Aquatic ecosystems
(adapted from SoE report see: and NLWRA see; )
Recently there has been an increased focus on protecting Australia's unique aquatic
ecosystems.
Drainage of floodplain wetlands to allow for agricultural development, and more recently
urban settlement, has caused much damage.
The building of levees to protect inappropriate development from flooding has often
isolated the rivers from their floodplains.
Irrigation development, and water-regulating structures (e.g. dams and weirs) also
contribute to changes in flow regimes and water character (e.g. temperature)
affecting aquatic ecology.
The recognised key pressures on aquatic ecosystems include:
# changes in natural flow regimes as a result of water extraction and supply
# direct modification or destruction of important habitats
# barriers to the movement of plants and animals, for example within rivers and
between rivers and their floodplain
# effects of poor water quality
# competition from introduced and exotic animal and plant species.
An example of changes in flow regimes can be found in the Murray River and its tributaries,
where the cycle of seasonal flows has been reversed. The river now runs near bank-full in
summer as it delivers irrigation water, and runs at low levels in winter as the dams are
refilling.
Weir pools help distribute water to the floodplain for irrigation and can be an ideal
habitat for blue-green algae.
The altered flow regime has also assisted pest species like European carp becoming dominant.
Only 13% of Australian river systems had agreed flow allocations for environmental
purposes in June 2000, but at least preliminary environmental flow allocations will be
established for many regulated rivers over the next five to 10 years.
As well as allocating a volume of water to meet environmental needs (i.e. a sufficient
flow of water for the species that inhabit the rivers), it is equally as important to
time water releases to mimic natural flow patterns (or regimes).
Much more research and monitoring is required to develop and assess environmental
flow allocations.
Inland waters downstream of most major water storages are probably affected by
cold bottom water discharges from dams.
Effects on water quality from cold-water pollution may have significant impacts on
ecosystem health in some areas.
A national assessment of river 'health' using the AusRivAS monitoring assessment
system found that at 31% of sites macroinvertebrate communities were significantly
impaired, at 8% they were severely impaired and at 1% they were extremely impaired.
The degree of impairment generally was related to land use in the catchment and
disturbance of the river system.
The AusRivAS results provide an important benchmark of river health.
Riparian vegetation is seriously degraded in many catchments as a result of
clearing, grazing and salinity (e.g. in some areas of Western Australia over
50% of rivers and creeks have lost their native fringing vegetation and less than
10% of wetlands have healthy fringing vegetation).
Riparian restoration and protection is becoming more commonplace, with successful
outcomes being measured in some projects. However, these projects are only a small
proportion of the total area affected.
Resnagging of rivers such as the Murray River is also being undertaken to provide
habitat for native aquatic species.
Wetlands are important in Australia's environment and often support high levels of
biodiversity. Since European settlement, the condition and extent of many wetlands
has decreased substantially.
ince 1996, there is little new information on changes in wetland area.
The area of many wetlands in the Murray-Darling Basin (and others) has declined significantly
as a result of many physical and biological factors.
Programs to better define and map changes in wetland extent and condition are underway.
Another 13 wetlands have been Ramsar-listed since 1996 and the EPBC Act could provide
additional protection to wetlands.
Management plans for many wetlands have been or are being prepared.
Of over 200 freshwater fish species in Australia, 11 are considered endangered and
10 are listed as vulnerable under the EPBC Act.