From carbon sink to carbon source: extensive peat oxidation in insular Southeast Asia since 1990

Abstract

Tropical peatlands of the western part of insular Southeast Asia have experienced extensive land cover changes since 1990. Typically involving drainage, these land cover changes have resulted in increased peat oxidation in the upper peat profile. In this paper we provide current (2015) and cumulative carbon emissions estimates since 1990 from peat oxidation in Peninsular Malaysia, Sumatra and Borneo, utilizing newly published peatland land cover information and the recently agreed Intergovernmental Panel on Climate Change (IPCC) peat oxidation emission values for tropical peatland areas. Our results highlight the change of one of the Earth's most efficient long-term carbon sinks to a short-term emission source, with cumulative carbon emissions since 1990 estimated to have been in the order of 2.5 Gt C. Current (2015) levels of emissions are estimated at around 146 Mt C yr À1 , with a range of 132-159 Mt C yr À1 depending on the selection of emissions factors for different land cover types. 44% (or 64 Mt C yr À1 ) of the emissions come from industrial plantations (mainly oil palm and Acacia pulpwood), followed by 34% (49 Mt C yr À1 ) of emissions from small-holder areas. Thus, altogether 78% of current peat oxidation emissions come from managed land cover types. Although based on the latest information, these estimates may still include considerable, yet currently unquantifiable, uncertainties (e.g. due to uncertainties in the extent of peatlands and drainage networks) which need to be focused on in future research. In comparison, fire induced carbon dioxide emissions over the past ten years for the entire equatorial Southeast Asia region have been estimated to average 122 Mt C yr À1 (www.globalfiredata.org/_index.html). The results emphasise that whilst reducing emissions from peat fires is important, urgent efforts are also needed to mitigate the constantly high level of emissions arising from peat drainage, regardless of fire occurrence.

AERONET Remotely Sensed Measurements and Retrievals of Biomass Burning Aerosol Optical Properties During the 2015 Indonesian Burning Season

“…As a result of these strong droughts, the biomass burning associated with agricultural practices was able to spread farther than in typical rainfall years, plus peat fuels were able to burn more effectively due to deeper drying of these soils. Draining and drying of peatlands for the purpose of expanding agriculture especially palm oil plantations (Miettinen, Hooijer, et al, ; Page & Hooijer, ; Sumarga et al, ) created additional conditions conducive to the burning of the underground organic peat soils that occurred primarily in historically susceptible southern Borneo (Kalimantan) and southeastern Sumatra. Once such peat fires are initiated, they typically burn until monsoonal inundation—sometimes months later (Reid et al, ).…”

CO2 emissions from an undrained tropical peatland: Interacting influences of temperature, shading and water table depth

“…Emissions from peat oxidation excluding fires in 2015 were estimated to range from 132 to 159 Mt C year -1 , and cumulative carbon emissions since 1990 are estimated at 2.5 Gt C (Miettinen, Hooijer, Vernimmen, Liew, & Page, 2017). In natural peatlands, peat soil accumulates under waterlogged conditions as the rate of plant productivity exceeds the rate of decomposition due to a lack of oxygen available for decomposition.…”

Tropical peat decomposability expressed through physical, chemical and biological properties under varying land management intensities

“…The combined impacts of fires and land-use change have led to the release of up to 0.25 Gt of C annually from peatlands in Southeast Asia, which is equivalent to approximately 2% of the global emissions from fossil fuel burning (Hooijer et al 2010;Page & Hooijer 2016;Miettinen et al 2017). In 2015, 54% (146 Mt C yr -1 ) of the total amount of CO2 emissions was released in decomposition processes, and the majority (113 Mt C yr -1 ) of the CO2 released in decomposition originated from smallholder farms and industrial plantations (Miettinen et al 2017). Land-use change is therefore turning tropical peatlands from globally significant C sinks and stores to major C sources.…”

“…Land management practices are another way of affecting the volume of CO2 released through decomposition, as the amount of CO2 emissions is known to depend on land management type (IPCC 2014;Miettinen et al 2017). Interestingly, CO2 emissions have been observed to decrease with time due to land alteration from PSF, being the lowest at stabilized, most intensively altered open sites (Hooijer et al 2012 and references within; IPCC 2014).…”