Even if farmers stopped using nitrogen fertilizers today, levels of dangerous nitrates in rivers and lakes would remain high for decades, researchers report.
Canadian scientists analyzed more than 2,000 soil samples from the Mississippi River Basin and found an accumulation of nitrogen. This buildup was not evident in the upper “plow” layer, but instead was found 2 inches to 8 inches beneath the soil surface.
“We hypothesize that this accumulation occurred not only because of the increased use of fertilizers, but also increases in soybean cultivation and changes in tillage practices over the past 80 years,” researcher Kim Van Meter, a doctoral student at the University of Waterloo in Canada, said in a university news release.
Nitrogen fertilizers have been contaminating rivers and lakes and getting into drinking water wells for more than 80 years, the researchers said. Nitrates in drinking water pose a number of health risks, they added.
Their findings suggest that this nitrogen could still find its way into waterways decades after being applied to the fields.
The study was published March 15 in the journal Environmental Research Letters.
“A large portion of the nitrogen applied as fertilizer has remained unaccounted for over the last decades,” Nandita Basu, a Waterloo professor, said in the news release.
“The fact that nitrogen is being stored in the soil means it can still be a source of elevated nitrate levels long after fertilizers are no longer being applied,” Basu added.
The U.S. Centers for Disease Control and Prevention has more about drinking water.