Spatial and Temporal Variation in Methane Concentrations, Fluxes, and Sources in Lakes in Arctic Alaska

摘要

Climate warming may lead to a positive feedback of increased emissions of CH4 from sediments beneath Arctic lakes, but the contribution of these lakes to the global CH4 budget is poorly quantified. Here we present results of a study of CH4 concentrations and sources from a series of 50 lakes in Arctic Alaska across an 80,000km(2) spatial gradient and a 2year time period. We measured dissolved CH4 concentrations and stable isotopes of CH4 in lakes in the North Slope of Alaska in August 2014 and 2015 and April 2015 (under ice). Stable isotopes indicated that biogenic CH4 dominated versus thermogenic sources, with both acetate fermentation and carbonate reduction sources. Dissolved CH4 was about 100 times higher under the ice than during the summer, indicating that the spring ice off period is a large source of atmospheric CH4. Open-water dissolved CH4 concentrations had a negative relationship with latitude in both years of our study, although CH4 fluxes were consistent among a subset of lakes measured along a similar to 150km north to south transect in both years (14 lakes in 2014 and 12 in 2015). Dissolved CH4 concentrations and fluxes were significantly higher in August 2015 versus August 2014, concurrent with a 3 degrees C higher mean water temperature in 2015 versus 2014. Much longer-term monitoring is needed, however, to conclude that CH4 emissions from Arctic lakes mirror observed warming trends. This study provides valuable baseline data and can inform methods for future studies investigating carbon cycle-climate change feedbacks in Alaskan Arctic lakes.