WASHINGTON, Nov. 4, 201 5- In the 35-year period following World War II, intensive farming in the Midwest increased nitrate levels in rivers in the region by up to 500 percent, according to a new U.S. Geological Survey (USGS) study. And despite the work farmers have done to reduce nitrogen applications in recent years, USGS researchers found “no widespread improvement” in nitrate concentrations at collection points on 22 major U.S. rivers.
Agri-Pulse talked with the study’s lead author, Edward Stets, a research biologist for USGS, who said even though the volume of nitrogen running off of farms into waterways has mostly plateaued, high nitrogen concentrations in rivers persist. In most basins, fertilizer and livestock nitrogen input peaked toward the end of the period 1945-1980 and has been static or declining slightly since then. The long-established goal has been to reduce nitrogen levels in rivers, but “that doesn’t seem to be happening, at least not at the scale we looked at,” he said.
According to a release, the report found that between 1945 and 1980, when farmers in some of the country’s most prolific agricultural states in the Midwest were “rapidly” increasing their use of manure and synthetic fertilizers, nitrate levels in tributaries flowing into the Great Lakes and the Mississippi River basin were also climbing.
Excess nitrogen in the water could present health risks to humans and cause hypoxia – low oxygen levels in the water – that often kills oxygen-dependent aquatic species and accelerates the growth of algal blooms.
The study also looked at water quality in coastal waters adjacent to more urbanized areas, such as Long Island Sound, the Delaware River estuary, Chesapeake Bay, San Francisco Bay and the Gulf of Mexico. In some of these waters, the study identified a doubling of nitrate levels over the same post-war 35-year period, which it mostly attributed to industrial point sources. Point sources, as opposed to non-point sources like farms, have been regulated heavily since 1973 when enforcement of the Clean Water Act began.
USGS says increases in river nitrate levels have become less dramatic since 1980 because increases in fertilizer use slowed across the Midwest. As agricultural production has become less reliant upon fertilizer inputs to achieve greater production, nitrate concentration has ceased increasing, the study points out.
USGS monitors long-term water quality through the National Water-Quality Program, and is now shifting its focus to the last 15 years of water quality trends in small and large rivers nationally. Stets said this leg of research, due out in 2018 at the latest, would be “more detailed,” and would use “more sophisticated modeling” that could turn up clues as to how specific initiatives within the agricultural community are helping or hurting water quality.
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