Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor

Matt D. Covington

Committee Member

Ralph K. Davis

Second Committee Member

Phillip D. Hays

Keywords

Earth sciences; Dissolution; Karst; Overflow springs; Underflow springs

Abstract

Physical dissolution experiments and numerical modeling have been used in the past to study limestone dissolution rates. Numerical models have typically used constant dissolution rates, whereas rates in nature vary in time. Limestone tablets allow natural estimation of rates over month time scales, but these rates cannot necessarily be extrapolated to geologic timescales and also do not aid our understanding of short term variability. This study characterizes natural variability in these rates and examines potential causes of that variability from first principles. This may enable more accurate projections of dissolution rates within models. This study combines measurement of physical and chemical time series with high-resolution measurements of PCO2 at two karst springs within the Savoy Experimental Watershed. These measurements were used to numerically estimate dissolution rates, and these rates were compared against insitu experiments with limestone tablets. This allowed for identification of the potential controlling variables of the dissolution rate at the two karst springs. Modeled dissolution rates for the two springs were strongly correlated with the temporal patterns of PCO2. PCO2 was a strong function of surface air temperature. The modeled rates calculated for the sites were then compared with the rate measured from the tablets. This comparison showed that, while the models generally overpredicted the rates, they matched the general trends in dissolution rates over time. The use of high-resolution PCO2 monitoring allowed for high resolution modeled dissolution rate calculations. This in turned allowed for dissolution rate characterization that showed how the variability of natural waters effects dissolution rates over time.

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