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Contemporary carbon balance and late Holocene carbon accumulation in a northern peatland
- ROULET, NIGEL T., LAFLEUR, PETER M., RICHARD, PIERRE J.H., MOORE, TIM R., HUMPHREYS, ELYN R., BUBIER, JILL
- Global change biology 2007 v.13 no.2 pp. 397-411
- carbon, carbon dioxide, climatic factors, dissolved organic carbon, ecosystems, greenhouse gas emissions, methane, net ecosystem exchange, peat, peatlands, soil
- 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 (±1 SD), 3.7±0.5, and 14.9±3.1 g m⁻² yr⁻¹, giving a 6-year mean balance of -21.5±39.0 g m⁻² yr⁻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⁻² yr⁻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⁻² yr⁻¹, which are not significantly different from the 6-year mean contemporary exchange.