Greenhouse Gas Emissions from Channels Draining Intact and Degraded Tropical Peat Swamp Forest

Kent, Matthew (2019). Greenhouse Gas Emissions from Channels Draining Intact and Degraded Tropical Peat Swamp Forest. PhD thesis The Open University.



Degradation of tropical peat swamp forest (PSF) can destabilise the ecosystem carbon balance with significant amounts of carbon lost via drainage channels. Peat-draining channels are typically supersaturated with greenhouse gases and can constitute evasive hotspots within catchments, but losses by fluvial emissions have not yet been quantified for intact and degraded PSF. These fluvial emissions are presented in this study, which considers differences between land-use classes, across both wet and dry seasons, and how fluvial greenhouse gas fluxes were affected by a strong El Niño.

Wet season CO2 emissions were ≤2-times higher than dry season emissions, for both land classes, with normal seasonal ranges of 3.36−4.67 and 2.58−3.13 g∙CO2-C∙m-2∙d-1 for the intact and degraded land classes, respectively. When scaled up, the intact and degraded PSF channels contributed less than a millionth, and <1%, of total CO2 flux, respectively, to landscape-scale ecosystem emissions. Radiocarbon dating of channel CO2 found that it was recently photosynthesised for the intact PSF, but the age of the degraded PSF CO2-C was 341−1655 BP, indicating that carbon from deep peat layers was being degraded.

Diffusive CH4 fluxes from channels were ≤9−times higher in degraded PSF than in intact PSF, the ranges being 9.47−16.8 and 1.25−2.16 mg∙CH4-C∙m-2∙d-1, respectively. The El Niño event caused an anomalous water table drawdown which resulted in a state shift in the intact PSF whereby channels produced quantities of CH4 comparable to the degraded PSF; however, CH4 fluxes returned to normal afterwards, demonstrating ecosystem resilience. The El Niño also promoted the lowest and highest fluxes of CO2 and CH4, respectively, at both land classes. Channel emissions made a negligible contribution to total CH4 fluxes at the intact PSF, but channels at the degraded PSF, which cover 0.5% of the landscape, may have contributed ≤68% of the total landscape CH4 flux when ebullition estimates are included.

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