Potential Carbon Loss from Soil Subsidence of Rewetted Tropical Agricultural Peatlands in West Kalimantan, Indonesia

Tropical peatland drainage accelerates soil subsidence and carbon loss, yet short-term responses to rewetting in agricultural peatlands remain insufficiently evaluated. This study assessed peat subsidence, groundwater-table dynamics, soil properties, and potential carbon loss in three land conditions in Punggur Kecil, Kubu Raya, West Kalimantan, Indonesia, i.e., canal-blocked agricultural peatland (CB), non-canal-blocked agricultural peatland (NCB), and shrub peatland (SB). At each site, nine plots were established along three transects, with one subsidence pole and one groundwater-table observation point per plot. Annualized subsidence and potential carbon-loss values were extrapolated from only five months of monitoring (June to October 2025), using regression-based monthly subsidence rates. Soil properties from the upper 0 to 50 cm were analyzed to interpret subsidence and carbon loss estimates. Results show that soil subsidence rates were 5.14±1.54 cm year-¹ in NCB, 5.23±1.40 cm year-¹ in CB, and 6.34±1.44 cm year-¹ in SB. Potential carbon loss was highest in NCB (125.29±57.97 tons CO₂-eq ha-¹ year-¹), followed by SB (111.92±29.85) and CB (108.13±38.62). These results show that carbon loss was determined not only by subsidence, but also by intrinsic soil properties, especially bulk density and organic carbon content. The CB site had slightly higher subsidence than NCB but lower carbon loss, indicating that rewetting effects require longer evaluation.