EUTROPHICATION OF WESTERN LONG ISLAND SOUND

Summer hypoxia in Western Long Island Sound (LIS) has been documented since the early 1970s, and a severe die-off of lobsters occurred in the late 1990s. These ecosystem and environmental changes of the last few decades were placed within an historical framework covering the last 900 years based on multiproxy records from an 2m long gravity coretaken in westernmost LIS (core WLIS75GGC1; 18 m water depth). The age model for the core was derived from metal pollution records and ¹⁴C dating. Eutrophication started in the first half of the 19th century, as indicated by biotic and sediment chemistry parameters. At that time, the weight % organic carbon increased from ~1.5% to ~3.5% and two groups of unicellular algae, diatoms (silica-walled) and dinoflagellates (organic-walled), show a strong eutrophication signature. The central to pennate ratio in diatoms increased from ~1.5 to ~4.0, and the heterotroph % in dinoflagellates increased from about 20% to 75%. At the same time, bottom-dwelling foraminifera (eukaryote unicellular heterotrophs) increased in number/gram of sediment by an order of magnitude (~100 to ~ 1000), and the % of diatom-consuming foraminiferal species increased from ~35% to ~70%. Carbon isotope data from the tests of the benthic foraminifer Elphidium excavatum were corrected for salinity effects, and fluctuated around -1 ‰ prior to the 19th century. These values decreased by ~2 ‰ in the early 19th century, indicating the addition of oxidized organic matter to the LIS waters. Oxygen isotope data show a decrease of >1 ‰ at the same time, indicating a decrease in salinity. We suggest that the decreased salinity resulted from increased fresh water inputs from a change in land use patterns and human water use with increased population density. These observations indicate that in western LIS eutrophication and associated low oxygen conditions already started in the early 19th century, conform our data on cores from central LIS.