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Abstract BackgroundMicroorganisms are the biotic foundation for nutrient cycling across ecosystems, and their assembly is often based on the nutrient availability of their environment. Though previous research has explored the seasonal lake turnover and geochemical cycling within the Salton Sea, California’s largest lake, the microbial community of this declining ecosystem has been largely overlooked. We collected seawater from a single location within the Salton Sea at 0 m, 3 m, 4 m, 5 m, 7 m, 9 m, 10 m, and 10.5 m depths in August 2021, December 2021, and April 2022. ResultsWe observed that the water column microbiome significantly varied by season (R² = 0.59,P = 0.003). Temperature (R² = 0.27,P = 0.004), dissolved organic matter (R² = 0.13,P = 0.004), and dissolved oxygen (R² = 0.089,P = 0.004) were significant drivers of seasonal changes in microbial composition. In addition, several halophilic mixotrophs and other extremotolerant bacteria were consistently identified in samples across depths and time points, though their relative abundances fluctuated by season. We found that while sulfur cycling genes were present in all metagenomes, their relative coverages fluctuated by pathway and season throughout the water column. Sulfur oxidation and incomplete sulfur oxidation pathways were conserved in the microbiome across seasons. ConclusionsOur work demonstrates that the microbiome within the Salton Seawater has the capacity to metabolize sulfur species and utilize multiple trophic strategies, such as alternating between chemorganotrophy and chemolithoautrophy, to survive this harsh, fluctuating environment. Together, these results suggest that the Salton Sea microbiome is integral in the geochemical cycling of this ever-changing ecosystem and thus contributes to the seasonal dynamics of the Salton Sea. Further work is required to understand how these environmental bacteria are implicated relationship between the Salton Sea’s sulfur cycle, dust proliferation, and respiratory distress experienced by the local population. 

Historically characterized by pristine streams that support robust populations of Arctic grayling, Dolly Varden, and chum salmon, the southern slopes of the Brooks Range provide valuable economic and subsistence resources for local communities. However, since 2019, dozens of formerly clear-running streams have turned turbid and orange with iron precipitates. Seeps have been identified in the tundra and in upland rock formations. Limited data show very low pH in seep water (less than 3.0), downslope vegetation mortality, and dramatic declines in juvenile fish abundance in affected headwaters. The causes of this rapidly spreading degradation of pristine streams remains unknown. The proliferation of turbid orange streams west of the Dalton Highway ( greater than 30 since 2019) is a threat to wilderness characteristics, drinking water, subsistence resource availability, and a growing commercial salmon fishery in northwest Alaska. With many terrestrial and aquatic species dependent upon the seasonal influx of salmon, the loss of fish habitat could induce ecosystem collapse, despite the protections afforded by a vast network of National Parks and Preserves. The degradation of formerly pristine streams is occurring at such a rapid pace that we may soon lose the opportunity to compare affected with nearby unaffected streams. This comparison is essential to develop the mechanistic, causal understanding that would allow us to predict which streams will turn next and the threats to downstream villages. The community of Kiana, for instance, sits at the confluence of the Squirrel and Kobuk Rivers. At least two streams in the Squirrel watershed have turned since 2020, while two large tributaries of the Kobuk turned in 2019. The Squirrel and large Kobuk tributaries, like the Salmon River, produce much of the fish harvested by Kiana residents. This dataset includes field measurements of pH, specific conductivity, dissolved oxygen and turbidity, along with laboratory measurements of metal concentrations in acidified water samples from tundra seeps, tributaries and rivers in the western Brooks Range. The watersheds that were sampled include Timber Creek, Tukpahlearik Creek, Salmon River, Kallarichuk River, Kobuk River and Devil's Lake, which is the drinking water source for the village of Kotzebue, Alaska.