Lateral carbon fluxes and CO2 outgassing from a tropical peat-draining river

[摘要] Tropical peatlands play an important role in the global carbon cycledue to their immense carbon storage capacity.However, pristinepeat swamp forests are vanishing due to deforestation and peatlanddegradation, especially in Southeast Asia. CO₂ emissionsassociated with this land use change might not only come from thepeat soil directly but also from peat-draining rivers. So far,though, this has been mere speculation, since there has been no data fromundisturbed reference sites. We present the first combinedassessment of lateral organic carbon fluxes and CO₂outgassing from an undisturbed tropical peat-draining river. Twosampling campaigns were undertaken on the Maludam River in Sarawak,Malaysia.The river catchment is covered by protected peat swampforest, offering a unique opportunity to study a peat-draining riverin its natural state, without any influence from tributaries withdifferent characteristics. The two campaigns yielded consistentresults. Dissolved organic carbon (DOC) concentrations rangedbetween 3222 and 6218 μmol L⁻¹ and accounted formore than 99 % of the total organic carbon (TOC). Radiocarbondating revealed that the riverine DOC was of recent origin,suggesting that it derives from the top soil layers and surfacerunoff. We observed strong oxygen depletion, implying high rates oforganic matter decomposition and consequently CO₂production. The measured median pCO₂ was 7795 and8400 μatm during the first and second campaign, respectively.Overall, we found that only 32 ± 19 % of the carbon wasexported by CO₂ evasion, while the rest was exported bydischarge. CO₂ outgassing seemed to be moderated by theshort water residence time. Since most Southeast Asian peatlands arelocated at the coast, this is probably an important limiting factorfor CO₂ outgassing from most of its peat-draining rivers.

[学科分类] 地球化学与岩石