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42-14 Shallow Subsurface and Surface Geochemistry of a Groundwater-Fed Endorheic Basin Rich in Sulfate Evaporites

Session: A Showcase of Undergraduate Research in Hydrogeology (Posters)

Poster Booth No.: 203

Presenting Author:

Jimena Guzman

Authors:

Guzman, Jimena¹, Paxton, Alex², Kantak, Mukta³, Camenisch, Chloe⁴, Lichter, Alexander⁵, Castle, Grace⁶, Janelle, Alexander⁷, deFabry, Cameron Mark⁸, Hudson-Rasmussen, Berit⁹, Cardenas, Meinhard Bayani R¹⁰, Alessi, Daniel¹¹, Hendrickson, Dean¹², Laredo-Alcalá, Elan Iñaky¹³, Gutiérrez-Martínez, Areli¹⁴, Rodríguez, Christian Lucas¹⁵, González-González, Arturo¹⁶, Villareal Wislar, Cristino¹⁷, Ruiz Smith, Gerardo¹⁸, Contreras Arquieta, Arturo¹⁹, Pérez, Ana Sofia²⁰r> (1) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (2) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (3) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (4) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (5) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (6) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (7) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (8) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (9) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (10) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (11) Department of Earth and Planetary Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (12) College of Natural Sciences, Biodiversity Center, University of Texas at Austin, Austin, Texas, USA, (13) Autonomous University of Coahuila, Saltillo, Coahuila, Mexico, (14) Autonomous University of Coahuila, Saltillo, Coahuila, Mexico, (15) Autonomous University of Coahuila, Saltillo, Coahuila, Mexico, (16) Museo del Desierto, Saltillo, Coahuila, Mexico, (17) Comisíon Nacional de Áreas Naturales Protegidas, Saltillo, Coahuila, Mexico, (18) Fundación Pro Cuatrociénegas, Cuatrociénegas, Coahuila, Mexico, (19) Desarollo Sustentable del Valle de Cuatro Ciénegas A.C., Cuatrociénegas, Coahuila, Mexico, (20) Fundación Pro Cuatrociénegas, Cuatrociénegas, Coahuila, Mexico,

Abstract:

The Cuatro Ciénegas Basin (CCB) in Coahuila, Mexico is a globally unique endorheic basin where groundwater upwells through faulted Cretaceous carbonate rocks to sustain a vast network of over 200 pozas. The CCB holds significant ecological and geological importance, hosting numerous endemic species, rare freshwater stromatolites, and unique gypsum dunes, a manifestation of a key phenomenon within the system where sulfate evaporites precipitate from sulfate-rich groundwater. However, it continues to face threat from groundwater overexploitation for regional agriculture and municipal demand. In this study, we use geochemical measurements to quantify the chemical makeup of different groundwater and surface water to understand the underlying causes of chemical variations within the shallow subsurface. We hypothesize that sulfur evaporite deposits heavily influence groundwater chemistry, effectively creating a sulfate dominated groundwater system. We established a network of monitoring wells across three major waterbodies within the CCB, where water quality was measured periodically and bottled samples were taken at several subsurface sampling points and surface water bodies to determine anion, cation, and alkalinity concentrations. We found that small differences in elevation (<0.1-0.25 m compared to surroundings) produced a high degree of variance in TDS and specific ions present, likely due to cyclic precipitation and dissolution of evaporite minerals in topographically low areas. We observed elevated levels of sulfate across the basin, meaning evaporite dissolution is a dominant geochemical process throughout the system. Additionally, we found that the source of water for most of the shallow subsurface was strongly chemically connected. Our results show that the shallow subsurface is chemically characterized by the same groundwater source. Our findings help to connect rainfall, water-evaporite interactions, and variations in topography with chemical variations in shallow groundwater. These results can be coupled with hydraulic head data to more accurately represent the processes taking place in the CCB under water-stressed conditions and how it affects the biological endemism as well as nearby communities that rely on the groundwater of the region.

Shallow Subsurface and Surface Geochemistry of a Groundwater-Fed Endorheic Basin Rich in Sulfate Evaporites

Description

Session Format: Poster

Presentation Date: 10/11/2026

Presentation Room: CCC, Hall F

Poster Booth No.: 203

Author Availability: 2:00 to 4:00 p.m.

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