Research about Cedar River basin

USGS1996

Movement of agricultural chemicals between surface water and ground water, lower Cedar River basin, Iowa

Movement of agricultural chemicals alachlor, atrazine, cyanazine, deethylatrazine, deisopropylatrazine, and metolachlor between surface water and ground water is documented by data collected from May 1989 through July 1991 at an unfarmed study site adjacent to the Cedar River in Iowa. During periods of runoff, these chemicals moved from the Cedar River into the alluvial aquifer with bank-storage water. Results of simulation of ground-water flow conditions during March-April 1990 indicated that bank-storage water moving through the river bottom accounted for 70 percent of the total bank-storage water, whereas the remaining 30 percent moved through the riverbank. The largest concentrations of the chemicals in bank-storage water during 1990 were: alachlor, 2.1 micrograms per liter ( μ g/L); atrazine, 4.7 μ g/L; cyanazine, 3.2 μ g/L; deethylatrazine, 0.54 μ g/L; deisopropylatrazine, 0.33 μ g/L; and metolachlor, 2.2 μ g/L. Larger concentrations of some herbicides and their metabolites were detected in the ground water after the study site was inundated by floodwater between June and August 1990. The concentrations in a water sample from one well after this flooding on February 5, 1991, were: alachlor, 0.06 μ g/L; atrazine, 18 μ g/L; cyanazine, 1.3 μ g/L; deethylatrazine, 1.4 μ g/L; deisopropylatrazine, 0.40 μ g/L; and metolachlor, 7.0 μ g/L. During base-flow conditions, the movement of agricultural chemicals from ground water to surface water was quantified for two periods of time in 1989 and 1990 along a 117-kilometer reach of the Cedar River. The principal source of atrazine, deethylatrazine, deisopropylatrazine, and metolachlor in the Cedar River during base flow was ground water discharged directly from the alluvial aquifer adjacent to the Cedar River. This discharge exceeded the combined tributary inflow of the chemicals along the entire reach. Bank storage is probably an important source of agricultural chemicals discharged from the alluvial aquifer but becomes depleted with time after surface runoff. Herbicides discharged from the alluvial aquifer during periods of extended base flow entered the alluvial aquifer with ground-water recharge at some distance from the river. The movement of nitrate between surface water and ground water is minor, when compared to the herbicides, even though nitrite was detected in the Cedar River during runoff.

Iowa, Minnesota↗

USGS1988

Surface-water quality of the Cedar River basin, Iowa-Minnesota, with emphasis on the occurrence and transport of herbicides, May 1984 through November 1985

The surface-water quality in the Cedar River basin was evaluated by analyzing the occurrence, distribution, and transport of common inorganic constituents and selected trace inorganic and organic constituents, with emphasis on herbicides. The surface-water quality of the Cedar River basin was monitored from May 1984 through November 1985. Depth integrated surface-water samples generally were collected monthly at six stations for a considerable range of river discharge. Samples were analyzed for concentrations of common inorganic constituents in the dissolved phase and for concentrations of primary nutrients, trace elements, organic carbon, and herbicides in the dissolved and the dissolved plus suspended phases. Water in the Cedar River was determined to be a calcium bicarbonate type; suspended-sediment concentrations ranged from 3 to 676 milligrams per liter. Concentrations of dissolved fluoride, dissolved nitrite plus nitrate, dissolved arsenic, dissolved lead, and dissolved mercury were less than those of the U.S. Environmental Protection Agency's drinking-water standards for public water supplies. Generally, herbicides were detected only in the dissolved phase, which indicates that herbicides are not being adsorbed on the suspended sediment. However, the lack of detection of adsorbed herbicides also may indicate a need for re-examination of traditionally acceptable methods of treating water samples at the sampling site, separating sediment and water, and extracting organic compounds from sediment. The largest concentrations of several dissolved herbicides were detected after application on agricultural areas in the spring and early summer in both wet and dry periods. However, dissolved atrazine concentrations also increased in the winter during periods of high streamflow resulting from snow melt. The maximum concentration of dissolved herbicides detected at all sampling sites during the study were: alachlor, 21 micrograms per liter; atrazine, 16 micrograms per liter; cyanazine, 8.7 micrograms per liter; metolachlor, 11.0 micrograms per liter; and metribuzin, 3.0 micrograms per liter. Herbicides can be transported from agricultural areas to the river by overland flow, drainage from agricultural areas conveyed by tile drains, and ground water. Hydrograph separation for 10 locations in the Cedar River basin indicates that the ground-water contribution varies within the basin and probably ranges from 56 to 80 percent of the annual river discharge. The predominance of ground-water contribution, the persistent detection of dissolved atrazine even during base flow, and the variety of dissolved herbicides detected in the river during the dry spring of 1985 indicate that some herbicides are being transported to the river by ground water. Atrazine transported to the Cedar River was estimated to be about 1.4 to 4.0 percent of that applied, depending on the assumed application rate. The large river discharge in June 1984, which was predominantly overland flow, contained about 70 percent of the atrazine transported to the river during 1984.

Iowa, Minnesota↗