The impact of disturbed peatlands on river outgassing in Southeast Asia

Abstract

River outgassing has proven to be an integral part of the carbon cycle. In Southeast Asia, river outgassing quantities are uncertain due to lack of measured data. Here we investigate six rivers in Indonesia and Malaysia, during five expeditions. CO2 fluxes from Southeast Asian rivers amount to 66.9±15.7 Tg C per year, of which Indonesia releases 53.9±12.4 Tg C per year. Malaysian rivers emit 6.2±1.6 Tg C per year. These moderate values show that Southeast Asia is not the river outgassing hotspot as would be expected from the carbon-enriched peat soils. This is due to the relatively short residence time of dissolved organic carbon (DOC) in the river, as the peatlands, being the primary source of DOC, are located near the coast. Limitation of bacterial production, due to low pH, oxygen depletion or the refractory nature of DOC, potentially also contributes to moderate CO2 fluxes as this decelerates decomposition.

Carbon Leaching from Tropical Peat Soils and Consequences for Carbon Balances

“…However, as indicated in experiment 1, such a low DOC groundwater concentration can only explain the DOC end-member concentration measured during our last expedition in April 2013 if one assumes an evapotranspiration of 67.7% as observed in pristine peat swamps ( Figure 3A). Considering however the overall status of Sumatran peat lands this appears unlikely which in turn supports the hitherto held assertion that an enhanced DOC respiration associated with the occurrence of a plankton bloom lowered the DOC concentrations in the Siak estuary in April 2013 (Wit et al, 2015).…”

“…Although this value is within the range of DOC end-member concentrations determined in the other studied rivers ( Table 1) it represents a real exception for the Siak. The low DOC concentrations in the Siak estuary which finally lead to the low DOC endmember concentrations were assumed to be caused by enhanced DOC respiration within an senescent plankton bloom that occurred in the estuary during our expedition (Wit et al, 2015).…”

Reviews and syntheses: Anthropogenic perturbations to carbon fluxes in Asian river systems: Concepts, emerging trends, and research challenges

“…A detailed study on rivers draining disturbed peatland areas in Indonesia and Malaysia revealed pCO2 values in the low-salinity areas between 4000 and > 8000 atm. Despite these relatively high pCO2 values, the rates of CO2 outgassing were found to be lower than what global models have generally suggested, implying that local-scale processes and sources of C need to be better constrained to improve region-specific C budgets (Wit et al, 2015).…”

“…An important factor affecting the riverine C fluxes in Southeast Asia is the rapid land use change including deforestation and associated peatland drainage, which can enhance C mobilization from the coastal peatlands and organic rich soils in the 140 region (Baum et al, 2007;Wit et al, 2015). A detailed study on rivers draining disturbed peatland areas in Indonesia and Malaysia revealed pCO2 values in the low-salinity areas between 4000 and > 8000 atm.…”

“…Nevertheless, land use change seems to be a critical factor affecting CO2 outgassing from the rivers of Southeast Asian 145 islands and lowland areas (Wit et al, 2015).…”