The ground-water data analysis given herein represent nutrient concentrations at 100 wells and pesticide and volatile organic compound concentrations at 11 wells; all wells used in the analysis have well-depth and hydrogeologic information available. The wells with water quality data are unevenly distributed within the study area. Nitrate concentrations in water from unconsolidated aquifers range from less than the analytical detection limit of 0.1 mg/L (milligram per liter) to 16 mg/L, with a median concentration of 0.23 mg/L, and those from bedrock aquifers range from less than 0.1 to 11 mg/L, with a median concentration of 0.3 mg/L. Nitrate concentrations decrease with depth in unconsolidated aquifers, but not in bedrock. Concentrations of all pesticides and volatile organic compounds in samples from the 11 wells with data were at or below the analytical detection limits, except for diazinon, which was detected at concentrations below 0.04 ug/L (micrograms per liter) at one well in Schenectady County, N.Y.. Data are insufficient to correlate nutrient and pesticide concentrations in ground water with land use in the Hudson River Basin.
Data on nutrient concentrations in surface water are sufficient for an assessment of water-quality conditions in large watersheds (greater than 200 mi2) dominated by agriculture and forest cover and in two watersheds dominated by urban, residential, or industrial land. Pesticide data are sufficient for analysis for DDT, chlordane, and aldrin in streambed sediments, and for 2,4-D in the water column; most of the pesticide analyses were done during 1972-77.
In general, median nutrient concentrations in streams that drain urban watersheds (those that are more than 7.8 percent urban, residential, and industrial land and less than 20 percent agricultural land) and agricultural watersheds (those that are more than 25 percent agricultural land and less than 11.5 percent urban land) exceed those in streams that drain forested watersheds (those that are more than 78 percent forest). Nutrient yields (mass transported per year per unit area) during 1970-80 differ among streams according to land use. The highest yields for dissolved nitrate, total nitrogen, and total phosphorus were in streams that drain agricultural and urban watersheds; these yields exceeded 3,200 lb/mi2 (pounds per square mile) for dissolved nitrate, 4,200 lb/mi2 for total nitrogen, and, 450 lb/mi2 for total phosphorus. The lowest nutrient yields were from streams that drain large forested watersheds (drainage areas greater than 2,000 mi2) and the two sites (dominated by agricultural land) on Schoharie Creek; dissolved nitrate yields at these two sites were less than 1,700 lb/mi2, and total nitrogen yields were generally less than 3,400 lb/mi2. Total nitrogen yields from the large forested watersheds were less than 150 lb/mi2; but those from Schoharie Creek sites were somewhat higher (231 and 396 lb/mi2, respectively). The low yields from the Schoharie Creek sites could be the result of water diversions from the upper reaches of Schoharie Creek to reservoirs.
Estimated nutrient inputs from fertilizer, manure, sewage, and atmospheric deposition to each watershed indicate that (1) the major sources of nitrogen and phosphorus in Hudson River watersheds correspond to the predominant land use, and (2) the largest inputs result from agricultural activities. Most of the nitrogen and phosphorus inputs to agricultural watersheds were derived from manure and fertilizer, and most of the nitrogen input to forested watersheds was from atmospheric deposition; nitrogen inputs to urban watersheds could not be attributed to any predominant source. Phosphorus input was mostly from agricultural sources at all but the urban-watershed sites. These results indicate that nutrient inputs to the largest streams in the Hudson River basin were largely attributable to nonpoint agricultural sources.
Sediment concentrations and transport rates reflect land use. The lowest median suspended sediment concentrations and transport rates were in forested watersheds; in contrast, the highest median suspended sediment concentration (26 mg/L) and transport rates (0.36 tons per day per square mile) were at the outlet of the Mohawk River basin, a watershed with little forest cover.
The available pesticide data indicate that pesticide concentrations can be related to spatial patterns of application. DDT was applied to agricultural, urban and forested areas during 1940-72 and was detected at nearly all sites from which data were available, regardless of predominant land use. In contrast, chlordane has been applied primarily to urban lands since 1945 and was detected primarily at urban-watershed sites.
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