosystems for the next SoE reporting cycle.
Since 1996, management responses to maintain and protect aquatic ecosystems have improved. These have included legislation to protect remnant riparian vegetation, threatened species and wetlands; strategies and policies for conservation of aquatic habitat, flora and fauna; and funding for research, community-based restoration projects and national conservation programs.
The emerging issues for aquatic ecosystems are as follows.
- Recent studies have shown that clear macrophyte-dominated ecosystems can switch to degraded turbid algal-dominated systems due to the effects of vegetation loss, poor water quality and reduced river flows. Once these ecosystems have 'switched' it is very difficult to return them to their former state.
- The future predicted extent of the salinisation of inland waters and their catchments is far greater than previous estimates. Based on impacts measured in currently affected ecosystems, many important aquatic ecosystems risk significant degradation from effects of salinity.
- Baseflows in rivers, streams and wetlands are essential for many aquatic ecosystems and are under threat from over extraction of linked groundwater resources.
The threats to the sustainability of inland aquatic ecosystems and riverine and floodplain wetlands can be summarised as follows:
- the extraction of water (including groundwater) in excess of sustainable yields for the maintenance of dependent aquatic flora and fauna
- the modification of surface water flow regimes and water storages
- poor water quality - primarily from catchment activities such as the removal of riparian vegetation, habitat modification, the discharge of pollutants, soil erosion, salinisation and pesticide use
- land clearing and modification - land clearing and modification impacts include direct loss of riparian habitat, increased soil erosion and a higher risk of dryland salinity
- introduction and spread of introduced exotic species - they can compete with native species for resources, may have no natural predators in Australia and can affect other environmental characteristics (e.g. water quality)
- lack of data on the condition and extent of most aquatic fauna, flora and habitats.