Assessing impacts of deepwater sewage disposal: A case study from New South Wales, Australia

To overcome the problems of beach pollution Sydney Water constructed three deepwater sewage outfalls off North Head, Bondi and Malabar. The outfalls were commissioned over the period September 1990–July 1991. A 5-year multi-disciplinary environmental monitoring programme was set up to assess the impacts on the demersal fish and soft-bottom macro-invertebrate communities. Assessment of impact was based on an asymmetrical analysis of variance which provided an a priori orthogonal contrast between a single outfall and multiple control sites sampled before and after commissioning. Impacts were detected in both communities, included several commercially and recreationally important species of fish, and occurred with the greatest frequency in the soft-bottom community. The results are summarized, and several examples are presented and show that the direction and magnitude of the impacts varied among outfalls and taxa. The results are then discussed in terms of the needs of future monitoring and the implications for the assessment of human-induced impacts in other parts of the world.