Wednesday, April 2, 2008 : 3:00 p.m.

Sulfur cycling and microbiology in deep, stratified cenotes (karst lakes), Yucatan Peninsula, Mexico

Bianca Pedersen1, Melissa Lenczewski2 and Eugene Perry2, (1)University of Wisconsin -Eau Claire, (2)Northern Illinois University

The aquifer of the northern Yucatan Peninsula is extremely susceptible to pollution because of the thin soil cover and the karstic nature of the region. Currently, the human population of the east coast is growing rapidly straining both the wastewater treatment and disposal facilities of the region. As a solution, large scale injection of wastewater into the saltwater lens below the freshwater aquifer has been proposed.  Injection of wastewater into the saline aquifer may result in partial mixing of this water with saline water containing high concentrations of sulfate. Mixing of water containing carbon and other nutrients with high-sulfate water can create optimal conditions for anaerobic bacterial growth and sulfate reduction. As a result, significant amounts of hydrogen sulfide could be produced and mixed into the drinking water supply.

The focus of this study is on linking sulfur isotope fractionation occurring during sulfate reduction in the natural systems of two deep cenotes with the microbial community and elucidation of factors that influence the amount of fractionation of sulfur isotopes resulting from microbial sulfate reduction. Organic material falls into the cenotes from above and reaches the saline water of the intrusion, creating an environment similar to the proposed wastewater injection scenario. High isotope fractionations are produced as a result of low nutrient and metal concentrations in conjunction with low light conditions.  The microbial community is dominated by microorganisms of the Desulfomena-Desulfosarcina-Desulfococcus genera which produces an increase the sulfide concentration of the water with depth. Results of this study indicate that sulfate reduction could be a serious problem to consider when evaluating the risks associated with wastewater injection in this environment.

Bianca Pedersen, University of Wisconsin -Eau Claire Bianca Pedersen is a visiting assistant professor in the department of Geology at University of Wisconsin –Eau Claire. She has a M. Sc degree in Environmental Engineering from the Technical University of Denmark and recently a PhD from the Department of Geology and Environmental Geosciences at Northern Illinois University. Her dissertation is entitled “Water Geochemistry and Geomicrobiology of two Sulfidic Cenotes, Yucatan, Mexico”. Research interest include redox chemistry of natural waters, groundwater modeling using chemical species as a calibration tool and nutrient transport into lakes and estuaries.

Melissa Lenczewski, Northern Illinois University Melissa Lenczewski is an Associate Professor of Geomicrobiology and Organic Geochemistry in the Departments of Geology and Environmental Geosciences and the Department of Biological Sciences at Northern Illinois University. She has substantial expertise with methods such as molecular techniques and PFLA techniques for detection of microorganisms in soil and water. She also has expertise in detection of simple organic compounds in water. She has been working in the Yucatan Peninsula for 3 years and will be having a sabbatical there in Fall 2008.

Eugene Perry, Northern Illinois University Eugene Perry is a Professor of Geology and Environmental Geosciences at Northern Illinois University. He has a long-standing interest in Yucatan geology and hydrogeology with a parallel interest in the Precambrian. His work related to bacterially mediated sulfur redox processes and their effect on the characteristics of the early Archean atmosphere and hydrosphere occurred before the exciting study of 33S and 36S anomalies was technically feasible. This research, namely studying the unique chemistry and biology of the water columns of deep Yucatan cenotes represents a convergence of seemingly disparate interests that Perry considers very exciting.


2008 Ground Water Summit