Tidal-driven variability of dissolved heavy metals and pollution index assessment in a tropical coastal system (Makassar, Indonesia)

Urbanized tropical coastal waters are increasingly exposed to heavy metal contamination due to rapid urbanization, industrial development, and domestic wastewater discharges, yet the role of tidal dynamics in regulating metal accumulation remains insufficiently understood.This study investigates the concentration patterns, tidal variability, and pollution status of dissolved heavy metals in the coastal waters of Makassar, Indonesia.Seawater samples were collected from ten representative riverine-coastal sites under contrasting high-and low-tide conditions and analyzed for Ba, Fe, Mn, Co, Ni, Cr, Zn, Pb, and Cd using Inductively coupled plasma optical emission spectrometry (ICP-OES).Pollution levels were assessed using the heavy metal pollution index (HPI), while metal associations and potential source characteristics were evaluated through correlation analysis and principal component analysis (PCA).The results demonstrate a clear tidal dependency, with systematically higher metal concentrations and HPI values observed during low-tide conditions, reflecting reduced hydrodynamic dilution and enhanced sediment resuspension.Multivariate analyses indicate that overall variability is primarily governed by background geochemical processes, whereas Pb and Cd are more strongly influenced by localized anthropogenic inputs.These findings highlight that tidal phase not only controls metal concentrations but also modulates source expression and cumulative pollution intensity.Incorporating tidal variability into coastal water quality assessment is therefore essential for improving contamination detection and supporting effective monitoring and management strategies in rapidly urbanizing tropical coastal regions.