Watershed planning in Central Iowa: an integrated assessment of the Squaw Creek Watershed for prioritization of conservation practice establishment

摘要

Non-point source pollutants are a dominant threat to aquatic ecosystems in agriculturally dominated watersheds of the Midwest. Erosion and run-off from crop fields not only lowers the productivity of the field, but also transports sediment and attached nutrients or other agri-chemicals to receiving waters. In-field and edge-of-field best management practices (BMPs) have long been recognized as efficient ways to alleviate sediment impacts; however, prioritizing placement of these BMPs is critical to efficiently utilize allocated resources. A watershed assessment, utilizing the Iowa Department of Natural Resources (IDNR) Watershed Project Planning Protocol (WPPP) framework, was conducted on the Squaw Creek Watershed (SCW) in central, Iowa and included four assessment components. The first component inventoried land cover and tillage management practices throughout the landscape, allowing for calculation of erosion and sediment delivery estimates and highlighting sources of sediment. The second component utilized the Rapid Assessment of Stream Conditions Along Length (RASCAL), to assess in- and near-stream assessment stream conditions, including riparian landuse and stream bank stability. The third component utilized a geographic information system (GIS) and terrain indices to develop a riparian buffer placement tool to locate stream lengths intercepting high sediment loads and providing optimal conditions for the placement of riparian buffers. The final component utilized the IOWATER volunteer water monitoring program to assess water quality parameters including nitrate-nitrogen, phosphate-phosphorus and E. coli. Results from these four components were analyzed within the seven hydrologic unit code (HUC) 12 sub-watersheds that make up the SCW. This allowed the prioritization of sub-watersheds based on need for conservation practice establishment. The Onion Creek sub-watershed was identified as potentially having high levels of delivered sediment with the prospect of benefiting from riparian buffer placement. Other sub-watersheds identified as higher priority for conservation practice establishment were Montgomery Creek because of intensive grazing effects and Worrell Creek and Crooked Creek 3 because of erosion concerns. These results can direct further work within these sub-watersheds with the intention of implementing watershed improvement projects that will include placement of BMPs to alleviate the effects of NPS pollutants.