History of Contamination and Coastal Hazards in Western Long Island Sound, N.Y.

The Long Island Sound, estuary borders metropolitan New York at its western end where it has been severely impacted by anthropogenic activities and natural hazards such as storm surges and floods. The waters and sediments of western Long Island Sound (LIS) accumulate many pollutants including heavy metals and organic matter loadings. Seasonal hypoxic conditions are a major water quality problem, not only with regards to the damage to its ecosystems, but also for the important fishing industry that LIS sustains. On June 2006, we surveyed LIS from 73°30'W to 73°50'W from the R/V Hugh Sharp collecting high-resolution subbottom seismic (chirp) profiles, multibeam bathymetric data and 25 gravity cores (up to 3 m long). The total organic carbon (TOC) and mercury contents measured in the sediments confirm that their concentrations systematically increase from east to west towards New York City. Mercury concentrations increase westward from 700 to 1200 ppb with pre-industrial values of 50 ppb. In contrast, TOC concentrations indicate that eutrophied conditions did exist in western LIS prior to industrialization with pre-industrial concentrations of 3.8% in the west. These concentrations increased due to anthropogenic activities to values in excess of 10%. High-resolution chirp and sonar data reveal that bottom circulation in western LIS is constrained by bedrock some of which outcrops near 73°45'W. The LIS western outlet to the East River at 73°55'W is controlled by the narrow, shallow sill of Hell Gate. The funnel shape of LIS and these bedrock constrictions contribute to significantly decrease tidal and wind induced currents from east to west (60 to10 cm/s). We propose that this decrease in flow velocity leads to sediment deposition and to the concentration of pollutants. We further suggest that hypoxic conditions possibly existed prior to anthropogenic activities due to the basin morphology and decreased circulation. Previous studies based on stable O and C isotopes do indeed indicate that it was hypoxic to anoxic. Finally, our measurements indicate that storms/floods also lead to erosion and deposition of pollutants in western LIS. We are developing a chronology to link erosional surfaces and peak abundances in heavy metals to the historical record of storms, and to a longer-term record to document their recurrence intervals. This will form a basis to assess future potential detrimental effects that storms may have on the Long Island Sound estuary due to climate change.