ZN VARIATIONS IN CENTRAL TEXAS WATERSHEDS ACROSS AN URBAN-RURAL CONTINUUM

Major cities in Texas are experiencing unprecedented rates of urbanization, with Austin’s population increasing 33% between 2010 and 2020. Additionally, climate projections indicate Austin’s summers could be 1.9°C warmer by the end of the century, increasing strain on water resources. As Austin grows and the surrounding areas become increasingly urbanized, understanding the impacts of urbanization on stream water will be essential to protecting water quality and the long-term resilience of urban communities reliant on dwindling water resources. Water quality declines in Austin area streams are strongly correlated with increasing population density and impervious cover. This study analyzes stream water samples from watersheds in the Austin area across an urban-rural continuum. Previous investigations using geochemical tracers of urban sources in Austin (i.e. elevated concentrations of fluoride, nitrate, and chloride together with diagnostic strontium isotope signatures) have identified inputs of municipal supply and wastewater to streams attributed to leaking infrastructure and irrigation. Mean concentrations of dissolved zinc in urbanized streams in the Austin area are an order of magnitude higher than those measured in less developed watersheds with lower impervious cover. When comparing Zn concentrations to 87Sr/86Sr values in stream waters, rural watersheds have low values and narrow ranges. In contrast, stream water from urban watersheds range to higher Zn values and Sr isotope values. These trends can be accounted for by mixing between natural stream water, municipal supply water, and wastewater. However, additional data are required to determine the extent to which Zn may be contributed from other sources, such as those related to non-exhaust traffic-related sources (i.e. tire wear and brake pads), paint, construction sources (i.e. galvanized steel and electroplated materials), medical waste, electronics manufacturing, and other industrial processes. To assess these additional sources of Zn, we will apply stable isotopes of zinc (δ66 Zn), a promising tracer of potential urban influences to water resources. This study will improve our understanding of anthropogenic sources contributing to water quality degradation in the Austin area, which is crucial to managing water quality.