DES MOINES (AP) — Nitrate levels in Iowa rivers have soared since the 1950s, though recent efforts to control the spread of the fertilizer byproduct appear to be helping, research shows.
The Des Moines Register reported Sunday that nitrate levels have more than tripled between the 1950s and 2010, from an average of around 2 milligrams per liter from 1906-1954 to more than 7 milligrams per liter from 1954-2010. The federal standard is to have no more than 10 milligrams of nitrates per liter of water.
“It’s unmistakable. The long-term trend is decidedly upward,” said Keith Schilling, who studies nitrate levels for the Iowa Geological Survey at the University of Iowa.
But despite that increase, the levels have shown signs of ebbing more recently as farmers began to employ conversation practices that help keep nitrates out of rivers and streams, the newspaper reported, citing an analysis of water-quality research.
Bill Stowe, CEO of Des Moines Water Works, said the upstream counties need to take responsibility for their role in the elevated nitrate levels.
“We believe those districts have completely shirked their responsibility” over their contribution to nitrate levels in the Raccoon River, he said. “You can’t sidestep that and say, ‘Oh, there are diluted impacts beneath us, so we can do what we want.’”
Chris Jones, an environmental specialist with the Iowa Soybean Association, said farm groups generally support working together to find a solution to the state’s nitrate concerns instead of resorting to lawsuits.
Farm groups, including the Soybean Association, acknowledge that nitrate levels have generally increased over the years. But the data also shows little change in nitrate levels between 1984 and 2014, and slight improvement when measuring from 1994 and 2004, Jones said.
Research also shows that some of the things that help make Iowa farms so productive also make it easier for nitrates to spread.
Iowa naturally has high levels of nitrogen and other organic material in the soil. Some of that is lost every year, and it is easier for nitrates to wash away when there aren’t any plants in the field to absorb them.
High organic soil matter is “one of the reasons why we have such high production in Iowa,” Iowa State University professor Michael Castellano said. “It’s also one of the reasons we have nitrate losses.”