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Water quality in the headwaters of the Little Conestoga Creek, Lancaster County, Pa., was investigated from April 1986 through September 1989 to determine possible effects of agricultural nutrient management on water quality. Nutrient management, an agricultural Best-Management Practice, was promoted in the 5.8-square-mile watershed by the U.S. Department of Agriculture Rural Clean Water Program. Nonpointsource-agricultural contamination was evident in surface water and ground water in the watershed; the greatest contamination was in areas underlain by carbonate rock and with intensive row-crop and animal production. Initial implementation of nutrient management covered about 30 percent of applicable land and was concentrated in the Nutrient-Management Subbasin. By 1989, nutrient management covered about 45 percent of the entire Small Watershed, about 85 percent of the Nutrient-Management Subbasin, and less than 10 percent of the Nonnutrient-Management Subbasin. The number of farms implementing nutrient management increased from 14 in 1986 to 25 by 1989. Nutrient applications to cropland in the NutrientManagement Subbasin decreased by an average of 35 percent after implementation. Comparison of base-flow surface-water quality from before and after implementation suggests that nutrient management was effective in slowing or reversing increases in concentrations of dissolved nitrate plus nitrite in the Nutrient-Management Subbasin. Although not statistically significant, the Mann-Whitney step-trend coefficient for the Nutrient-Management Subbasin was 0.8 milligram per liter, whereas trend coefficients for the Nonnutrient-Management Subbasin and the Small Watershed were 0.4 and 1.4 milligrams per liter, respectively, for the period of study. Analysis of covariance comparison of concurrent concentrations from the two subbasins showed a significant decrease in concentrations from the Nutrient-Management Subbasin compared to the Nonnutrient-Management Subbasin. The small, positive effect of nutrient management on base-flow water quality should be interpreted with caution. Lack of statistical significance for most tests, short-term variation in climate and agricultural activities, unknown ground-water flow rates, and insufficient agricultural-activity data for farms outside of the Nutrient-Management Subbasin were potential problems. A regression model relating nutrient applications to concentrations of dissolved nitrate plus nitrite showed no significant explanatory relation. INTRODUCTION The Conestoga River discharges to the Susquehanna River. The U.S. Environmental Protection Agency's (USEPA) Chesapeake Bay Study reported that the Susquehanna River contributes 40 percent of the nitrogen and 21 percent of the phosphorus that are discharged to the Chesapeake Bay. Of this contribution, 85 percent of the nitrogen and 60 percent of the phosphorus were estimated to have come from cropland runoff (U.S. Environmental Protection Agency, 1983). The Chesapeake Bay Study recommended implementation of agricultural Best-Management Practices (BMP's) to reduce nonpoint-source nutrient discharges. The U.S. Geological Survey (USGS), in cooperation with the Pennsylvania Department of Environmental Protection (PaDEP) 1 and as part of the Rural Clean Water Program (RCWP) administered by the U.S. Department of Agriculture (USDA), studied the effects of agricultural BMP's on water quality in the headwaters of the Conestoga River Basin in south-central Pennsylvania. The Conestoga River Headwaters was 1 of 20 RCWP projects nationwide. These projects were designed to accelerate the installation of agricultural BMP's for the purpose of reducing agricultural nonpoint-source contamination. In addition, the Conestoga River Headwaters RCWP was one of five RCWP projects selected for Comprehensive Monitoring and Evaluation (CM&E) of the effects of BMP's in improving water quality. CM&E in the Conestoga River Headwaters RCWP was conducted at three scales: regional, small watershed, and field. CM&E in the project area began in 1982 with the establishment of the 188-mi2 Regional Network component. Data collected from the Regional Network during 1982-83 indicated that the major water-quality problem in the upper Conestoga River Basin is elevated nitrate concentrations in surface and ground water. Concentrations of nitrate as great as 40 mg/L as N were measured in ground water closely associated with intensively farmed areas having carbonate geology (Fishel and Lietman, 1986). This report presents the results of CM&E at the small watershed scale. A detailed presentation of the background of the Conestoga River Headwaters RCWP project can be found in "Evaluation of Agricultural Best-Management Practices in the Conestoga River Headwaters, Pennsylvania: Methods of Data Collection and Analysis, and Description of Study Areas," by Chichester (1988). Abbreviated discussions of background and methodology are included here for clarity. Nutrient management is a BMP intended to reduce the occurrence of excess nutrients on cropland. Under nutrient management, application rates and application timing of manures and commercial fertilizer are chosen to satisfy crop nutrient requirements while reducing the availability of fertilizer nutrients for transport to surface and ground water. For this study, nutrient management was a combination of fertilizer management and animal-waste management. Purpose and Scope This report describes the effects of nutrient management on water quality in a 5.82-mi2 drainage basin designated the Small Watershed (fig. 1) in the Conestoga River headwaters, Pa. Data used in the evaluation were collected from April 1,1984, through September 30,1989, after implementation of nutrient management. Data include precipitation, agricultural activity, soil nutrient, streamflow, surface water, base-flow and stormflow quality, monthly loads, and annual yields of nutrients and suspended sediment. The effects of nutrient management on water quality are evaluated by statistical and qualitative comparison of the data collected from April 1,1984, through March 31,1986 (pre-BMP period), to the data collected from April 1,1986, through September 30,1989 (post-BMP period). Data for the pre-BMP period were previously published in "Evaluation of Agricultural Best-Management Practices in the Conestoga River Headwaters, Pennsylvania: Description and Water Quality of the Little Conestoga Creek Headwaters Prior to the Implementation of Nutrient Management," by Fishel and others (1992). The study was conducted as a preand post-treatment experimental design; nutrient management was the treatment. A pre-BMP period from April 1,1984, to April 1,1986 (2 years), and a post-BMP period from April 1986 to September 1989 (3.5 years) defined the treatment periods. Data from the post-BMP period were compared to data from the pre-BMP period to determine the effects of BMP implementation on water quality and nutrient inputs. By delineation of two smaller subbasins within the Small Watershed, three different levels of implementation were included in the experimental design. Additionally, a paired-basin experiment was conducted in two subbasins of approximately 1.4 mi2 each. The use of paired subbasins that are geologically, hydrologically, and climatically similar helps in distinguishing water-quality changes resulting from BMP implementation from those changes resulting from factors other than BMP's. 1 Prior to 1995, the Pennsylvania Department of Environmental Protection was the Pennsylvania Department of Environmental Resources.

water-resources investigations report

Evaluation of agricultural best-management practices in the Conestoga River headwaters, Pennsylvania; description and water quality of the Little Conestoga Creek headwaters prior to the implementation of nutrient management