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.
Additional Publication Details
USGS Numbered Series
Hydrologic data for the Big Spring basin, Clayton County, Iowa, water year 1991
U.S. Geological Survey ;
USGS Earth Science Information Center, Open-File Reports Section [distributor],