Broken Stream Banks

Failure to maintain buffer zones worsens farm pollution

April 25, 2014

Broken Stream Banks: Introduction

Water pollution from farmland is a major problem in southern Minnesota and wherever row crops dominate the landscape across the United States. According to the Environmental Protection Agency, agriculture is the number one source of pollution in waterways identified by states as too polluted to be used as public water supplies, for recreation or for other purposes. The Agency’s most recent water quality report found that agricultural runoff degraded more than 125,000 miles of surveyed rivers and streams across the country.1

Much of this pollution can be prevented by the conscientious use of riparian buffers – strips of grass, trees or other permanent vegetation that are maintained along the banks of rivers, streams, lakes and other waterways. Buffers play a critical role reducing the amount of sediment and nutrients that wash off crop fields.

Minnesota is a national leader in recognizing the importance of these buffers in combatting agricultural pollution. The state's shoreland management rule confers legal protection of riparian buffers between most waterways and farm land.2 The rule promulgated to implement the law established a “shore impact zone,” defining it as the area between the stream bank and “a line parallel to and 50 feet from the ordinary high water level.” For “parcels with permitted agricultural land uses,” the statute requires that the shore impact zone be “maintained in permanent vegetation or operated under an approved conservation plan.”

These progressive requirements, which are rare in large agricultural states, create a remarkable opportunity to improve water quality. Like any other law, however, it must be enforced to be effective.

In 2013, the Environmental Working Group launched a project to assess how well the law is working and to help county and state officials in their efforts to make sure that the required buffers are maintained between row crops and public waterways. EWG’s research follows on a 2010 study by the Minnesota Board of Water and Soil Resources that also sought to measure the condition and maintenance of the state’s riparian buffers.3 That study concluded that:

  • conflicting interpretations of the law’s definitions of riparian land use had left public waters at risk;
  • drainage ditches in heavily agricultural areas often had the fewest buffers;
  • the limited financial incentives to install and maintain buffers were usually outweighed by other factors, such as the lure of higher prices for commodities; and
  • there was no digital geographic information system (GIS) data available with the necessary precision to accurately assess the state of riparian buffers.

That same year, the Minnesota Center for Environmental Advocacy (MCEA) set out to build a GIS data layer that could accurately reflect land cover within the 300-foot shoreland zone - including the presence or absence of buffering vegetation within 50 feet of public waterways. Due to the enormity of this task, the Center limited the project to public waterways in Blue Earth County and in the Middle Minnesota, Cedar River, Sauk River, Root River and Pomme de Terre watersheds.4 5 6 7 8 9 The analysis yielded numerous detailed atlases classifying the vegetative cover adjacent to all public waters in the area. In all, the Center found that cropland often encroached into the 50-foot shoreline protection zones.

In its own study, EWG used a combination of high resolution aerial photography and the Minnesota Public Waters Inventory (PWI) GIS data layer to evaluate how much of the required buffer acres were actually in place along perennial rivers and streams in 37 southern Minnesota counties. We also looked at a small sub-sample of the public drainage ditches and intermittent streams in the Inventory’s GIS layer. We limited our analysis only to waterways that flowed through land planted with row crops.

This report and the interactive maps below show what EWG found.