Spatial variability of heavy metals in surficial sediments: Tajan River Watershed, Iran

In this paper, we assessed the spatial distribution of heavy metal concentrations (Al, As, Cd, Co, Cr, Cs, Fe, Ni, Sn and Zn) in the sediments of the Tajan River Watershed, an inflow to the Caspian Sea in the Northern Iran. Comparison of four interpolation techniques (ordinary kriging, simple kriging, inverse distance weighted and local polynomial interpolation) via cross validation suggested that kriging was the most accurate spatial analysis technique for the majority of the elements. Variogram models obtained by geostatistical procedures indicate existence of spatial correlation between samples, with the exceptions for Al, Cd and Zn. The mapped spatial distributions are showing a clear coincidence of variation pattern for different groups of the heavy metals. This indicates similar origin and affecting factors for these analyzed metals. Possible anthropogenic and natural sources of heavy metals were discussed based on the distribution maps and correlation analysis with other elements and geologic units. The results have shown that the accurate spatial pattern of heavy metals could improve our understanding of possible sources, controlling factors and involving processes. This is essential for monitoring and remediation of the contaminant sites in the watershed.