Nitrous Oxide Emissions From US Corn Belt Greatly Underestimated
The emissions of nitrous oxide, a potent greenhouse gas, from agricultural operations in the central United States may be greatly underestimated, and in some instances are as much as 40% higher than previously thought, according to a new study.
A recent study of the indirect emissions of nitrous oxide from agriculture, which was led by scientists from the University of Minnesota, measured how much of the greenhouse gas (also implicated in stratospheric ozone depletion) was emitted from streams in “an agriculturally dense area” located in southern Minnesota. Nitrous oxide is said to be almost 300 times more potent (by weight) as a greenhouse gas than carbon dioxide, and agriculture is a leading source for nitrous oxide emissions, which can happen both directly (nitrogen fertilizer and manure applications) and indirectly (runoff and leaching of fertilizers into waterways).
According to the University of Minnesota (UMN), the measurement of nitrous oxide emissions at the University’s Tall Tower Trace Gas Observatory gives researchers a “top-down” look at regional emissions, and “bottom-up” measurements for nitrous oxide provide an on-the-ground view of the issue. But “very large differences” between the two measurements have indicated “large uncertainties” that could undermine the development of appropriate mitigation practices for nitrous oxide emissions. The difference, it appears, may be from not accounting for the nitrous oxide emissions from streams and stream networks, and for the variations in the size and flow of these waterways.
The results of the study, titled Indirect nitrous oxide emissions from streams within the US Corn Belt scale with stream order, indicated that calculations of nitrous oxide emissions have been underestimated by the Intergovernmental Panel on Climate Change (IPCC) by as much as 40%, and that by integrating the methodology used by the study, “much of the difference” between the top-down and bottom-up measurements can be resolved.
“Nitrous oxide emissions from rivers have been an overlooked and uncertain source because the variability in stream sizes and land-use types has made an accurate estimation difficult. We identified an important relationship between the size of the stream and its potential to emit nitrous oxide that can be used to scale up emission estimates. Understanding the riverine nitrous oxide source is an important step forward for understanding the global nitrous oxide budget.” – Peter Turner, one of the study’s authors and PhD candidate in UMN’s Department of Soil, Water, and Climate
While this study informed the scientists of the local scope of agricultural nitrous oxide emissions, the team acknowledges that confirmation is needed of nitrous oxide degassing in drainage channels in other agricultural regions such as India and China, where intensive application of nitrogen fertilizers occurs.
Image: eutrophication&hypoxia
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