Understanding the contribution of pools to boreal peatland carbon exchange

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Peatlands play an important role in regulating the climate system as they are a net long-term sink for carbon dioxide (CO2). However, these ecosystems are also a net source of methane (CH4) to the atmosphere. While studies have shown that peatlands remain net sinks of carbon (C) when both CO2 and CH4 are accounted for, the short-term rates of exchange and their direction are functions of the environmental conditions experienced by the spatially variable microforms on an individual peatland. To date, studies at the ecosystem scale have overwhelmingly excluded the contribution of pools to the net exchange. Since pools are net sources of both CO2 and CH4, a peatland ecosystem with pools may be a weaker net sink than previously considered. To begin to better define the role that pools play in peatland carbon exchange, in the first phase of the research, the controls on exchanges of CO2 and CH4 will be explored on multiple instrumented pools representing a distribution of depth and size. Ebullition (bubbling) can contribute greater than 50% of the total CH4 flux from lakes and beaver ponds and yet is not often measured routinely. The contribution of ebullition to the overall pool gas exchange will be quantified and the controls on the production of bubbles determined. This study will investigate if relationships found in lakes can be extended to the numerous shallow and small pools inherent in boreal peatlands. In the same pools, near continuous dissolved CO2 concentration measurements will be made during the ice-free period to quantify diffusive flux. Profile measurements will provide information on possible stratification and turn-over within the pools during the ice free season while winter data will provide concentrations to calculate gas release during the ice melt at the end of the cold season. Sedimentation rates and water column productivity will be evaluated. Rates of CO2 and CH4 production will be determined in relation to temperature and oxygen content using incubations of bottom sediments/organic layer. In the second phase of the research, a multi-year investigation in a boreal peatland will use dual flux towers to determine continuous ecosystem scale fluxes of CO2 and CH4 from an area with pools and one without pools to identify the contribution from the pools. Relationships developed in the first phase will be used to scale fluxes in combination with remote sensing classification and tower flux footprint models. This research program will provide information to reduce uncertainty around current estimates of peatland net C exchange and will produce relationships useful to modellers for future climate simulations of these sensitive ecosystems. The program will train PhD, MSc and undergraduate students.