In-situ activities of anaerobic bacteria and methanogenic archaea in shallow lakes over the Anthropocene: A case study of Lake Wuliangsu

Abstract

Understanding microbial activities in shallow lake system under anthropogenic interferences is very important for evaluation on organic carbon (OC) source-sink behaviors. Theoretically, glycerol dialkyl glycerol tetraethers (GDGTs) could signal in-situ anaerobic microbial activities in shallow lakes. Here we test this theory by analyzing GDGTs of sediment samples collected in Lake Wuliangsu, a typical large and shallow lake located in the Yellow River Reaches. Considering that lake surface sediments show different occurrences and distribution patterns with lake shore and riverine sediments, brGDGTs and GDGT-0 should be mainly produced by heterotrophic anaerobic bacteria (Acidobacteria) and methanogenic archaea (Euryarchaeota) within the lake, while crenarchaeol from soil OC transported through the Yellow River system. With the assistant of a two end-member model, in-situ and soil-derived brGDGTs can be quantitatively evaluated. Following these discoveries, we further utilized GDGT-based records from a well-dated sedimentary core to disentangle the past ∼180-year history of anaerobic microbial activities in Lake Wuliangsu. The in-situ anaerobic microbial activities started to increase at CE 1926 and showed stronger predominance over soil-derived tetraether lipids after CE 1954, largely due to a combined effect from hydrological change and in-situ OC production resulting in OC-rich and anaerobic conditions for heterotrophic anaerobic microorganisms to prosperous. However, the relative contribution of in-situ anaerobic microbial GDGTs to overall sedimentary OC shows complex relations with both OC production and recycling behaviors, tentatively suggesting that anaerobic microbial activities only conduct a minor impact on OC burial in the shallow and eutrophic Lake Wuliangsu over the Anthropocene.