RECONSTRUCTING HISTORICAL URBAN INFRASTRUCTURE FAILURE AND ITS IMPACTS ON WATERSHED RESILIENCE

Globally, urban water resources are degrading at a time when increasing drought and population growth will place more demand on municipal water infrastructure. As urban infrastructure degrades, municipal water can enter the hydrogeologic system through irrigation and leakage of aging water networks. To better understand how and when this degradation occurs and its effects on the hydrogeologic system, we reconstruct temporal stream baseflow conditions using stream geochemistry and riparian bald cypress tree-ring growth and chemistry. Three watersheds are used including a rural endmember, an urban endmember, and a watershed that has rapidly urbanized over the past 50 years. In central Texas, bald cypress tree-ring width is sensitive to drought and streamflow. Further, strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) incorporated into tree-ring cellulose reflect mixing between naturally occurring water and municipal water of Austin, Texas at the time of ring growth. Bald cypress tree-ring chronologies in the rural watershed are strongly correlated with drought but urban watershed chronologies are not, suggesting that urban stream baseflow is supplemented by municipal water input, providing trees with supplemental water. Consistent with this result, bald cypress ⁸⁷Sr/⁸⁶Sr in the rural watershed are lower relative to the ⁸⁷Sr/⁸⁶Sr in the urban watershed, which approach values characteristic of municipal water. In the rapidly urbanizing watershed bald cypress ⁸⁷Sr/⁸⁶Sr increase over the past four decades in conjunction with population density, which is used as a proxy for water infrastructure density through time. These findings highlight the use of stream geochemistry and bald cypress wood chemistry as multidecadal records of municipal water infrastructure degradation with relevance to informing sustainable urban planning.