Benthos around an Outfall of the Werribee Sewage-treatment Farm, Port Phillip Bay, Victoria

Abstract

A 2-km² area adjacent to the 145W outfall of the Werribee sewage-treatment farm was sampled for sediment, water chemistry and macrobenthos. Sediments nearshore were more sandy and more uniform than those offshore. Water salinity and nutrient concentrations (particularly ammonia) in overlying and interstitial water decreased rapidly with increasing distance from shore. The fauna was rich and contained several euryhaline and opportunistic species.

Classification analysis revealed an offshore and a nearshore group of stations, and possibly a third group around the outfall. The distributions of common species were correlated with depth, sediment parameters or interstitial phosphate concentrations.

The benthos of the 145W drain was distributed patchily but the station closest to the outfall (within 300 m) had high densities, high proportions of scavengers and deposit-feeders, high sediment organic fraction and high interstitial nutrient concentrations.

The effect of the drain on the macrobenthos is exerted through particulate organic matter, dissolved nutrients and freshwater inputs.