The Connecticut River is a significant source of nitrogen to Long Island Sound, where high nitrogen loads cause seasonal hypoxia. To respond to this problem with effective strategies for reducing nitrogen loads in the Connecticut River, it is important to determine the amount of nitrogen originating from various sources and regions. Therefore, the U.S. Geological Survey (USGS), in cooperation with the New England Interstate Water Pollution Control Commission (NEIWPCC), has conducted a 4-year nitrogen monitoring program in the Upper Connecticut River basin. The project included a 3-year water sampling program to assess annual nitrogen loads in the Connecticut River and its tributaries, nitrogen loads from urban and agricultural land uses, monitoring of nitrogen loads in effluent at selected municipal and industrial wastewater-treatment facilities, and updates to the New England SPARROW model for total nitrogen loads in the Connecticut River basin. A fourth year of sampling was conducted at 5 sites on the Connecticut River.
Samples were collected approximately monthly from December 2002 to September 2005 (water years 2003-2005) and from October 2006 to September 2007 (water year 2007), with additional sampling during spring high flow when the greatest loads occur. Results from the water samples were statistically analyzed to determine nitrogen loads and correlations to land-use settings. Revised load estimates were then used to recalibrate the New England SPARROW nitrogen model. The States in the Upper Connecticut River Basin, U.S. Environmental Protection Agency, and NEIWPCC anticipate using the improved SPARROW model to define nitrogen load allocations associated with Upper Connecticut River nitrogen management.
A USGS Scientific Investigations Report summarizing the results of this project was published in 2006 (see link below). The study found a median concentration of 0.24 milligrams per liter (mg/L) of total nitrogen at forested sites, 0.48 mg/L at agricultural sites, 0.54 mg/L at urban sites, 0.48 mg/L at main-stem Connecticut River sites, and 14 mg/L at wastewater-treatment sites. Annual yields of total nitrogen ranged from 732 to 1,920 pounds per square mile per year (lb mi-2 yr-1) at forested sites; 1,550 to 2,980 lb mi-2 yr-1 at agricultural sites; 1,280 to 1,860 lb mi-2 yr-1 at urban sites that were not directly affected by wastewater effluent; 7,090 to 7,770 lb mi-2 yr-1 at an urban site directly affected by wastewater effluent; and 1,300 to 2,390 lb mi-2 yr-1 at main-stem sites. Estimated mean annual loads of total nitrogen ranged from 49,100 to 21.6 million pounds per year (lb yr-1), with about 30 to 55 percent of the loads being transported during the spring.