Water Resources Investigations Report 93-4069 "Hydrology and the effects of selected agricultural best-management practices in the Bald Eagle Creek Watershed, York County, Pennsylvania, prior to and during nutrient management " Langland, M.J., and Fishel, D.K.       The U.S. Geological Survey, in cooperation with the Susquehanna River Basin Commission and the Pennsylvania Department of Environmental Resources, conducted a study as part of the U.S. Environmental Protection Agency's Chesapeake Bay Program to determine the effects of nutrient management of surface-water quality by reducing animal units in a 0.43-square-mile agricultural watershed in York County. The study was conducted primarily from October 1985 through September 1990 prior to and during the implementation of nutrient-management practices designed to reduce nutrient and sediment discharges. Intermittent sampling continued until August 1991.      The Bald Eagle Creek Basin is underlain by schist and quartzite. About 87 percent of the watershed is cropland and pasture. Nearly 33 percent of the cropland was planted in corn prior to nutrient management, whereas 22 percent of the cropland was planted in corn during the nutrient-management phase. The animal population was reduced by 49 percent during nutrient management. Average annual applications of nitrogen and phosphorus from manure to cropland were reduced by 3,940 pounds (39 percent) and 910 pounds (46 percent), respectively, during nutrient management. A total of 94,560 pounds of nitrogen (538 pounds per acre) and 26,400 pounds of phosphorus (150 pounds per acre) were applied to the cropland as commercial fertilizer and manure during the 5-year study.      Core samples from the top 4 feet of soil were collected prior to and during nutrient management and analyzed from concentrations of nitrogen and phosphorus. The average amount of nitrate nitrogen in the soil ranged from 36 to 135 pounds per acre, and soluble phosphorus ranged from 0.39 to 2.5 pounds per acre, prior to nutrient management. During nutrient management, nitrate nitrogen in the soil ranged from 21 to 291 pounds per acre and soluble phosphorus ranged from 0.73 to 1.7 pounds per acre. Precipitation was about 18 percent below normal and streamflow was about 35 percent below normal prior to nutrient management, whereas precipitation was 4 percent above normal and streamflow was 3 percent below normal during the first 2 years of nutrient management. Eighty-four percent of the 20.44 inches of streamflow was base flow prior to nutrient management and 54 percent of the 31.14 inches of streamflow was base flow during the first 2 years of the nutrient-management phase. About 31 percent of the measured precipitation during the first 4 years of the study was discharged as surface water; the remaining 69 percent was removed as evapotranspiration or remained in ground-water storage.      Median concentrations of total nitrogen and dissolved nitrate plus nitrite in base flow increased from 4.9 and 4.1 milligrams per liter as nitrogen, respectively, prior to nutrient management to 5.8 and 5.0 milligrams per liter, respectively, during nutrient management. Median concentrations of ammonia nitrogen and organic nitrogen did not change significantly in base flow. Median concentrations of total and dissolved phosphorus in base flow did not change significantly and were 0.05 and 0.03 milligrams per liter as phosphorus, respectively, prior to the management phase, and 0.05 and 0.04 milligrams per liter, respectively, during the management phase.      Concentrations and loads of dissolved nitrite plus nitrate in base flow increased following wet periods after crops were harvested and manure was applied. During the growing season, concentrations and loads decreased as nutrient utilization and evapotranspiration by corn increased. About 4,550 pounds of suspended sediment 5,300 pounds of nitrogen, and 70.4 pounds of phosphorous discharged in base flow in the 2 years prior to nutrient management. During the first 2 years of nutrient management about 2,860 pounds of suspended sediment, 5,700 pounds of nitrogen, and 46.6 pounds of phosphorus discharged in base flow. Prior to nutrient management, about 260,000 pounds of suspended sediment, about 2,180 pounds of nitrogen, and about 235 pounds of phosphorus discharged in stormflow. During the first 2 years of nutrient management about 464,000 pounds of suspended sediment, 6,120 pounds of nitrogen, and 912 pounds of phosphorus discharged in stormflow.      The seasonal rank-sum test indicated that significant differences were detected in the medians of total nitrogen and dissolved nitrite plus nitrate in base flow prior to and during nutrient management. The seasonal Kendall test indicated significant upward trends in concentrations and loads of total nitrogen and dissolved-nitrite plus nitrate measured in base flow during the entire study. Neither significant differences nor trends were detected in the concentrations and loads for ammonia, ammonia plus organic nitrogen, phosphorus, or suspended sediment in base flow. 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