Date of Award

Fall 12-12-2025

Degree Type

Thesis

Degree Name

PhD Earth Science and Engineering

Department

Earth Science

Committee Chair

Alysia Cox

First Advisor

Marisa Pedulla

Second Advisor

Glenn Shaw

Third Advisor

Kaleb Scarberry

Fourth Advisor

Everett Shock

Abstract

Microbial uptake of trace metal cofactors such as copper (Cu), iron (Fe), and zinc (Zn) is governed by biogeochemical processes in hydrothermal systems where metal bioavailability varies widely. In situ microbial metal uptake rates were quantified by applying metal stable isotope probing (MSIP) in the Yellowstone hydrothermal system across diverse geochemical conditions in hydrothermal springs. The findings in these studies revealed that pH exerts a dominant influence on microbial copper uptake rate, also enhanced by increased Cu²⁺ ion availability and dissolved oxygen. Microbial iron uptake, in contrast, displayed a broad tolerance to environmental variability, occurring across a pH range of 2–9 without a clear pH dependence, indicating microbial communities have evolved flexible strategies for iron acquisition under fluctuating geochemical conditions. As with copper, dissolved oxygen increased microbial Fe uptake rates. Interactions between copper and zinc uptake rates in an alkaline sulfidic spring highlighted the interconnected influence of pH, oxygen, speciation, and organic carbon on microbial metal acquisition. Copper uptake rates increased with pH and dissolved oxygen, whereas zinc uptake rates decreased and were more closely tied to zinc speciation and dissolved organic carbon (DOC). Under combined Cu and Zn isotope additions, the uptake rates of both metals were enhanced, suggesting microbial co-utilization of Cu and Zn rather than competition for their uptake. Collectively, these results demonstrated that microbial metal uptake in hydrothermal systems is controlled by a complex interplay of aqueous geochemical parameters in which microbes thrive.

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