Shoreline and salinity shifts along the Chennai coast: Environmental and ecological implications

Indian coastal ecosystems are increasingly vulnerable to the synergistic pressures of anthropogenic development and climatic variability. This study assesses shoreline dynamics and seawater intrusion along an 86 km stretch of the Chennai coast (1990–2024). Using the Digital Shoreline Analysis System (DSAS), results reveal that 58.65 % of the monitored coastline is characterised by erosion and 40.53 % by accretion, primarily driven by port expansions at Chennai (34.8 m/yr), Ennore (25 m/yr), and Kattupalli (20 m/yr). New port construction triggered significant down-drift erosion at rates of 21.3 m/yr (Ennore) and 16 m/yr (Kattupalli). In parallel, groundwater (GW) integrity was evaluated using the Hydrochemical Facies Evolution (HFE-D) analysis. All samples reside within saline or mixing zones, reflecting a coastal aquifer under chronic multi-source saline stress. The study indicates that shoreline retreat, sea-level rise, intensive groundwater abstraction, and recurrent droughts consistently amplify an aquifer's salinity, whereas extreme rainfall provides only transient relief through episodic recharge. These combined stressors are temporally associated with a sharp decline in Olive Ridley turtle ( Lepidochelys olivacea ) hatching success, from 84 % to 20 % (R² = 0.63) in high-erosion zones. These findings underscore the need to preserve Chennai's fragile ecosystems amid accelerating anthropogenic and climatic pressures.