title: Winter precipitation and snow accumulation drive the methane sink or source strength of Arctic tussock tundra.
abstract: Arctic winter precipitation is projected to increase with global warming, but some areas will experience decreases in snow accumulation. Although Arctic CH4 emissions may represent a significant climate forcing feedback, long-term impacts of changes in snow accumulation on CH4 fluxes remain uncertain. We measured ecosystem CH4 fluxes and soil CH4 and CO2 concentrations and (13) C composition to investigate the metabolic pathways and transport mechanisms driving moist acidic tundra CH4 flux over the growing season (Jun-Aug) after 18 years of experimental snow depth increases and decreases. Deeper snow increased soil wetness and warming, reducing soil %O2 levels and increasing thaw depth. Soil moisture, through changes in soil %O2 saturation, determined predominance of methanotrophy or methanogenesis, with soil temperature regulating the ecosystem CH4 sink or source strength. Reduced snow (RS) increased the fraction of oxidized CH4 (Fox) by 75-120% compared to Ambient, switching the system from a small source to a net CH4 sink (21 ± 2 and -31 ± 1 mg CH4  m(-2)  season(-1) at Ambient and RS). Deeper snow reduced Fox by 35-40% and 90-100% in medium- (MS) and high- (HS) snow additions relative to Ambient, contributing to increasing the CH4 source strength of moist acidic tundra (464 ± 15 and 3561 ± 97 mg CH4  m(-2)  season(-1) at MS and HS). Decreases in Fox with deeper snow were partly due to increases in plant-mediated CH4 transport associated with the expansion of tall graminoids. Deeper snow enhanced CH4 production within newly thawed soils, responding mainly to soil warming rather than to increases in acetate fermentation expected from thaw-induced increases in SOC availability. Our results suggest that increased winter precipitation will increase the CH4 source strength of Arctic tundra, but the resulting positive feedback on climate change will depend on the balance between areas with more or less snow accumulation than they are currently facing.
authors: Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, 60607, USA.
authors: Elena
authors: E
authors: Blanc-Betes
authors: Department of Biological Sciences, University of Alaska, Anchorage, Anchorage, AK, 99501, USA.
authors: Jeffrey M
authors: JM
authors: Welker
authors: Department of Geological Sciences, University of Delaware, Newark, DE, 19716, USA.
authors: Neil C
authors: NC
authors: Sturchio
authors: Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL, 32306, USA.
authors: Jeffrey P
authors: JP
authors: Chanton
authors: Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, 60607, USA.
authors: Miquel A
authors: MA
authors: Gonzalez-Meler
mesh_terms: D001110:Arctic Regions; D057231:Climate Change; D008697:Methane / Q000032:analysis*; D012621:Seasons; D012914:Snow; D012987:Soil; D065929:Tundra
chemical_list: D012987:Soil; D008697:Methane
keywords: Arctic; isotope; methane; methanogenesis; methanotrophy; snow accumulation; temperature; tundra