Effect of permafrost thawing on organic carbon and trace element colloidal speciation in the thermokarst lakes of western Siberia

• Published in: Biogeosciences
• Main Authors: O. S. Pokrovsky, L. S. Shirokova, S. N. Kirpotin, S. Audry, J. Viers, B. Dupré
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2011
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; palsa; permafrost; Thermokarst; Siberia
• Online Access: https://doi.org/10.5194/bg-8-565-2011; https://doaj.org/article/4f1a9aae89984ef88c543a90e331beaf

To examine the mechanisms of carbon mobilization and biodegradation during permafrost thawing and to establish a link between organic carbon (OC) and other chemical and microbiological parameters in forming thermokarst (thaw) lakes, we studied the biogeochemistry of OC and trace elements (TEs) in a chronosequence of small lakes that are being formed due to permafrost thawing in the northern part of western Siberia. Twenty lakes and small ponds of various sizes and ages were sampled for dissolved and colloidal organic carbon, metals and culturable heterotrophic bacterial cell number. We observed a sequence of ecosystems from peat thawing and palsa degradation due to permafrost subsidence in small ponds to large, km-size lakes that are subject to drainage to, finally, the khasyrey (drained lake) formation. There is a systematic evolution of both total dissolved and colloidal concentration of OC and TEs in the lake water along with the chronosequence of lake development that may be directly linked to the microbial mineralization of dissolved organic matter and the liberation of the inorganic components (Fe, Al, and TEs) from the organo-mineral colloids. In this chronosequence of lake development, we observed an apparent decrease in the relative proportion of low molecular weight <1 kDa (1 kDa ~ 1 nm) OC concentration along with a decrease in the concentration of total dissolved (<0.45 μm) OC. This decrease was accompanied by an increase in the small size organic ligands (probably autochthonous exometabolites produced by the phytoplankton) and a simultaneous decrease in the proportion of large-size organic (humic) complexes of allochthonous (soil) origin. This evolution may be due to the activity of heterotrophic bacterioplankton that use allochthonous organic matter and dissolved nutrients originating from peat lixiviation. Most insoluble TEs demonstrate a systematic decrease in concentration during filtration (5 μm, 0.45 μm) exhibiting a similar pattern among different samples. At the same time, there is an ...