Master of Science (MS)


Geology and Geophysics

Document Type



El Tatio geyser field, northern Chile, impacts regional water quality, policy, and agricultural commerce due to the geothermal waters containing high concentrations of naturally-occurring arsenic (As). In the circumneutral pH, non-sulfidic thermal waters at El Tatio, dissolved arsenite [As(III)] dominates geyser discharge water upstream, but dissolved arsenate [As(V)] dominates downstream. Microbial mats and sediments were analyzed for changes in As speciation using X-ray spectroscopy methods, such as XANES and EXAFS at both the As and Fe K-edges, combined with ATR-FTIR spectroscopy and molecular genetics, to understand As cycling. The sediments and microbial mats were dominated by As(V) speciated as both inorganic and organic forms of arsenic, whereby inorganic As(V) is sorbed as an inner-sphere complex to ferric oxyhydroxides and/or organic matter, and organoarsenical compounds. Differences in As speciation and presence of organic matter in the mats are attributed to microbial activity. Therefore, the 16S rRNA gene framework was used to evaluate microbial diversity within the mats. Near the geyser pool (at ~76-80oC), microbial groups in biofilms and sediments were distinct from thick microbial mats downstream. Upstream taxonomic groups belonged to the Proteobacteria division, Deinococci, Aquificales, with rarer Chloroflexi and other groups. Downstream communities also consisted of members of the Proteobacteria division, but were dominated by Chloroflexi. Sequences of arsenite oxidase (aroA)-like genes retrieved from microbial mats downstream belonged predominantly to a unique clade within the Chloroflexi, as well as several groups of Proteobacteria previously known to oxidize As(III). Chloroflexi, however, have not been previously linked to As(III) oxidation in geothermal habitats and could contribute to the As(V) flux downstream. The microbial diversity associated with changes in As speciation expand our current understanding of the distribution of aroA-like genes from geothermal habitats and of the environmental and microbial controls on As remediation during geothermal development.



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Committee Chair

Engel, Annette