Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra watersheds: Evidence from analysis of stable isotopes

• Published in: Global Biogeochemical Cycles
• Main Authors: Throckmorton, Heather M., Heikoop, Jeffrey M., Newman, Brent D., Altmann, Garrett L., Conrad, Mark S., Muss, Jordan D., Perkins, George B., Smith, Lydia J., Torn, Margaret S., Wullschleger, Stan D., Wilson, Cathy J.
• Language: unknown
• Published: 2023
• Subjects: 54 ENVIRONMENTAL SCIENCES; Arctic; Barrow; Tundra; Alaska
• Online Access: http://www.osti.gov/servlets/purl/1267037; https://www.osti.gov/biblio/1267037; https://doi.org/10.1002/2014GB005044

Arctic soils contain a large pool of terrestrial C and are of interest due to their potential for releasing significant carbon dioxide (CO 2 ) and methane (CH 4 ) to the atmosphere. Due to substantial landscape heterogeneity, predicting ecosystem-scale CH 4 and CO 2 production is challenging. This study assessed dissolved inorganic carbon (DIC = Σ (total) dissolved CO 2 ) and CH 4 in watershed drainages in Barrow, Alaska as critical convergent zones of regional geochemistry, substrates, and nutrients. In July and September of 2013, surface waters and saturated subsurface pore waters were collected from 17 drainages. Based on simultaneous DIC and CH 4 cycling, we synthesized isotopic and geochemical methods to develop a subsurface CH 4 and DIC balance by estimating mechanisms of CH 4 and DIC production and transport pathways and oxidation of subsurface CH 4 . We observed a shift from acetoclastic (July) toward hydrogenotropic (September) methanogenesis at sites located toward the end of major freshwater drainages, adjacent to salty estuarine waters, suggesting an interesting landscape-scale effect on CH 4 production mechanism. The majority of subsurface CH 4 was transported upward by plant-mediated transport and ebullition, predominantly bypassing the potential for CH 4 oxidation. Thus, surprisingly, CH 4 oxidation only consumed approximately 2.51± 0.82% (July) and 0.79 ± 0.79% (September) of CH 4 produced at the frost table, contributing to <0.1% of DIC production. DIC was primarily produced from respiration, with iron and organic matter serving as likely e- acceptors. Furthermore, this work highlights the importance of spatial and temporal variability of CH 4 production at the watershed scale and suggests broad scale investigations are required to build better regional or pan-Arctic representations of CH 4 and CO 2 production.