Northern peatlands contain up to 25% of the world's soil carbon (C) and have an estimated annual exchange of CO2-C with the atmosphere of 0.1-0.5 Pg yr-1 and of CH4-C of 10-25 Tg yr-1. Despite this overall importance to the global C cycle, there have been few, if any, complete multiyear annual C balances for these ecosystems. We report a 6-year balance computed from continuous net ecosystem CO2 exchange (NEE), regular instantaneous measurements of methane (CH4) emissions, and export of dissolved organic C (DOC) from a northern ombrotrophic bog. From these observations, we have constructed complete seasonal and annual C balances, examined their seasonal and interannual variability, and compared the mean 6-year contemporary C exchange with the apparent C accumulation for the last 3000 years obtained from C density and age-depth profiles from two peat cores. The 6-year mean NEE-C and CH4-C exchange, and net DOC loss are -40.2±40.5 (±1SD), 3.7±0.5, and 14.9±3.1 g m-2yr-1, giving a 6-year mean balance of -21.5±39.0 g m-2yr-1 (where positive exchange is a loss of C from the ecosystem). NEE had the largest magnitude and variability of the components of the C balance, but DOC and CH4 had similar proportional variabilities and their inclusion is essential to resolve the C balance. There are large interseasonal and interannual ranges to the exchanges due to variations in climatic conditions. We estimate from the largest and smallest seasonal exchanges, quasi-maximum limits of the annual C balance between 50 and -105 g m-2yr-1. The net C accumulation rate obtained from the two peatland cores for the interval 400-3000 bp (samples from the anoxic layer only) were 21.9±2.8 and 14.0±37.6 g m-2yr-1, which are not significantly different from the 6-year mean contemporary exchange.

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Global Change Biology
Department of Geography and Environmental Studies

Roulet, N.T. (Nigel T.), Lafleur, P.M. (Peter M.), Richard, P.J.H. (Pierre J.H.), Moore, T.R. (Tim R.), Humphreys, E, & Bubier, J. (Jill). (2007). Contemporary carbon balance and late Holocene carbon accumulation in a northern peatland. Global Change Biology, 13(2), 397–411. doi:10.1111/j.1365-2486.2006.01292.x