Highest methane concentrations in an Arctic river linked to local terrestrial inputs

[摘要] Large amounts of methane ( CH 4 ) could be released as a result of thegradual or abrupt thawing of Arctic permafrost due to global warming. Onceavailable, this potent greenhouse gas is emitted into the atmosphere ortransported laterally into aquatic ecosystems via hydrologic connectivity atthe surface or via groundwaters. While high northern latitudes contribute upto 5 % of total global CH 4 emissions, the specific contribution ofArctic rivers and streams is largely unknown. We analyzed high-resolutioncontinuous CH 4 concentrations measured between 15 and 17 June 2019(late freshet) in a ∼120  km transect of the Kolyma River innortheast Siberia. The average partial pressure of CH 4 ( p CH 4 ) intributaries (66.8–206.8  µatm ) was 2–7 times higher than in themain river channel (28.3  µatm ). In the main channel, CH 4 was upto 1600 % supersaturated with respect to atmospheric equilibrium. Keysites along the riverbank and at tributary confluences accounted for 10 %of the navigated transect and had the highest p CH 4 (41  ±  7  µatm ) and CH 4 emissions (0.03  ±  0.004  mmol m - 2 d - 1 )compared to other sites in the main channel, contributing between 14 % to 17 % of the total CH 4 flux in the transect. These key sites werecharacterized by warm waters ( T >14.5   ∘ C ) and lowspecific conductivities ( κ <88   µS cm −1 ). Thedistribution of CH 4 in the river could be linked statistically to T and κ of the water and to their proximity to the shore z , and theseparameters served as predictors of CH 4 concentrations in unsampledriver areas. The abundance of CH 4 -consuming bacteria and CH 4 -producing archaea in the river was similar to those previouslydetected in nearby soils and was also strongly correlated to T and κ . These findings imply that the source of riverine CH 4 is closelyrelated with sites near land. The average total CH 4 flux density in theriver section was 0.02  ±  0.006  mmol m - 2 d - 1 , equivalent to anannual CH 4 flux of 1.24×10 7   g CH 4  yr −1 emitted during a 146 d open water season. Our study highlights theimportance of high-resolution continuous CH 4 measurements in Arcticrivers for identifying spatial and temporal variations, as well as providinga glimpse of the magnitude of riverine CH 4 emissions in the Arctic andtheir potential relevance to regional CH 4 budgets.

[学科分类] 大气科学