The national grids of the agricultural use of 199 pesticides were developed to support hydrologic studies that are part of the U.S. Geological Survey's (USGS) National Water Quality Assessment (NAWQA) Program. The goal of the NAWQA program is to develop long-term consistent and comparable information on streams, ground water, and aquatic ecosystems to support sound management and policy decisions (U.S. Geological Survey, 2001; Gilliom and others, 1995). The NAWQA program, which began in 1991, consists of long-term cyclical studies in over 50 major river basins and aquifers in the United States. Pesticide-use grids are used in the NAWQA program to: 1) determine overall estimates of agricultural pesticide use in major watersheds (as documented in Nakagaki and Wolock, 2005) and other large study areas; 2) provide input into national models, such as the regression model for predicting concentration of pesticide distributions in unmonitored rivers and streams (as described in Larson and others, 2004); and 3) display the spatial distribution and use intensity of agricultural pesticides in the conterminous United States in USGS publications (as shown in Gilliom and others, 2006). Purpose References: Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995, Design of the National Water-Quality Assessment Program--occurrence and distribution of water-quality conditions: U.S. Geological Survey Circular 1112, 33 p. Gilliom, R.J., Barbash, J.E., Crawford, C.G., Hamilton, P.A., Martin, J.D., Nakagaki, Naomi., Nowell, L.H., Scott, J.C., Stackelberg, P.E., Thelin, G.P., and Wolock, D.M., 2006, The Quality of Our Nation's Waters -- Pesticides in the Nation's Streams and Ground Water, 1992-2001: U.S. Geological Survey Circular 1291, 172 p. Larson, S.J., Crawford, C.G., and Gilliom, R.J., 2004, Development and application of watershed regressions for pesticides (WARP) for estimating atrazine concentration distributions in streams: U.S. Geological Survey Water-Resources Investigations Report 03-4047, 68 p. Nakagaki, Naomi, and Wolock, D.M., 2005, Estimation of agricultural pesticide use in drainage basins using land cover maps and county pesticide data: U.S. Geological Survey Open-File Report 2005-1188, 46 p. U.S. Geological Survey, 2001, The National Water Quality Assessment Program-- entering a new decade of investigations: U.S. Geological Survey Fact Sheet 071-01, accessed 1/30/06, at https://pubs.usgs.gov/fs/fs-071-01/
