Use of Watershed Modeling to Target Management Practices in an Agricultural Watershed

View the project final report

Commodities

• Animal Products: dairy

Practices

• Crop Production: conservation tillage, crop rotation
• Sustainable Communities: sustainability measures

Agriculture plays an important role in the economy of Wisconsin (WI) and the United States (US). Phosphorus (P) loss (dissolved and sediment bound) in agricultural runoff can increase the frequency of toxic algal blooms and fish kills in receiving waters. As funding levels for sediment-control best management practices (BMPs) are likely to decline, there is a need for targeted approaches that can identify the most significant sediment sources in a watershed. The study being proposed is an integrated watershed project that will employ research, education and extension to gain a better understanding of how a targeted management approach could be used to improve water quality and long-term profitability for farmers. Sediment fingerprinting techniques and watershed models (e.g., the Soil and Water Assessment Tool, SWAT) have been used to identify areas contributing a disproportionate amount of pollutants to streams. While both these approaches have certain limitations, in conjunction they can be effective in identifying pollutant hotspots both at field- and watershed- scales. For example, in the SWAT model, the smallest land management unit at which source areas can be identified is the Hydrologic Response Unit (HRU). The boundary of a SWAT HRU seldom matches the actual field boundaries within a watershed. This characteristic of SWAT limits the incorporation of field-level management information into the model and in-turn the evaluation of management practice alternatives on water quality and farm profitability for a particular field in the long-term. We will modify the HRU delineation method in SWAT to match HRU boundaries with actual field boundaries, thereby allowing the incorporation of specific field-level management information. The sediment fingerprinting data from an on-going study will be used to better represent the sediment transport processes within SWAT. The fields contributing disproportionate amounts of pollutants will be identified and targeted for appropriate BMPs that are both compatible with current farm operations (alternate crop rotations, reduction in the fertilizer manure application, etc.) and profitable to farmers in the long-term. The results from this study will be disseminated to the Dane County Land Conservation Division (DCLCD), Dane County, WI; WI Department of Natural Resources (DNR); Natural Resource Conservation Service (NRCS); and U.S. Geological Survey (USGS). The DCLCD will work with farmers to implement recommendations based on study outcomes. Results from this study will help develop a template for a targeted BMP approach that can be expected to improve water quality and increase long-term farm profitability and sustainability.

1. Identification of fields contributing disproportionate amount of pollutants to streams.
2. Evaluation of best management practices which result in significant pollutant reductions at the watershed outlet and are acceptable to farmers using watershed modeling.