Paleoproductivity indicators in Long Island Sound

TitlePaleoproductivity indicators in Long Island Sound
Publication TypeConference Paper
Year of Publication2004
AuthorsAndersen, N, Varekamp, JC
Conference NameAmerican Geophyscial Union, Joint Assembly
Date Published2004
PublisherAmerican Geophysical Union (AGU)

Oxygen depletion in bottom waters is considered to be the most pressing environmental problem affecting Long Island Sound (LIS). Summer anoxia occurs as a result of two factors: 1) Stratification of the water column due to warming of the shallow water preventing mixing and thus homogeneous distribution of oxygen. 2) Eutrophication resulting in increased primary productivity leading to a greater oxygen demand in the bottom waters as the larger amount of organic matter decays. The goal of this project is to create a paleoproductivity record for LIS and to attempt to link recent increases in productivity with anthropogenic nutrient sources, most notably wastewater treatment plant effluent. Two cores, WLIS-75 from the western narrows and B1GGC1 from near the mouth of the Housatonic River, have been analyzed for biogenic silica (BSi), total carbon, nitrogen, and sulfur. The BSi data was obtained through analyses of timed sequential extracts from an alkaline solution that reacted with the sediment at 85 C. Sediment densities were calculated from measured core water contents and assumed dry rock densities. A preliminary age model was developed using the onset of mercury pollution (about 1820 AD) as a reference point. At around 1800, the C, N, S and BSi concentrations all start to increase. In WLIS-75, BSi was higher throughout the core compared to core B1GGC1, suggesting an overall higher rate of productivity in the western section of LIS. In both cores the mass accumulation rates of BSi, C, N, and S increased exponentially over the last 300 years. A coarse layer was deposited around 1950-1960 in core WLIS-75, and is marked by abundant coarse debris of rocks and coal fragments. This layer may represent a flood deposit or stem from local (illegal?) dumping; its presence impacts the data for the last 30-40 years of the core. A strong correlation between total S and total C is observed, suggesting that Sulfide formation is limited by the amount of labile organic matter present. The data from the two cores show strong evidence for eutrophication over the last 200 years, with a strong increase in the N supply.