Tropical peatlands are one of the largest near-surface reserves of terrestrial organic carbon, and hence their stability has important implications for climate change. In their natural state, lowland tropical peatlands support a luxuriant growth of peat swamp forest overlying peat deposits up to 20 metres thick. Persistent environmental change-in particular, drainage and forest clearing-threatens their stability, and makes them susceptible to fire. This was demonstrated by the occurrence of widespread fires throughout the forested peatlands of Indonesia during the 1997 El Niño event. Here, using satellite images of a 2.5 million hectare study area in Central Kalimantan, Borneo, from before and after the 1997 fires, we calculate that 32% (0.79 Mha) of the area had burned, of which peatland accounted for 91.5% (0.73 Mha). Using ground measurements of the burn depth of peat, we estimate that 0.19-0.23 gigatonnes (Gt) of carbon were released to the atmosphere through peat combustion, with a further 0.05 Gt released from burning of the overlying vegetation. Extrapolating these estimates to Indonesia as a whole, we estimate that between 0.81 and 2.57 Gt of carbon were released to the atmosphere in 1997 as a result of burning peat and vegetation in Indonesia. This is equivalent to 13-40% of the mean annual global carbon emissions from fossil fuels, and contributed greatly to the largest annual increase in atmospheric CO(2) concentration detected since records began in 1957 (ref. 1).

Accurate inventory of tropical peatland is important in order to (a) determine the magnitude of the carbon pool; (b) estimate the scale of transfers of peat‐derived greenhouse gases to the atmosphere resulting from land use change; and (c) support carbon emissions reduction policies. We review available information on tropical peatland area and thickness and calculate peat volume and carbon content in order to determine their best estimates and ranges of variation. Our best estimate of tropical peatland area is 441 025 km2 (∼11% of global peatland area) of which 247 778 km2 (56%) is in Southeast Asia. We estimate the volume of tropical peat to be 1758 Gm3 (∼18–25% of global peat volume) with 1359 Gm3 in Southeast Asia (77% of all tropical peat). This new assessment reveals a larger tropical peatland carbon pool than previous estimates, with a best estimate of 88.6 Gt (range 81.7–91.9 Gt) equal to 15–19% of the global peat carbon pool. Of this, 68.5 Gt (77%) is in Southeast Asia, equal to 11–14% of global peat carbon. A single country, Indonesia, has the largest share of tropical peat carbon (57.4 Gt, 65%), followed by Malaysia (9.1 Gt, 10%). These data are used to provide revised estimates for Indonesian and Malaysian forest soil carbon pools of 77 and 15 Gt, respectively, and total forest carbon pools (biomass plus soil) of 97 and 19 Gt. Peat carbon contributes 60% to the total forest soil carbon pool in Malaysia and 74% in Indonesia. These results emphasize the prominent global and regional roles played by the tropical peat carbon pool and the importance of including this pool in national and regional assessments of terrestrial carbon stocks and the prediction of peat‐derived greenhouse gas emissions.

Abstract. Conversion of tropical peatlands to agriculture leads to a release of carbon from previously stable, longterm storage, resulting in land subsidence that can be a surrogate measure of CO 2 emissions to the atmosphere. We present an analysis of recent large-scale subsidence monitoring studies in Acacia and oil palm plantations on peatland in SE Asia, and compare the findings with previous studies. Subsidence in the first 5 yr after drainage was found to be 142 cm, of which 75 cm occurred in the first year. After 5 yr, the subsidence rate in both plantation types, at average water table depths of 0.7 m, remained constant at around 5 cm yr −1 . The results confirm that primary consolidation contributed substantially to total subsidence only in the first year after drainage, that secondary consolidation was negligible, and that the amount of compaction was also much reduced within 5 yr. Over 5 yr after drainage, 75 % of cumulative subsidence was caused by peat oxidation, and after 18 yr this was 92 %. The average rate of carbon loss over the first 5 yr was 178 t CO 2eq ha −1 yr −1 , which reduced to 73 t CO 2eq ha −1 yr −1 over subsequent years, potentially resulting in an average loss of 100 t CO 2eq ha −1 yr −1 over 25 yr. Part of the observed range in subsidence and carbon loss values is explained by differences in water table depth, but vegetation cover and other factors such as addition of fertilizers also influence peat oxidation. A relationship with groundwater table depth shows that subsidence and carbon loss are still considerable even at the highest water levels theoretically possible in plantations. This implies that improved plantation water management will reduce these impacts by 20 % at most, relative to current conditions, and that high rates of carbon loss and land subsidence are inevitable consequences of conversion of forested tropical peatlands to other land uses.

1The global peat carbon pool exceeds that of global vegetation and is similar to the current 2 atmospheric carbon pool. Because fire is increasingly appreciated as a threat to peatlands 3 and their carbon stocks, here we review the controls on and effects of peat fires across 4 biomes. Peat fires are dominated by smouldering combustion, which ignites more easily 5 than flaming combustion and persists in wet conditions. In undisturbed peatlands, most of 6 the peat C stock typically is protected from smouldering, and resistance to fire has 7 increased peat carbon storage in boreal and tropical regions over long time scales. 8

Abstract. Forested tropical peatlands in Southeast Asia store at least 42 000 Million metric tonnes (Mt) of soil carbon. Human activity and climate change threatens the stability of this large pool, which has been decreasing rapidly over the last few decades owing to deforestation, drainage and fire. In this paper we estimate the carbon dioxide (CO 2 ) emissions resulting from drainage of lowland tropical peatland for agricultural and forestry development which dominates the perturbation of the carbon balance in the region. Present and future emissions from drained peatlands are quantified using data on peatland extent and peat thickness, present and projected land use, water management practices and decomposition rates. Of the 27

Gauci, Vincent. 2013 Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes. Nature, 493. 660-663. 10.1038/nature11818Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. 39Unlike boreal and temperate forests 5,6 , and higher latitude wetlands 7 , however, the loss of fluvial 40 organic carbon from tropical peats has yet to be fully quantified. 41To quantify the effect of peatland degradation on fluvial organic C loss, we monitored DOC and , and experienced similar annual rainfall (Table 1). 9TOC ( ; Fig. 1). This represents a 55% increase in 12TOC export from the disturbed sites (DPSF1 and 2) over IPSF. Of the annual TOC flux from each land-13 cover class, 94% was lost during the wet season (October-June), the result of higher measured 14 discharge rates (3.9 m 3 s -1 cf. 1.0 m 3 s -1 in the dry season). This was associated with high rainfall 15 rather than changes in C concentration, which remained relatively constant over the study period. 16As with seasonal flux variability, differences in discharge between land-cover classes determined TOC 17flux with higher discharge rates causing larger fluxes in DPSF1 and DPSF2 (1744 mm and 1724 mm, 18respectively) than in IPSF (907 mm). These higher discharge rates in disturbed land-cover classes 19were not counterbalanced by lower TOC concentrations, and occurred despite uniform rainfall across 20 sites (Table 1). This likely reflects a decline in evapotranspiration and increased runoff as a 21consequence of large scale biomass loss and drainage in both disturbed land-cover classes. DOC 22accounted for between 91-98 % of the TOC lost, with lower DOC:POC ratios for disturbed sites ( Table 23 1) suggesting that the drained and exposed peat is vulnerable to mechanical breakdown associated 24 with the increased runoff. 25Surface water DOC can derive from multiple sources, ranging from recent photosynthates to 26 decomposition or dissolution products from deep within the peat column. We used radiocarbon ( 3These data indicate that the increased DOC fluxes from disturbed peatlands are derived from 4 previously stable C stored within the peat column, and suggest that this loss of C from depth is 5 occurring throughout the seasonal hydrologic cycle. Application of an age attribution model (Fig. 2d) 6suggests that two-thirds of DOC in runoff from the DPSF2 site derives from peat carbon of 500-5000 7 years age. 35To quantify the impact peatland disturbance has had on regional long-term fluvial C loss, we applied 36 our TOC flux estimates to land areas of intact and deforested PSF prior to and after peatland 37 disturbance. We omitted industrial plantations from our calculations as, to our knowledge, there are 38 no quantitative data on fluvial C flux from this land cover class, although our DO 14 C data suggest that 39 these ecosystems may also ...

No abstract

S. H. 2004. A record of Late Pleistocene and Holocene carbon accumulation and climate change from an equatorial peat bog (Kalimantan, Indonesia): implications for past, present and future carbon dynamics.ABSTRACT: A 9.5 m core from an inland peatland in Kalimantan, Indonesia, reveals organic matter accumulation started around 26 000 cal. yr BP, providing the oldest reported initiation date for lowland ombrotrophic peat formation in SE Asia. The core shows clear evidence for differential rates of peat formation and carbon storage. A short period of initial accumulation is followed by a slow rate during the LGM, with fastest accumulation during the Holocene. Between $ 13 000 and 8000 cal. yr BP, >450 cm of peat were deposited, with highest rates of peat (>2 mm yr À1 ) and carbon (>90 g C m À2 yr À1 ) accumulation between 9530 and 8590 cal. yr BP. These data suggest that Kalimantan peatlands acted as a large sink of atmospheric CO 2 at this time. Slower rates of peat (0.15-0.38 mm yr À1 ) and carbon (7.4-24.0 g C m À2 yr À1 ) accumulation between $ 8000 and 500 cal. yr BP coincide with rapid peat formation in coastal locations elsewhere in SE Asia. The average LORCA (long-term apparent carbon accumulation rate) for the 9.5 m core is 56 g C m À2 yr À1 . These data suggest that studies of global carbon sources, sinks and their dynamics need to include information on the past and present sizeable peat deposits of the tropics.