Water Resources Research Act Program

Details for Project ID 2013AK119B

Surface water and sub-permafrost groundwater exchange effects on Alaska thermokarst-lake methane cycling

Institute: Alaska
Year Established: 2013 Start Date: 2013-03-01 End Date: 2014-02-28
Total Federal Funds: $13,446 Total Non-Federal Funds: $6,656

Principal Investigators: Katey WalterAnthony, Katey WalterAnthony

Project Summary: The proposed research addresses a critical water-related research problem in the State of Alaska: the exchange of surface and groundwater causing escape of water-born methane (CH4), a potent greenhouse gas, to the atmosphere as permafrost thaws beneath Alaska's lakes. This research integrates field studies in a range of disciplines (hydrology, limnology, climate, permafrost, and nutrient cycling) with laboratory tests of microbial processes that may help mitigate the problem of methane emissions from lakes as permafrost thaws. Methane, released in association with thawing permafrost, is one of the most important greenhouse gases expected to drive a positive climate feedback. Microbial production of methane from organic matter decomposition within anaerobic thaw bulbs (taliks) of thermokarst lakes is well known (Zimov et al. 1997, Walter et al. 2006), but the release of geologic methane (e.g. thermogenic methane from coal, petroleum, hydrates; or fossil microbial methane) produced beneath permafrost to the atmosphere through thermokarst lakes is less well documented. Recent observations of anomalously strong gas seeps of geologic origin in Alaska's thermokarst lakes (Walter Anthony et al. 2012) suggest that permafrost thaw, the development of through-going taliks and groundwater transport provide the means for the escape of geologic methane previously trapped by permafrost to the atmosphere. Discontinuous-permafrost thaw is sensitive to atmospheric warming particularly where warmer surface water and deeper ground groundwater exchange (Rowland et al. 2011), a hydrological process that accelerates permafrost thaw and increases the potential for sub-permafrost methane escape. The addition of this sub-permafrost geologic methane release to ecologic methane produced by microbes inside lake taliks exacerbates the permafrost-hydrology-methane climate feedback. However, other hydrological and microbial processes may work together to migitate the release of methane from Alaska's lakes. Oxidation of methane by microbes, potentially in conjunction with denitrification (microbial conversion of nitrate supplied by groundwater to N2), may reduce methane emissions from thermokarst lakes as surface-and ground-water sources mix. The net balance of methane production, oxidation, and atmospheric emission processes in scenarios of hydrologically open and closed talik lake systems is unknown. The objective of this study is to relate field and laboratory observations of methane cycling to the hydrological, thermal, biogeochemical, and geophysical character of two thermokarst lakes (open vs. closed talik) in the discontinuous permafrost zone of interior Alaska. This objective will be met by determining hydraulic potentials in taliks and rates of microbial methane production and oxidation (aerobic and anaerobic) through laboratory incubations of lake sediments, thawed permafrost sediments beneath lakes, and permafrost collected from a >200-m tunnel extending beneath one of the lakes. Activity rates for methane production and emission determined in the lab will be compared with field observations of methane emissions from lakes. They will also be related to physical and hydrogeochemical characteristics measured by multilevel piezometers, including potential surface and sub-permafrost groundwater exchange. The project will support one post-doctoral fellow to conduct the research, present results at UAF departmental seminars and to 7th and 8th grade sciences classes at the Fairbanks Watershed School, and lead a peer-reviewed publication of results. We perceive this study to increase understanding of the role of surface and groundwater exchange in the formation, transmission and release of methane from thermokarst lakes to the atmosphere as climate warms in the discontinuous permafrost region of interior Alaska.