The Impact of Fire, Landscape Position, and Nitrogen Availability on Carbon Dioxide and Methane Emissions in the Yukon-Kuskokwim Delta, Alaska

Over the past few decades, warming temperatures in the Arctic have resulted in increased permafrost thaw and more frequent and severe fires. Both of these climate change induced issues have the potential to increase nitrogen availability in arctic tundra, which may have important implications for microbial decomposition and greenhouse gas emissions. Many questions remain, however, on the effect of nitrogen on greenhouse gas emissions in this region. To enhance our understanding, we measured carbon dioxide and methane fluxes as well as the extractable concentrations of nitrogen in soil and water from burned (2015) and unburned peat plateau tundra, fens, and pond surface water in the Yukon Kuskokwim Delta, Alaska. Additionally, to better focus on nitrogens effect on carbon dioxide (CO2) and methane (CH4) production, we conducted nitrogen addition experiments in aerobic and anaerobic soil incubations. We also examined the potential for additional nitrogen inputs from thawing permafrost by measuring extractable nitrogen along a permafrost depth profile ( 1m) from burned and unburned areas. Both CH4 emissions and extractable nitrogen concentrations were highest in saturated, lowland regions. The 2015 burn reduced CO2 from soil respiration in upland areas, but there was no detectable effect of fire on CO2 or CH4 fluxes from wetlands or ponds. Across landscape positions, both CO2 and CH4 emissions were significantly positively correlated with the concentration of extractable ammonium found in the corresponding soils. These results highlight the importance of nitrogen and landscape position in driving nitrogen availability and carbon emissions from tundra landscapes. If nitrogen availability increases in tundra as the climate warms, this may stimulate microbial activity and lead to enhanced emissions of greenhouse gasses, CO2 and CH4.