In Minnesota, warning flags are up because harmful nitrates are contaminating surface waters and private wells. See McVan, Agriculture pollutes underground drinking water in Minnesota. Well owners pay the price. In April a formal petition was submitted to the U.S. EPA by the Minnesota Center for Environmental Advocacy (MCEA) and other environmental groups raising the alarm that nitrate contamination in southeastern Minnesota waters is an “imminent and substantial endangerment to public health.” Land applications of manure from animal feedlots and excessive use of nitrate fertilizers in this area must be reduced to protect public health.
The state’s health standard for nitrates in drinking water is 10 mg/L. Many wells exceed this level, but the state does not test nor does it oversee water quality of private drinking water wells. Studies suggest the standard should be reduced to 2 mg/L. There is some good news: nitrate levels in 96.7 % of public drinking water supplies are in the 0-3 mg/L range; less than 1% of public water supplies have 5-10 mg/L; and none exceed 10.
What about other waters – lakes, wetlands, and streams where a diversity of awe-inspiring underwater creatures depend on clean water? To date, the Minnesota Pollution Control Agency (MPCA) has no water quality standard for nitrates in surface waters – yet they have documented elevated nitrates in some streams, lakes and urban ponds. In 2010, the agency was given a state grant by the Legislature to create a water quality standard for nitrates in surface waters, but they didn’t.
In 2012 MPCA and other agencies produced a major report on nitrogen in Minnesota, but not about its environmental impacts. A stunning 158 million pounds of nitrates flow every year from Minnesota landscapes into the Mississippi River, 73% of this coming from agricultural sources – crop land and feed lots.
In 2022, MPCA water quality scientists released a comprehensive report in which they assembled and analyzed information from national scientific studies that tested the impacts of nitrates on various aquatic species. The agency’s review lists aquatic invertebrates impaired by nitrates: caddisfly, mayfly, and midge larvae are the most sensitive, followed by a crustacean amphipod, a freshwater mussel, a fingernail clam, tiny crustacean daphnia (my favorite) and a stonefly. Nitrates can impact or kill lake trout and other cold water fish, disrupt fish hormonal systems, harm frogs and freshwater mussel reproduction.
MPCA proposes a water quality standard for protecting aquatic life at 8 mg./L for most surface waters and 5 mg./L for cold waters. Let’s hope the Agency moves forward in its rule-making process and monitors state waters sooner rather than later. Stay tuned.
Why isn’t agricultural runoff regulated under the Federal Clean Water Act (CWA)?
In my view, discharges from tiled farm land across the state should be regulated to protect all waters of the state. In many ways, industrial agriculture has been ‘off the hook,’ not responsible for its impacts. As said, 73% of Minnesota’s annual 150 million pounds of nitrates released into the Mississippi comes from agricultural land. The big elephant in the room is a clause in the Clean Water Act that states it regulates point source discharges of pollutants, namely wastewater treatment plants and industries that discharge into rivers, but not non-point pollutants that flow off the landscape. This ties the hands of state water pollution regulators. Nonpoint source pollution is the biggest threat to water quality in the United States today, said one scientist in the Ecology Law Quarterly article “Realigning the Clean Water Act. Comprehensive Treatment of Nonpoint Source Pollution.”
Water-soluble nitrate seeps into groundwater. It is conducted by a vast network of underground tile lines, many installed decades ago in order to drain wetlands and create cropland. In southwestern Minnesota, an astonishing 95% of historic wetlands were drained. Those of us who love wetlands and the beauty of the life they support can’t help grieving the loss. The drainage continues. The extensive underground networks of tiles convey wetland water to collecting pipes which discharge into ditches and streams. This is “point source” and should be regulated and monitored by the MPCA under the Clean Water Act.
Globally, excessive agricultural use of nitrogen has exceeded “planetary boundaries” (Nature, 2022); this continues to worsen the Dead Zone in the Gulf of Mexico, where tens of thousands of dead fish recently washed on shore in Texas. Action is needed on local, state and national levels because nitrates keep increasing in surface waters and in private drinking water wells. I applaud the dedicated people who are working hard to raise awareness and protect our waters.
Judy Helgen is a retired research scientist from the Minnesota Pollution Control Agency. She worked on biological monitoring of wetlands water quality based on aquatic invertebrate communities and led the investigation into widespread deformed frogs. She lives in Falcon Heights.