Carbon Dioxide Exchange in a Permafrost-Dominated Boreal Wetland in the Northwest Territories, Canada.

摘要

Northern boreal wetland complexes are substantial reservoirs for carbon and playa crucial role in both regional and global carbon budgets but they are showing significant signs of impact by climate change. This study examined the carbon dioxide flux of a high boreal wetland during the snowmelt and growing season of 2008 in Scotty Creek Basin, located near Fort Simpson (61 °18'N, 121° 18'W), Northwest Territories. This basin is not only responding to shifts in atmospheric temperatures, but it is also under additional pressure from increasing permafrost degradation. A dynamic closed-system chamber was used to monitor and quantify mid-day total respiration (Rtot), gross ecosystem production (GEP), and net ecosystem exchange (NEE) at nine sites, in order to characterize and compare the gas flux gradients for three landscape units typical of the lower Liard River valley (channel fens, ombrotrophic flat bogs and peat plateaus).;These relationships for the 2008 season were used with assistance from meteorological stations to develop a continuous dataset for this region. In addition, remote sensing technology was used to scale the continuous dataset to the ecosystem level. Results showed that while the individual channel fen examined was the greatest emitter of CO2 into the atmosphere, it was the permafrost plateau that had the greatest total flux over a larger area. The potential future regional flux for this region as a sink or source for CO2 was also examined through site specific instantaneous gas flux and a simplified continuous model. This study highlights the need for long term measurement in order to develop an annual budget for CO2 and capture a more complete carbon profile of permafrost-dominated boreal wetlands. Further study will also result in a more holistic understanding of how CO2 gas flux gradients vary between the three distinct landscape units and periods of climatic variability. As the climate in northern ecosystems continues to alter, understanding the interactions between the physical, biochemical, and environmental conditions of different landscapes and the processes which define them can aid in the parameterization and interpretation of current and future climate and biogeochemical models.;Each landscape unit exhibited increasing rates of Rtot and GEP for the duration of study. Instantaneous rates of Rtot and NEE were highest in the permafrost plateau and channel fen, while the flat bog remained consistently low throughout the season. While there was significant variation in magnitude, the results demonstrated relatively similar temporal variability between landscapes. Temporal and spatial variability in CO 2 exchange was further examined through the relationships with local environmental conditions: photosynthetically active radiation, air temperature, soil temperature, soil moisture, and frost table and water table depth. Light response curves derived using an exponential model showed GEP was primarily driven by photosynthetically active radiation, yet significant scatter suggested additional environmental influences. Differential development in Rtot appeared to be most influenced by temperature and moisture regimes. Ambient air temperature, and soil and water temperatures at 20 cm all showed strong positive correlations with Rtot, while decreasing frost and water table depth, and soil moisture enhanced Rtot.