Sheboygan County, Wisconsin, is seeking alternative ways to manage and control nonpoint source pollution, which is a major contributor of phosphorous to the Mullet River. Stakeholders are interested in identifying potentially restorable wetland sites within the Mullet River watershed that could provide multiple ecosystem services such as water quality protection, surface water storage, and flood risk reduction.
OpenNSPECT was used to model surface water runoff and phosphorus loads from different land use scenarios. The model employed local land use data and runoff coefficients to determine areas of high runoff and nutrient loading under normal precipitation conditions. These results were integrated into a broader assessment of wetland function to identify sites that might benefit most from wetland services of nutrient capture and flood storage and abatement. The assessment identified potentially restorable wetlands likely to provide multiple benefits. Those sites were incorporated into OpenNSPECT as a “what-if” management scenario to estimate the impacts that restoration might have on runoff within the watershed. The management scenario assumed that all multi-beneficial sites were restored to fully functioning wetlands, thereby changing the existing land use and associated curve numbers. Results from the management scenario were then compared to the base scenario to determine the impact in terms of reducing surface water and phosphorus runoff.
The recommendations from this assessment inform sustainable farming and watershed management practices within the Mullet River watershed. The results of this analysis can help stakeholders prioritize restoration efforts by identifying areas that contribute high levels of runoff and phosphorus, as well as wetlands that have the potential to provide the most flood abatement and water quality benefits. Additionally, the results were combined with 20-year development projections to determine areas where future development pressure may inhibit the health and growth of wetlands.