Trace element fixation in sediments rich in organic matter from a saline lake in tropical latitude with hydrothermal inputs (Sochagota Lake, Colombia): The role of bacterial communities

We studied the relationships between the trace element concentration in sediments from a saline lake at a tropical latitude (Sochagota Lake, Colombia) containing hydrothermal and anthropic inputs with the organic matter content, the mineral assemblage composition and the activity of the bacterial communities of the sediments. Organic matter-poor sediments (TOC < 0.7%) with quartz and kaolinite near the southern entrance of the lake were enriched in Zr (up to 603 mg/kg) and some major detrital elements (Na, Ti, Al and Si). Fine-sized clay-rich sediments deposited in the deep zones of the lake (central and northern segments) were characterized by substantial organic matter (up to 11.10%) and the crystallization of S-bearing minerals, clay mineral mixed layers and illite. These sediments were enriched in S, Fe, Zn, Mo, Rb, Co, K, Cr, Sb, Ni, As, Ba, Cu, Mn, Pb, P, Mg, and Sr. The presence of Fe sulfide nanoparticles enriched in heavy metals encrusting microbial cells and a dominant sulfate-reducing bacteria (SRB) community (Desulfatiglans, Desulfobacterales and Sva0485) suggested that the precipitation of the hydrothermal S and the accumulation of trace elements in the sediments was regulated by SRB activity. The crystallization of S°, barite and calcite and the good correlations between Ba, Sr and Ca indicated that previously precipitated sulfide can be oxidized by the activity of a relevant sulfur-oxidizing bacterial community (Thioalkalimicrobium, Sulfurovum, Arcobacter and Sulfurimonas), possibly facilitating the release of the metals.