Effect of plant-mediated oxygen supply and drainage on greenhouse gas emission from a tropical peatland in Central Kalimantan, Indonesia

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Abstract

To evaluate the hypothesis that plant-mediated oxygen supplies decrease methane (CH4) production and total global warming potential (GWP) in a tropical peatland, the authors compared the fluxes and dissolved concentrations of greenhouse gases [GHGs; CH4, carbon dioxide (CO2) and nitrous oxide (N2O)] and dissolved oxygen (DO) at multiple peatland ecosystems in Central Kalimantan, Indonesia. Study ecosystems included tropical peat swamp forest and degraded peatland areas that were burned and/or drained during the rainy season. CH4 fluxes were significantly influenced by land use and drainage, which were highest in the flooded burnt sites (5.75 +/- 6.66 mg C m(-2) h(-1)) followed by the flooded forest sites (1.37 +/- 2.03 mg C m(-2) h(-1)), the drained burnt site (0.220 +/- 0.143 mg C m(-2) h(-1)), and the drained forest site (0.0084 +/- 0.0321 mg C m(-2) h(-1)). Dissolved CH4 concentrations were also significantly affected by land use and drainage, which were highest in the flooded burnt sites (124 +/- 84 mu mol L-1) followed by the drained burnt site (45.2 +/- 29.8 mu mol L-1), the flooded forest sites (1.15 +/- 1.38 mu mol L-1) and the drained forest site (0.860 +/- 0.819 mu mol L-1). DO concentrations were influenced by land use only, which were significantly higher in the forest sites (6.9 +/- 5.6 mu mol L-1) compared to the burnt sites (4.0 +/- 2.9 mu mol L-1). These results suggest that CH4 produced in the peat might be oxidized by plant-mediated oxygen supply in the forest sites. CO2 fluxes were significantly higher in the drained forest site (340 +/- 250 mg C m(-2) h(-1) with a water table level of -20 to -60 cm) than in the drained burnt site (108 +/- 115 mg C m(-2) h(-1) with a water table level of -15 to +10 cm). Dissolved CO2 concentrations were 0.6-3.5 mmol L-1, also highest in the drained forest site. These results suggested enhanced CO2 emission by aerobic peat decomposition and plant respiration in the drained forest site. N2O fluxes ranged from -2.4 to -8.7 mu g N m(-2) h(-1) in the flooded sites and from 3.4 to 8.1 mu g N m(-2) h(-1) in the drained sites. The negative N2O fluxes might be caused by N2O consumption by denitrification under flooded conditions. Dissolved N2O concentrations were 0.005-0.22 mu mol L-1 but occurred at < 0.01 mu mol L-1 in most cases. GWP was mainly determined by CO2 flux, with the highest levels in the drained forest site. Despite having almost the same CO2 flux, GWP in the flooded burnt sites was 20% higher than that in the flooded forest sites due to the large CH4 emission (not significant). N2O fluxes made little contribution to GWP.

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