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Conclusions (continued)

Water quality and pollutant sources

Key findings

Quality of groundwater is impacted by many land uses and there are differing mechanisms for pollution of groundwater to occur. Apart from nitrate pollution, most groundwater pollution is localised in its impact. Groundwater quality degradation can occur via the following pathways:

• pollution from industries and agricultural use of land
• salinisation of groundwater because of groundwater pumping, recycling of salts through the unsaturated zone, and mobilisation of naturally occurring salts in the soils and rocks as water tables rise
• seawater intrusion, which is caused by groundwater pumping and can draw seawater into the aquifer reducing its quality.

The key findings in relation to surface water quality and pollutant sources are as follows.

Salinity

Rivers, streams and wetlands in south-west Western Australia and western Victoria are already salinised. With the area of land affected by dryland salinity predicted to at least double over the next 50 years, higher salinities will be experienced in many other river systems in Western Australia and the Murray-Darling Basin. Higher salinities will adversely affect irrigation and drinking water supplies and damage aquatic ecosystems.

Eutrophication and algal blooms

Diffuse-source pollution and especially soil loss from catchments continues to contribute to the widespread nutrient enrichment and turbidity of inland waters. Soil washed into rivers and reservoirs will remain a source of nutrients for decades into the future. In some catchments, wastewater from sewage treatment plants and intensive agriculture also contribute significantly to nutrient enrichment. Nutrient enrichment and reduced streamflow due to over-extraction of water have increased the frequency and extent of toxic blue-green algal blooms, with some reservoirs being unsuitable for recreation or drinking-water supply over 25% of the time.

Pollutants

Contamination of inland waters by heavy metals, chemicals and pathogens is thought to be localised; however, there is no reliable information to support this assumption. There is evidence of pesticide contamination of rivers and streams draining cotton and rice-growing areas in New South Wales. It is likely that other waterways in Australia are affected, but no recent information exists on the extent or impact of pesticide contamination of other areas.

Acidification

This is an emerging issue in some catchments where increasing trends in water acidity and the area of land affected by soil acidity have been found. Higher water acidity may lead to increased availability and movement of pollutants as well as fundamental changes in the chemistry of rivers and streams.

Integrated catchment management

The threats of salinisation, eutrophication, acidification and over-extraction to human water uses and aquatic ecosystems require an integrated response that considers the land, surface waters and groundwater. There have been some improvements in our knowledge that will enable better management of land and water resources, however, the implementation of better management practices is patchy.

Comparison with the key findings of Australia: State of the Environment 1996

The key findings for surface water quality and pollutant sources are similar to those of Australia: State of the Environment 1996 (State of the Environment Advisory Council 1996). The water quality of rivers, streams and wetlands is significantly affected by reduced flow and catchment pollutant sources such as land salinisation, sewage discharge, erosion, diffuse-source pollution and pesticide use in agricultural areas. The potential impact of dryland salinity on the salinity of inland waters is clearer since 1996, with many rivers risking increased salinity over the next 100 years if no measures to manage and prevent dryland salinity are implemented.

Since 1996, there have been some increases in the knowledge of the processes, causes and extent of the degradation in water quality of inland waters. There have also been some advances and initiatives to improve water quality such as:

• the preparation of land and water management plans
• the development of state and national strategies to tackle significant issues such as salinity
• improved management of some polluting activities such as pesticide use and point-source pollution
• the increased recognition of the importance in protecting aquatic ecosystems.

Despite these improvements, there are still fundamental issues that have yet to be addressed such as the sustainability of land and water management practices, and the societal change required to implement sustainable management frameworks. The current management frameworks and funding arrangements do not appear adequate to address these issues.

Emerging issues

The emerging issues for surface water quality and catchment sources of pollutants are:

• The extent of impacts from dryland salinity are much more significant than previously thought and this will require major changes in the management of land and water resources in some areas.
• Management actions to reduce soil acidity (such as large-scale liming) will be required, otherwise water acidity will become a significant problem in many river systems.
• Pesticide contamination of rivers and streams draining agricultural areas has been measured; however, it is unclear what the effects of new pesticides and genetically modified crops will have on pesticide use and impact.

Threats to sustainability

The threats to sustainability in terms of water quality are:

• increasing salinity of rivers and streams due to dryland salinity and irrigation-induced salinity
• nutrient enrichment and frequent blue-green algal blooms
• pesticides in rivers, streams and sediments.

Table 43: Issues that threaten long-term sustainability of water quality.

Resource issue	Process	Threat to sustainability
Use of water for irrigation	Increased recharge and rising water tables.	Irrigation-induced salinity causes the salinity of surface waters to increase, affecting drinking water resources and aquatic ecosystems.
	Discharge of excess irrigation water into rivers and streams.	Pesticide contamination of water and sediments. Nutrient enrichment and increased risk of algal blooms. Increase in turbidity.
	Reduced flows in rivers and streams.	Decrease in 'flushing' of nutrients and algal blooms.
Land use changes (e.g. clearing)	Increased recharge and rising water tables.	Dryland salinity causes the salinity of surface waters to increase, affecting drinking-water resources and aquatic ecosystems.
Wastewater disposal	Discharge of effluent from sewage treatment plants, industry and intensive agriculture.	Contamination of water and sediments. Nutrient enrichment and increased risk of algal blooms. Increase in turbidity.
Stormwater management (i.e. diffuse-source pollution)	Run-off from agricultural and urban land.	Contamination of water and sediments. Nutrient enrichment and increased risk of algal blooms. Increase in turbidity.

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