UC Riverside

The Salton Sea lies at the forefront of scientific and socio-economic interests. An endorheic, polymictic lake, the Sea is characterized by elevated sulfate concentrations and sulfide eruptions within its hypersaline waters. As the lake experiences intense evaporation due to hot, arid conditions and diminishing water supply, it undergoes stratification and increasing salinity. In the summer, wind-driven mixing events cause the upwelling of anoxic hydrogen sulfide-rich bottom waters, leading to hypoxic/anoxic conditions throughout.

This study aims to elucidate the links between microbial consortia and geochemistry by teasing out spatial and temporal data for redox patterns, particularly in light of the Sea’s recent shallowing and evolving thermally supported chemoclines. Water column samples were surveyed from the Sea’s southern basin across three seasons and four dates, including a sulfide-rich upwelling event. Geochemical data were gathered, and microbial diversity was analyzed using 16s rRNA Amplicon sequencing.

Results reveal significant seasonal microbial assemblage variations (p= 0.001). Changes in microbial diversity and species richness did not significantly differ by depth (p > 0.05); however, there were notable changes at the chemocline, as shifts in microbial taxa reflected stratified summer waters and mixed winter/ spring waters. Microbial community composition was significantly impacted by temperature (p= 0.001) and oxidation-reduction potential (ORP) (p=0.001). Variations in diversity were evident when analyzing seasonal shifts and geochemical constituents, as modifications to metabolic pressure and electron acceptor availability determined microbial ecologies influenced by redox conditions.

Archaeal diversity was lower than bacterial diversity, with Halobacterota and Nanoarchaeota as the only two taxa found. DS001 spp. and Litoricola spp. were the most abundant genera across all samples. Truepera spp. was abundant in the winter and spring, while cyanobacteria Synechococcus spp. was abundant in August. The novel presence of DS001 suggested the microbial capacity for detoxifying pesticides by mineralizing Methyl Parathion as a carbon source in the Sea, where this toxic contaminant is pervasive in the water, sediments, and fish species. Actinobacteria, Gammaproteobacteria, Alphaproteobacteria, and Bacteroidetes were the most prevalent microbial classes. Abundance of these taxa suggests that the Salton Sea’s evolving microbial composition mirrors soda saline lake patterns, indicating a potential shift towards similar ecosystems.