Bert Tanner Award 2015 - Luc Pelletier, McGill

May 13, 2015

Congratulations to Luc Pelletier, PhD Student at McGill University for winning the 2015 Bert Tanner Award at last week's meetings. His presentation was titled “The Impact of Open-Water Pools on the Net Ecosystem CO2 Exchange of a Boreal Peatland” and a summary of his findings are below.

Peatland ecosystems are long-term net carbon (C) sinks but the open water pools that are characteristic of these temperate to subarctic wetlands have been found to be C sources to the atmosphere. Their contribution to the ecosystem level C budget has often been ignored even if they cover a significant area of the peatland surface. There is therefore a question as to whether peatlands containing pools are smaller net sinks of atmospheric C compared to peatlands without pools; the total C loss measured from pools is the same order of magnitude, but with the opposite sign, as the published average net ecosystem carbon balance for pool-free northern peatlands. In my research, I evaluated the annual C release from peatland open water pools and its impact on the net ecosystem carbon dioxide exchange (NEE-CO2) in a boreal bog located near the city of Baie Comeau, Quebec, Canada.

My results showed that the pools at the study site released 103 g C m-2yr-1, of which 15% was released during the spring ice melt. Although this estimate is within the range of other published studies, my results suggest that previous assessments of C release underestimate the annual loss by not including the spring melt release. The ecosystem scale measurements performed using the eddy covariance technique (EC) showed that the 30-min maximum CO2 uptake rates decreased by close to 25% for an increase in pool fraction within the EC tower source area from 0-10% to 20-30%. I found that pools lower the overall NEE-CO2components (maximum photosynthetic uptake and ecosystem respiration rates) by reducing the ecosystem’s aboveground vegetation biomass. The lower total vegetation biomass at the ecosystem scale reduced net CO2 uptake during the day but also reduced ecosystem respiration (ER) at night, as ER from the pools is mainly heterotrophic. The net effect was that the site remained a sink for CO2 during the measurement period despite the inclusion of pools.

Overall, my results demonstrate that peatland open water pools can play a significant role in the ecosystem level surface to atmosphere C exchange. Measurements of interannual NEE-CO2 variability from different peatlands with pools will expand the validity of these findings. Future studies should also include an evaluation of the annual CH4 exchange, CO2 loss during the winter along with dissolved organic carbon export from peatland with pools in order to obtain a complete net ecosystem carbon balance.

Posted by: Andy VanderZaag

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