Seasonal hydrologic and geologic forcing drive hot spring geochemistry and microbial biodiversity

Hot springs integrate hydrologic and geologic processes that vary over both short- and long-term time scales. However, temporal hydrologic and geologic influences on hot spring biodiversity is unknown. We coordinated seasonal (~140 days) geochemical and microbial community analyses of three hot springs in Yellowstone National Park. A gradient in the responsiveness of spring geochemistry and microbiology to local aquifer changes was observed, with one spring exhibiting evidence of highly-responsive geochemical and biological changes following precipitation events, one exhibiting intermediate changes, and another exhibiting minimal changes. This variability is largely attributed to differences in the timing and extent of aquifer recharge with oxidized near-surface water from precipitation that then alters the abundances of sulfur-oxidizing microorganisms that generate sulfate and acidify spring waters. During sampling, a new spring formed after a period of heavy precipitation. The geochemistry and microbiology of the spring following its formation exhibited evidence of successional dynamics that were also influenced by surface water recharge. Collectively, these results indicate that changes in short-term hydrology driven by precipitation can significantly impact hot spring geochemistry and microbial biodiversity. These results point to the susceptibility of hot springs and their biodiversity to sustained, longer-term hydrologic changes that could accompany climate change.