18-6 Trace Metals in Austin-area Streams: Baselines for Urbanization Impacts and Climate Resilience Planning

Session: Shaping a Sustainable Future with Geology in the Twenty-First Century: Geology and Society Division Turns 22

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Urban Stream Syndrome affects several streams in Austin, Texas, where recent and rapid development characterized by expanding impervious surfaces within watersheds is altering stream hydrographs and pollutant loading, leading to growing concerns about water quality, urban heat, and ecosystem health. One climate resilience strategy gaining attention is the use of reflective pavement sealants, which contain titanium dioxide (TiO₂) to reduce urban heat due to impervious cover through increased reflectivity. While pilot programs show cooling effects, the environmental fate and ecological risks of TiO₂ in waterways remain poorly understood. This highlights the importance of understanding baseline conditions and the transport, sequestration, and fate of trace metals entering urban aquatic environments. Previous studies have analyzed water quality impacts along an urban-to-rural gradient of Austin watersheds, identifying both point and non-point sources of contaminants, however, they have not focused on metals as indicators. Using long-term streamwater monitoring data, we analyze urban, urbanizing, and rural watersheds across Austin to assess trace metal concentrations and their association with dissolved and suspended loads. We find significantly higher concentrations of dissolved manganese (p < 0.005) and copper (p < 0.005) in urban relative to rural streams, and significantly higher dissolved titanium (p < 0.005), manganese (p < 0.005), iron (p < 0.005), and copper (p < 0.005) in urban vs. urbanizing streams. Titanium, while primarily in the dissolved load in these streams, shows significant differences between total (unfiltered) and dissolved (filtered) concentrations, indicating that particulate contributions are significant. This partitioning is important because dissolved and sediment-sorbed metals have different exposure pathways and timelines. Dissolved metals may travel farther downstream, increasing their exposure radius, while sediment-sorbed metals can accumulate in benthic environments, posing greater risks to bottom-feeding organisms and introducing new exposure pathways. Additionally, this comparison indicates that environmental assessments based on filtered samples alone may underestimate the environmental burden of some metals. These findings will help evaluate the impact of climate resilience measures on trace metal exposure and ecosystem health in urban settings and establish baselines for assessing future changes in response to ongoing urbanization.

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

doi: 10.1130/abs/2025AM-7648

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