The National Water Quality Network (NWQN) for Rivers and Streams includes 113 surface-water river and stream sites monitored by the U.S. Geological Survey (USGS) National Water Quality Program (NWQP). The NWQN represents the consolidation of four historical national networks: the USGS National Water-Quality Assessment (NAWQA) Project, the USGS National Stream Quality Accounting Network (NASQAN), the National Monitoring Network (NMN), and the Hydrologic Benchmark Network (HBN). The NWQN includes 22 large river coastal sites, 41 large river inland sites, 30 wadeable stream reference sites, 10 wadeable stream urban sites, and 10 wadeable stream agricultural sites. In addition to the 113 NWQN sites, 3 large inland river monitoring sites from the USGS Cooperative Matching Funds program are also included in this annual water-quality reporting Web site to be consistent with previous USGS studies of nutrient transport in the Mississippi-Atchafalaya River Basin. This data release provides estimated agricultural pesticide use for 83 NWQN watersheds for 110 pesticide compounds from 1992-2014. Pesticide use was not estimated for the 30 wadeable stream reference sites, or from 3 large river coastal sites (07381590, "Wax Lake Outlet at Calumet, LA3"; 07381600, "Lower Atchafalaya River at Morgan City, LA2"; or 15565477, "Yukon River at Pilot Station, AK"). Use was not estimated for reference sites because pesticides are not monitored at reference water-quality sampling sites. Pesticide use data are not available for Alaska and thus no data is available for the Yukon River site. The other two coastal sites (07381590 and 07381600) where use was not estimated are outflow distributaries into the Gulf of Mexico. This data release provides use estimates for the same pesticide parent compounds sampled in water and analyzed by USGS, National Water Quality Laboratory (NWQL), Schedule 2437: http://wwwnwql.cr.usgs.gov/USGS/catalog/index.cfm. Pesticide use data are not available for degradate compounds or for compounds not used in agricultural applications.
County-level pesticide use estimates and methods for making the estimates are available on the USGS Pesticide National Synthesis Project (PNSP) page: https://water.usgs.gov/nawqa/pnsp/usage/maps/ , https://dx.doi.org/doi:10.5066/F7NP22KM . County-level estimates are based on farm surveys of pesticide use. Two estimates, EPestLOWkg and EPestHIGHkg, provide a range of values of pesticide use and differ in how they treated situations where surveys were done but pesticide use was not reported for a particular pesticide-by-crop combination. The HIGH method tends to spread estimated use over a larger geographic area. EPestLOWkg annual-use totals can be greater than EPestHIGHkg totals when the LOW method of estimation concentrates the use to a particular area while the HIGH method spreads the use over a larger area. Details on the difference between the two estimates are explained on the PNSP page. There is uncertainty in both the HIGH and LOW estimates that is difficult to quantify. A user should become familiar with the two methods to decide which estimate is best for a specific application.
To obtain estimates for NWQN watersheds county-level estimates were proportionally allocated to agricultural land within each NWQN watershed. Zero values indicate that pesticide use was estimated for that watershed but that the total use for the watershed was less than 0.1 kg. Null values indicate that use was not estimated because there was not enough farm survey data available to make an estimate for that particular compound in that watershed. Place holder rows were kept for all compounds and years regardless of whether an estimate was made so that users know which compounds were included in the estimation process.