Hydrologic data for the Big Spring basin, Clayton County, Iowa, water year 1991

Open-File Report 94-56




Hydrologic data were collected in the Big Spring Basin located in Clayton County, Iowa, during the 1991 water year. The data were collected to pro- vide information on variation and movement of agricultural chemicals in the hydrologic cycle in the basin. Precipitation, surface-water, and ground-water data were collected. Calcium and sulfate were the predominant ions in the rain, and the median concentrations of nitrate and ammonia as nitrogen were 0.36 and 0.49 mg/L (milligrams per liter), respectively. Discharge, specific conductance, pH, and water temperature were monitored continuously, and monthly water-quality samples were collected at Big Spring and at a site on Roberts Creek. Nitrite plus nitrate as nitrogen concentrations in water from Roberts Creek ranged from 1.8 to 22 mg/l, and herbicide concentrations ranged from less than 0.10 to 43 micrograms per liter. Alachlor was detected in 42 percent; atrazine in 92 percent; and cyanazine and metolachlor in 35 percent of the samples from Roberts Creek. Total suspended-sediment load discharged in Roberts Creek was about 160,000 tons. Water from Big Spring, the ground-water discharge point, contained concentrations of nitrite plus nitrate that ranged from 4.2 to 17 mg/L. Total measured suspended sediment discharged from Big Spring was about 17,000 tons. Alachlor was detected in 26 percent; atrazine in 100 percent; cyanazine in 26 percent, and metolachlor in 9 percent of the samples from Big Spring. The maximum atrazine concentration was 16 micrograms per liter.

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USGS Numbered Series
Hydrologic data for the Big Spring basin, Clayton County, Iowa, water year 1991
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Open-File Report
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U.S. Geological Survey ; USGS Earth Science Information Center, Open-File Reports Section [distributor],
vi, 87 p. :ill., maps ;28 cm.