Estimates of the seafloor area impacted by sewage sludge dumped at the 106-mile site in the mid-atlantic bight

Abstract

Approximately 8 × 10 6 wet tons of sewage sludge is dumped annually at the 106-Mile Deep Water Municipal Sewage Sludge Disposal Site, 185 km off the New Jersey coast (Sano, 1989). A simple particle-tracking model is used to estimate the areas of sludge deposition using current meter observations made as part of the Mid-Atlantic Slope and Rise (MASAR) Study (Brown et al., 1987) and Lavelle et al.'s (1988) settling velocity distribution for sewage sludge. Model results indicate that sewage particles settle primarily to the southwest of the dump site due to the mean southwesterly flow throughout the water column. Only the coarser fraction (particles with settling velocities greater than 0·04 cm s −1), about 23% of the sludge discharged, is predicted to settle on the seafloor within 350 km of the site. The model predicts a maximum flux in the southwestern quarter of the site of 60 mg m −2 day −1 which decreases to about 25 and 1 mg m −2 day −1 at distances of approximately 50 and 350 km to the southwest, respectively. Little material is predicted to reach the shelf and the finer particles are assumed to be widely dispersed in the water column. These estimated fluxes compare with a natural particle flux of 100–150 mg m −2 day −1 as measured by sediment traps to the north of the 106-mile site (Biscaye et al., 1988). Field studies to assess the effects of sludge dumping on benthic organisms should initially focus on the region 0–50 km southwestward of the site.