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.

Carbon balance, DOC, Methane, Net ecosystem exchange, Peatland
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