Nitrogen in Minnesota Surface Waters

This study of nitrogen (N) in surface waters was conducted to better understand the N conditions in Minnesota's surface waters, along with the sources, pathways, trends and potential ways to reduce N in waters. Nitrogen is an essential component of all living things and is one of the most widely distributed elements in nature. Nitrate (NO3), the dominant form of N in waters with high N, is commonly found in ground and surface waters throughout the country. Human activities can greatly increase nitrate, which is typically found at low levels in undisturbed landscapes. Concern about N in Minnesota's surface waters has grown in recent decades due to: 1) increasing studies showing toxic effects of nitrate on aquatic life, 2) increasing N concentrations and loads in the Mississippi River combined with nitrogen's role in causing a large oxygen-depleted zone in the Gulf of Mexico, and 3) the discovery that some Minnesota streams exceed the 10 milligrams per liter (mg/l) standard established to protect potential drinking water sources. Minnesota recently initiated two state-level efforts related to N in surface waters. The Minnesota Pollution Control Agency (MPCA) is developing water quality standards to protect aquatic life from the toxic effects of high nitrate concentrations. The standards development effort, which is required under a 2010 Legislative directive, draws upon recent scientific studies that identify the concentrations of nitrate harmful to fish and other aquatic life. Also in development is a state-level Nutrient Reduction Strategy, as called for in the 2008 Gulf of Mexico Hypoxia Action Plan. Minnesota contributes the sixth highest N load to the Gulf and is one of 12 member states serving on the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force. The cumulative N and phosphorus (P) contributions from several states are largely the cause of a hypoxic (low oxygen) zone in the Gulf of Mexico. This hypoxic zone affects commercial and recreational fishing and the overall health of the Gulf, since fish and other aquatic life cannot survive with low oxygen levels. Minnesota is developing a strategy which will identify how further progress can be made to reduce N and P entering both in-state and downstream waters. The scientific foundation of information documented in this report will be useful as the MPCA and other state and federal organizations further their nitrogen-related work, and also as local government considers how high N levels might be reduced in their watersheds. The Minnesota Department of Agriculture is completing a separate but concurrent effort to revise the state's Nitrogen Fertilizer Management Plan, as required under Minnesota's Ground Water Protection Act. The plan addresses groundwater protection from nitrate. Yet because groundwater baseflow is an important contributor to surface water nitrate, certain groundwater protection efforts will also benefit surface waters.