Stopping the Nitrogen Super-Highway

Boarding the Magnolia Blossom at Watergate Marina

Down the creaky metal walkway we bounced before climbing aboard the stylishly retro Magnolia Blossom docked at Watergate Marina on the Mississippi River. Each year, the Metro WaterShed Partners, a coalition of more than 60 public, private and non-profit entities in the Twin Cities, sponsors a “floating workshop” to help members connect with one another and learn more about issues impacting the water resources we work so hard to protect. During this year’s tour, WaterShed Partners chose to travel upstream on the Minnesota River to provide a backdrop for discussion about nitrogen in our water and agricultural policy in Minnesota.

Last year, the Minnesota Pollution Control Agency (MPCA) released a study of nitrogen conditions, trends, sources and reduction strategies for streams and rivers in Minnesota, based on monitoring results from 50,000 water samples collected at more than 700 sites. During our boat tour, Dave Wall, lead author and coordinator of the nitrogen study, shared some of the key findings.

Nitrogen is an organic, naturally occurring nutrient that is also added heavily to croplands to help plants grow bigger and faster. The amount of nitrogen flowing downstream in the Mississippi River has doubled since 1976 and nitrogen levels are increasing in about half of the other rivers and streams in Minnesota as well.  The implications for our groundwater drinking supplies, aquatic stream life, and the Gulf of Mexico are alarming. Excess nitrogen in the Gulf of Mexico where the Mississippi River ends results in a hypoxic zone, better known as the “dead zone,” where fish, shellfish, shrimp, crabs and other marine animals aren’t able to live due to lack of oxygen. In 2013, the National Centers for Coastal Ocean Science found that the dead zone covered at least 5,800 square miles of sea floor, or about the size of the State of Connecticut. Meanwhile, here in Minnesota, Wall and other researchers are concerned that nitrogen may be affecting aquatic life in our streams and rivers as well. Nitrogen concentrations in the Minnesota River are 7 – 8 mg/L, and research has shown that nitrogen can become toxic to aquatic life at concentrations of 4 – 14 mg/L. In southern Minnesota, many drinking wells have also been contaminated with nitrates, making the water unsafe for infants and pregnant women to drink.

Dave Wall talks about nutrient sources and reduction strategies.

The majority of nitrogen in our rivers comes from groundwater beneath agricultural fields and tile drainage, which is installed in agricultural fields to help them dry out more quickly in the spring. The MPCA study found that 3 billion pounds per year of nitrogen enter the water supply from fertilizer and the soil itself, while an additional 1 billion come from manure and leguminous, nitrogen-fixing crops. Minnesota is responsible for 6% of the nitrogen reaching the Gulf of Mexico and our state, along with others in the Mississippi River Basin, has set a goal of reducing nitrogen by 45% in order to shrink the Gulf’s dead zone.

The top three strategies for reducing nitrogen in Minnesota all focus on changes in farming practices. Wall and other researchers have estimated that optimizing fertilizer management on farms across Minnesota could reduce nitrogen in our water by 13%. This includes testing soil to determine how much fertilizer is needed, as well as applying fertilizer at the right time so that plants are best able to absorb the nutrients. Installing practices to help remove nitrogen from tile drainage will cut nitrogen by 5%, and utilizing cover crops and other vegetation to help take up nitrogen during the winter will take away another 12%. Even if these practices are implemented statewide, however, we will still be only two-thirds of the way towards our goal of reducing nitrogen flowing to the Gulf of Mexico by 45%. What then? Says Wall, “That’s when research and development comes into play. We need folks at the University of Minnesota and other institutions to continue researching new cover crops and new ways of farming.” Otherwise, the nitrogen super-highway will keep on flowing.

For more information, read the MPCA Nitrogen Study.