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).

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 ...

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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.

Tropical peatlands have accumulated huge soil carbon over millennia. However, the carbon pool is presently disturbed on a large scale by land development and management, and consequently has become vulnerable. Peat degradation occurs most rapidly and massively in Indonesia, because of fires, drainage, and deforestation of swamp forests coexisting with tropical peat. Peat burning releases carbon dioxide (CO2) intensively but occasionally, whereas drainage increases CO2 emission steadily through the acceleration of aerobic peat decomposition. Therefore, tropical peatlands present the threat of switching from a carbon sink to a carbon source to the atmosphere. However, the ecosystem‐scale carbon exchange is still not known in tropical peatlands. A long‐term field experiment in Central Kalimantan, Indonesia showed that tropical peat ecosystems, including a relatively intact peat swamp forest with little drainage (UF), a drained swamp forest (DF), and a drained burnt swamp forest (DB), functioned as net carbon sources. Mean annual net ecosystem CO2 exchange (NEE) (± a standard deviation) for 4 years from July 2004 to July 2008 was 174 ± 203, 328 ± 204 and 499 ± 72 gC m−2 yr−1, respectively, for the UF, DF, and DB sites. The carbon emissions increased according to disturbance degrees. We found that the carbon balance of each ecosystem was chiefly controlled by groundwater level (GWL). The NEE showed a linear relationship with GWL on an annual basis. The relationships suggest that annual CO2 emissions increase by 79–238 gC m−2 every 0.1 m of GWL lowering probably because of the enhancement of oxidative peat decomposition. In addition, CO2 uptake by vegetation photosynthesis was reduced by shading due to dense smoke from peat fires ignited accidentally or for agricultural practices. Our results may indicate that tropical peatland ecosystems are no longer a carbon sink under the pressure of human activities.