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The Susquehanna River Basin Commission and the U.S. Environmental Protection Agency cooperated with the U.S. Geological Survey in a study to quantify nonpoint-source loadings from an agricultural area in Pennsylvania. Pequea Creek, a tributary to the Susquehanna River, drains a 154-square mile agricultural area in Lancaster County, Pennsylvania. Previous studies defined the Pequea'Creek basin as a contributor of sediment, nutrients, and pesticides from nonpoint sources to the Susquehanna River. The purpose of this intensive watershed investigation was to determine the effects of various land uses on water quality of receiving streams. Streamflow was measured and monthly base-flow samples and water-weighted composite storm samples were analyzed for suspended sediment, nutrients, organic carbon, and triazine herbicides. Constituent loadings were calculated to quantify their discharge from the entire Pequea Creek basin and from four specific subbasins: forest, cornfield, rural residential, and pasture. Soil samples were analyzed for nutrients and selected herbicides, and land use and application data were collected to determine the source of loadings. Precipitation amounts and chemistry were also measured. Precipitation and streamflow were below average for much of the investigation period, May 1979 to December 1980. The annual precipitation for 1980 was 10 inches below normal, with drought conditions the last half of the year. During base flow, the highest concentrations of individual constituents generally observed were: 4.0 milligrams per liter total organic nitrogen and 1.4 milligrams per liter total phosphorus from the downstream pasture site; 24 milligrams per liter total nitrate nitrogen and 3.9 micrograms per liter total atrazine from the cornfield site; and 0.5 micrograms per liter total prometone, and 2.3 micrograms per liter total simazine from the residential site. Nearly all total nitrate nitrogen concentrations from the cornfield site during base flow were about double the U.S. Environmental Protection Agency (1977) criterion of 10 milligrams per liter. The highest constituent concentrations found in composite storm samples were nearly all in samples from the cornfield site. The highest concentrations found were: 16,000 milligrams per liter suspended sediment, 54 milligrams per liter total organic nitrogen, 41 milligrams per liter total nitrate nitrogen, 19 milligrams per liter total phophorus, and 200 micrograms per liter total atrazine. The highest concentrations found in composite storm samples for total prometone was 6.4 micrograms per liter at the residential site and for total simazine was 4.8 micrograms per liter at the downstream pasture site. Generally, concentrations of all the constituents, except nitrate, were higher during storms than during baseflow at all sites. Total concentrations of the constituents increase during storms predominantly due to increases in suspended concentrations. The highest storm concentrations of most constituents occurred at the cornfield site. Fertilizer and herbicide applications increase the available sources of nutrients and herbicides for transport to the stream. The highest phosphorus, atrazine, and suspendedsediment concentrations at the cornfield site occurred during intense storms soon after application and planting. Constituent yields (tons per square mile) from storms, about evenly distributed throughout the basin, were compared from the other specific landuse sites to the forest site, which represents a relatively undisturbed land use. During storms, yields for suspended sediment, total organic nitrogen, and total phosphorus were highest for the pasture and lowest for the forest site. Total nitrate-nitrogen yields were highest for the cornfield and about the same for the forest and residential sites. Yields of total organic carbon were about the same for the cornfield and residential sites, which were both slightly higher than the forest site. The total loads discharged into the Susquehanna River from Pequea Creek from January 1 to December 31, 1980 with 100,000 acre-feet of water were: 12,000 tons of suspended sediment, 840 tons of nitrate nitrogen, 72 tons of organic nitrogen, 21 tons of phosphorus, 540 tons of organic carbon, 93 pounds of atrazine, 52 pounds of simazine, and 5.0 pounds of prometone. Loads for 1980 were much lower than loads for 1978 and 1979 from the Pequea Creek basin, due to below normal precipitation. A comparison of data from Pequea Creek at Martic Forge and the Susquehanna River at Harrisburg shows that during some months, Pequea Creek significantly increased the loads of nitrate nitrogen and suspended sediment of the Susquehanna River. INTRODUCTION The Susquehanna River Basin Commission and the U.S. Environmental Protection Agency cooperated with the U.S. Geological Survey in a study to quantify nonpoint-source loadings from an agricultural area in Pennsylvania. Eutrophication and toxic substances are primary water-quality problems in the Chesapeake Bay (Chesapeake Bay Program, Environmental Protection Agency, written commun. 1982). The lower Susquehanna River basin has been identified as a primary source of sediment and nutrients to the Upper Chesapeake Bay (Clark and others, 1973, 1974). Levels of suspended sediment, nitrogen, and phosphorus in the past have been controlled only by regulating the quality of point discharges from industries and waste-water treatment plants. However, it has become evident that, in many areas, regulation of all point discharges cannot reduce levels of these constituents in receiving streams to acceptable limits. Therefore, nonpointsource loadings need to be investigated. Because agriculture was suspected of contributing much of the sediment and nutrients to the lower Susquehanna River and the Chesapeake Bay, a study of nonpoint-source discharges from an agricultural area was conducted from 1977 to 1981. Pequea Creek was selected for an investigation because the basin is typical of agricultural areas in southeastern Pennsylvania, and is a significant nonpoint-source contributor of suspended sediment, nitrogen, and phosphorus to the Susquehanna River (Ward and Eckhardt, 1979). Loads of these constituents and of triazine herbicides increased significantly during storms. High nitrate nitrogen concentrations during base flow in streams sampled from 1977 to 1979 (Ward and Eckhardt, 1979) tend to confirm studies in Lancaster County (Poth, 1977) which showed widespread nitrate nitrogen contamination of ground-water supplies. Contamination is generally confined to areas underlain by limestone and dolomite, as is most of the Pequea Creek basin. The factors found most influential in determining the transport of these nonpoint constituents are rainfall, runoff, and farming practices. The purpose of this study was to determine the effects of agricultural practices and other land uses on water quality of receiving streams in the Pequea Creek basin by measuring streamflow and concentrations of suspended sediment, nutrients, organic carbon, and herbicides during various hydrologic conditions. Information concerning land use, application rates, and soil data were used to determine sources of loadings. Precipitation quantities and chemistry were also measured. This report presents the results of data collected from May 1979 to December 1980. For ease in comparison of data, all references to species of nitrogen and phosphorus in this report are to be considered in their elemental form. For example, regardless of whether ammonium or nitrate is being discussed, the values and discussion all refer to their concentrations expressed as nitrogen. The information in this report should be useful to water managers and the agricultural community. Also, the Chesapeake Bay Program is using the data to develop runoff, transport, and routing models that can simulate water quality in the Chesapeake Bay and its major tributaries. Acknowledgments The authors acknowledge the dedicated efforts of many U.S. Geological Survey employees both in the field and laboratory, which enabled the successful completion of this study. Mr. Charles Takita and Mr. John Hauenstein of the Susquehanna River Basin Commission provided continuing technical and field assistance. The Chesapeake Bay Program, U.S. Environmental Protection Agency, spent many weeks identifying and digitizing land uses on aerial photographs to develop land use maps for the study area. The Pesticide Research Laboratory, Pennsylvania State University, analyzed soil pesticides. Mr. Marvin Herr and Mr. Kenneth Groff provided continuous land-use and application data for sites located on their properties. General Basin Factors Affecting Streamflow and Constituent Transport The Streamflow and water-quality characteristics of streams are affected by numerous factors. These include physiography, geology, soils, climate, land use, and land cover. Pequea Creek basin is in the southern part of the Conestoga Valley, a carbonate and shale section of the Appalachian Piedmont. The 154-mi2 basin is long and narrow and stretches about 60 mi from the Welsh Mountains to the Susquehanna River (fig. 1). Basin slopes are mostly less than 15 percent. Most of the basin is underlain by limestone and dolomite of Ordovician and Cambrian age. There is quartzite, schist, and gneiss of Cambrian and Precambrian age along the northeast border and schist of early Paleozoic age along the southern border of the basin. Most soils are classed as silt loams belonging to the ConestogaHollinger, Duffield-Hagerstown, and Chester-Glenelg associations. They are productive, well-drained soils that have high moisture-holding capacities (U.S. Dept. of Agriculture, 1956). Because of intense farming practices, the soils are generally classified as moderately eroded with some cases of severe erosion. The growing season generally lasts from May 3 to October 10 and averages 160 days. Monthly mean temperatures during the stud

Effects of specific land uses on nonpoint sources of suspended sediment, nutrients, and herbicides, Pequea Creek basin, Pennsylvania, 1979-80