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- Title
Geology, groundwater flow, and water quality in the Walnut Creek watershed
- Authors
Simpkins, W. W.; Eidem, J. M.; Burkart, M. R.
- Abstract
An investigation of the Walnut Creek watershed was performed to characterize the geology, groundwater flow, and water quality in geological units impacted by agriculture. Six Quaternary lithostratigraphic units including alluvium of the DeForest Formation, till of the Dows and Woff Creek Formations, and loess of the Peoria, Pisgah, and Loveland Formations, along with two pedostratigraphic units, the Farindale and Sangamon Geosols, were identified. The thickness and spatial distribution of the units were controlled by the formation of a paleo-valley before the advance of the Des Moines Lobe, sediment movement intothe paleo-valley, and later erosion and deposition by the Des MoinesLobe. Groundwater flows toward the creek under unconfined conditionsin the fractured, oxidized zone of till of the Dows Formation. Tritium data indicate that recent recharge occurs at the water table and that the 1963 bomb peak occurs near the bottom of the oxidized zone. Fifty-five percent of groundwater samples taken in 1995 showed NO3-N concentrations at or above the MCL of 10 mg/L; pesticides were detected in two samples. Some of the highest concentrations of NO3-N occur in bomb peak groundwater near the base of the oxidized zone. This relationship implies that NO3-N leachinghas decreased during a period of increased N application in Iowa. Itmay actually reflect an increase in tile drain efficiency, decrease in groundwater recharge, and resultant isolation of NO3-N in less-mobile groundwater. Agricultural practices that further decrease NO3-N leaching will be needed to improve the quality of shallow groundwater in the watershed.
- Subjects
AGRICULTURE; WATER quality
- Publication
Journal of Environmental Quality, 1999, Vol 28, Issue 1, p60
- ISSN
0047-2425
- Publication type
Article