Spatial variations of relationship between heavy metals transportation and particle size distribution of suspended sediments

The particle size distribution (PSD) of suspended sediment has fundamental importance in understanding its role in a variety of environmental processes, modeling the transport of sediment and sediment-associated contaminants including heavy metals, nutrients, radionuclide and synthetic organic compounds in river systems. This paper aimed to assess spatial variation of relationship between transport of heavy metals (iron, chromium, nickel and zinc) and PSD of suspended sediment. The study was conducted in Educational and Research Watershed of Tarbiat Modares University comprises some 50000 ha. Towards this attempt, twenty two sediment samples were collected from beginning and end of a study reach (700 m) during May 2007 to June 2008. The samples were then prepared through direct digestion and finally analyzed by atomic absorption spectrophotometer (AAS). The sediment samples were also analyzed for PSD determination based on Stokes’ law with the help of modified pipette method after sample preparation. The relationship between PSD and heavy metals contents were thus evaluated applying bivariate regression models. Proposed models were then selected based on statistical criteria. The results showed a quite high correlation between iron, nickel, chromium and zinc content in suspended sediment and fine PSD (silt and clay) at confidence level of beyond 95% and with correlation coefficient greater than 0.71%. However, the variability of type and quality of relationships at two study points were also well proved.