Governor Mark Dayton announced in January his proposal to require an additional 125,000 acres of perennial vegetation along lakes, rivers and streams. There is a long history of utilizing such living borders to filter out fertilizers and herbicides, while fortifying streambanks and reducing the amount of eroded soil that ends up in the water. While not a silver bullet, establishing buffer protections between our crop fields and our water is, as LSP farmer-member Darrel Mosel says, “ …one of the most significant farmland stewardship initiatives for water quality and wildlife habitat proposed by a Minnesota governor in decades.…”
The Land Stewardship Project decided to support this proposal after talking with leaders who are farmer-members. As proposed, the initiative emphasizes stewardship of land and water, is supported by sound science and is flexible enough to provide options for sizing buffers appropriately and to allow them to be used as working farmland.
Buffer Strips 101
Vegetative buffers, sometimes called filter strips, are typically from 16.5 to 120 feet wide. These strips are designed with perennial vegetation such as grass to intercept runoff that also may carry sediment, nutrients and other contaminants into sensitive areas such as streams, lakes, wetlands or drainage ditches. Fifty-foot buffers are already required on “public waters” in Minnesota’s agricultural areas by shore land management rules. Several reports have been done on compliance and found that a sizeable number of landowners have required buffers in place, but others do not. Some counties have high rates of compliance. In Dakota County, for example, 99 percent of the Department of Natural Resources-designated shore land has a 50-foot buffer.
Governor Dayton’s initiative calls for uniform enforcement of buffer requirements and would extend 50-foot strips to perennial waters not now included in the state’s current inventory of public waters. It would not change Minnesota ditch law. Perennial waters are waters having a defined bed and bank, and have flowing water during the majority of the growing season in most years. A recent Board of Water and Soil Resources assessment showed that this may apply to about 64 percent of streams in 67 counties that are planted to more than 30 percent cropland.
The Science Behind Buffer Strips
Extensive monitoring of established buffers, experiments with buffer configurations and modeling have all shown that these living filters can significantly reduce sediment, nutrients and other contaminants in surface runoff from crop fields. The efficiency of this filtering depends on such characteristics as soils, management, slope and size of the field and buffer, the intended contaminants to be filtered or trapped and intensity of rainfall events. The USDA Natural Resources Conservation Service (NRCS) considers buffers a “Core 4” practice that has “conservation impact and can be implemented on almost every farm.” The Minnesota NRCS has specific designs for buffers that are between 30 and 160 feet, depending on resource concerns and site characteristics.
Here’s a partial rundown of why buffers are one go-to practice for cleaning up water in rural areas:
- A Nebraska study found that doubling the width of a buffer from a little less than 25 feet to almost 50 feet significantly increased infiltration and dilution of runoff. Increasing the width of the buffer cut the amount of nitrogen and total dissolved phosphorous making its way to the water by 15 percent, and the amount of total suspended solids — defined as the amount of solids in water that can be trapped by a filter — by 6 percent. Volume of outflow was also reduced significantly with increased width, contributing to the reduction of contaminants making their way to the water.