172-4 Geochemical Variability of Point Sources of Water Quality Degradation Contributing to Urban Stream Syndrome in Austin, Texas

Session: Urban Geochemistry

Presenting Author:

Authors:

Abstract:

Rapid urbanization in the Austin, Texas area poses challenges to the resilience of its water resources, including creeks and springs that provide potential amenities to many communities. Urbanization often leads to degradation of the water quality, ecology, and morphology of streams, with the cumulative effects referred to as Urban Stream Syndrome (USS) (Walsh et al, 2005). Austin also faces the increased risk of water scarcity with frequent droughts that add an additional burden on urban watersheds. Waller Creek is a small (15 km²), extensively urbanized (61% impervious cover) and impaired watershed in Austin that serves as a framework to examine processes that lead to USS. Previous research across Austin-area watersheds demonstrates the impacts of inputs from the degrading municipal infrastructure, runoff events, and water-rock interaction with Cretaceous limestone bedrock and soils (Christian et al, 2011, Manlove et al, 2024, Beal et al, 2020). We analyze geochemical data for Waller Creek stream water samples, three distribution pipe outfalls that drain under baseflow conditions to Waller Creek, and water from the municipal water network, all collected over the period 2001-2023. We compare two sites and observe differences between, P1, an upstream pipe outfall, to the nearest stream sample site, WC1, in terms of the concentration ranges of major ions, Na/Cl ratios, and Ca/HCO₃ ratios. For Pipe P1, Na/Cl ratio (mmol/L) has lower R²=0.89, slope=1.04, and for Ca/HCO₃ ratio (mmol/L), R²=0.92, slope=1.36. Whereas, WC1, Na/Cl ratio (mmol/L), R²=0.99, slope=0.97, and for Ca/HCO₃ ratio (mmol/L), R²= 0.98, slope=1.51. NO₃^- concentration values for P1 (0.015-1.935 mmol/L) are higher than downstream pipe P3 (0.013-0.030 mmol/L). Median NO₃^- concentration (0.003 mmol/L) in municipal waste water is two orders of magnitude lower than P1, indicating that P1 has additional contributions. Two of the point source inputs along Waller Creek have a high degree of geochemical variability outside the range of the stream waters, indicating that point sources are not necessarily consistent spatially or temporally. Assessing point source inputs is important to identify and differentiate pollutant sources, track changes over time, and have true representation of factors that contribute to USS and impact water quality in urban environments.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11152

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