Changes in ecosystem carbon balance where permafrost is thawing

One of the biggest potential feedbacks to global climate change from high latitude ecosystems may come from thawing of permafrost, which stores more than 50% of the total global terrestrial soil carbon. Thawing of permafrost may accelerate decomposition of soil organic matter and increase carbon dioxide (CO2) emissions. When permafrost thaws in ice-rich areas, it creates localized topographical surface subsidence called thermokarst, which can induce variations in soil abiotic properties. Also, depending on the location of thermokarst formation it can create anaerobic conditions in soil. By altering multiple resources in soil, thermokarst can change C-cycling in high latitude ecosystems beyond simple increases in temperature alone. My research was conducted at a subarctic tundra site near Healy, Alaska (Latitude: 63.7°N), where permafrost thaw and thermokarst development have been observed and monitored for two decades. I established soil gas wells to explain how thermokarst affects soil respiration and to determine which depth in the soil profile has the greatest soil CO2 flux. I also established plot-scale studies to determine how thermokarst affects ecosystem C exchange by measuring above ground CO2 fluxes using clear chambers. Then I collected permafrost soils with different substrate qualities and incubated them at 15°C under aerobic and anaerobic conditions to observe C loss and climate forcing in different environments after permafrost thaw. I found that there was an increase in soil CO2 production where thermokarst development progressed this was mostly driven by surface soil layer CO2 production rather than deeper soil layer CO2 production. This was likely due to changes in the environment such as soil temperature, moisture, and vegetation. I was able to estimate the annual ecosystem carbon balance using surface subsidence created by thermokarst development, thaw depth, and plant biomass. Permafrost soil incubation showed that carbon loss was 3 times greater under aerobic conditions, but climate forcing was 1.15 times greater under anaerobic conditions due to methane emissions. Therefore, permafrost thaw and thermokarst development may stimulate soil CO2 production, ecosystem carbon exchange, but will affect climate warming more under anaerobic conditions. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)...