Michael D. Bilger — Page 2

USGS1997

Water-quality assessment of the Lower Susquehanna River Basin, Pennsylvania and Maryland: Design and implementation of water-quality studies, 1992-95

From 1992 through 1995, nearly 1,200 water-quality samples from about 500 sites were collected, processed, and analyzed for the U.S. Geological Survey's (USGS) National Water-Quality Assessment (NAWQA) Program in the Lower Susquehanna River Basin in Pennsylvania and Maryland. Sites were selected and samples were collected for 28 integrated water-quality studies designed to provide a comprehensive and nationally consistent description of current water-quality conditions, to begin to identify trends in water quality, and to determine the major factors that affect observed water quality. To achieve this, stream-water, ground-water, streambed-sediment, and biota samples were collected, and habitat assessments were conducted at selected data-collection sites. This report discusses the water-quality study design, site-selection strategy, and implementation steps used to obtain water-quality and related data. Methods employed to collect, process, and analyze samples, characterize sites, and assess habitat are described. A comprehensive list of all sites employed in these studies and their characteristics is provided. Sample analyses conducted for the water-quality studies described in this report, including nutrients, pesticides, major ions, volatile organic compounds (VOC's), and trace elements, as well as measured or observed physical properties and habitat characteristics, also are listed.

Maryland, Pennsylvania↗

USGS1997

Surface-water quality changes after 5 years of nutrient management in the Little Conestoga Creek headwaters, Pennsylvania, 1989-91

A 5.82-square-mile drainage basin in the headwaters of the Little Conestoga Creek in Lancaster County, Pa., was investigated from October 1989 through September 1991 as part of a longer-term effort to determine the effects of nutrient management on surface-water quality. A previous investigation found no statistical evidence that implementation of nutrient management from 1986 to 1989 affected water quality. Basin land use is 68 percent agriculture and includes all or part of 51 farms. Agricultural land under nutrient management ranged from 55 percent in 1989 to 80 percent in 1991. Nitrate nitrogen, the dominant nonpoint-source contaminant, averaged about 7.5 milligrams per liter in base flow. Implementation of nutrient management on 90 percent of applicable land in a 1.42-square-mile subbasin resulted in a 7 percent decrease in nitrogen applications from before nutrient management. Recognizing that some uncertainty exists in the nutrient-application data, the decrease consisted of a 44-percent decrease in commercial fertilizer nitrogen combined with a 3-percent increase in manure nitrogen applications. Manure accounted for 83 percent of the applied nitrogen. Amounts of nitrate nitrogen in the top 4 feet of soil ranged from 43 to 315 pounds per acre in the subbasin and were not substantially reduced from before nutrient management. Statistical analysis of nutrient and suspended-sediment concentrations detected few significant step trends in water quality in a comparison with water quality before nutrient management. A decrease in base-flow concentrations of dissolved ammonium and suspended sediment was detected at a site draining a 1.43-square-mile subbasin with 40-percent implementation of nutrient-management plans. An increase in base-flow concentrations of suspended sediment was detected at a site draining the 1.42-square-mile subbasin with 90-percent implementation. A comparison of the dissolved nitrate plus nitrite in base-flow relations between paired subbasins detected no change from 1984-86 (before nutrient management) to 1989-91. Mean concentrations in stormflow were not reduced significantly from 1984-86 to 1989-91. Data collected during the entire 1986-91 nutrient-management period suggest a reduction in nitrogen input as large as the 30-percent reduction recorded from 1986-89 is needed to effect a 0.5-milligram-per-liter decrease in dissolved nitrate plus nitrite.

Pennsylvania↗