Broken Stream Banks

Failure to maintain buffer zones worsens farm pollution

April 25, 2014

Broken Stream Banks: Agricultural Runoff Clouds Waterways

Polluted runoff from row crops creates serious water pollution problems in southern Minnesota.

After years of neglect, however, state officials are taking action to clear the sediment-laden waters of the Mississippi River, from its confluence with the Minnesota River to the upper half of Lake Pepin. Water that is too cloudy – the technical term is turbidity – prevents sunlight from reaching aquatic plants and suffocates much of a river’s aquatic life.

Recently, the Minnesota Pollution Control Agency (MPCA) released a statewide Minnesota Nutrient Reduction Strategy designed to reduce the nutrient pollution – primarily phosphorus and nitrogen – that threatens lakes, streams and groundwater and contributes to the massive “dead zone” that appears each year in the Gulf of Mexico. The strategy seeks to reduce phosphorus pollution by 35 percent and nitrogen pollution by 25 percent by 2025.10

Runoff from agricultural land – primarily row crops – is the major source of this pollution. As the nutrient reduction strategy states, “agricultural sources contribute an estimated 38 percent of the statewide phosphorus load” and “73 percent of the statewide nitrogen load.” MPCA is also developing a complementary strategy to cut sediment pollution.

The primary culprit for the pollution threatening Lake Pepin and the Mississippi River south of the Minneapolis–St. Paul area is the Minnesota River, which is overloaded with sediment and nutrients after flowing hundreds of miles through the state’s rich farmland. By the time it meets the Mississippi, the cloud of sediment carried by the Minnesota River is so dense it is visible from the sky. (Figure 1)

Figure 1: Minnesota River delivers sediment and nutrients to the Mississippi River

A heavy load of sediment makes the Minnesota River look paler where it joins the cleaner Mississippi River in the Twin Cities. (2013, NAIP)

The Pollution Control Agency has been working with a coalition of local agencies and organizations to set a regulatory limit on the amount of sediment in the water – called a Total Maximum Daily Load (TMDL) – at the point where the Minnesota River flows through the south metro area. The goal is to increase water clarity, rejuvenate plant and animal life and improve recreational opportunities. Implementation of the agency’s proposed water quality standard for turbidity is to begin after officials respond to public comments and the U.S. Environmental Protection Agency signs off.11 12

The Pollution Control Agency has also developed water quality standards for Lake Pepin, where excess nutrients clog the water with toxic algae blooms and deplete the oxygen that sustains aquatic life. These standards, too, are currently awaiting public comment.13 14 Upstream, along the Minnesota River and Blue Earth River Basin, planning has begun to reduce the sediment runoff in order to reach the TDML targets.15 16