Impacts of Rewetting Degraded Peatlands on Greenhouse Gas fluxes in West Kalimantan, Indonesia

Indonesia has more than 13 million hectares of peatlands, however almost half of them are degraded or drained, thereby emitting significant amounts of greenhouse gases (GHG). Peatland restoration is recognized as one of the main mitigation strategies in achieving Indonesia’s emission reduction target by 2030. Unfortunately, there is considerable uncertainty surrounding emissions from peatland restoration, primarily from rewetting efforts.  Therefore, our study aims to refine the science surrounding the impact of rewetting on GHG fluxes in drained peatlands in three ecosystems: secondary forest, oil palm plantation, and shrublands. We monitored CO₂ and CH₄ fluxes biweekly using LiCOR LI-7810 Trace Gas Analyzer from January to December 2022 in five sites in Mempawah Regency, West Kalimantan, Indonesia. We deployed two transects (both rewetted and drained) in oil palm and shrublands, and one transect in secondary forest. Each transect had five pairs (both trenched-non-trenched) of collars, with 50 chambers total to measure total soil and heterotrophic respiration and CH₄ emissions. GHG fluxes were measured concomitantly with water table depth, soil temperature, air temperature, and soil moisture. Soil samples were collected (0–10 cm soil depth) to determine physicochemical properties, including bulk density, soil organic C content, nitrogen content, and other relevant parameters. In rewetted oil palm plantations, total CO₂ emissions were reduced by 30% (29 tons CO₂/ha/yr) compared to drained areas (41.9 tons CO₂/ha/yr). The emissions from the secondary forest (29.2 tons CO₂/ha/yr) were relatively similar compared to that of rewetted oil palm plantations, even though the water table level in the rewetted oil palm plantation site was higher (44cm below the surface) than in the secondary forest (60cm below the surface), indicating the importance of the role of vegetation in controlling CO₂ emissions. We did not detect a significant difference in the total soil CO₂ emissions in rewetted (55.5 tons CO₂/ha/yr) and drained shrublands (60.8 tons CO₂/ha/yr), which we attributed to improperly installed canal blocks as the water table level is relatively similar between two transects. Heterotrophic respiration contributed 53%, 77%, and 84% of the total soil CO₂ emissions in shrublands, secondary forests, and oil palm plantations, respectively. In addition, we did not observe any significant difference in CH₄ emissions from drained and rewetted areas either in shrub or oil palm sites. A dependency of soil CO₂ emissions on changes in water table level and vegetation cover was demonstrated in all sites. The findings of this research indicate that, if properly installed, canal blocking employed as a rewetting approach can reduce CO₂ emissions in tropical drained peatlands. However, they don’t have a measurable impact on CH₄ emissions