Minnesota State Wire

A recent study conducted by the Minnesota Department of Agriculture, the University of Minnesota’s Minnesota Geological Survey, and the Minnesota Department of Natural Resources has provided insights into groundwater age and nitrate trends in southeastern Minnesota's Driftless Area.

The study analyzed current concentrations of a discontinued herbicide from the 1970s and 1980s found in springs and wells. Researchers compared this data with historical herbicide use, using independent age-dating methods to determine that groundwater ages range from 10 to 40 years old in many shallower springs and wells, to thousands of years old in deeper aquifers.

By combining groundwater ages with historical land use data and climate information, researchers interpreted nitrate concentration trends between 2000-2021 for nearly 1,200 monitoring locations. The findings indicated that most sites with elevated nitrate levels had groundwater less than 20 years old, where nitrate levels were either decreasing or stable. Improved agricultural practices and record-setting precipitation over two decades might have influenced these results. Older groundwater showed lower nitrate concentrations but had a higher chance of increasing trends as contaminated water moved into deeper systems.

The authors emphasized that while it may take decades to observe clean water activities' impact on certain aquifers, best management practices implemented today will eventually reduce nitrate entry into groundwater.

The study is published in the Hydrogeology Journal. Funding was provided by various sources including Minnesota’s Clean Water, Land and Legacy Amendment, MDA’s Pesticide Regulatory Account, Root River Field to Stream Partnership, the Minnesota Environment and Natural Resources Trust Fund, legislative appropriation to the Minnesota Geological Survey, and the University of Minnesota.