Resetting of soil compositions by irrigation in urban watersheds: Evidence from Sr isotope variations in Austin, TX

Alessandro A Mauceri; Jay L Banner

doi:10.1016/j.scitotenv.2023.166928

Resetting of soil compositions by irrigation in urban watersheds: Evidence from Sr isotope variations in Austin, TX

Sci Total Environ. 2023 Dec 15:904:166928. doi: 10.1016/j.scitotenv.2023.166928. Epub 2023 Sep 9.

Authors

Alessandro A Mauceri¹, Jay L Banner²

Affiliations

¹ Department of Geology, Macalester College, Saint Paul, MN 55105, USA. Electronic address: a.a.mauceri@wustl.edu.
² Environmental Science Institute, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, USA.

PMID: 37690754
DOI: 10.1016/j.scitotenv.2023.166928

Abstract

Human activities in urban areas disturb the natural landscape upon which they develop, disrupting pedogenic processes and ultimately limiting the ecosystem services urban soils provide. To better understand the impacts on and resiliency of soils in response to urban development, it is essential to understand the processes by which and degree to which soil physical and chemical properties are altered in urban systems. Here, we apply the source-tracing capabilities of Sr isotopes (⁸⁷Sr/⁸⁶Sr) to understand the impacts of urban processes on the composition of soils in eight watersheds in Austin, Texas. We evaluate natural and anthropogenic Sr sources in watersheds spanning a wide range of urbanization, comparing soils by variations in their natural (including mineralogy, thickness, soil type, and watershed) and anthropogenic (including irrigation, soil amendments, and fertilization) characteristics. A strong positive correlation between soil thickness and ⁸⁷Sr/⁸⁶Sr is observed among unirrigated soils (R² = 0.83). In contrast, this relationship is not observed among irrigated soils (R² = 0.004). 95 % of 42 irrigated soil samples have ⁸⁷Sr/⁸⁶Sr values approaching or within the range for municipal supply water. These results indicate soil interaction with municipal water through irrigation and/or water infrastructure leakage. Soils irrigated with municipal water have elevated ⁸⁷Sr/⁸⁶Sr values relative to unirrigated soils in seven of eight watersheds. We propose that original soil ⁸⁷Sr/⁸⁶Sr values are partially to completely reset by irrigation with municipal water via ion exchange processes. Our results demonstrate that in urban systems, Sr isotopes can serve as an environmental tracer to assess the overprint of urbanization on natural soil characteristics. In the Austin region, resetting of natural soil compositions via urban development is extensive, and the continued expansion of urban areas and irrigation systems may affect the ability of soils to retain nutrients, filter contaminants, and provide other ecosystem services that support environmental resilience.

Keywords: Irrigation; Strontium isotopes; Urban soils; Urbanization.