A Systemic Review of the Effects of Rewetting Tropical Peatlands on Methane and Carbon Dioxide Emissions

Tropical peatlands are important stores of carbon. Despite covering only 0.25 % of the earth’s surface they hold 3 % of all soil carbon. Rapid population growth, urban expansion, depletion of existing agriculture lands and increased demands for commodities such as palm oil and wood pulp are leading to rapid conversion of tropical peatlands and associated peat swamp forests. One of the main consequences of their conversion is increased GHG emissions following drainage because of peat decomposition. We reviewed the published literature using a systematic approach to investigate the effects of rewetting tropical peatlands on soil respiration, carbon accumulation and CH4 emissions. We also appraised the robustness of the emission factors for CO2 and CH4 from rewetted tropical peatlands derived in the 2013 IPCC Wetland Supplement. Rewetting tropical peatlands results in a reduction of CO2 while at the same time increasing CH4 emissions. Rewetting tropical peatlands may also restore their carbon sink function. We found the emission factor for CH4 did not fit well with the newly published data and was significantly lower than an alternative emission factor derived from this review. An alternative emission factor was also derived for CO2 and indicates rewetted tropical peatlands will sequester carbon (-0.58 t CO2-C ha-1 yr-1.). The emission factors derived by the Wetland Supplement and the alternative emission factors derived from this review are associated with large uncertainties arising from the lack of data on tropical peatlands. Given the role rewetting tropical peatlands will play in countries reaching their Nationally Determined Contributions under the Paris Agreement, further research is needed to derive more robust, country specific emission factors to assist in the formulation of meaningful mitigation strategies.