May 2023 Virtual Meeting

Monday, May 8, 2023
6:00 - 7:30 pm

Note: ETGS members will receive an email with info for logging into the meeting.

May Presentation

Hyporheic zone hydrodynamics, biogeochemistry, and microbial community distributions of the San Saba River, Texas



Ethan G. Sweet
Department of Earth and Planetary Sciences
University of Tennessee, Knoxville
MS Candidate


The hyporheic zone (HZ) in riparian ecosystems plays a vital role in providing habitat and facilitating biogeochemical cycling. However, studies on the HZ have varied in scale, with limited research on microbial communities and their role in geochemical processes. This study examined the HZ at pool-riffle sequences in the San Saba River in Central Texas at varying scales. Water physiochemistry and geochemical parameters were measured in the field, and microbial samples were collected for DNA analysis.

The results showed that the biogeochemical and hydrogeological effects of the HZ directly impact river water quality, nutrient availability, and riparian habitat. These effects were observed at both individual sample locations and throughout the entire river reach. The study also revealed that microbial communities varied in composition at different riffle locations, HZ sites, and overlying surface water, with differences correlating with hydrogeology, geochemistry, and spatial position at pool-riffle sequences.

Specifically, gaining headwater sites had lower relative abundances of photosynthetic bacteria but higher concentrations of hydrogen sulfide and methane as well as higher relative abundances of anaerobes, indicating sustained anaerobic conditions in the HZ. These findings highlight the importance of integrating microbial community diversity information into ecological models to better understand how riverine ecosystems may respond to human infrastructure, climate change, and improve river restoration outcomes.

This study contributes to our understanding of the HZ and its processes at both small and large scales, providing insights into the hydrogeology, geochemistry, and microbial communities in riparian ecosystems. The San Saba River in Central Texas serves as a valuable study site for investigating the impacts of human activities on water resources and the role of the HZ in river hydrology and biogeochemistry. Further research in this area will aid in better modeling and management of riparian ecosystems, addressing the challenges of accurately predicting and managing biogeochemical processes in the HZ.


Ethan is a Master of Science (MS) candidate at the University of Tennessee, conducting research on biogeochemical cycling in the hyporheic zone of Texas Rivers. He holds a Bachelor of Science (B.S.) degree in Geology, which he obtained in 2018 from Eastern Kentucky University. During his undergraduate studies, Ethan specialized in hydrogeologic investigation and aquifer modeling of geographically isolated ridgetop wetlands in the Daniel Boone National Forest. After completing his undergraduate studies, Ethan worked as a certified Geologist-in-Training (GIT) with Stantec Consulting in Lexington, KY, where he worked for three years before returning to school.


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Page updated May 10, 2023