Luc Pelletier

Carbon release from boreal peatland open water pools: Implication for the contemporary C exchange

While peatland ecosystems overall are long-term net carbon (C) sinks, the open water pools that are characteristic of boreal peatlands have been found to be C sources to the atmosphere. However, the contribution of these pools to the ecosystem level C budget is often ignored even if they cover a significant area of the peatland surface. Here we examine the annual CO2 and CH4 ecosystem-atmosphere exchange, including the release following ice melt, from pools in a boreal maritime peatland, in order to estimate the annual loss of C from these water bodies. Over a 16 month period, dissolved CO2 and CH4 were measured periodically in five pools while continuous measurements of CO2 were made in one pool using a nondispersive infrared (NDIR) sensor. Fluxes were calculated using the thin boundary layer model and the eddy covariance technique (spring release only). We calculated an annual C release from pools of 103.3 g C m−2 yr−1 of which 15% was released during the spring ice melt. This release is the same order of magnitude, but with the opposite sign, as the average net ecosystem carbon balance for pool-free northern peatlands (−22 to −70 g C m−2 yr−1). We discuss the origin of the released C, as the magnitude of the release could have a significant impact on the contemporary C exchange of boreal peatlands.

Can boreal peatlands with pools be net sinks for CO2

Peatland open-water pools, a common feature on temperate to subarctic peatlands, are sources of carbon (C) to the atmosphere but their contribution to the net ecosystem carbon dioxide exchange (NEE-CO2) is poorly known; there is a question as to whether peatlands with pools are smaller sinks of atmospheric C, or even C-neutral, compared to other peatlands. We present growing season NEE-CO2 measurements using the eddy covariance technique in a peatland with pools. We found the maximum photosynthetic uptake and ecosystem respiration rates at 10 °C to be in the lower range of the published data. The lower total vegetation biomass, due to the presence of pools, reduced CO2 uptake during day and the autotrophic component of ecosystem respiration. The low CO2 uptake combined with reduced CO2 loss resulted in the site being a net sink for CO2 of a similar magnitude as other northern peatlands despite the inclusion of pools.

Effect of open water pools on ecosystem scale surface-atmosphere carbon dioxide exchange in a boreal peatland

Peatland carbon dioxide (CO2) exchange can vary spatially over a few meters because of the heterogeneity in plant communities, differing responses to environmental conditions, and the presence of pools in patterned peatlands. In contrast to the plant communities comprising a peatland’s vegetated surface, permanent pools that are characteristic of peatlands in temperate to subarctic regions are net sources of CO2 to the atmosphere. Measurements of net ecosystem CO2 exchange using the eddy covariance (EC) technique over peatlands without permanent pools do not show the smaller plant scale spatial heterogeneity in fluxes because the atmosphere mixes the variations in fluxes over the EC tower source area. However, if different vegetation communities and pools approach the spatial scale that they form a significant proportion of an EC tower’s source area, such as might be the case in peatlands with pools, they should be able to be discriminated if the surface fluxes by cover type are significantly different. In the present study, we evaluate if the observed variability in peatland surface CO2 exchange can be identified from 30-min net ecosystem CO2 exchange measurements using the proportion of the different plant communities or pools within the eddy covariance tower source area. Our results show that the variability in CO2 exchange at the local scale across the peatland surface has a measureable impact on the ecosystem level measurement, primarily when open water pools are present within the tower source area. Our results also suggest that large CO2 exchange rates measured above Sphagnum spp. hummocks with Picea mariana, combined with their large fractional contribution to the source area, counterbalanced the CO2 loss from the open water pools, explaining why the ecosystem as a whole was a net CO2 sink during the measurement period.