Effects on the Ecosystem of Sewage Sludge Disposal from a Pipeline

About 57,000 m tons (dry wt) of sewage sludge has been discharged each year for the last 22 years at the brink of a steep-sided submarine canyon in Santa Monica Bay, California. The discharge point is 100 meters deep and 10 km offshore. An area of about 3 sq km of the upper canyon has been substantially changed by the high concentration of sewage solids but the ecosystem is stable. There are fewer species of invertebrates but more species of fish in the canyon; the biomass of both fish and invertebrates is larger than controls. In the region near the canyon rim there are extraordinary populations of clams and molluscs; fishing is far above average for the bay. This solution to sludge disposal causes both negative and positive effects which seem to be about balanced.