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 pressures on inland waters can be divided into two main categories. The first category includes pressures from the extraction of surface water and groundwater for human uses such as agriculture, drinking water and industry. The effects of water extraction include:
- reducing river flows and groundwater to levels that are not sustainable for dependent aquatic ecosystems
- the alteration of natural flow patterns in rivers, stream and wetlands
- the construction of instream dams and weirs which provide a barrier to fish movement, but ideal conditions for algal bloom development.
The second category includes pressures arising from activities in the catchment such as land clearing, agriculture and urbanisation. These activities can result in dryland salinity, increased soil erosion and the associated transport of nutrients into waterways, and localised pollution of surface and groundwaters with chemical and biological contaminants. Because of the intrinsic link between inland waters and their catchments, the effects of land use and management must be considered. Other pressures on inland waters include the introduction and spread of exotic plant and animal species, and climate change.
The major pressures on the inland waters are introduced in more detail in the following sections.
The key findings on inland waters in the Australia: State of the Environment (SoE) 1996 report (State of the Environment Advisory Council 1996) are presented below. These key findings are assessed against the latest information to determine whether there has been an improvement, no change or deterioration in condition. Other key findings are also presented.
Australia's inland waters are increasingly being consumed, diverted, polluted and degraded, particularly by population centres and intense land use areas, although many good quality rivers and aquifers remain, mainly in the north.
Drinking water quality - is generally high in large cities, but is less satisfactory in many rural and remote communities.
Water quality - sediments from land erosion and increased salt from rising water tables continue to load inland waters; sedimentation and salinisation adversely affect aquatic biota, increase the cost of water treatment, reduce options for using water, and reduce the storage capacity of dams and reservoirs.
Algal blooms - nutrient levels remain too high and, combined with reduced stream flow, lead to frequent and extensive blooms of blue-green algae which are often toxic. Main nutrient sources are land run-off, erosion and sewage outfalls.
Pollutants - localised problems occur from contaminants e.g. oils, metals, pesticides, acid, chemicals and bacteria; sources include industry, mining, agriculture, forestry, urban development and sewage effluent.
Wetlands - large areas have been destroyed or seriously degraded; the banks of many rivers have been damaged. Drainage, changes to water regimes, and increases in sediment run-off and nutrient inputs are the main causes of wetland deterioration.
Threats to aquatic biota - pollution, over-allocation of water, changed flow regimes and exotic and displaced species are all affecting native species. Many species of aquatic animals are endangered, in decline or extinct.
Household water use - has increased because of increasing populations and rising consumption per person.
Over-allocation - river regulation and damming (mainly to provide a buffer against droughts) have drastically altered seasonal flow regimes in developed regions, particularly in the south-east.
Irrigation - uses the greatest amount of water; irrigation demands contribute to over-allocation of water, and inappropriate practices lead to problems with waterlogging, salinisation of soils, and nutrient and pesticide pollution of inland waters.
Groundwater mining - reserves are generally being used much faster than they are being replenished, e.g. in the Great Artesian Basin (GAB), Pioneer and Namoi valleys and Burnett Basin. A program to cap running bores is under way for the GAB.
Data issues - Australia lacks nationally coordinated basic data on water quality and catchment characteristics. Initiatives such as the National River Health Program, Waterwatch, and other community-based groups can address this need.
Integrated catchment management - most inland water issues require whole catchment management scale solutions.
Australia has only limited surface and groundwater resources, and in many areas large volumes of water are extracted for human uses. The volume of water that can be extracted from a river or groundwater resource while maintaining sufficient water to protect and maintain the aquatic environment is called the sustainable yield. Current estimates of sustainable yields suggest that, on average, only 20% of total run-off can be sustainably captured for human use. In some catchments the current water use is close to or exceeds the sustainable yield and the aquatic environment is under considerable pressure.
As well as reducing flows, the harnessing of rivers and streams to supply water for drinking and agriculture has also fundamentally changed the natural regime of low and high flows that many of Australia's unique ecosystems have adapted to. For example, many inland wetlands in Australia are decreasing in area because the size and variability of minor flooding events has decreased significantly due to the regulation of flows by dams (Kingsford 2000). The lower flows have also provided ideal conditions for stratification of water storages (which leads to the leaching of nutrients and pollutants from sediments) and the development of blue-green algal blooms.
Water storages such as dams, weirs and barrages have a secondary effect on Australia's native fish populations by providing a barrier to fish movement. Many of Australia's native fish migrate upstream as part of their reproductive cycle. By preventing fish movement both up and downstream, barriers also prevent access to important fish habitat. There are over 1700 barriers to fish movement in inland New South Wales alone.
Although groundwater resources are widespread, not all aquifers contain groundwater of sufficient yield and quality for human uses. In addition, with the cap on surface water use in the Murray-Darling Basin and increased cost of surface water, the development of groundwater resources has increased. For example, total groundwater use increased by 90% between 1983/84 and 1996/97. The volume of groundwater extracted from aquifers in some areas exceeds their sustainable yield.
Once an aquifer is exhausted it can take decades or even centuries for it to recover. It is also increasingly recognised that many terrestrial ecosystems are dependent on groundwater and that groundwater inflow provides the baseflow in many rivers and streams. There are also many unique ecosystems (e.g. wetlands) that are directly dependent on groundwater.
The impacts of indiscriminate land clearing are affecting Australia's inland aquatic environments. The replacement of deep-rooted perennial vegetation with shallow-rooted short-lived pastures and crops has increased the 'leakage' of water into the groundwater. This has caused groundwater tables to rise in many areas resulting in land salinisation, water logging and higher salinity in rivers and streams. Over the last five years the threat posed by dryland salinity has been quantified with up to 5.7 million hectares already affected (primarily in south-western Australia, western Victoria and South Australia) and another 7.5 million hectares at risk. In some areas, river and stream salinities are predicted to increase substantially over the next 50 years resulting in stress on flora and fauna, salinisation of freshwater wetlands, damage to riparian vegetation and fundamental changes to water chemistry. These impacts are already being seen in Western Australia and western Victoria. Drinking-water supplies for many inland towns in New South Wales and Victoria and much of South Australia are also threatened by increasing river and stream salinity.
Land clearing and agriculture have also contributed to nutrient enrichment of many inland waters. Soil erosion from grazing is the largest source of nutrients in many catchments. High nutrient levels, combined with the increased periods of low flow due to river regulation and water extraction, have caused blue-green algal blooms to become a persistent problem in some dams, wetlands and lakes. Point sources of nutrients such as wastewater discharges from sewage treatment plants or intensive livestock enterprises (e.g. cattle feedlots) can also contribute to nutrient enrichment in some rivers and streams.
The clearing and grazing of riparian vegetation and salinisation can have particularly severe effects, and many inland waters have severely degraded riparian vegetation. Riparian vegetation creates an important buffer between polluting land uses and rivers and streams. The loss of riparian vegetation leads to a reduction in buffering capacity, leaf litter deposition, streambank stability and habitat, and has the potential to alter stream metabolism.
Modern agriculture, and especially irrigated agriculture, relies on pesticides to maintain crop and pasture health and productivity. As in most other countries, pesticide use by agriculture in Australia has increased substantially over the past 20 years, with close to $1 billion spent annually. Although new pesticides have been developed and the management and application of pesticides has improved, high concentrations of pesticides have been measured in water bodies and groundwater in agricultural areas. Pesticides have been implicated in at least 20 fish kills in New South Wales rivers, streams and dams alone since 1990.
Other activities in catchments such as urbanisation, mining and industry can also result in the pollution of surface water, groundwater and sediments. The introduction and invasion of exotic animals and plants have displaced some native species, reduced biodiversity and caused other problems such as changes in water quality.
Unstable stream banks resulting from clearing of riparian vegetation contributing to river silt loads.
Source: Robert Simpson.