Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes

Journal name:
Nature
Volume:
493,
Pages:
660–663
Date published:
DOI:
doi:10.1038/nature11818
Received
Accepted
Published online

Tropical peatlands contain one of the largest pools of terrestrial organic carbon, amounting to about 89,000 teragrams1 (1Tg is a billion kilograms). Approximately 65 per cent of this carbon store is in Indonesia, where extensive anthropogenic degradation in the form of deforestation, drainage and fire are converting it into a globally significant source of atmospheric carbon dioxide1, 2, 3. Here we quantify the annual export of fluvial organic carbon from both intact peat swamp forest and peat swamp forest subject to past anthropogenic disturbance. We find that the total fluvial organic carbon flux from disturbed peat swamp forest is about 50 per cent larger than that from intact peat swamp forest. By carbon-14 dating of dissolved organic carbon (which makes up over 91 per cent of total organic carbon), we find that leaching of dissolved organic carbon from intact peat swamp forest is derived mainly from recent primary production (plant growth). In contrast, dissolved organic carbon from disturbed peat swamp forest consists mostly of much older (centuries to millennia) carbon from deep within the peat column. When we include the fluvial carbon loss term, which is often ignored, in the peatland carbon budget, we find that it increases the estimate of total carbon lost from the disturbed peatlands in our study by 22 per cent. We further estimate that since 1990 peatland disturbance has resulted in a 32 per cent increase in fluvial organic carbon flux from southeast Asia—an increase that is more than half of the entire annual fluvial organic carbon flux from all European peatlands. Our findings emphasize the need to quantify fluvial carbon losses in order to improve estimates of the impact of deforestation and drainage on tropical peatland carbon balances.

At a glance

Figures

  1. Total and seasonal fluvial organic carbon losses from intact (PSF1) and disturbed (PSF2 and PSF3) catchments.
    Figure 1: Total and seasonal fluvial organic carbon losses from intact (PSF1) and disturbed (PSF2 and PSF3) catchments.

    a, Annual TOC flux (±s.e.m.). ‘a’, ‘b’ and ‘c’ denote significant differences between land-cover classes (P<0.05, unpaired, two-sample t-test) and mean radiocarbon (14C) levels (±s.e.m.) measured in DOC (wet-season samples); ‘I’, ‘II’ and ‘III’ denote significant differences (P<0.05, unpaired, two-sample t-test). The solid horizontal line (104% of the modern value) represents the current atmospheric 14CO2 level; the dashed horizontal line (100% modern) represents the composition of the atmosphere in 1950, in the absence of any anthropogenic influences (that is, fossil fuel burning and above-ground nuclear testing). b, Weekly TOC flux from all land-cover classes from June 2008 to June 2009 (grey shading indicates the dry season). PSF1 TOC is the sum of fluxes from three channels, PSF2 is the sum of fluxes from two channels and PSF3 is the sum of fluxes from three channels, all divided by the total area of the land-cover class. c, Intact PSF. d, Disturbed PSF. Copyright for Fig. 1c, d, S.E.P.

  2. Carbon balance and DOC age attribution of intact and disturbed PSF.
    Figure 2: Carbon balance and DOC age attribution of intact and disturbed PSF.

    a, b, Schematic showing net ecosystem exchange (black arrows; in grams of carbon in CO2 per m2 per year) and fluvial TOC loss (white arrows; in grams of carbon per m2 per year) estimates in the PSF1 (a) and PSF2 and PSF3 (b) land-cover classes. *Net ecosystem exchange estimated from average 500-year estimate of carbon accumulation from a peat core taken within PSF117 to which mean fluvial carbon loss (63gCm−2yr−1) has been added, thus approximating the net ecosystem exchange that would be measured by gaseous exchange alone. Carbon gain of intact PSF estimated to be 94gCm−2yr−1 (net C sink). **Net ecosystem exchange measured from tower-based gaseous exchange measurements (eddy covariance) within the disturbed PSF catchments, which measures CO2 fluxes across flat, deforested areas of the Mega Rice Project that are drained but do not contain drainage channels18. The net ecosystem carbon balance of disturbed PSF is estimated to be 530gCm−2yr−1 (net C source). c, d, Modelled down-profile attribution of DO14C age from PSF1 (c) and PSF3 (d) land-cover classes respectively (wet season) as estimated from an age attribution model of DO14C age (see Supplementary Information for explanation).

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Author information

Affiliations

  1. Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR), Department of Environment, Earth and Ecosystems, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK

    • Sam Moore &
    • Vincent Gauci
  2. Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road, Bangor, LL57 2UW, UK

    • Chris D. Evans
  3. Department of Geography, University of Leicester, University Road, Leicester, LE1 7RH, UK

    • Susan E. Page
  4. Natural Environment Research Council Radiocarbon Facility, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, UK

    • Mark H. Garnett
  5. School of Biological Sciences, Bangor University, Deiniol Road, Gwynedd, LL57 2UW, UK

    • Tim G. Jones &
    • Chris Freeman
  6. Deltares, PO Box 177, 2600 MH Delft, The Netherlands

    • Aljosja Hooijer
  7. Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK

    • Andrew J. Wiltshire
  8. CIMTROP, University of Palangka Raya, Palangka Raya, Central Kalimantan, 73112, Indonesia

    • Suwido H. Limin
  9. Present address: Environment Change Institute, School of Geography and the Environment, University of Oxford, OX1 3QY Oxford, UK.

    • Sam Moore

Contributions

V.G., S.E.P. and C.D.E. conceived and led the research conducted in Kalimantan. S.M., V.G., S.E.P. and C.D.E. designed the study and S.M. performed all the Kalimantan field data collection and analysis. C.D.E. and M.H.G. coordinated, analysed and interpreted the radiocarbon component of the work. S.M., V.G. and S.E.P. performed the scaling-up calculations. C.F. conceived and led the Malaysian study, T.G.J. performed the field data collection and analysis, A.H. provided hydrological data and interpreted land surface information to allow catchment definition. A.J.W. provided modelled estimates of evapotranspiration. S.H.L. provided expertise on the history of land-cover change and field site selection. S.M., V.G., S.E.P. and C.D.E. led the writing of the paper. All authors discussed results and commented on the manuscript.

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The authors declare no competing financial interests.

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Supplementary information

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  1. Supplementary Information (491K)

    This file contains Supplementary Text, Supplementary Figures 1-4 and Supplementary References. Formatting of Equation S1 was corrected on 21 February 2013.

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