Projected Consequences of Dumping Sewage Sludge at a Deep Ocean Site near New York Bight

Abstract

Projections are made of the distribution of and biological response to New York/New Jersey sewage sludges if they are slowly discharged from barges at a deepwater location in annual volumes of 7 × 106 m3. We have used available information on sludge composition, dispersion of barge-dumped wastes, flow through the dumpsite, sewage sludge settling under quiescent conditions, rates of horizontal dispersion in the deep sea, chemical composition of open ocean water, ambient mass fluxes to the seafloor, sediment characteristics, bioturbation rates, and biological responses to sludge and its components. Within a 20-m surface mixed layer between the dumpsite and the Gulf Stream a chemical signal of dumping may be evident in iron, lead, zinc, chromium, and PCB concentrations. Water column contamination would appear to be less than necessary to affect planktonic organisms or fish. Seafloor contamination would be due primarily to sludge particles falling at 10−2 cm∙s−1 or faster. Allowing for bioturbation, the major sediment contaminants, PCB s and PAHs, could reach concentrations at the sediment surface of 0.2 and 0.3 μg∙g−1, respectively, after 100 yr. Concentrations of that order in shallow ocean benthic systems are not obviously related to altered benthic life. The strength of these projections would be increased with better understanding in many areas, especially on the effect of natural and barge-induced turbulence on particle flocculation and on rates of horizontal dispersion in the deep ocean. If sludge is dumped, the water column should be studied for chemical evidence of sludge and response of open ocean plankton. Arrays of sediment traps could be deployed to quantify the rate and areal extent of the settling sludge flux.