Experimental Evidence for Microbially Mediated Carbonate Dissolution from the Saline Water Zone of the Edwards Aquifer, Central Texas

Abstract

Microbially induced carbonate dissolution was evaluated from sulfidic wells in the Edwards Aquifer, Texas. Filamentous biomass covers rock surfaces, with Gammaproteobacteria and Epsilonproteobacteria dominating the attached community, but novel Alphaproteobacteria dominating the planktonic community. Despite fluids being saturated with respect to calcite, experimental calcite from in situ microcosms had significantly greater mass loss when colonized. Moreover, neoformed gypsum crystals were observed on colonized surfaces where fluids were undersaturated with respect to gypsum. The results are similar to findings from shallow cave and karst environments, and highlight the underappreciated role of microbes in the modification of carbonate aquifers and reservoirs.

Keywords:

• subsurface microbiology
• groundwater
• biofilm
• molecular ecology
• carbonate dissolution

Acknowledgments

We thank G. Schindel and other scientists at the Edwards Aquifer Authority for access to wells, field assistance, and down well video acquisition. J. Waugh and D. Mahula at the San Antonio Water System assisted in the field and in well access for microcosm experiments. The manuscript benefited from valuable suggestions made by J. Mylroie, P.J. Moore, and D.E. Northup. The work was funded by the Sigma Xi Graduate Student Research Grant and the South Texas Geological Society Jones-Amsbury Research Scholarship to K.W.R., and by the Louisiana State University Council of Research and Louisiana Board of Regents [LEQSF(2006-09)-RD-A-03] to A.S.E.