CLIMATE - CARBON DYNAMICS IN NORTHERN PEATLANDS

Northern wetlands contain 30% of the worlds terrestrial carbon store and are believed to be a contemporary sink of CO2 (0.1 to 0.5 Pg C yr-1) and a source of CH4 (10 C 30 Tg C yr-1). Until recently, most of the studies on the atmosphere-biosphere exchange of greenhouse gases from northern peatlands were short-term and seasonal, and there were few models of peatland carbon cycling that could be used in climate simulations. In 1998 the Peatland Carbon Study began continuous measurements of the carbon dynamics of a northern peatland. This research has continued, now as part of the Fluxnet Canada Research Network. As part of the Land Surface Processes node of the former Climate Research Network and now as an integral part of the Global Canadian Coupled Carbon Climate Model research network, we have developed several ecosystem models to simulation the response of northern peatlands to climate variability and change. The continuous measurements indicate that over a six-year, the C balance can be either positive (source to the atmosphere) or negative (net sink). Further our results show that one or two years worth on measurements are inadequate to conclude the role of a peatland as a sink or source, and that a C balance without the inclusions of the losses of C via the export of dissolved organic carbon (DOC) and/or CH4, is too uncertainty to be useful in climate-greenhouse gas exchange assessments. Development, evaluation and sensitivity analysis of two different process models, the Peatland Carbon Simulator (PCARS), and a more recent McGill Wetland Model (McWM), show the critical importance of climate, hydrology and plant community structure to simulating peatland greenhouse gas exchanges. If the hydrology of a peatland can not be simulated with reasonable success C e.g. water table evaluation with 0.1 m accuracy, then the results of the ecosystems models are too large to help in climate and greenhouse gas assessments. This presents a huge challenge for the peatland modelling community. We have been reasonably successful in simulated peatland hydrology and surface climate for northern bogs and mineral poor fens using a wetland version of the Canadian Land Surface Scheme at a point, but scaling the models to the region and global remains elusive. Using a long-term paleo-ecological model for northern peatlands, the Peat Accumulation Model (PAM), and a very simple carbon cycle and radiative forcing model, we have examined how the sink/source function of northern peatlands involving multiple greenhouse gases C e.g. CO2 and CH4, can be assessed. We have concluded, in all but constant conditions, the Global Warming Potential, that is widely used by the peatland community, is not a particularly, appropriate metric.

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