CHARACTERIZING ORGANIC MATTER AVAILABILITY AND ITS POTENTIAL LINK TO THE METHANE CYCLE IN THERMOKARST LAKES

In northern latitudes, thawing permafrost leads to the formation of thermokarst lakes, surrounded by a thawed zone (talik), in which anoxic conditions prevail. Under these conditions, methane is produced by microorganisms (methanogenesis). Organic matter serves as a substrate in one of the two methanogenesis pathways. It can also act as an electron acceptor or shuttle, enabling more efficient metabolic pathways alongside methane oxidation, mitigating methane emissions. This research aims to characterize the availability of organic matter for microbial degradation in thermokarst settings and its potential link to the methane cycle. Three 5-m cores were extracted from the talik near a thermokarst lake, from: (1) lake sediments, (2) lake margin, and (3) lake terrace. Porewater was analyzed for chemical composition and dissolved organic carbon (DOC). Sediment was collected for total soil organic carbon (SOC) characterization, and incubation experiments were conducted to measure methane accumulation rates. Methanogenesis was dominant in depths greater than 2 meters in the margin and terrace, while in the lake's sediments, it prevailed across the profile, with higher methane accumulation rates in shallow depths. Low DOC freshness index values suggest that DOC is mainly derived from leaching of SOC. At shallow depths in the lake's margin, root exudates may contribute to a "fresher" DOC pool and provide oxygen, which suppresses methanogenesis. Also, a correlation between SOC fractions and methanogenesis rates offers insight into methane emissions during lake evolution.

Presentation Preference: Poster

Primary Presenter: Oren Magori Cohen, Ben-Gurion University of the negev (orenmag@post.bgu.ac.il)

Authors:

Oren Magori Cohen, Ben-Gurion University of the negev  (orenmag@post.bgu.ac.il)

André Pellerin, Institut des sciences de la mer, Université du Québec à Rimouski  (AndrePierre_Pellerin@uqar.ca)

Katey Walter-Anthony, Water and Environmental Research Center, University of Alaska Fairbanks  (kmwalteranthony@alaska.edu)

Nicholas Hasson, Water and Environmental Research Center, University of Alaska Fairbanks  (nhasson@alaska.edu)

Sarah Johnston, University of Alaska Fairbanks  (sejohnston2@alaska.edu)

Efrat Eliani-Russak, Ben Gurion University of the Negev  (elianief@bgu.ac.il)

Yarden Gerera, Ben-Gurion University of the negev  (yardenge@post.bgu.ac.il)

Paige Kehoe, University of Alaska Fairbanks  (pkehoe2@alaska.edu)

Orit Sivan, Ben Gurion University of the Negev  (oritsi@gmail.com)