HR: 13:40h
AN: H53J-01 INVITED    [Abstracts]
TI: Transport processes of nitrogen, phosphorus, and pesticides in five agricultural watersheds in the United States
AU: * Domagalski, J
EM: joed@usgs.gov
AF: U.S. Geological Survey, 6000 J Street Placer Hall, Sacramento, CA 95819, United States
AU: Phillips, S P
EM: sphillip@usgs.gov
AF: U.S. Geological Survey, 6000 J Street Placer Hall, Sacramento, CA 95819, United States
AB: Transport processes affecting agricultural chemicals in the hydrological cycle were investigated at five watersheds in major agricultural settings, representing both different agricultural practices and climatic settings of the United States. Watersheds were chosen in two semi-arid regions of California and Washington that utilized irrigation; in Nebraska (typical of mid-west corn and soybean rotation); in an Indiana basin with tile drainage; and in a Maryland watershed where ground-water discharge supplied a substantial portion of the annual streamflow. The study design was to provide a mass-balance of water and agricultural chemicals originating from the atmosphere or irrigation water, through the unsaturated zone, along a ground-water flow path, and discharge of the ground water to a stream. Although overland flow associated with storms transported the bulk of nutrient and pesticide compounds to streams in most of these watersheds, ground-water transport, as indicated by flow separation analysis, was also important for annual loads of nitrate and pesticide degradates. Total nitrogen, mainly in the form of nitrate, was the most important nutrient with respect to mass loading in these streams, and pesticide transport was usually greatest during the first few rainfall events following application. In contrast, ground-water transport of pesticide degradates contributed to their mass loading throughout the year in base-flow dominated streams. Although subsurface transport of phosphorus has not been given much attention in previous studies of agricultural chemicals, concentrations were elevated in the unsaturated zone and along ground-water flow paths to streams in some of the watersheds, and contributed to the annual stream load. This was particularly true in the basins of the western United States. For instance, in the Washington basin, discharging ground water accounted for up to 30 percent of the annual phosphorus stream load.
DE: 1830 Groundwater/surface water interaction
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting