Abstract:

Variability of midday net ecosystem CO₂ exchange (NEE) and respiration was measured using a transect of closed system chambers spanning transitions from channel fen, permafrost plateau, and ombrotrophic flat bog land cover types during the spring melt season (26 April—6 June 2008). The primary objective was to compare fluxes from different land cover types and topographic variability within zones adjacent to and including rapid permafrost thaw. During this period, the bog was the greatest net source of CO₂ to the atmosphere, followed by plateau, and fen. NEE was slightly positive (indicating CO₂ loss to the atmosphere) during the snowmelt period (average = 0.009 ± 0.004 mg CO₂ m^-2 s^-1), and increased to 0.025 ± 0.012 mg CO₂ m^-2 s^—1, on average, possibly due to soil thaw and increased microbial activity within two days of completely snow-free conditions. Near surface soil temperature and depth to the water table were the most significant controls of soil and ground cover CO₂ fluxes within chambers at all sites (p < 0.05). Analysis of historical aerial photographs and satellite imagery of the area from 1947 to 2008 indicates that plateaus are converting more rapidly into bogs than fen, where 73% of plateau areas (since 1970) that thawed had become bogs (as opposed to 27% conversion into fen). Future research requires establishment of a full ecosystem or land cover greenhouse gas and soil nutrient exchange/transfer program, including CO₂and water fluxes as well as dissolved organic and inorganic C, and CH₄ losses from the soil. These results contribute to a better understanding of northern soil and ground-cover carbon exchanges as greater areas of permafrost plateaus collapse and form bogs.

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