Fertilizer runoff from farms contributes to global warming

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The mechanics of how rivers, carrying increased nitrogen loads, emit greenhouse gases revealed by UMass Amherst researcher

Fertilizer can run off agricultural fields and into rivers, potentially resulting in N2O emissions. Credit: vpopovic / E + / Getty Images

AMHERST, Mass. (WWLP) – Researchers at UMass Amherst have published a study on how fertilizer runoff from agricultural fields releases nitrogen into rivers and streams.

Microbes in the water break down the fertilizer into nitrous oxide (N2O) which is a powerful greenhouse gas with 300 times the warming capacity of carbon dioxide.

“Humans fundamentally alter the nitrogen cycle,” says Matthew Winnick, sole author of the new article, recently published in AGU Advances, and professor of geosciences at the University of Massachusetts at Amherst. “We have changed the way nitrogen moves through the environment.

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

An experiment by Winnick in 72 streams across the United States tracked how nitrate moved from creek to creek bed. Upon discovery, the greater the efficiency of the stream bed in converting nitrate, the less N2O is released. But where denitrification efficiency is low, Winnick found comparatively higher levels of N2O emissions.

Stream beds also play a role in how nitrate is delivered or prevent the release of N2O with small anoxic areas or oxygen starved plaques.

New understanding of the nitrogen cycle could help inform climate change mitigation efforts.

If we were to stop using fertilizers today, they would still be in the environment for many years. However, if we reduce the amount of fertilizer we use each day, that would be a long-term solution to reducing the amount of greenhouse gases released into the atmosphere. While this is great, global warming calls for an immediate solution.

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


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