Date of Award

Fall 12-2022

Degree Type


Degree Name

MS Geosciences/Geochemistry



Committee Chair

Alysia Cox

First Advisor

Chris Gammons

Second Advisor

Kaleb Scarberry


Chemical speciation helps define habitability and bioavailability of elements to microbes in extreme environmental conditions such as Yellowstone and Icelandic geothermal systems. Chemical speciation is critical to understanding the system's behavior, including chemical toxicity, environmental fate, and transport. This research presents the description and comparison of the geochemistry and chemical speciation of sixty-four geothermal waters using the EQ3 chemical equilibrium software and the Water-Organic-Rock-Microbe (WORM) Portal. These use values of pH, temperature, dissolved oxygen, silica, inorganic carbon, major anions and cations, trace elements and gases (CO2, CH4, and H2). The analyzed acidic (pH ~ 1.9) and alkaline (pH ~ 9) water samples ranged from a temperature of ~50°C to slightly superheated. Yellowstone showed higher major anion and cation content compared to Iceland. SO4-2 and Cl- dominated in Yellowstone waters and only SO4-2 in Icelandic waters. On the other hand, Na+ dominated in Yellowstone hot springs and Mg+2 and Ca+2 in Iceland. Results revealed that the aqueous geochemistry is determined by the chemical composition of the host rock, which is mainly rhyolitic in Yellowstone and predominantly basaltic in Iceland. A classification of hot springs in the two sites studied is also shown. These include (1) steam-heated acid waters, (2) chloride or alkaline waters, and (3) mixed waters. The models presented the calculated chemical speciation of the nutrients (phosphorus, nitrogen, sulfur, and carbon) and of chosen vital and toxic trace elements (aluminum, manganese, iron, zinc, copper, cobalt, arsenic, antimony, and selenium). These trace elements are used for rock classification, participate as co-factors for enzymes, tend to form ions with charge +2 or oxyanions, or are known toxins. Similar speciation ocurred in Yellowstone and Iceland with respect to pH. Differences in manganese and iron speciation in waters with pH > ~ 6.00 between Yellowstone and Iceland suggested a different aqueous behavior. Also included is the relationship of oxidation and reduction reactions, plus the sum of the presence of carbon dioxide, methane, and hydrogen gas with respect to microorganisms present in these extreme environments. Finally, the outcomes together provide a framework for aqueous geochemistry that creates a diverse habitat for microbes.


A thesis submitted in partial fulfillment of the requirements for the degree of

Master of Science in Geoscience: Geochemistry