NUTRIENTS IN STREAMS OF THE NORTHEASTERN UNITED STATES, 1975-2003

Nutrient data for 130 U.S. Geological Survey (USGS) water-quality monitoring stations were evaluated for instream concentrations, trends, loads, or yields during 1975-2003 (the long-term period), and 1993-2003 (the recent period) as part of a USGS National Water Quality Assessment Program study extending from Maine to Virginia.

Concentrations of nutrients in many streams persist at levels that are likely to promote freshwater or estuarine eutrophication and affect aquatic habitat adversely. Instream concentrations of total nitrogen and total phosphorus persist at levels higher than ecoregion-based criteria proposed by the U.S. Environmental Protection Agency at more than one-third and about one-half, respectively, of 46 stations analyzed.

Long-term downward trends in flow-adjusted concentrations of total nitrogen and total phosphorus (18 and 19 of 32 stations, respectively) indicate regional improvements in nutrient-related conditions. Upward trends in total phosphorus in the recent period (17 upward and 6 downward, among 83 stations) indicate possible reversals to long-term improvements.

Long-term downward trends in stream loads of two or more nutrients were detected in four of the five largest rivers evaluated, including: total nitrogen loads for the Connecticut, Delaware, and James Rivers; total Kjeldahl nitrogen and ammonia nitrogen loads for the Susquehanna River; ammonia nitrogen and nitrite-plus-nitrate nitrogen loads for the James River; and total phosphorus loads for the Connecticut and Delaware Rivers. No trends in loads were detected for the Potomac River.

The Quinebaug, Raritan, Patuxent, and James Rivers were evaluated for effects of point-source discharges. Long-term downward trends in flow-adjusted concentrations and loads of two to five nutrients at the major monitoring stations on all four streams indicate long-term reductions in delivery of nutrients to surface water in these drainage basins. However, recent instream concentrations of total nitrogen and total phosphorus exceed proposed criteria most of the time on the Quinebaug and Patuxent Rivers, and 100 percent of the time on the Raritan River. During dry years, the total nutrient load from point sources in the Raritan, Patuxent, and James Rivers equals about 50 to 100 percent of the nutrient load transported by the stream.