Title:

Lateral Carbon Transport Across a Permafrost Thaw Gradient

Methane is a potent greenhouse gas that can be produced in a process called methanogenesis. In this process, microbes called methanogens go through anaerobic respiration and create methane as an end product. This process frequently occurs in water-logged soils like wetlands and mires. In mires like Stordalen Mire, in Abisko, Sweden, methanogenesis is less common than in other wetlands due to the presence of permafrost underlying the palsa areas of the mire. As climate continues to change, scientists are worried that increased permafrost thaw with create wetter soil conditions, leading to higher rates of methane production. There is also concern that increased thawing of permafrost will increase hydrologic connectivity throughout the mire, which could potentially increase the transport of methane, as well as other forms of carbon across thaw transects. To better understand the extent to which carbon dynamics are driven by lateral transport, rather than in situ production, collars were installed next to control plots to serve as mesocosms. In these mesocosms, lateral transport would be eliminated, allowing porewater and flux measurements to isolate production within the column. For this project, porewater samples and gas fluxes were measured along a permafrost thaw gradient at two sites, the thaw front, and the riparian zone. Within both of these sites, there were control plots, where lateral transport was unrestricted, and mesocosm sites where lateral transport was prevented. Analysis of the methane concentration in porewater shows that concentrations in the thaw front were higher in control plots than mesocosm plots, and the opposite relationship was observed within the riparian zone. The concentrations of dissolved organic carbon were higher in the mesocosm plots in both the thaw front and riparian zone. Analysis also showed that dissolved organic carbon was not a primary control on porewater methane concentrations, as was hypothesized. Instead, physical processes like dilution and transport out of the system may be more influential to porewater methane concentrations. Future data analysis would measure concentrations of dissolved inorganic carbon, to better understand the quantity of carbon along the transect when able to be transported through the water table, and when unable to do so.

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