Mass balance of heavy metals in New Haven Harbor, Connecticut: Predominance of nonpoint sources

A mass balance A as constructed quantifying all known sources and sinks for the metals Ag, Cd, Cu, and Pb in New Ha en Harbor. Connecticut, USA. Sourc es included direct atmospheric deposition, rivers, treated sewage effluent. combined sewer overflows, and permitted industrial discharge. Sinks were b urial in sediments, tidal exchange with Long Island Sound, removal in salt marshes, and dredging. All of these fluxes were measured directly, rather t han estimated, and uncertainties were quantified. The mass balance closed s uccessfully within the uncertainty of the measurements. Riverine inputs acc ount for most of the total yearly metal flux. Metal concentrations in the r iver can he approximated is a simple linear function of discharge. Salt mar shes remove an amount of metal equivalent to 20%-30% of the flux from the r iver before it reaches the harbor. Burial in sediments is the major sink fo r all metals examined, but dredging acts as a substantial short-circuit of this sink. Tidal exchange appears to be a relatively small term: however, i t is also the least well quantified. Sewage treatment plant (STP) effluent and combined sewer overflow discharge are minor contributors to the overall metal balance. except in the case of Ag. Metal concentrations in STP efflu ent are a linear function of discharge. Atmospheric deposition is of minor importance but is comparable to sewage effluent. Lakes can he used as natur al collectors and indicators of atmospherically deposited metals.