Submitted to: Water Environment Federation
Publication Type: Proceedings
Publication Acceptance Date: June 6, 1996
Publication Date: N/A
Technical Abstract: Agricultural practices have been linked to nonpoint source pollution because of different reconnaissance studies in the Midwest. However, there is little detailed understanding of the linkage between agricultural practices and water quality at the watershed scale. Research was conducted in Walnut Creek watershed, a 5600 ha area, located south of Ames, Iowa. This watershed is located on the Des Moines lobe landform region and consists of moderately- to poorly-drained soils overlying Wisconsinan till. The watershed has been monitored since 1991 to observe the movement of atrazine, alachlor, metolachlor, metribuzin, and nitrate-nitrogen in stream flow, surface runoff, tile drainage, shallow ground water, and precipitation. Intensive sampling of the field operations provides a data base of herbicides and nitrogen rates applied to each field of the watershed. Atrazine and metolachlor are the most dominant herbicides used in the watershed, and the loss is typically less than 1% per year, however, in the high rainfall year of 1993, loss was nearly 7%. Nitrate-nitrogen losses are much higher and are nearly 40% of the commercial fertilizer applied. Most of the loss of herbicides and nitrate is through the tile drains and where there is little movement into shallow ground water. The water balance for the watershed shows that less than 10% of the precipitation moves to the shallow ground water. Understanding the movement patterns of agricultural chemicals within the watershed allows better interaction with farm operators to make management changes that will benefit water quality.