Fertilizer runoff from farms contributes to global warming

Hampshire County

Mechanics of how rivers, bearing increased loads of nitrogen, emit greenhouse gasses revealed by UMass Amherst Researcher

AMHERST, Mass. (WWLP) – Researchers at UMass Amherst released a study on how fertilizer runoff from farm fields is releasing nitrogen into rivers and streams.

The microbes in the water break the fertilizer down into nitrous oxide (N2O) is a potent greenhouse gas with 300 times the warming ability of carbon dioxide.

“Humans are fundamentally altering the nitrogen cycle,” says Matthew Winnick, sole author of the new paper, published recently in AGU Advances, and professor of geosciences at the University of Massachusetts Amherst. “We’ve changed how nitrogen moves through the environment.”

According to Winnick, the change can be attributed to enormous amounts of nitrogen-rich chemical fertilizers used at agricultural fields, which run off into streams and rivers when it rains, and get converted to nitrate. Scientists have known that microbes in the soil and streambed contribute to the “denitrification process,” whereby nitrate is converted to either harmless dinitrogen gas or N2O. But the exact mechanics of the conversion processes have remained a mystery, as evidenced by the wide range of N2O emissions estimates, somewhere between 0.5% and 10% of global emissions, annually attributable to streams.

An experiment by Winnick from 72 streams across the U.S. traced how nitrate moved from the stream to the streambed. In the discovery, the greater the streambed’s efficiency in converting nitrate, the less N2O is released. But where denitrification efficiency is low, Winnick found comparatively higher levels of N2O emissions.

Streambeds also play a role on how the nitrate is delivered or preventing the release of N2O with small anoxic zones, or patches starved of oxygen.

The new understanding of the nitrogen cycling could help inform efforts at climate-change mitigation.

If we were to stop using fertilizer today, it would still be in the environment for many years to come. However, if we reduce the amount of fertilizer that we are using each day, this would be a long term solution to reducing the amount of greenhouse gas that is put into the atmosphere. While this is great, a warming climate calls for an immediate solution.

“These engineering restoration solutions may be the only option for remediating a lot of these effects,” said Winnick. He says that now the next step will be to go out to streams and prove this research and show that it works.

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