Semester

Fall

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Dorothy J Vesper

Committee Co-Chair

Robert Behling

Committee Member

Harry M Edenborn

Committee Member

James Toro.

Abstract

Precipitation rates for travertine have been studied in many natural settings and compared to theoretical calcite (CaCO3) precipitation rates; in most studies, the emphasis is placed on the degassing of CO 2 as the primary controlling mechanism. Little research has been done in natural settings to evaluate precipitate composition, rates of precipitation, and the role of potential inhibitors of calcite growth. This study addresses these questions in a Sweet Springs Creek, West Virginia-Virginia: a karst stream fed partly by thermal mineral waters with high CO2. For this study, travertine plates were deployed to measure the accretion of precipitates in the presence of natural inhibitors. The mass change on the plates was interpreted as calcite precipitate and converted to precipitation rates by accounting for the plates' length of time in-situ. The Plummer-Wigley-Pinkhurst calcite precipitation rate equation was used to estimate calcite precipitation rates based on bulk water chemistry and compared to the measured plate rates, which were on average one order-of-magnitude lower. SEM-EDS analysis of the mineral precipitate on the travertine plates showed extensive biological activity which correlated with sites with higher variability between calculated and observed precipitation rates. Analysis of precipitate with XRF-Fusion found that >10% of the mass in some samples was not calcite. Gypsum selenite (CaSO 4˙2H2O) crystals were found in addition to detrital quartz on plates surfaces as well, suggesting non-calcite mineral precipitation significant enough to introduce error into estimates. These results suggest that further evaluation of mineral precipitates is needed in order to accurately gauge true precipitation rates in-situ and that previous studies likely underestimated the difference between estimated and actual precipitation rates.

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