Surface sediment zonation of the Zayandehroud Dam reservoir based on geochemical indices[پهن هبندی رسوبات سطحی دریاچۀ سد زایندهرود ب ر اساس شاخ صهای زمینشیمیایی]

Abstract

Dam reservoirs serve as suitable places to settle sedimentary materials carried by rivers. Pollutants absorbed into these sediments may lead to water contamination, increased aquatic animal mortality, and loss of biodiversity. Potentially toxic elements (PTEs) are classified as highly hazardous pollutants due to their long persistence in the environment. Due to their destructive effects on humans and the environment, it is important to examine sensitive and special areas for contamination with them. Therefore, spatial zoning of these pollutants in surface sediments of aquatic ecosystems is very effective in identifying the entry routes and determining their origin, as well as in identifying sedimentation conditions and determining sensitive zones for pollution reduction management. The sampling of surface sediments with the aim of zoning the sediments of the Zayandehroud Dam reservoir in terms of the level of contamination with PTEs based on geochemical indicators was carried out from 20 stations in this lake in December 2022. Then, the physical and chemical variables of the sediments were measured, including pH, EC, Eh, percentage of moisture, bulk density, dry density, grain size, percentage of organic matter, percentage of calcium carbonate, and concentrations of 26 elements. The results showed overall increasing changes in pH, bulk density, dry density, percentage of organic matter, percentage of calcium carbonate, and sand-sized particles from the dam crest to the lake entrance, while the percentage of moisture and Eh showed an overall decreasing trend. Only some elements, including silver, arsenic, chromium, copper, nickel, and lead, exceeded the US sediment quality guidelines (ERL and ERM) at some stations, among the 26 elements measured in the 20 surface sediment samples. Which was found towards the dam crest for arsenic and lead, chromium except for a few points, nickel and copper were found throughout the study area, and silver was found towards the lake entrance. Also, the Enrichment Factor (EF) of lead and copper was lowest at the lake entrance (EF<2) and increased towards the dam crest, and there was also very high enrichment (EF= 20-40). The EF of silver showed the highest enrichment (EF> 40) at one station at the lake entrance. The Geoaccumulation Index also showed non-polluted (Igeo < 1) to slightly polluted (Igeo = 1-2) for cadmium and antimony in the entire study area, and slightly polluted (Igeo = 1-2) for silver towards the lake entrance and for lead near the dam crest. The PLI index based on total elements showed pollution (PLI>1) only near the dam crest. © 2025 University of Isfahan.