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Contemporary carbon balance and late Holocene carbon accumulation in a northern peatland

Authors

  • NIGEL T. ROULET,

    1. Department of Geography, McGill University, 805 Sherbrooke Street West, Montreal, QC H3A 2K6, Canada,
    2. McGill School of Environment, McGill University, Montreal, QC, Canada,
    3. The Global Environment and Climate Change Centre, McGill University, Montreal, QC, Canada,
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  • PETER M. LAFLEUR,

    1. Department of Geography, Trent University, 1600 Westbank Drive, Peterborough, ON K9J 7B8, Canada,
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  • PIERRE J. H. RICHARD,

    1. The Global Environment and Climate Change Centre, McGill University, Montreal, QC, Canada,
    2. Laboratoire Jacques-Rousseau, Département de géographie, Université de Montréal, C.P. 6128, Succursale Centre-ville, Montréal, QC H3C 3J7, Canada,
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  • TIM R. MOORE,

    1. Department of Geography, McGill University, 805 Sherbrooke Street West, Montreal, QC H3A 2K6, Canada,
    2. The Global Environment and Climate Change Centre, McGill University, Montreal, QC, Canada,
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  • ELYN R. HUMPHREYS,

    1. Department of Geography & Environmental Studies, Carleton University, B349 Loeb Building, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada,
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  • JILL BUBIER

    1. Environmental Studies Program, Department of Earth and Environment, Mount Holyoke College, Clapp Laboratory, 50 College Street, South Hadley, MA, 01075, USA
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Nigel Roulet, Department of Geography, McGill University, 805 Sherbrooke St. W., Montreal, QC H3A 2K6 Canada. tel. +514 398 4945, e-mail: nigel.roulet@mcgill.ca

Abstract

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.

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