HR: 0830h
AN: H51C-05    [Abstracts]
TI: Evaluating nitrate sources in nested agricultural sub-basins using nitrate stable isotopes
AU: * Chang, C C
EM: ccchang@usgs.gov
AF: U.S. Geological Survey, 435 Middlefield Mailstop 434, Menlo Park, CA 94025 United States
AU: Frey, J W
EM: jwfrey@usgs.gov
AF: U.S. Geological Survey, 5957 Lakeside Blvd, Indianapolis, IN 46278 United States
AU: Kim, M
EM: mkim@usgs.gov
AF: U.S. Geological Survey, 5957 Lakeside Blvd, Indianapolis, IN 46278 United States
AU: Kendall, C
EM: ckendall@usgs.gov
AF: U.S. Geological Survey, 435 Middlefield Mailstop 434, Menlo Park, CA 94025 United States
AB: Nutrient enrichment is the second leading cause of drinking water contamination in the United States. To provide environmental managers with nutrient source and transport information, the U.S. Geological Survey' s National Water-Quality Assessment (NAWQA) Program conducted a multi-component study in Sugar Creek Basin, Indiana, in which major nutrients, cations, anions, and pesticides were analyzed. Land use at Sugar Creek (246 square km basin) is dominated by row crop agriculture, primarily corn and soybeans. The soils are largely heavy clay, glacial till in origin, and require tile drains to move excess water and make the land farmable. As one component of the study, stable isotopes of nitrate (N-15 and O-18) were used to examine nitrate sources and transport, and possible transformations of nitrate. Water samples were collected in 2003 and 2004 from major environmental compartments involved with the movement of nutrients into the creek, (precipitation, tile drain, and overland flow). Samples were also collected from Leary-Weber Ditch, a 6.2 square km basin is nested within Sugar Creek. Collection times bracketing four distinct periods of the agricultural cycle: pre-application of fertilizer, post-application of fertilizer, growing season, and post-harvest periods. Nutrient samples (nitrate, phosphate, ammonia) were also collected several times between storm events during baseflow conditions. Preliminary nutrient and pesticide data indicate that tile drains are the primary pathway into streams. Little interaction occurs between the ground water and surface water interface. Nitrate stable isotopes will enable us to determine the relative contribution of nitrate sources feeding in from the tile drains, into Leary-Weber Ditch and Sugar Creek.
DE: 1803 Anthropogenic effects
DE: 1860 Runoff and streamflow
DE: 4845 Nutrients and nutrient cycling
DE: 4870 Stable isotopes
SC: Hydrology [H]
MN: 2005 Joint Assembly