Estimates of the remineralization and burial of organic carbon in Lake Baikal sediments

Sediment cores collected from several stations throughout lake Baikal in water depths from 100 m off the Selenga River delta to the deepest basin of the lake (similar to 1640 m), have been analyzed for sedimentary organic carbon, nitrogen, and the remineralized components in pore water. The organic carbon content of surface sediments generally varied from 2.3 to 3.2% by weight, and profiles typically showed an exponential decrease in both organic carbon and nitrogen in the upper 20-30 cm of the sediment column. Steady state models of organic matter diagenesis yield first order decomposition rate constants which range from 0.0009 to 0.022 y(-1). The calculated residence times for the metabolizable fraction of the organic matter in these sediments increases roughly with increasing water depth and is on the order of 50-300 years. Pore water concentration profiles were determined for dissolved inorganic carbon, dissolved organic carbon (DOC), methane, and dissolved ammonium. At depth (25-30 cm) methane concentrations ranged from 50 to 800 mu mol L-pw(-1) and DOC from 400 to 900 mu mol L-pw(-1). Estimation of carbon recycling rates based upon diffusion along pore water concentration gradients at the sediment-water interface, indicate that combined DOC and methane fluxes generally contribute <15% of the overall turn-over of sedimentary organic carbon. Comparisons to Laurentian Great Lakes environments show trends in sediment deposition, organic matter remineralization, and the time scales of carbon recycling across nearly two orders of magnitude with the fraction of organic content buried generally decreasing with decreasing sedimentation rates. (C) 2019 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.