Geochemistry and ecological risk assessment of the coastal Tajan River using sediment quality indices (Southern Caspian Sea, Iran)

Highlights: • The implication of the Caspian Sea-level changes on the geochemistry of sediments • Long-term in geochemistry and pollution of the riverine environment • Event-base geochronology of the sediment column of sedimentary environments • The Tajan River is experiencing a mean sedimentation rate of 2 cm year⁻¹. • Modest toxic metals enrichment resulted in moderate contamination during wet seasons. The present study aimed to reveal correlations between environmental events and geochemistry variation and ecological risks of the coastal Tajan River. Sediment quality indices (Cf, Cd, Er, and RI) were applied to achieve the research objectives based on the concentration of toxic metals (As, Cd, Cr, Cu, Ni, Pb, Zn). The probably effective level is based on the concentration of As, Cr, and Ni observed. The coastal zone and the urban sector of the river have experienced a moderate ecological risk since 1975, especially during wet seasons (1988–1997) with a mean sedimentation rate of 2 cm/year. A significant correlation (r=0.439–0.633, p-values < 0.0001) between the toxic metal concentration and the Caspian Sea level fluctuation was obtained. The lowest concentration of toxic metals coincided with the high stand water level. Management practices recommend controlling toxic metals (As, Cd, Ni, Cr, Pb) from the sources and dredging of retention pounds along the Tajan River.