This review was a synthesis of studies that monitored the effects of sewage disposal in the marine environment. Twenty studies that were conducted between 1973 and 1997 and met specific design requirements (i.e. no confounding factors, appropriate replication) were included in the review.
Background data relating to discharge type, quantity, level of detail and sampling procedures of the investigation in each study were collated. Any impact that was detected was recorded for each endpoint. The magnitude of change or effect size was calculated for each study and was defined as the percent change at the impact site relative to the control sites.
There were some consistencies in the monitoring strategies and benthic responses between studies in different areas. Multivariate indicators and population level analyses were the most sensitive measures for detecting sewage related impacts. Abundance usually increased at outfall sites relative to controls (30-250% magnitude of change) while species richness, diversity and evenness tended to decrease (16-90% magnitude of change). The geographic extent of the studies were limited to temperate regions except for 1 study that was conducted in Antarctica.