Sponsor: Okoboji Homeowners Association

Background: IGS researchers used groundwater monitoring targeted to discrete land cover and landscape position across the basin to assess groundwater recharge and loading patterns.

Goals: Our objectives were to assess groundwater level fluctuations and nutrient concentrations under representative land use classes and to develop an allocation model for groundwater nutrient loads based on land cover class.

IGS Strategies: We installed monitoring wells at 21 locations around the lake and sampled throughout a three-year study period to understand how groundwater quality varied over the different land cover types.

Sponsor: Iowa Department of Natural Resources

Background: IGS watershed studies have sometimes incorporated the use of models such as the Soil Water Assessment Tool (SWAT) to quantify nonpoint source impacts at a watershed scale and analyze remedial scenarios. In this example, IGS analyzed nitrate loading patterns for the Des Moines River basin using SWAT.

Goals: To model streamflow and nitrate loads and evaluate a suite of basin-wide changes and targeting configurations to potentially reduce nitrate loads in the river.

IGS Strategies: IGS used SWAT to model streamflow and nitrate loads and evaluate a suite of basin-wide changes and targeting configurations to potentially reduce nitrate loads in the river. The SWAT model comprised 173 subbasins and 2,516 hydrologic response units and included point and nonpoint nitrogen sources. Researchers calibrated the model for an 11-year period and three basin-wide and four targeting strategies were evaluated.

More information: Results indicated that nonpoint sources accounted for 95% of the total nitrate export. The most efficient load reductions occurred when fertilizer applications were reduced in subbasins nearest the watershed outlet. The SWAT model results provide much needed guidance on how to begin implementing load reduction strategies most efficiently in the Des Moines River Watershed.