Greenhouse gas fluxes from tropical peatlands in south‐east Asia

Abstract

The lowland peatlands of south-east Asia represent an immense reservoir of fossil carbon and are reportedly responsible for 30% of the global carbon dioxide (CO 2 ) emissions from Land Use, Land Use Change and Forestry. This paper provides a review and meta-analysis of available literature on greenhouse gas fluxes from tropical peat soils in south-east Asia. As in other parts of the world, water level is the main control on greenhouse gas fluxes from south-east Asian peat soils. Based on subsidence data we calculate emissions of at least 900 g CO 2 m À2 a À1 ($ 250 g C m À2 a À1 ) for each 10 cm of additional drainage depth. This is a conservative estimate as the role of oxidation in subsidence and the increased bulk density of the uppermost drained peat layers are yet insufficiently quantified. The majority of published CO 2 flux measurements from southeast Asian peat soils concerns undifferentiated respiration at floor level, providing inadequate insight on the peat carbon balance. In contrast to previous assumptions, regular peat oxidation after drainage might contribute more to the regional long-term annual CO 2 emissions than peat fires. Methane fluxes are negligible at low water levels and amount to up to 3 mg CH 4 m À2 h À1 at high water levels, which is low compared with emissions from boreal and temperate peatlands. The latter emissions may be exceeded by fluxes from rice paddies on tropical peat soil, however. N 2 O fluxes are erratic with extremely high values upon application of fertilizer to wet peat soils. Current data on CO 2 and CH 4 fluxes indicate that peatland rewetting in south-east Asia will lead to substantial reductions of net greenhouse gas emissions. There is, however, an urgent need for further quantitative research on carbon exchange to support the development of consistent policies for climate change mitigation.

Planning hydrological restoration of peatlands in Indonesia to mitigate carbon dioxide emissions

“…Rewetting of drained tropical peatlands will potentially lead to large mitigations of carbon dioxide emissions (Couwenberg et al 2009). Quantifying the rise in groundwater levels of hydrological restoration projects in peatlands together with an estimation of the mitigation in CO 2 emissions caused by this rise, is important information to make greenhouse gas emission mitigations tradable under the voluntary carbon market or REDD (Reducing Emissions from Deforestation and Degradation) mechanism.…”

“…After construction of all dams, hydrological modelling indicates a rise of annual average groundwater levels of 20 cm. With a reported emission mitigation of approximately 0.8-0.9 t CO 2 ha −1 a −1 per centimetre groundwater level rise (Couwenberg et al 2009;Hooijer et al 2006), rewetting of the 590 km 2 area of the combined Bakung and Bangah catchments results in an estimated mitigated emission of 1.4-1.6 Million tons CO 2 annually. This estimated emission mitigation will not be achieved in the first year after all dams have been constructed because only with time sedimentation of organic and mineral material upstream of the dams makes them fully effective.…”

“…In the project area, long-term measurements of groundwater levels (before and after dam construction) as well as subsidence and gas flux emissions are needed to confirm these preliminary results. In this study, conservative estimates were used of both the reduced CO 2 emission rate per centimetre groundwater level rise (Couwenberg et al 2009;Hooijer et al 2006) as well as of the magnitude of the groundwater level rise itself. Results are reported as a class to reflect the uncertainty in the calculations.…”

“…Lowering the groundwater level which naturally is close to the peat surface throughout the year while fluctuating with the intensity and frequency of rainfall, results in an increase in CO 2 emissions. In a recent review it is estimated that an increase of drainage depth by 10 cm results in the emission of about 9 t CO 2 ha −1 a −1 (Couwenberg et al 2009). …”

Peat decomposability in managed organic soils in relation to land use, organic matter composition and temperature

“…Drained organic soils under forest can act as both net sinks or sources of atmospheric CO 2 (Cannell et al, 1993;Minkkinen and Laine, 1998;Minkkinen et al, 1999;Wüst-Galley et al, 2016), although they are in general considered to represent a source with average net CO 2 emissions of 2.0-3.3 t C ha −1 a −1 in the temperate zone (IPCC, 2014). Temperature and soil moisture regime, which depends on drainage depth, among other factors, have the greatest influence on peat decay in drained organic soils (Hogg et al, 1992;Berglund, 1995;Scanlon and Moore, 2000;Chimner and Cooper, 2003;Couwenberg et al, 2010;Leifeld et al, 2012). However, there are substantial differences in CO 2 emissions from organic soils with similar drainage and cultivation properties.…”