Subsidence and soil CO2 efflux in tropical peatland in southern Thailand under various water table and management conditions

At the Bacho peatland in southern Thailand, peat subsidence was measured at four locations on abandoned agricultural land (degraded peat swamp forest) and at one location in a conservation zone, at monthly intervals over a period of more than 20 years. Average peat subsidence rates during the observation period were 3.1–5.2 cm y?1 on the degraded peatland, reducing to 1.8–2.6 cm y?1 when peat loss due to field fires was discounted, and 1.0 cm y?1 reducing to 0.7 cm y-1 in the conservation zone. Due to martial law restrictions on access to the Bacho site, measurements of the peat soil respiration rate under various water table conditions were made mostly at other sites in Thailand with similar climate. During these measurements the position of the water table ranged from 0.92 m above the peat surface to more than one metre below it, and daily mean respiration rates ranged from 0.57 to 8.20 ?mol CO2 m?2 s?1. The CO2 efflux attributed to peat respiration was 13.7–18.9 Mg ha?1 y?1 on the degraded peatland but only 7.5 Mg ha?1 y?1 in the conservation zone. To simulate the CO2 efflux resulting from soil respiration at Bacho on the basis of data collected elsewhere, we developed an empirical three-stage model (NAIS Peat Model) that treats the position of the water table as a proxy variable. The observed values of peat subsidence were in good agreement with simulated values of CO2 efflux in two tests. The implications for peatland management are considered.