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Geomicrobiology of the Edwards Aquifer "Bad-water"
 Louisiana State University, Geomicrobiology & Environmental Microbiology Studies Group

Louisiana State University
Dr. Annette Summers Engel

Department of Geology and Geophysics
E235 Howe-Russell Geoscience Complex
Louisiana State University
Baton Rouge, LA 70803
office:  225-578-2469  fax:  225-578-2302


More than one million people depend on water from the Edwards Aquifer in Central Texas. The Edwards Aquifer is an important freshwater aquifer, but the aquifer’s eastern edge is marked by a steep, freshwater-saline water interface, known locally as the “bad-water” line. The “bad-water” line is defined by a 1,000 mg/L concentration line for total dissolved solids (TDS); the freshwater, in comparison, has TDS concentrations from 250 to 300 mg/L. Bad-water TDS can range up to 230,000 mg/L and has high concentrations of hydrogen sulfide (H2S), conditions that result from leakage of brine and H2S gas from oil-fields along the eastern edge of the aquifer.

Understanding the details of bad-water geochemistry and hydrogeology has been critical for water supply and resource development since the early settlement of Central Texas, as the bad-water line nearly parallels population growth along the Austin-San Antonio corridor. Although most people do not want the bad-water pumped into their homes, historically thousands of tourists were attracted to San Antonio and Austin to bathe in the warm sulfidic water for better health (see Hot Wells website). Public interest in the Edwards Aquifer and the bad-water has shifted over the years, from the economic viability of sulfidic spas to the freshwater availability due to continuous economic, social, and political urbanization and agricultural demands. Unfortunately, pumping the freshwater to the millions of thirsty citizens has caused slow encroachment of the bad-water westward into the public water supplies.

Even given this somewhat tumultuous situation, the Edwards Aquifer is also an important ecological ‘hot spot’; the freshwater harbors as many as 164 cave-adapted species, with >40 being endangered or threatened endemic species. Eight aquatic species are associated with the bad-water. The juxtaposition of the two geochemically distinct waters creates an energy (redox) gradient that has the potential to support a diverse ecosystem. Invertebrates (e.g., isopods, amphipods) and catfish have been retreived from wells that penetrate the deep parts of the aquifer. One endemic, toothless blind catfish (Trogloglanis pattersoni) has a mouth morphology consistent with foraging organic (e.g., microbial) biofilms on rocks.

The biofilms have been seen in down-hole video camera footage  The microbes comprising the biofilms may consist of sulfur-oxidizing bacteria, based on the observations of white microbial filaments, seen as ‘snow’ by down-hole video cameras (See video clip link at right).

This research focuses on understanding 1) bad-water microbial diversity and ecology, 2) the geochemical controls on microbial community structure and dynamics, 3) chemosynthesis related to nutrient acquisition and cycling (e.g., of carbon and sulfur compounds), and 4) the microbial effects on the aquifer environment.

 
Scanning electron photomicrographs from calcite chips deployed in aquifer using in situ microcosms. Images from K.W. Randall.

 

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Well-head near San Marco, Texas. The tubing is leaky,
and the tubes are coated with a white biofilm.
 Photo by A.S. Engel.
 

This research is being supported by the:

Inquire with Dr. Engel if interested in this research.
Assistantships are available.

 
Down-well video image - brown lines are from camera cage. The white stringy material at the upper left is microbial filaments floating in the well water. Depth is approx. 600 ft. Photo by A.S. Engel.

 

See video clip; VOB file, approx. 2 min 30 sec and requires Media Player Classic
or similar program (warning: large file, ~200 MB). Video details: The number at the upper left is the depth in feet from the ground surface. There is no sound. Video was acquired by the Edwards Aquifer Authority in San Antonio and graciously provided to the PI for research purposes; video was converted to digital format (DVD); multiple videos were spliced together for this clip.
 

 

Cave and Karst Organization and Links


Sampling surface water at Hondo Creek, which recharges into the Edwards Aquifer, Central Texas. Photo by A.S. Engel.


 Stay tuned for more data and research results!



In situ microcosms before being put in a sulfidic,
bad-water well in the Edwards Aquifer, Central Texas.
Photo by A.S. Engel.


Please contact Dr. Annette Engel for more information regarding the research or photographs. Call (225) 578-2469 or email.
Address: Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803.   
©AS Engel2007