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Water Quality (continued)

Conclusions and Implications

Many of Australia's coastal waters continue to receive ecologically unsustainable levels of pollutants. Algal blooms, triggered by excess nutrients, are causing massive ecological damage, threatening aquaculture production, and prejudicing the recreational amenity of many highly valued coastal waters. Meanwhile, sewage overflows and untreated urban stormwater threaten aquaculture production (e.g. oyster farming) and cause authorities to close swimming beaches. Extreme rainfall events cause massive soil erosion and sediment discharges to coastal systems, carrying with it nutrients and other contaminants, and smothering benthic communities.

Over the last 20-30 years, increasingly stringent limits have been placed on point-source emissions, so that in many areas (e.g. Port Phillip Bay in Victoria, Cockburn Sound in Western Australia, Botany Bay in New South Wales, and Lake Illawarra in New South Wales) sediment pollutant concentrations have declined. However, there is still considerable potential for further reducing industrial discharges.

Of the point sources of pollution, wastewater treatment plant effluent remains the most intractable. The discharges from large treatment plants are orders of magnitude greater than other point source discharges and in some areas, the discharges are into relatively protected, poorly flushed coastal water systems where concentrations of pollutants and sediment loads can be high. Sydney Water and Western Australia's Water Corporation, for example, have constructed deep ocean outfalls to discharge large volumes of waste to areas where currents dilute and disperse the pollutants. Monitoring to date suggests there are no unacceptable environmental impacts from this practice, but the long-term sustainability is yet to be demonstrated because the indirect and possibly accumulating effects of various subtle-acting substances (such as hormone mimics) has yet to be assessed.

Wastewater discharges to estuaries and embayments (such as the Derwent River in Tasmania and Moreton Bay in Queensland) continue to contribute substantial loads of nutrients and toxicants to these poorly flushed systems, enhancing the accumulation of these substances in sediment and biota.

To date, the pursuit of estuarine and marine water quality objectives has been through waste management technologies treating point-source pollution, with the current major focus on reducing discharges from wastewater treatment plants. However, it is clear that estuarine and marine water quality will not be protected through point source controls alone. Emissions information in the National Pollutant Inventory indicates that diffuse source pollution is the major contributor to water quality degradation, whether derived from agricultural or urban stormwater.

All of society faces a major challenge to reduce pollution, and all levels of government must show leadership in this regard. There is a pressing need for governments to implement the National Water Quality Management Strategy, identify the environmental values and water quality objectives of our coastal waters, and estimate and pursue the pollutant load reductions needed to protect those environmental values. Once load reductions are established, economically efficient and equitable strategies must be formulated to address point and diffuse sources of the major pollutants of concern.

Also, suitable benchmarks for environmental values, including targets for species and habitats, must be established and incorporated into environmental quality objectives as part of an integrated approach to the management of pollutant loads.

A cooperative reporting and standardisation of methods for water quality assessment will be a key part of building a shared understanding of the problems and potential solutions.

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