TRANSPORT RATES OF NUTRIENTS AT SURFACE-WATER SITES IN THE HUDSON RIVER BASIN

Nutrient-transport rates in surface waters of the Hudson River basin, and nutrient-deposition rates within the watersheds, indicate that nutrients are derived mainly from nonpoint agricultural sources. Average nutrient-transport rates during 1970-80 were calculated for 15 sites in the Hudson River basin. The transport rate for each site was calculated as the mean of values for 3 years---(1) a year with a high mean annual flow, (2) a year with a medium mean annual flow, and (3) a year with a low mean annual flow. Transport estimates for each site were based on 20 or more samples and included at least one sample collected during high flows (within the upper 10 percent of the range). Standard errors of estimate are generally between 5 and 15 percent. Input rates for nutrients are based on animal populations, fertilizer sales, water discharges at sewage-treatment plants, and precipitation-chemistry data.

The highest nutrient-transport rates were at three sites representing basins with a high percentage of agricultural or urban cover---the Mohawk River at Fonda (agricultural cover greater than 34 percent of basin area), Wallkill River at Rosendale (agricultural cover greater than 50 percent of basin area), and Hoosic River at North Petersburg (urban cover greater than 9 percent of basin area). Calculated annual nutrient-transport rates for these sites were: dissolved nitrate, at least 5.7 kg/ha (kilograms per hectare), total nitrogen, at least 7.5 kg/ha, and total phosphorus, at least 0.82 kg/ha. In contrast, the lowest nutrient-transport rates were at two sites with large amounts of forest cover--- Hudson River at Corinth (forest cover at least 91 percent of basin area), and Esopus Creek at Shandaken (forest cover greater than 94 percent of basin area). Calculated annual rates of nutrient transport at the two highly forested sites are: dissolved nitrate, less than 2.8 kg/ha, and total phosphorus, less than 0.16 kg/ha. Total nitrogen-transport rates calculated for the Hudson River at Corinth and Schoharie Creek at Burtonsville were less than 4.5 kg/ha.

Estimates of nitrogen and phosphorus inputs from fertilizer, manure, and sewage, as well as atmospheric inputs of nitrogen, indicate that the major source is agricultural activities. Average nutrient inputs to the Hudson River above Green Island (near Troy, at the upstream end of the Hudson estuary) during 1982-1985 indicate that agriculture accounted for 66 percent of the nitrogen inputs and 76 percent of the phosphorus inputs; atmospheric deposition accounted for 27 percent of the nitrogen inputs; and sewage accounted for 7 percent of the nitrogen inputs and 24 percent of the phosphorus inputs. Watersheds with high percentage of agricultural cover can transport large amounts of nutrients; even though the Mohawk River at Fonda represents less than 25 percent of the drainage area of the Hudson River at Green Island, the mass of dissolved nitrate and total nitrogen transported by the Mohawk River at Fonda per year is 40 percent of the mass and the mass of phosphorus 50 percent of the mass of total phosphorus transported at the Hudson River at Green Island.

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