New research suggests that streams near farms emit high levels of greenhouse gas

Streams in agricultural regions are emitting significant amounts of nitrous oxide, a potent greenhouse gas, according to new research led by Zhongjie Yu, a hydrologist at the University of Illinois Urbana-Champaign. In a recent study conducted in the upper reaches of a Minnesota watershed, Yu found that the water contained levels of dissolved nitrous oxide tens of thousands of times higher than what would be expected under normal atmospheric conditions.

Yu, an assistant professor in the Department of Natural Resources and Environmental Sciences, and his team have published two papers highlighting that the majority of these emissions are derived from nitrification processes in agricultural soils. This phenomenon contributes to a larger portion of the annual nitrous oxide budget than previously estimated.

Traditionally, nitrous oxide emissions have been measured directly from the soil. However, Yu’s research points to significant emissions from streams and rivers that receive nitrogen runoff from agricultural lands. “Focusing only on soil emissions does not account for the nitrous oxide lost to downstream ecosystems,” Yu explained. His studies suggest that these indirect emissions could constitute up to one-third of total emissions in the Corn Belt region.

Agriculture is a well-known source of nitrous oxide, which is nearly 300 times more effective at trapping heat than carbon dioxide and remains in the atmosphere for long periods. The process typically begins when nitrogen-based fertilizers are applied to fields. While some of the nitrogen is absorbed by crops, a significant portion can be washed into nearby waterways or transformed into nitrous oxide by soil microbes.

Yu’s findings indicate that the conventional approach of measuring nitrous oxide emissions might underestimate the contribution from streams and rivers. By improving our understanding of these indirect pathways, more accurate regional emission inventories can be developed, aiding in the design of effective mitigation strategies.

The research also identified critical periods and locations for nitrous oxide emissions, such as following heavy rainfall or snowmelt and in areas with strong hydrological connections between soils and streams. Yu stressed the importance of targeted mitigation efforts during these times.

In addition to practical implications for agricultural management, the study underscores the need for holistic approaches that consider both nitrogen and water cycles. This could include practices like using winter cover crops or controlled irrigation to reduce leaching and enhance water quality, which may also help in lowering greenhouse gas emissions.

The findings from these studies, supported by the National Science Foundation and other international funding bodies, have been published in Environmental Science & Technology and Geophysical Research Letters. Further research will continue across a network of seven towers to gain a broader understanding of the regional impact of these emissions.