programs Natural Resources

Edwards and Trinity Aquifers eDNA


The Edwards-Trinity aquifer system directly or indirectly provides water supplies for every city from Del Rio to Salado, as well as the baseflow for every river from the Rio Grande to the Brazos. From its inaccessible and submerged labyrinth of tunnels, caverns and crevasses to its spring orifices, it also provides habitat for species found nowhere else and protected by the Endangered Species Act (ESA).

While much depends on these aquifers, little is known about the species living in the submerged world beneath the Interstate 35 corridor. There are catfish living a thousand feet below the sidewalks of San Antonio. There are invertebrates biologists have never recorded. Of the relatively well-studied species, like the endangered salamanders of Austin’s Barton Springs, basic information remains unknown, such as their full range.

Why this work matters

Environmental DNA (eDNA) could change this situation; that is why the Comptroller’s office is funding this work. Every species in the aquifer system leaves a trace of themselves in the water – fragments of DNA discarded when they shed, defecate, mate, give birth or die. These fragments can be picked up as easily as taking water from a swimming hole or a groundwater well.

In 2019, with a grant from the Texas Parks and Wildlife Department (TPWD), Dr. David Hillis’ lab at the University of Texas at Austin proved eDNA could be collected and used to identify the salamander species it came from. With additional funding from the Natural Resources Program, Hillis and members of his lab – Ruben Tovar and Tom Devitt – and Andy Gluesenkamp from San Antonio Zoo will develop tools to establish an accurate, affordable and easily repeatable methodology to evaluate eDNA from all the known salamanders living in the aquifer system.

Coordinating with biologists at the U.S. Fish and Wildlife Service and TPWD, Hillis’ lab will process samples from wells, caves and springs across the Edwards Aquifer region to establish the range of these species.

In the lab, the biologists will create a library of eDNA samples spanning the full range of the aquifer to support future research on other aquifer species. All data and methodologies developed under the contract will be free and made available to the public. Collecting a large baseline of samples across the entire system will enable future researchers to monitor changes in the aquifer ecosystem; consequently, the Edwards Aquifer may become a little less mysterious.

Deliverables Due at Contract’s End, Dec. 31, 2023

  • An easily followed and readily accessible eDNA survey methodology for the Edwards and Trinity aquifer systems that will include:
    • A workshop to train potential users of the methodology;
    • A manual to do the surveys; and
    • An online instructional video.
  • A map showing the range of all Central Texas Eurycea salamanders
  • A long-term collection of eDNA extraction samples from a broad range of habitats within the Edwards and Trinity aquifers to serve as a public database and depository for future research