Impact of Watershed Hydrologic, Thermal, and Nutrient Inputs on Wetland Methane Emissions in Subarctic Bogs

Authors

Joel Eklof¹ (jeklof@uw.edu), Jing Tao², Qing Zhu², William J. Riley², Baptiste Dafflon², Katie Ring¹, Rebecca Neumann*¹

Institutions

¹University of Washington, Seattle, WA; ²Lawrence Berkeley National Laboratory, Berkeley, CA

 

Abstract

Methane, a potent greenhouse gas, accounts for a large portion of the global warming potential of permafrost thaw. This is particularly true in areas with ice-rich permafrost. When ice-rich permafrost thaws, the ground subsides, creating thermokarst features such as thaw bogs. These bog systems are the topographically lowest points of their surrounding landscape, and therefore, receive and collect runoff from the surrounding permafrost-underlain watershed. This hydrologic connection between bog systems and their surrounding watersheds can amplify bog methane emissions through the transport of thermal energy and nutrients into the bog complex.

Data previously collected by the research team showed warm rain early in the growing season can advect heat into wetland soils from the surrounding watershed. This thermal input increased wetland soil temperatures, and in turn, significantly increased methane emissions by supporting microbial and vegetative processes. These results highlight how the watershed-bog connection can influence methane. Currently, the ability of inputs from the permafrost plateau to affect biogeochemical processes is not recognized in field studies nor implemented in models.

This project is advancing understanding of the watershed-bog connection and clarifying the conditions in which inputs from the permafrost plateau affect land-atmospheric exchange of carbon. Researchers continue to increase the understanding through field observations at a well-instrumented bog-complex in Interior, AK, and pair these observations with Earth System modeling. Recently installed field equipment allows the research team to track hydrologic, thermal, and nutrient inputs across the permafrost plateau and throughout the bog complex. This data is then paired with observed methane fluxes to better understand watershed-bog dynamics and the resulting methane emissions. Through coupled modeling of lateral water and heat transport with E3SM Land Model (ELMv1-ECA), researchers have confirmed the important role of advective heat transport in affecting bog soil temperatures and methane emissions. Specifically, results demonstrated that incorporating advective heat transport improved the transect-scale simulations of soil temperature and moisture profiles compared to models omitting this process, reasonably recapturing summer thaw depth along the transect from the forest to the bog complex. Researchers also found rainfall intensity and timing in the warming season, and rain-on-snow events in the cold season, strongly modulated soil freeze/thaw cycles, bog inundation dynamics, bog plant phenology, and bog methane emissions. Researchers concluded that the coupled water and heat transport significantly impacts permafrost thaw and possibly speeds thermokarst development, especially over hillslope landscapes affected by ice-rich permafrost.