Reaching rivers as nitrous oxide slings

Excessive river systems release three times more nitrous oxide as protected by the IPCC

Yangtze River - China's largest river © USGS
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Earth's rivers release three times as much nitrous oxide into the atmosphere as the IPCC estimates. This emerges from a study now published in the "Proceedings of the National Academy of Sciences" (PNAS). According to this, rivers are the source of at least ten percent of the total anthropogenic emissions of the strong greenhouse gas. The main cause is the increased fertilization of agricultural soils.

Nitrous Oxide, chemical dinitrogen monoxide, is a potent greenhouse gas: its greenhouse effect in the atmosphere is 298 times that of carbon dioxide. It is caused by bacterial activity in the process of so-called denitrification as a degradation product of nitrate in soil or water. In the last century, the concentration of nitrous oxide in the atmosphere has increased by 20 percent and continues to increase at a rate of 0.2 to 0.3 percent per year. Climatologists estimate that nitrous oxide accounts for about six percent of anthropogenic climate change. In addition, the gas damages the ozone layer of the earth.

"Human activity, including the use of fossil fuels and intensive agriculture, has increased the availability of nitrogen in the environment, " explains Jake Beaulieu of the University of Notre Dame. "Much of this nitrogen is being fed into rivers and aquifers, where it can be converted into nitrous oxide by the activity of microbes, a potent greenhouse gas."

Far more nitrous oxide than expected

To determine the amount of nitrous oxide emitted by the waters, Beaulieu and scientists from various American research institutes have measured dinitrogen monoxide production in 72 rivers in different landforms. The results were then incorporated into a global flow model.

The result was clear: it shows that the rivers as source of nitrous oxide have so far been underestimated. "Although more than 99 percent of the denitrified nitrogen in the rivers is converted to inert nitrogen gas, the flux systems still account for at least 10 percent of the global anthropogenic nitrous oxide emissions, " said Stephen Hamilton of Michigan State University. display

Fertilization and urban areas as nitrogen source

The increased production of nitrous oxide in the waters can be directly attributed to the increased use of nitrogen fertilizers and the cultivation of crops that support the soil's natural nitrogen fixation. These nitrogen compounds then enter the waters via the water cycle, where they are converted into nitrous oxide.

"This multi-site study clearly establishes rivers as an important source of nitrous oxide, " said Henry Gholz, head of the National Science Foundation's Environmental Research Department. This is especially the case for waters whose catchment areas are nitrogen enriched urbanized and agricultural areas. These new global emissions data are surprising

(National Science Foundation, 22.12.2010 - NPO)