Date of Award:


Document Type:


Degree Name:

Master of Science (MS)



Committee Chair(s)

Dennis Newell


Dennis Newell


Alexis Ault


Eric Boyd


Geochemistry and microbiology are inherently tied in the natural world. The study of geomicrobiology has historically taken place in extreme systems, like hot springs of Yellowstone National Park and deep-sea hydrothermal vents, because the organisms that exist there have deep lineages on the tree of life and provide insight into early life on Earth. These microbes use chemical energy from nutrients available in their environment rather than relying on photosynthesis, energy obtained from the sun, to support their metabolism. The goal of this study is to improve our understanding of geological controls (for example the tectonic setting) on hot spring geomicrobiology. Fourteen thermal springs were sampled for aqueous and gas geochemistry and molecular microbiology along a transect from the Peruvian flat-slab subduction segment southward to the back-arc setting with steep-dip subduction in the Altiplano. The flat-slab region currently lacks active magmatic activity in contrast to southern Peru that is characterized by active arc volcanoes and behind the arc volcanism. Flat-slab springs (FSS) are cooler, more geochemically varied, and are supported by cooler subsurface reservoir temperatures compared to back-arc springs (BAS). Conversely, BAS have higher temperatures, exclusively Na-Cl rich waters, and are supported by hot subsurface temperatures. Statistical analyses were employed to meaningfully interpret and link the geochemistry and microbial community datasets. Significant relationships between spring geochemistry, spring temperature, microbial community composition, and geologic setting show that the FSS and BAS contain different phyla based on geologically influenced characteristics (i.e. temperature, chemistry). Our findings show that geological processes deep in the subsurface impart a primary control on surface geomicrobiological diversity.