Submitted to: Soil and Water Conservation Society Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: July 25, 2007
Publication Date: July 25, 2007
Citation: Tomer, M.D., James, D.E., Green, C.H., Hadish, G., Moorman, T.B. 2007. Water Quality and Conservation Practices in the South Fork of the Iowa River [abstract]. Soil and Water Conservation Society Proceedings. p. 40.
The South Fork of the Iowa River drains 87,000 ha under intensive, high-production agriculture. About 100 swine confined animal feeding operation (CAFOs) generate manure applied onto about a quarter of the watershed annually. Hydric soils cover 54% of the watershed because the young glacial terrain is poorly dissected. Artificial subsurface drainage is extensive and SWAT modeling indicates that this dominates the hydrology. Water quality monitoring data show spring and early summer NO3-N concentrations often exceed 20 mg L-1. Loads during 2002-2004 were 16-26 kg NO3-N ha-1yr-1, but only 0.4-0.7 kg P ha-1yr-1. Mean E. coli populations in the stream exceed 150 cells per 100 ml. Subsurface drainage plays an important role in the transport of nitrate, but is less important in the transport of E. coli and phosphorus. E. coli concentrations are governed by seasonal trends and runoff events. Natural Resources Conservation Service (NRCS) conducted a conservation-practices inventory in 2005 that was combined with a sequence of annual crop cover photos to identify dominant management systems in the watershed. About 85% of the agricultural land is in corn-soybean or corn-corn-soybean rotations with 8% in no-tillage or zone-tillage. Inadequate residue (<30%) often follows soybeans, and maintaining this residue during manure application is a key management challenge in the watershed. Grassed waterways, filter strips and riparian buffers are the most common edge of field conservation practices. Wetlands are uncommon, but construction of additional wetlands would help remove nitrate carried in artifical drainage water.