PINHOLES IN A GIANT BLACK BOX: STUDYING A DEEP, CONFINED, CHEMOLITHOAUTOTROPHIC SYSTEM, THE EDWARDS AQUIFER, TEXAS (USA) (Invited Presentation)

In 1896, biologists first peered through a ‘pinhole’ drilled into a water-filled ‘black box’ that we now call the Edwards Aquifer. Stygobitic animals, some of the first described in the USA, came from the artesian well water. After the initial discoveries, sporadic biological research occurred until the 1960s when Dr. Glenn Longley began a ~20-yr intensive sampling campaign. The unprecedented aquifer biodiversity that was subsequently described promoted thinking ‘outside the black box.’ In 1981, Longley suggested the exceptional biodiversity might be explained and supported by organic materials produced in situ. He also proposed that the ecosystem had a complex trophic structure, and asked whether it might be “Earth’s most diverse groundwater ?”

More than 120 years after the initial discoveries, we still cannot fully answer the question, but we do know much more about the aquifer’s complex and interconnected hydrogeologic, geochemical, microbiological, and biological processes. Intensive interdisciplinary sampling of the large and heterogeneous black box through pinholes was revived in the 2000s, and modern geochemical and molecular tools and models help place patterns of animal biodiversity and community structure within a more nuanced biogeochemical framework. Our current understanding of linked geochemical and biological processes in the deep aquifer includes revelations that chemical gradients drive chemolithoautotrophy, which in turn supports biological productivity and diversity, maintains water quality, and creates permeability in the deepest parts of the aquifer. The aquifer and biological systems have evolved together.

Finally, the Edwards Aquifer may only be ‘unique’ in that it has been studied; most analogous deep aquifer systems in the USA and globally remain entirely or nearly unstudied. Approaches for studying, and the findings from, the Edwards Aquifer can be transferred and used to understand the significance of biogeochemical interactions in other aquifers, but the Edwards model should be tested and revised based on studies and results from other aquifers.