Microbial Impact on Carbonate Dissolution along a Geochemical Gradient in the Edwards Aquifer, Texas

Cassie Gray
Louisiana State University Department of Geology and Geophysics, Baton Rouge, LA.
[email protected]

This research aims to determine how the interactions between physical, chemical, and biological components of an aquifer affect rates of carbonate dissolution. The main focus is the karstified Edwards Aquifer, one of the most prolific aquifers in the U.S. The aquifer consists of distinct fresh and saline water zones, but the two water types converge along the eastern edge of the freshwater aquifer, known locally as the “bad-water” line. Because microbial activities that affect carbonate geochemistry can vary as a function of aquifer geochemistry, wells within and across the transition zone in New Braunfels, Texas, were sampled using standard geochemical and microbiological methods. Carbonate dissolution rates will be experimentally determined using in situ microcosms, whereby suspended calcite and dolomite fragments will be exposed to the aquifer solutions under sterile (only fluids) and non-sterile (fluids and microbes) conditions. The microcosms will be retrieved after ~1 to 3 months and examined to determine changes in weight and surface area of the mineral fragments. Additionally, the reactive and non-reactive surfaces will be examined using scanning electron microscopy and fluorescence in situ hybridization to distinguish between possible dissolution and precipitation features, as well as the identity of microbes colonizing the surfaces. These results will aid in our understanding of the microbial diversity of carbonate aquifers and in the evaluation of microbially-mediated processes affecting secondary porosity generation in carbonate aquifers and reservoirs.

AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid