Widespread Drainage, Subsidence and CO2 Emissions in Tropical Peatlands

Abstract:

Tropical peatlands in Southeast Asia are a globally important carbon stock, which have sequestered carbon over thousands of years. However, they are being rapidly deforested and drained. In natural peat swamp forests, high water levels inhibit decomposition due to anoxic conditions. Peatland drainage lowers the water table and enables peat decomposition, resulting in large CO₂ emissions and subsidence of the land surface. In this work, we use InSAR remote sensing to track peatland subsidence at 90m resolution across 2.7Mha of peatland area in Indonesia and Malaysia. We observe widespread subsidence across all land uses on drained tropical peatlands, from plantations to smallholder agriculture to degraded peatland areas, with a mean rate of 2.2 cm/yr. In many cases, subsidence rates follow land use boundaries, demonstrating the importance of local management practices in controlling subsidence rates. Finally, we use these new subsidence measurements to suggest updates to IPCC emissions factors and to calculate regional CO₂ emissions in Southeast Asia. We find total CO₂ released as a result of peat oxidation is 155 ± 30 MtC/yr in 2015. Overall, InSAR offers a promising tool to map subsidence hotspots, monitor improved water table management practices, and quantify CO₂ emissions from drainage in tropical peatlands.