Organic Carbon in the Bottom Sediments of Lake Baikal: Geochemical Processes of Burial and Balance Values

Abstract

This is the first study of dissolved organic matter (DOM) at the Lake Baikal water-bottom interface. High-resolution profiles of dissolved organic carbon (DOC) were obtained simultaneously with dissolved inorganic carbon (DIC), total dissolved carbon, cations (Na+, K+, Ca2+, Mg2+, Fe2+, and Mn2+), and anions (HCO3−, Cl−, NO3−, and SO42−) in the pore water of Lake Baikal deepwater oxidized sediments. We evaluated the DOC fluxes quantitatively and qualitatively. They changed their direction twice under different redox conditions in the sediments (at the redox interfaces). The study revealed that the mobilization of DOC in anoxic sediments was closely related to the reductive dissolution of Fe(III) minerals, and the oxidized surface lake sediments represented an effective DOC trap binding DOC to ferric minerals. Redox conditions appeared to be the main regulator of the DOC exchange. Oxygen conditions led to the uptake of DOC by sediments (31–78 mmol C m−2 yr−1), i.e., the Lake Baikal sediments are a sink of DOC. The DOC flux was approximately 25–35% of the carbon flux at the sediment–water interface. The results of this study allow for a better understanding of the nature and properties of DOC in freshwater ecosystems and compensate for the underestimation of DOC in the internal carbon cycle of the lake.