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The bluffs and cropland of southeastern Minnesota sit on a geologic terrain called karst, which is made up of limestone and dissolves easily to form fractures and holes below the surface. The porous quality of karst allows water to travel quickly underground and because limestone dissolves so easily, little filtration occurs. This leads to karst being extremely vulnerable to contamination, according to the U.S. Geological Survey (USGS).

Contaminants such as nitrates from fertilizers and manure travel easily through the limestone and end up in groundwater and rivers.

The karst region of southeastern Minnesota consists of Dodge, Fillmore, Goodhue, Houston, Mower, Olmsted, Wabasha and Winona Counties. In this region, more than 300,000 people rely on public water supplies and more than 94,000 rely on private wells for drinking water. High nitrate levels in karst aquifers have caused many public water suppliers to pursue additional water treatment or to dig deeper wells.

Minnesota Department of Agriculture nitrate monitoring suggests that over 9,200 karst region residents are at risk of consuming water that contains over 10 milligrams of nitrate per liter. Those tests showed 12.1% of private wells in the region exceeded that limit. Such levels can lead to colorectal cancer, thyroid disease, neural tube defects and a sometimes-fatal condition in infants called methemoglobinemia.

Because of the nitrate contamination found in many wells in southeastern Minnesota, 11 Minnesota environmental groups sent a petition to the Environmental Protection Agency (EPA) in April 2023. They urged the EPA to use its emergency authority to address the danger that nitrate in the region poses to human health.

On Nov. 3, the EPA sent a letter to Minnesota state commissioners of the agriculture and health departments and the state Pollution Control Agency requesting immediate plans be implemented to ensure the nitrate contamination crisis is taken care of. By early December, the EPA wants the state to have a plan on how to identify, contact, conduct drinking water testing and offer alternate water to impacted persons in the karst region. The letter mostly regards immediate actions but also insists the state develops a long-term solution to lowering nitrate concentrations in drinking water supplies.

Debra Shore, the EPA Region 5 administrator, suggested that Minnesota adopt more "protective permits for wastewater and large animal feedlots, and stronger guidelines for applying manure and fertilizer to fields."

Minnesota's First District U.S. Rep. Brad Finstad has slammed the EPA, claiming it's "targeting Minnesota family farmers at the behest of environmental extremists."

However, farmers already implement, and can continue to implement, practices that reduce nitrate runoff. One such practice is planting perennial cover crops. Cover crops lower the erosion rate of soil and nutrients and can decrease nitrogen runoff by 70% according to a study done by agronomists at Iowa State University. Cover crops also build back organic matter in soil and improve crop yields over time.

The EPA lists other farming practices that also reduce nitrogen runoff, including minimum tillage practices and wood chip bioreactors in drainage ditches. Among the most effective is buffer stripping. Grass buffer strips between cropland and water sources absorb and filter nutrients, thus reducing sediment, nutrient and pollutant runoff into waterways.

According to the USDA, one acre of buffer land stops 2.5 tons of soil, 6.4 pounds of nitrogen and 1.1 pounds of phosphorus from being lost to runoff. When farmers implement buffer strips through the Conservation Reserve Program (CRP), they even receive financial benefits and a continuous acre rental rate from the program.

Since Gov. Mark Dayton created a buffer strip mandate in 2015, compliance has increased from 87.2% in 2017 to 99.6% in 2023. The hard work that farmers and government officials did at the local level to follow the mandate led to its overall success. However, nitrate contamination is still a problem. The success of the buffer mandate shows that state government and farmers can take the lead again in setting guidelines to further stop nitrates from contaminating groundwater in the karst region.

Lydia Gillis, of Kasson, Minn., is a student at Gustavus Adolphus College.