Decades of Urban Water Quality Data: A Multivariate Exploration Using Indianapolis as a Case Study

Long-term datasets are critical for assessing the impacts of urbanization on water quality. This study analyzes 24 years of monitoring data from urban Marion County (Indianapolis), Indiana, to evaluate spatial and temporal patterns in surface waters across Eagle Creek, Fall Creek, and the Lower White River. Principal component analysis (PCA) combined with k-means clustering and linear discriminant analysis (LDA) was applied to nutrients, heavy metals, and microbial indicators to identify dominant drivers of variability and group sampling locations with similar water quality signatures. Results revealed significant spatial differences across sites, with phosphate linked to fertilizer runoff, chloride and sulfate elevated in urban areas due to road salt and stormwater, and arsenic, chromium, and other metals associated with industrial activity and legacy contamination. Temporal shifts in pollutant concentrations reflected both urban growth and watershed management efforts. Despite broad similarities in land use at the county scale, localized conditions and pollution sources contributed to distinct site-specific outcomes that persisted over decades. These findings highlight the importance of sustained monitoring and integrated watershed management to mitigate pollution risks and safeguard aquatic ecosystems in urban environments.