A105-02
CH4 and CO2 fluxes from stream and river networks in the Midwest

Thursday, 10 December 2020: 17:33
Virtual
Ashish Singh, Minneapolis, MN, United States, Zhongjie Yu, University of Minnesota, Minneapolis, MN, United States, Malte Julian Deventer, University of California Berkeley, Berkeley, CA, United States, John M Baker, USDA ARS, Saint Paul, MN, United States, Matt D Erickson, University of Minnesota Twin Cities, Department of Soil, Water, and Climate, St Paul, MN, United States, Dylan B Millet, University of Minnesota Twin Cities, St Paul, MN, United States and Timothy J Griffis, Univ Minnesota, Saint Paul, MN, United States
Abstract:
Rivers and streams play an important role in carbon (C) budgets as they transport large quantities of C from upstream and terrestrial sources to coastal and aquatic reservoirs. In this study, we broadly explore the extent of C-evasion in the Midwest from stream and river network from one of the highly perturbed agriculture land use in the world. Here we present the temporal and spatial distribution of CH4 and CO2 and dissolved concentrations and fluxes from a stream and river network in the Cannon River Catchment (~1500 mi2) in Southern Minnesota.Approximately 65 stream and river sites of different stream order in the Cannon River Watershed was sampled using a floating chamber, and headspace measurement in four sampling cycles from April to December 2019.Ubiquitous and wide-range of supersaturation were observed for dissolved CH4 (1.52 to >105), and CO2 (7.11 to 103). Headwater streams showed the highest concentration and flux (CH4:0.07-6261 nmol m-2 s-1; CO2:4.3-39.5 µmol l-1) across the stream and sampling months; the distribution of CO2 followed an exponential decrease with stream order, in contrast to CH4 which showed a variable distribution across stream order. Apart from likely terrestrial input of CH4, high dissolved CH4 in streams in this region could be associated with in-situ production in the river sediment. CH4 hotspots streams were mainly characterized by wetland influence and showed a significant association with dissolved organics and oxygen. Based on our flux measurements in the streams and rivers, the annual emission estimate of CH4, and CO2 were approximately 37 Gg yr-1, and 20 Tg yr-1 in the Midwest. CH4 seasonable breakdown of the emission showed the highest emission in the spring (~11 Gg) and early summer months (~12 Gg) and a substantial drop in the late summer and fall/winter months.
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