2024 Abstracts

Examining Microbial Respiration and Chemical Signatures of Urban Rivers Differing in Flow History


Allison M. Veach1* (allison.veach@utsa.edu), Mariana Vergara1, Brian Laub1, Vanessa Garayburu-Caruso2, James Stegen2


1University of Texas–San Antonio, Texas; 2Pacific Northwest National Laboratory, Richland, WA


Intermittent rivers and ephemeral streams (IRES) comprise up to 60% of the total length of all river networks on the globe. Due to both climate change impacts and water abstraction, stream intermittency is predicted to become more widespread in the future. Water and sediment chemistry in IRES may differ from perennial streams due to the occurrence of hot spots or hot moments of biogeochemical activity caused by drying and rewetting of streambed sediments in IRES. This project examines how stream water and sediment chemistry in intermittent and perennial stream reaches differ spatially in the San Antonio River (SAR) watershed, which is located in the metropolitan area of San Antonio, TX. This work is in collaboration with staff scientists at Pacific Northwest National Laboratory and is, in part, using protocols developed by the Worldwide Hydro-biogeochemistry Observation Network for Dynamic River Systems consortium to gain a mechanistic understanding of organic matter recalcitrance and quantity across streams with varying flow history. Initial results indicate variable dissolved organic carbon (DOC) and total nitrogen (TN) concentrations across sites in the SAR watershed. During dry periods, intermittently flowing sites generally yield greater DOC (9.7 ± 3.3 mg L-1) but lower TN (1.2 ± 0.5) than perennial (DOC: 6.7 ± 0.9, TN: 7.1 ± 5.0 mg L-1). This effect is likely due to perennial sites having baseflow maintained by high N-sourced water such as treated wastewater or impounded reservoirs with fertilizer runoff. Identification of specific microbial taxa via amplicon-gene sequencing (16S rRNA) in variable flow streams are in progress. Additionally, wet-season sampling and targeted in situ respiration measurements of candidate intermittent and perennial sites are planned for 2024.