Analysis of surface water quality and ground water flow in the Carmans River Watershed, Long Island, New York

Agriculture and urban development on Long Island, New York have caused many of its rivers and streams to become eutrophic, and have led to poor water quality in the Great South Bay. The Carmans River provides the largest discharge into the Great South Bay, and therefore may be a primary contributor of nitrate and other constituents. In this investigation, ground water flow was simulated using a calibrated, steady state model, and a synoptic sampling of base flow was conducted and analyzed for major anions and cations. The dominant cations are sodium and calcium, the dominant anions are chloride and bicarbonate, and the average nitrate [NO3-] concentration is 5.5 mg L-1. Modeling results suggest that there are two aquifer sources that feed the river, but the majority of streamflow is derived from the Upper Glacial Aquifer, which has a residence time of less than 20 years.