Evaluating Spatiotemporal Impacts of Urban Growth on Hydrochemical Dynamics in the Zahedan Aquifer, Iran

The Zahedan aquifer, a vital water resource in southeastern Iran’s arid region, is experiencing significant quality deterioration due to combined anthropogenic and geogenic pressures. This study presents a comprehensive spatiotemporal analysis of groundwater hydrochemistry across the aquifer system, employing year-long monitoring data to quantify urbanization impacts. Results reveal severe contamination gradients, with electrical conductivity (EC) increasing from 2,000 µS/cm in eastern regions to 8,500 µS/cm in western zones, paralleled by chloride concentrations rising from 500 to 3,500 mg/L. Spatial analysis identifies the urban northern and eastern sectors as contamination hotspots, where high-density well extraction for municipal, industrial, and agricultural use interacts with inadequate wastewater infrastructure. Seasonal variations demonstrate temporary water quality improvement during precipitation events, though parameters consistently exceed potable and irrigation thresholds without treatment. Three primary contamination mechanisms are characterized:(i) Anthropogenic wastewater infiltration through urban aquifers (ii) Mobilization of geogenic salinity from detrital formations (iii) Hydraulic gradient alterations from over-extraction. The findings provide critical insights for sustainable groundwater management in semi-arid urban environments, emphasizing the need for targeted infrastructure upgrades, extraction zoning, and nature-based remediation strategies to mitigate compounding salinity sources.