Lateral carbon fluxes and CO<sub>2</sub> outgassing from a tropical peat-draining river

Abstract

Abstract. Tropical peatlands play an important role in the global carbon cycle due to their immense carbon storage capacity. However, pristine peat swamp forests are vanishing due to deforestation and peatland degradation, especially in Southeast Asia. CO2 emissions associated with this land use change might not only come from the peat soil directly, but also from peat-draining rivers. So far, though, this has been mere speculation, since there was no data from undisturbed reference sites. We present the first combined assessment of lateral organic carbon fluxes and CO2 outgassing from an undisturbed tropical peat-draining river. Two sampling campaigns were undertaken on the Maludam river in Sarawak, Malaysia. The river catchment is covered by protected peat swamp forest, offering a unique opportunity to study a peat-draining river in its natural state, without any influence from tributaries with different characteristics. The two campaigns yielded consistent results. Dissolved organic carbon (DOC) concentrations ranged between 3222 and 6218 μmol L−1 and accounted for more than 99 % of the total organic carbon (TOC). Radiocarbon dating revealed that the riverine DOC was of recent origin, suggesting that it derives from the top soil layers and surface runoff. We observed strong oxygen depletion, implying high rates of organic matter decomposition and consequently CO2 production. The measured median pCO2 was 7795 and 8400 μatm during the two campaigns, respectively. Overall, we found that only 26 ± 15 % of the carbon was exported by CO2 evasion, while the rest was exported by discharge. CO2 outgassing seemed to be moderated by the short water residence time. Since most Southeast Asian peatlands are located at the coast, this is probably an important limiting factor for CO2 outgassing from most of its peat-draining rivers.

Riverine carbon fluxes to the South China Sea

“…The CO 2 outgassing flux is determined by gas exchange velocities and differences between the partial pressure of dissolved CO 2 ( p CO 2 ) in the water and in the atmosphere. There are high p CO 2 values (6000–9000 μatm) in peat‐draining rivers, because numerous soil organic carbon decompose into inorganic carbon and release hydrogen ion [ Müller et al ., ]. The contributors of high p CO 2 values (mean = 1090 μatm) in the Mekong River include the fresh soil organic carbon influx to rivers and in situ aquatic primary production, but the p CO 2 values decrease due to the dilution effect of rain [ Li and Bush , ; Li et al ., ].…”

Riverine CO2 emissions in the Wuding River catchment on the Loess Plateau: Environmental controls and dam impoundment impact

“…The surface water pCO 2 was determined using the headspace equilibrium method [Müller et al, 2015]. Using an 1100 mL conical flask, we collected 550 mL of water from~10 cm below the surface and the remaining Journal of Geophysical Research: Biogeosciences 10.1002/2016JG003713 550 mL was filled with ambient air.…”

The Potential Hidden Age of Dissolved Organic Carbon Exported by Peatland Streams

“… 14 C values for dissolved organic carbon exported from peatland catchments that have been heavily disturbed (e.g., by drainage; Moore et al, ), semidisturbed (e.g., by long‐term impacts from minor human activity; Billett et al, ), or relatively undisturbed by human activity (Aiken et al, ; Dean, van der Velde, et al, ; Campeau et al, ; Hulatt, Kaartokallio, Oinonen, et al, ; Hulatt, Kaartokallio, Asmala, et al, ; Ledesma et al, ; Leith et al, ; Marwick et al, ; Müller et al, ; Stimson et al, , ). Modern DO 14 C values plot above the dotted line; the number of modern values for each catchment type is shown in blue, and the number of values older than modern is shown in red (total n = 209; see supporting information for data sources).…”