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.
Highlights
River outgassing has proven to be an integral part of the carbon cycle
The importance of inland waters in the global carbon cycle has gained more awareness since the last decade through studies which have revealed that inland waters are not a passive conduit but play an integral role both for carbon storage and greenhouse gas emissions to the atmosphere[1,2,3,4]
An estimate of inland water outgassing by Raymond et al.[6] revealed an emission of 2.1 Pg C per year, of which 1.8 Pg C per year from streams and rivers, which is significantly larger than previous estimates
Summary
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. The importance of inland waters in the global carbon cycle has gained more awareness since the last decade through studies which have revealed that inland waters (rivers, streams, lakes, reservoirs and estuaries) are not a passive conduit but play an integral role both for carbon storage and greenhouse gas emissions to the atmosphere[1,2,3,4] These studies estimate, in line with the 5th Assessment IPCC Report[5], that on a global scale B45–60% (0.9–1.4 Pg C per year) of carbon entering the freshwater system is decomposed and emitted back to the atmosphere as CO2. CO2 fluxes for SE-Asia are calculated, which reveal moderate fluxes and show that SE-Asia is not a hotspot for river outgassing
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