GEOMICROBIOLOGY OF THE SEVILLETA NATIONAL WILDLIFE REFUGE SPRINGS AND WELLS: PREDICTING THE METABOLIC ENERGY AVAILABLE TO MICROORGANISMS

In the semiarid Southwest, where rainfall is scare and rivers are few, groundwater wells and springs provide a vital source of water to all forms of life. Despite the incredibly important role groundwater plays in this environment, there is a minimal understanding of the aqueous geochemistry and microbiology of these small desert oases. This study conducted a comprehensive survey of the hydrochemical composition of nearly 20 wells and springs in the Sevilleta National Wildlife Refuge (NWR) located within the Rio Grande rift, New Mexico. We measured pH, temperature, conductivity, DO, and TDS in the field, and major, minor, and trace elements, Cl/Br ratios, δ¹⁸O, and δD in the lab. Using the geochemical modeling software PHREEQc and basic thermodynamics we focused on 6 springs and wells with contrasting geology to predict the chemical reactions that could potentially occur in these waters as well as the metabolic energy available to any microorganism that facilitates one of these reactions. Results show that although nearly all the sources contain a similar suite of energetically-favorable metabolic reactions, affinity coefficients associated with these reactions differ due to the influences of local geology and the tectonic offsetting within the rift valley. Additionally, while the local geology influences the surrounding natural systems and thus water chemistry, the microorganisms that live in each system can manipulate the water quality as well, further creating distinct microenvironments within the Sevilleta NWR. This method of evaluation alone cannot confirm the existence of certain microorganisms, but by combining thermodynamics with geochemical analyses we can expose relationships between geology, water chemistry, and microbial metabolism that provides useful information for future geomicrobiological research in this region.