Microbial dolomite precipitation using sulfate reducing and halophilic bacteria: Results from Qinghai Lake, Tibetan Plateau, NW China

Past studies have revealed the important roles of certain types of microbes in precipitating dolomite in coastal hypersaline lakes and lagoons, and marine sediments, however, it is still poorly known if other types of microbes can precipitate dolomite in low-salinity lakes without any marine influence. The objective of this study was therefore to expand the microbial dolomite precipitation model by investigating the origin of dolomite in the sediments of Qinghai Lake, an inland, slightly saline lake (salinity 12.5 g/L) on the Tibetan Plateau, NW China. This objective was accomplished via an integrated approach combining geochemical investigations of natural dolomite present in the lake sediments with laboratory precipitation experiments. A 5-m sediment core was collected and pore water chemistry was analyzed. Calculation of saturation index indicated that dolomite was oversaturated in sediment pore water. Sub-spherical grains of dolomite with abundant pores and microstructures, similar to microbially precipitated dolomite, were found in the sediments, suggesting a biogenic origin. Dolomite precipitation experiments were set up in the laboratory to simulate the natural conditions of the Qinghai Lake. Dolomite was precipitated using sulfate reducing bacterium (SRB) Desulfotomaculum ruminis and aerobic halophilic bacterium Halomonas marina present in the Qinghai Lake sediments. Aqueous geochemistry and mineral characterization data collectively suggest that dolomite precipitation was accomplished via increase of pH and alkalinity to overcome the kinetic inhibitors and exopolymeric substances (EPS) and cell walls as possible nucleation sites. These results expand the current microbial dolomite precipitation model and have implications for dolomite formation in slightly saline, inland lake environments.

Research Highlights
► Biogenic dolomite was revealed in a non-hypersaline inland lake, Qinghai Lake, NW China.
► Pore water of the Qinghai Lake sediments was supersaturated with respect to dolomite.
► Laboratory experiment confirmed the role of SRB and halophilic bacteria in dolomite precipitation.
► Increase of pH and alkalinity overcame the kinetic inhibitors to dolomite formation.
► Exopolymeric substances and cell walls serve as nucleation sites for dolomite precipitation.