Ecosystem Productivity and Carbon Exchange in Northern Peatlands

The annual net primary productivity of northern peatlands is relatively small compared to that of many other ecosystems, yet peatlands contain between 200 and 450 Gt C, or 15 to 20% of the world�_s terrestrial organic carbon. This large carbon store, which is 99% in the form of peat, has resulted from the inhibition of decomposition due to water saturated anoxic conditions. Five years of CO$_{2}$ eddy covariance measurements at the Fluxnet-Canada eastern peatland station, Mer Bleue, indicate that the net annual exchange between the peatland and the atmosphere varies between -60 (sink from the atmosphere) and 10 (source to the atmosphere) g C m$^{-2}$ yr$^{-1}$. Additional carbon losses as methane, DOC and DIC, yield annual changes in the peatland\u27s carbon store of between 50 to -20 g C m$^{-2}$ yr$^{-1}$. The annual NPP of the Mer Bleue bog is quite small, ranging from 290 to 360 g m$^{-2}$ yr$^{-1}$ (�� 145 to 180 g C m$^{-2}$ yr$^{-1}$) depending on location within the peatland. The long-term carbon accumulation rate for the last 3,000 years, estimated from age-depth relationships and carbon content and bulk desnity profiles of the peat, varies between -10 and -20 g C m$^{-2}$ yr$^{-1}$. Analyses of ancillary environmental variables and simulations of the short-term carbon dynamics using the Peatland Carbon Simulator (PCARS) show a combination of factors control the variations in ecosystem productivity. However, the peat winter thermal regime and the summer temperatures and moisture storage appear of be of primary importance. Over the long term (decades to millennia) the feedbacks among peatland wetness, primary productivity, and the partitioning of decomposition between aerobic and anaerobic pathways simulated by the Peat Accumulation Model (PAM) explain a significant portion of the dynamic changes in the carbon storage