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10,00012,000 1 9 5 9 1 9 6 1 1 9 6 5 1 9 6 3 1 9 7 1 1 9 7 3 1 9 6 7 1 9 7 5 1 9 7 7 1 9 6 9 1 9 7 9 1 9 8 1 1 9 8 3 1 9 8 7 1 9 8 5 1 9 9 3 1 9 9 5 1 9 8 9 1 9 9 7 1 9 9 9 1 9 9 1 2 0 0 1 2 0 0 3 2 0 0 5 2 0 0 7Streamflow, in cubic feet per square mile 1 9 5 9 1 9 6 1 1 9 6 5 1 9 6 3 1 9 7 1 1 9 7 3 1 9 6 7 1 9 7 5 1 9 7 7 1 9 6 9 1 9 7 9 1 9 8 1 1 9 8 3 1 9 8 7 1 9 8 5 1 9 9 3 1 9 9 5 1 9 8 9 1 9 9 7 1 9 9 9 1 9 9 1 2 0 0 1 Cover. Estimated flow-duration curves and hydrographs generated by the Baseline Streamflow Estimator. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod Estimation of Baseline Daily MeanTo order this and other USGS information products, visit http://store.usgs.gov

Status yields and trends of nutrients and sediment and methods of analysis for the nontidal data-collection programs, Chesapeake Bay Basin, 1985-96: U.S. Geological Survey Open-File Report 98-17, 60 p.

IfSJTRODU,The Pequea Creek and Mill Creek Basins within Lancaster and Chester Counties in Pennsylvania have been identified as areas needing control of nonpoint-source (NFS) pollution to improve water quality. The two basins are a total of approximately 200 square miles and are primarily underlain by carbonate bedrock. Land use is predominantly agriculture. The most common agricultural NFS pollution-control practices implemented in the Pequea Creek and Mill Creek Basins are barnyard-runoff control and Streambank fencing. To provide land managers information on the effectiveness of Streambank fencing in controlling NFS pollution, a study is being conducted in two small paired watersheds within the Mill Creek Basin. 5CRIPTIONThe objective of the project is:To evaluate the effect of streambank fencing of pasture land on surface-and near-stream groundwater quality within a small watershed underlain by carbonate bedrock.To attain the project objective, the hydrology and water quality of the study area needs to be characterized and quantitative relations between paired basins A cooperative effort between the U.S. Geological Survey (USGS) and the Pennsylvania Department of Environmental Protection (PaDEP), this project supports the study initiative of the U.S. Department of Agriculture within the Pequea and Mill Creeks Hydrologic Unit Area. The project is funded by PaDEP through the National Monitoring Program (NMP) of the U.S. Environmental Protection Agency (USEPA). The NMP stems from Section 319 of the 1987 amendment to the Clean Water Act. The NMP was developed to document the effects of NPS pollutioncontrol measures and associated landuse modifications on water quality (Osmond and others, 1995).

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 Nutrient-Management 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.