Diploma Thesis

Arsenic speciation and sulfide determination in alkaline geothermal drainage channels in Yellowstone National Park

Ulli Seifert (02/2010)

Support: Britta Planer-Friedrich, Cornelia Härtig

Five alkaline geothermal hot springs in Yellowstone National Park (USA) were investigated for their thioarsenate transformation sequences. This included, besides the determination of the arsenic speciation along the drainage channels, the measurement of sulfide contents and field parameters (water temperature, pH, oxygen saturation, electrical conductivity and redox potential). Concurrently, the occurrence of thermophilic microorganisms as streamers or microbial mats, as well as changes in the sediment color were observed, photographically documented and furthermore overview pictures of the outflow channels were created to facilitate subsequent investigations.

Spike tests were conducted, proving microbially mediated acceleration of arsenite oxidation. The microbial influence on direct biotic catalysis of thioarsenate conversion to arsenite is indeed indicated, but not really clear yet. Thus, transformation of thioarsenate to arsenate detected in the drainage channels is presumed to be the result of interactions between abiotically and biotically induced mechanisms.

In the course of the on-site sulfide determination, additional off-site laboratory experiments were accomplished, certifying reliable functionality for both techniques applied in the field: voltammetric (ion-selective electrode), as well as photometric (methylene blue method according to Hach) measurements. The tests on the photometric method showed that it is only negligibly affected by changes in diverse parameters (reaction time, pH, amount of reagents, etc.), only increased temperatures decrease the measured sulfide concentration.