262 Advances in Ecohydrogeology (Posters)

Ecohydrogeology is the unifying, synthetic field of study integrating the approaches from the ecological and hydrogeological sciences in the study of groundwater-related ecosystems, habitats, and organisms. We encourage submissions of research that advances the science, stewardship, and policy at the intersection of ecology and hydrogeology.

Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Geochemical and Microbial Processes Associated with Methane Cycling in the Hyporheic Zone of Central Texas Rivers Before and After Drought

Paper number: 262-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Geochemical and microbial processes in the hyporheic zone (HZ) of a river, where surface and groundwater mix, are controlled by hydrogeomorphic and ecological conditions. When extreme weather events cause drought, groundwater discharge into gaining reaches can offset drying conditions to the HZ and sustain perennial flow. For losing reaches that do not receive groundwater input, drying impacts the HZ in many ways because of sediment dehydration, diminished nutrient transport, organic matter and biota desiccation, among other processes. This study focused on understanding changes to biogeochemical processes and microbial communities within the HZ from reaches that experienced periodic, nonperennial flow from 2021 to 2023 compared to perennial reaches of the Llano, Concho, and San Saba rivers in Central Texas. Specific emphasis was placed on understanding changes associated with methane cycling because recent findings suggest that rivers can be important emission sources. Up to seven pool–riffle locations were visited in each river, and HZ porewater was extracted using Bou-Rouch samplers and water was analyzed for major and trace ions, inorganic and organic carbon and nitrogen species, and dissolved gases. Environmental DNA was extracted from filtered HZ porewater and used to sequence 16S rRNA genes, from which taxonomic profiles were compared. Relative abundance of all archaeal taxa from the HZ remained similar over time. Reaches that maintained perennial flow had higher relative abundances of putative methanogens, such as classes within Methanobacteriota, compared to reaches that experienced nonperennial flow due to drought. Following rewetting, however, the HZ from those losing reaches had higher dissolved methane concentrations (with some reaching over 3000 nM) compared to before drying. These findings suggest that HZ rewetting following drought has the potential to serve as an emission source. Higher temperatures also correspond to higher methane concentrations. With the potential for prolonged drought to expand north and eastward across watersheds in Texas in the future, processes like groundwater withdrawal could contribute to shifts from perennial to nonperennial flow that should also affect methane flux. Overall, these findings emphasize the role that rivers and the HZ play in methane cycling.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413704

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.