Patterns and controls on methane and carbon dioxide fluxes on the Arctic Coastal Plain, Alaska.

摘要

My research focuses on the patterns and controls of CO 2 and CH4 fluxes in vegetated drained lake basins on the Arctic Coastal Plain in northern Alaska. These land features account for the majority of the landscape in the Arctic Coastal Plain, but have never been systematically investigated with respect to their impact on trace gas fluxes in the global carbon budget. In the first part of my research I focused on the impacts of water table change on CO2 and CH4 fluxes in a vegetated drained lake basin, where the water table was manipulated. I showed that the water table drop below the surface may not decrease CH 4 emissions if a simultaneous increase in thaw depth increases the soil volume available for methanogenesis. On the other hand, an increase in water table above the surface could increase the diffusive resistance to CH 4 release and decrease its emission. The impact of water table increase on CO2 was also surprising. Contrary to the common prediction, I demonstrated that increasing the water table level can increase CO 2 injection into the atmosphere. This CO2 loss from the ecosystem is likely due to an increase in respiration, for the increase soil volume in the flood area, and decrease in light at the level of the photosynthetic organs.In the last part of my research, I study the carbon dynamics of a number of vegetated drained lake basins, which drained from 50 to 2000 years ago, in the Arctic Coastal Plain. I characterized 12 vegetated drained lake basins in terms of net ecosystem exchange (NEE), ecosystem respiration (ER) and gross primary production (GPP), and investigated the seasonal patterns and environmental controls on CO2 fluxes. The comparison of the seasonal CO 2 fluxes in vegetated drained lake basins of different age allowed me to test the validity of the traditional view that net primary production decreases with ecosystem maturity (Odum 1969). I showed that ecosystems thousands of years old (i.e. old vegetated drained lake basins) are still a CO2 sink in the global carbon budget.