National Water Quality Assessment Program: Eastern Iowa Basins

Agricultural Chemical Transport study, South Fork Iowa River: Overview of ground water and hyporheic zone investigations

Erik A. Smith, U.S. Geological Survey, Iowa City, IA

Program abstracts of the Iowa Academy of Sciences 119th meeting, April 28, 2007, Pella, Iowa

The USGS (U.S. Geological Survey) is initiating a two-year hydrologic process study to determine the transport and fate of selected nutrients and pesticides within a focused ground water-surface water interaction site as part of the USGS ACT (Agricultural Chemicals Transport) program. The ACT program project objective is to quantify transport of natural and agricultural chemicals through an alluvial aquifer to the South Fork Iowa River. The study area includes a gently sloping 15-acre agricultural field (corn/soybean rotation) separated from the river by about 200 feet of grassy and wooded riparian buffer. Water chemistry and level data will be collected at 22 upland wells and 10 ground water/surface water interaction wells. Upgradient wells will be monitored for changes in water-levels, temperature variations, and well water chemical composition. Data also will be collected from paired vadose zone lysimeters and soil moisture probes installed at the edges of the field and riparian buffer. During 2007 and 2008, wide-scale chemical assessments of well water will be completed several times during the growing season. Initial data collection efforts include well and lysimeter installation, temporal and spatial water-level monitoring, soil core sampling, and an initial site-wide well water chemical assessment. Continuous water-level measurements collected to date indicate strong hydraulic connectivity throughout the alluvial aquifer and a limited hydraulic connectivity between the stream and the adjacent aquifer within the riparian zone. Initial chemical data suggests strongly iron-reducing conditions across most of the site, based upon 10,000 micrograms/L iron concentrations and less than 10 mg/L nitrate concentrations.

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