title: Indirect nitrous oxide emissions from streams within the US Corn Belt scale with stream order.
abstract: N2O is an important greenhouse gas and the primary stratospheric ozone depleting substance. Its deleterious effects on the environment have prompted appeals to regulate emissions from agriculture, which represents the primary anthropogenic source in the global N2O budget. Successful implementation of mitigation strategies requires robust bottom-up inventories that are based on emission factors (EFs), simulation models, or a combination of the two. Top-down emission estimates, based on tall-tower and aircraft observations, indicate that bottom-up inventories severely underestimate regional and continental scale N2O emissions, implying that EFs may be biased low. Here, we measured N2O emissions from streams within the US Corn Belt using a chamber-based approach and analyzed the data as a function of Strahler stream order (S). N2O fluxes from headwater streams often exceeded 29 nmol N2O-N m(-2) ⋅ s(-1) and decreased exponentially as a function of S. This relation was used to scale up riverine emissions and to assess the differences between bottom-up and top-down emission inventories at the local to regional scale. We found that the Intergovernmental Panel on Climate Change (IPCC) indirect EF for rivers (EF5r) is underestimated up to ninefold in southern Minnesota, which translates to a total tier 1 agricultural underestimation of N2O emissions by 40%. We show that accounting for zero-order streams as potential N2O hotspots can more than double the agricultural budget. Applying the same analysis to the US Corn Belt demonstrates that the IPCC EF5r underestimation explains the large differences observed between top-down and bottom-up emission estimates.
authors.affiliation: Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108; turne289@umn.edu.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Turner
authors.affiliation: Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108;
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Griffis
authors.affiliation: School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511; Yale-Nanjing University of Information, Science and Technology Center on Atmospheric Environment, Nanjing University of Information, Science and Technology, Nanjing, Jiangsu Province 210044, China;
authors.forename: Xuhui
authors.initials: X
authors.lastname: Lee
authors.affiliation: Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108; US Department of Agriculture-Agricultural Research Service, St. Paul, MN 55108.
authors.forename: John M
authors.initials: JM
authors.lastname: Baker
authors.affiliation: Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108; US Department of Agriculture-Agricultural Research Service, St. Paul, MN 55108.
authors.forename: Rodney T
authors.initials: RT
authors.lastname: Venterea
authors.affiliation: Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108;
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Wood
keywords: IPCC emission factors; aquatic nitrous oxide fluxes; regional emission upscaling; river emission hotspots