CO2 supersaturation is sustained by coupled CH4 production and oxidation in a tropical flood-pulse lake

Abstract:

CO₂ supersaturation within lakes and rivers worldwide is commonly attributed to terrestrial-aquatic transfers of inorganic and organic C and subsequent, in-situ aerobic respiration. However, anaerobic metabolism such as coupled CH₄ production and oxidation can also contribute CO₂ to inland waters. Many tropical lakes and rivers have a distinct flood-pulse hydrology, seasonally inundating floodplains and creating widescale reducing conditions. We measured partial pressures and isotopic compositions of CO₂ and CH₄ and aerobic ecosystem metabolism in Tonle Sap Lake (Cambodia) to address the hypothesis that CO₂ supersaturation in this tropical flood-pulse lake is sustained by CH₄ production and oxidation. CO₂ supersaturation ranged from 3,200 to 41,900 uatm and could not be explained by in-situ aerobic respiration, alone. Stable C isotopes showed that 70-90 % of dissolved CO₂ was derived from coupled CH₄ production and oxidation. Our results demonstrate that anaerobic metabolism can play an important role in CO₂ supersaturation within inland waters.