MULTIPROXY RECORDS OF EUTROPHICATION IN LONG ISLAND SOUND

Western Long Island Sound (LIS) suffered summer hypoxia since the early 1970s, and lobsters died off in the late 1990s. We place these ecological changes in a historical framework covering the last 1000 years based on multiproxy records from cores in central and western LIS. Age models for the cores were derived from metal (Hg) pollution records and ¹⁴ C dating, ²¹⁰Pb, ¹³⁷Cs data and pollen data for some cores. From the first half of the 19^th century, the weight % organic carbon increased in all cores, but most (by a factor of 3-5) in western LIS; the concentration of biogenic Si increased. At the same time, benthic foraminifera increased in number/gram of sediment by one to two orders of magnitude, and sediment accumulation also increased, so that accumulation rates of foraminifera, organic carbon and Si increased strongly. The relative abundance of the diatom-consuming foraminifer (Elphidium excavatum) increased at all depths, and the species migrated into deep water (> 18 m) where earlier only agglutinated species had been present. Before the early 1800s, salinity-corrected carbon isotope data (E. excavatum) fluctuated between –1 and –2 per mille in cores from the Narrows, around -1 per mille in others. Then these values declined precipitously, showing increased fluctuation in all cores, with lowest values in shallow water cores (< 10m) in central LIS, all cores in western LIS, indicating addition of oxidized organic matter to the waters, thus possibly hypoxic conditions. At the same time, oxyen isotope values decreased by 1 to 2 per mille, indicating a decrease in salinity, possibly due to increased fresh water input from a change in land use patterns and water use, including re-routing of water from the Hudson watershed into LIS as a consequence of aqueduct building in New York City. Eutrophication and associated low oxygen conditions thus started in the early 19^th century in western and central LIS, but was more severe in the Narrows and western LIS. We are investigating how anthropogenic changes in terrestrial and marine ecosystems (e.g., near eradication of beavers, over-harvesting of oysters) may have impacted sediment budgets and the trophic state of LIS in addition to nutrient influx from waste-water treatment plant effluent.