Carbon fluxes from tropical peatlands : methane, carbon dioxide, and peatland subsidence

Abstract

Tropical peatlands in Southeast Asia have sequestered carbon over thousands of years and are an important global carbon stock. In natural peat swamp forests, high water levels inhibit decomposition due to anoxic conditions. However, they are being rapidly deforested and drained, releasing stored carbon to the atmosphere. In this thesis, we investigate the carbon dioxide and methane fluxes from both pristine and degraded peat swamp forests in Borneo using field measurements, modeling and remote sensing. We first study methane fluxes from natural peatlands. We use an isotope-based mass transport model to evaluate the extent of methane production, transport and oxidation. We find an order of magnitude more methane is produced than surface fluxes suggest. This dissolved methane is transported belowground to the rivers and streams draining peatlands. However, much of this methane is oxidized before reaching the atmosphere. We then study CO₂ emissions from peatlands. At the local scale, we use automated soil respiration chambers to assess how CO₂ emissions depend on temperature and water table. At a regional scale, we use remote sensing to investigate carbon losses due to peatland degradation. Drainage of peatlands enables peat decomposition and results in subsidence of the land surface. We track this subsidence using InSAR satellite data and use it to quantify regional CO₂ emissions. The spatial resolution of our technique allows us to uncover correlations with past and present land uses and peatland hydrology.