A Tale of Three Watersheds: Non-point Source Pollution and Conservation Practices Across Iowa

Authors: SCHILLING, KEITH - IA GEOLOGICAL SURVEY BUR; Tomer, Mark; GASSMAN, PHILIP - IA STATE UNIVERSITY; ISENHART, THOMAS - IA STATE UNIVERSITY; Moorman, Thomas; SIMPKINS, WILLIAM - IA STATE UNIVERSITY; WOLTER, CALVIN - IA GEOLOGICAL SURVEY BUR

Submitted to: Choices
Publication Type: Other
Publication Acceptance Date: 4/30/2007
Publication Date: 7/15/2007
Citation: Schilling, K.E., Tomer, M.D., Gassman, P., Isenhart, T.M., Moorman, T.B., Simpkins, W., Wolter, C.F. 2007. A Tale of Three Watersheds: Non-point Source Pollution and Conservation Practices Across Iowa. Choices. 22(2):87-95.

Interpretive Summary: This study summarizes the results of three Iowa watershed studies that have varying terrain, land use histories, and conservation practices. Results emphasized the importance of watershed-specific information in assessing agricultural impacts on water quality. In the South Fork watershed, where low relief till plains from recent glaciation were available to early settlers, wetlands were drained, and agricultural development intensified over the last century. Although the land is well-suited for crop growth and concentrated livestock production, subsurface tile drainage increases opportunities for losses of nitrate, while surface runoff and the rapid routing of tile discharge enhance movement of bacteria, phosphorus (P), and sediment. In Squaw Creek, with steeper slopes in row crops, conservation practices such as reduced tillage and contour farming methods are more prevalent. However, nutrient, sediment and bacteria losses remain a major concern in the watershed, possibly a consequence of utilizing hydrologically sensitive areas for row crops or grazing. Row crop acreage in the Sny Magill watershed constitute only about 25 percent of the land area and most row crop fields have conservation tillage or structural practices. However, the steep slopes and karst drainage in the watershed make Sny Magill watershed perhaps the most vulnerable among the three streams evaluated. Conservation systems need to be tailored to each watershed, including its environmental, agricultural, and economic contexts. Significant challenges remain to develop better assessment, monitoring and modeling techniques to capture the inherent differences among our watersheds in order to design conservation practices and programs providing greater water quality benefits for lower cost. Results are of interest to policy makers who need to consider varied needs of resource conservation, agricultural production, and volunteerism in designing conservation policies.

Technical Abstract: This research was conducted as part of a Conservation Effects Assessment Project (CEAP) - Watershed Assessment Study supported by USDA-CSREES. The objectives of the project are to evaluate the effects of watershed conservation practices on water quality, with a focus on understanding how the suite of conservation practices, the timing of these activities, and the spatial distribution of these practices throughout a watershed influence their effectiveness. An additional component of the project is to evaluate social and economic factors influencing implementation and maintenance of practices. The Sny Magill Creek, Squaw Creek, and the South Fork of the Iowa River (South Fork) watersheds are representative of three distinct landform regions of Iowa. In the South Fork watershed, where low relief till plains from recent glaciation were available to early settlers, wetlands were drained, and agricultural development intensified over the last century. Although the land is well-suited for crop growth and concentrated livestock production, subsurface tile drainage increases opportunities for losses of nitrate, while surface runoff and the rapid routing of tile discharge enhance movement of bacteria, phosphorus (P), and sediment. In Squaw Creek, with steeper slopes in row crops, conservation practices such as reduced tillage and contour farming methods are more prevalent. However, nutrient, sediment and bacteria losses remain a major concern in the watershed, possibly a consequence of utilizing hydrologically sensitive areas for row crops or grazing. Row crop acreage in the Sny Magill watershed constitute only about 25 percent of the land area and most row crop fields have conservation tillage or structural practices. Recent advances in assessment technologies and record-keeping are only now beginning to allow us to understand the distribution of practices on the land and their impacts on water quality. Significant challenges remain to develop better assessment, monitoring and modeling techniques to capture the inherent differences among our watersheds in order to design conservation practices and programs providing greater water quality benefits for lower cost.