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ARS Home » Midwest Area » St. Paul, Minnesota » Soil and Water Management Research » Research » Publications at this Location » Publication #410679

Research Project: Developing Aspirational Practices Through Improved Process Understanding to Protect Soil and Air Resources and Increase Agricultural Productivity in the Upper Midwest U.S.

Location: Soil and Water Management Research

Title: Hydrologic connectivity regulates riverine N2O sources and dynamics

item HU, MINPENG - University Of Illinois
item YU, ZHONGJIE - University Of Illinois
item GRIFFIS, TIMOTHY - University Of Minnesota
item YANG, WENDY - University Of Illinois
item MOHN, JOACHIM - Swiss Federal Institute
item MILLET, DYLAN - University Of Minnesota
item Baker, John
item WAN, DONGQI - Beijing Normal University

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2024
Publication Date: 5/23/2024
Citation: Hu, M., Yu, Z., Griffis, T.J., Yang, W.H., Mohn, J., Millet, D.B., Baker, J.M., Wan, D. 2024. Hydrologic connectivity regulates riverine N2O sources and dynamics. Environmental Science and Technology. 58(22):9701-9713.

Interpretive Summary: Nitrous oxide (N2O) is a greenhouse gas that is nearly 300 times more potent permolecule than CO2. Agriculture is the primary source, but there is much uncertainty about the relative importance of direct (in field) emissions versus indirect emissions, which are those that occur beyond the field, due to nitrate losses to streams and volatile losses from fields that deposit elsewhere before subsequent transformation to N2O. In particular, there is evidence that losses from streams and water bodies may be much larger than has been previously assumed. Here we report extensive sampling of streams in an agricultural waterahed in southern MN that were subjected to isotopic analysis to determine the process(es) by which the N2O in each sample was produced. Results indicate that spatial and seasonal differences were strongly influenced by the degree of landscape connectivity in water flow paths from field to stream. Based on these results, a new conceptual framework has been proposed to guide improved modeling of N2O emissions.

Technical Abstract: Indirect emissions of nitrous oxide (N2O) from streams and rivers are a poorly constrained term in the global N2O budget due to the complex biogeochemical and hydrological processes that underlie these emissions. Current global models of riverine N2O emissions place a strong focus on denitrification in groundwater and riverine environments as a major driver of N2O emissions from stream and river systems. Here, we combine synoptic N2O isotopocule measurements and spatial stream network modeling to show that terrestrial-aquatic interactions driven by changing hydrologic connectivity play an important role in regulating riverine N2O sources and dynamics in a mesoscale agricultural river network. We find that N2O produced from nitrification constituted a substantial fraction (i.e., > 30%) of riverine N2O across the entire river network. Moreover, riverine N2O concentrations and source mechanisms were largely modulated by landscape processes that operated at multiple spatial scales and were responsive to different flow regimes. Based on these results, we propose a conceptual framework that emphasizes stream-landscape connectivity as a dominant control of N2O dynamics along the stream continuum. More realistic model predictions of global riverine N2O emission will require a better understanding of this connectivity under variable hydroclimatic conditions.