Fall 07 Nitrogen Trends in LIS

Long Island Sound has a large and highly developed watershed. Nitrogen contributions from the watershed, combined with strong summer thermal stratifi cation in its western half, render Long Island Sound susceptible to seasonal low dissolved oxygen levels (hypoxia). Since 1985, the causes and effects of hypoxia have been the subject of intensive monitoring, modeling, and research through the Long Island Sound Study (LISS). The Connecticut Department of Energy and Environmental Protection (CT DEEP) and the Interstate Environmental Commission (IEC) are the two LISS partners that have conducted the lion’s share of the monitoring in the far western Sound.

Monitoring conducted by the CT DEEP on behalf of the LISS has shown an annual recurrence and persistence of hypoxia over the last 17 years. CT DEEP’s Long Island Sound Ambient Water Quality Monitoring Program (the “Program”) collects samples for nutrient analysis and water quality parameters year-round from 17 fi xed sites located throughout Long Island Sound. In response to March 2002 Long Island Sound monitoring workshop, CT DEEP expanded the scope of monitoring to include identifi cation of zooplankton and a new technique to identify phytoplankton by analyzing their pigments (see page 5). Summer hypoxia surveys, part of the broader Program, provide annual descriptions of the extent and duration of hypoxia (defi ned as DO levels below 3.5 mg/L) in the bottom waters of Long Island Sound. The Program currently monitors between 25 and 35 fi xed stations during the summer hypoxia surveys. The hypoxia surveys focus on areas in the Narrows and western and central basins historically affected by hypoxic conditions. The number of stations sampled during these surveys is adjusted according to the severity of the hypoxic event.

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