LRES PhD Dissertation Defense
- Monday, August 14, 2017 at 2:00pm
- Animal Biosciences Building, 134 - view map
Land-Atmosphere Exchange of Carbon and Energy at a Tropical Peat Swamp Forest in Sarawak, Malaysian Borneo
Abstract: Tropical peatlands comprise 11% (44 Mha) of the global peat area of ca. 400 Mha, largely in the coastal lowlands of Southeast Asia (56% or 25 Mha). Tropical peat ecosystems are estimated to store about 89 Gt of carbon (C), equivalent to the C stock in the aboveground biomass of the Amazonian rainforest. However, considerable uncertainties remain about their present role in global C cycle as interannual ecosystem-scale measurements of undisturbed tropical peat forests have not been measured to date. Hence, an eddy covariance tower was instrumented in a tropical peat forest in Sarawak, Malaysia over four years from 2011 to 2014. We found that the forest was a net source of CO2 to the atmosphere during every year of measurement, similar to a hydrologically disturbed tropical peat forest in central Kalimantan, Indonesian Borneo. The inter-annual variation in net ecosystem CO2 exchange (NEE) was largely modulated by the variation in gross primary production (GPP), which was jointly controlled by vapor pressure deficit (VPD) and leaf area index (LAI) in addition to photosynthetically active photon flux density (PPFD). Greater reduction of GPP in 2011 and 2012, resulting in relative high CO2 emissions, are attributed to the relative low atmospheric transmission due to massive peat fires in Indonesia. Temporal changes in ecosystem respiration (RE) were closely related to water table depth.
Similarly, no analysis to our knowledge has measured whole-ecosystem methane (CH4) flux from a tropical peat forested wetland to date despite their importance to global CH4 budget. The two-month average of C-CH4 flux measurements, on the order of 0.024 g C-CH4 m-2 d-1, suggests that tropical peat forests are not likely to be disproportionally important to global CH4 flux if the study ecosystem is representative of other tropical peat forests. Results demonstrate a limited ability for simple models to capture the variability in the diurnal pattern of CH4 efflux, but also consistent responses to soil moisture, water table height, and precipitation over daily to weekly time scales.
We found that both sensible heat flux (H) and latent heat flux (LE) and their ratio (the Bowen ratio, Bo) were relatively invariant compared to other tropical rainforests with LE values on the order of 11 MJ m-2 day and H on the order of 3 MJ m-2 day-1.Annual evapotranspiration (ET) did not differ among years and averaged 1579 ± 47 mm year-1. The magnitude of average daily LE across the calendar year tended to be higher at MY-MLM (11 MJ m-2 day-1) than most other tropical rainforest ecosystems in the FLUXNET2015 database Results demonstrate important differences in the seasonal patterns in water and energy exchange in tropical rainforest ecosystems that need to be captured by models to understand how ongoing changes in tropical rainforest extent impact the global climate system.
- Department of Land Resources and Environmental Sciences