Sewage effluent as an ecological service provider?

Reducing nutrient inputs to aquatic environments has become a priority concern for regulating agencies worldwide and point source inputs such as sewage treatment plants have received attention as part of these initiatives.... [ view full abstract ]

Reducing nutrient inputs to aquatic environments has become a priority concern for regulating agencies worldwide and point source inputs such as sewage treatment plants have received attention as part of these initiatives. Organic inputs such as sewage effluent can be important in structuring the invertebrate assemblages that are an important resource to higher trophic levels such as fish and birds. Improvement to wastewater treatment has raised the question as to how the birdlife dependent on the often highly productive invertebrate assemblages might be affected. The Western Treatment Plant (WTP), owned and operated by Melbourne Water, occupies an area of 10,500 hectares and is located on the western shores of Port Phillip Bay. The WTP first received flows in 1897 and has discharged treated effluent into Port Phillip Bay ever since. There have been numerous studies documenting the effects of the WTP discharges on the nearshore environment including the intertidal infaunal assemblages and clear links to the role of the effluent in stimulating productivity. During 1982 the WTP was included as a component in the Port Phillip Bay (Western shoreline) and Bellarine Peninsula Ramsar site, because of the numerous bird populations there, (including migratory shorebirds that use the intertidal area as a feeding ground). As in other parts of the world, there has been concern that, as water quality discharging from the WTP improves, the reduction in nutrients will negatively impact these shorebird populations through reducing the diversity and biomass of their invertebrate prey assemblages. We present results from a monitoring program that aims to identify changes in assemblage structure and / or populations of intertidal organisms that may reduce prey abundance, biomass and diversity for internationally significant migratory shorebird populations using the site as a key foraging ground. We will discuss these results in the context of other drivers of change in the invertebrate assemblages and future management directions.