The present investigation provides a thorough study of eliminating soluble and colloidal elements
of copper, iron, magnesium and zinc during estuarine mixing of Gorganrood River water with Caspian Sea water in Iran. The processes of flocculation were carried out in 10 aquariums in order to furnish the salinity in an interval of 0.3 - 4.4 ppt. The obtained result is indicative of non- conservative behavior of studied metals. Higher flocculation resulted in a lower salinity and vice-versa. The obtained results indicated that most metal were eliminated during the initial mixing of fresh water with sea water at 0.6 - 1.0 ppt salinity interval. The trend of flocculation rates of elements in the river were obtained as follows: Fe (97.33%)> Mn (91.66%) >Zn (72.72%) > Cu (52.63%).The annual average elimination of soluble elements of iron(Fe), manganese(Mn),
zinc(Zn) and copper(Cu) from Gorganrood river to Caspian Sea decreases from 1040.68, 59.1498, 302.26, 263.64 tons per year to 27.75, 124.88, 83.255, 124.88 tons per year, respectively. According to the cluster analysis, parameters such as salinity, temperature, electrical conductivity, Eh and suspended solid materials do not have any impact on flocculation of elements. The only parameter that influences the flocculation of elements is the pH. This research illustrates that estuarine processes are effective mechanisms in self- purification of heavy metals from water resources. Metal speciation studies that are carried out by Eh-pH software show that studied metals are present as solid (in case of Cu), free ions (Fe and Mn) and finally hydroxides (Zn).