Ecosystem Respiration in a Cool Temperate Bog Depends on Peat Temperature But Not Water Table P.M. Lafleur, 1 * T.R. Moore, 2 N.T. Roulet, 2 and S. Frolking 3 1 Department of Geography, Trent University, Peterborough, ON K8P 2W6, Canada; 2 Department of Geography and The Centre for Climate & Global Change Research, McGill University, 805 Sherbrooke St. W., Montreal, QC H3A 2K6, Canada; 3 Institute for the Study of Earth, Ocean and Space, University of New Hampshire, Durham, New Hampshire 03824, USA ABSTRACT Ecosystem respiration (ER) is an important but poorly understood part of the carbon (C) budget of peatlands and is controlled primarily by the thermal and hydrologic regimes. To establish the relative importance of these two controls for a large ombrotrophic bog near Ottawa, Canada, we analyzed ER from measurements of nighttime net ecosystem exchange of carbon dioxide (CO 2 ) determined by eddy covariance technique. Mea- surements were made from May to October over five years, 1998 to 2002. Ecosystem respiration ranged from less than 1 lmol CO 2 m )2 s )1 in spring (May) and fall (late October) to 2–4 lmol CO 2 m )2 s )1 during mid-summer (July-August). As anticipated, there was a strong relationship between ER and peat temperatures (r 2 = 0.62). Q 10 between 5° to 15°C varied from 2.2 to 4.2 depending upon the choice of depth where tem- perature was measured and location within a hummock or hollow. There was only a weak relationship between ER and water-table depth (r 2 = 0.11). A laboratory incubation of peat cores at different moisture contents showed that CO 2 production was reduced by drying in the surface samples, but there was little decrease in production due to drying from below a depth of 30 cm. We postulate that the weak correlation between ER and water table position in this peatland is primarily a function of the bog being relatively dry, with water table varying between 30 and 75 cm below the hummock tops. The dryness gives rise to a complex ER response to water table involving i) compensations between production of CO 2 in the upper and lower peat profile as the water table falls and ii) the impor- tance of autotrophic respiration, which is rela- tively independent of water-table position. Key words: ecosystem respiration; carbon diox- ide; peatland; bog; eddy covariance; soil climate. INTRODUCTION Northern peatlands occupy about 3.5 million km 2 and contain up to one-third of the worldÕs soil carbon (C) pool (Gorham 1991). These peatlands have accumulated C through an imbalance be- tween plant uptake of atmospheric CO 2 by photo- synthesis and the release of CO 2 to the atmosphere through plant respiration and the decomposition of organic matter. The C budget of these systems under a changing climate will depend on the rela- tive response of plant productivity and the rate at which organic matter decomposes, with thermal and hydrologic regimes being of critical impor- tance. Ecosystem respiration (ER) is the emission of carbon dioxide to the atmosphere from vegetation (autotrophic) and soil (heterotrophic) activities. Compared to photosynthetic uptake, ER is a poorly Received 23 September 2003; accepted 16 April 2004; published online: 9 September 2005. *Corresponding author; e-mail: plafleur@trentu.ca Ecosystems (2005) 8: 619–629 DOI: 10.1007/s10021-003-0131-2 619