Journal of Watershed Management Research

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Amjadi M, Khaledi Darvishan A. (2021). Downstream Changes in Heavy Metal Concentrations and Pollution Indices of Bed Sediments in Khamsan Representative Watershed. jwmr. 12(24), 159-169. doi:10.52547/jwmr.12.24.159
URL: http://jwmr.sanru.ac.ir/article-1-1118-en.html

Extended Abstract
Introduction and Objective: Stream sediment load usually acts as an important source and indicator in geochemical elements concentration changes especially heavy metals and the extent of human impact. Studying the trend of downstream changes in sediment pollution indices and the factors affecting it is one of the most important interdisciplinary research needs. In present research, the concentration of heavy metals and pollution indices of bed sediments were investigated in the main river of Khamsan representative watershed and the factors affecting the downstream changes of indices were analyzed. This river is one of the two important rivers entering the lake of Gawshan dam and for this reason; the study of water and sediment pollution of this river is of special importance.
Material and Methods: To achieve the research purposes, along the main stream, 10 bed sediment samples were taken from upstream to downstream and the concentrations of heavy metals including beryllium, chromium, nickel, copper, zinc, arsenic, selenium, cadmium, mercury, thallium and lead were measured using ICP-MS. Then the indices of contamination factor (Cf), degree of contamination (Cd), modified degree of contamination (mCd), pollution load index (PLI) and geo accumulation index (Igeo) and the downstream changes of these indices were calculated and analyzed. In addition, the percentage change index was used to determine the downstream change of the heavy metals concentrations.
Results: The results showed that reducing the steam slope and increasing the density of vegetation along the stream was effective in downstream reduction of the heavy metals concentrations and neutralizing the effect of residential area. Toxic elements such as selenium, cadmium, mercury and arsenic have been reduced by about 40% in the downstream direction and the effect of check dams in reducing the transfer of lead, zinc, cadmium, copper and selenium along with bed sediment was also confirmed. The results also showed that after the qanat water joined the main stream, the concentration of heavy metals in the bed sediments increased and the highest increase with 1/116, 3/114, 0/100 and 5/79% was observed in selenium, cadmium, mercury and beryllium, respectively.
Conclusion: Conclusion of the present study shows that although according to the studied indices, none of the bed sediment samples of the studied river from the upstream to the downstream is contaminated, but the trend of changes is especially worrying for heavy metals nickel, zinc and cadmium and can be an alarm for water and sediments entering the Gawshan dam reservoir.