ASSESSING IMPACTS OF DEEP-WATER SEWAGE DISPOSAL - A CASE-STUDY FROM NEW-SOUTH-WALES, AUSTRALIA

To overcome the problems of beach pollution Sydney Water constructed t hree 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-in vertebrate communities. Assessment of impact was based on an asymmetri cal analysis of variance which provided an a priori orthogonal contras t between a single outfall and multiple control sites sampled before a nd after commissioning. Impacts were detected in both communities, inc luded several commercially and recreationally important species of fis h, and occurred with the greatest frequency in the soft-bottom communi ty. The results are summarized, and several examples are presented and show that the direction and magnitude of the impacts varied among out falls and taxa. The results are then discussed in terms of the needs o f future monitoring and the implications for the assessment of human-i nduced impacts in other parts of the world.