Farm Chemicals as Indicators of Sediment Sources in Iowa Rivers

Determination of the source of sediment in rivers and streams is important in order to effectively implement a program to reduce its concentration. This project uses agricultural chemicals as indicators of current sources of sediment from farm fields in the Cedar River, Iowa watershed. We hypothesized that the relations of sediment, nitrogen, and phosphorous yields to precipitation would indicate whether sediment originated from erosion of fields or from channel bank erosion of floodplains. The changes in sediment, nitrate, and phosphorus in the channel in response to rainfall events were determined. In simple regressions, all three variables have similar slopes when regressed on seven-day precipitation sums. On the basis of the results of the regressions, it appears that, for the months used for this project, the major source of channel sediment is agricultural land. KEW WORDS: nitrate, non-point source pollution, phosphorous, sediment, water quality.