عنوان مقاله [English]
Introduction: Geochemical studies of sediments of aquatic bodies such as rivers, estuaries and beaches can be an effective step to find the origin and distribution pattern of sediments and associated elements As a result of environmental assessment of pollutants in coastal areas. Rivers are one of the most important sources of dissolved and suspended metals in coastal water River sediments are one of the most important areas for measuring and monitoring the pollution of aquatic ecosystems; Because sediments not only play an important role in the transport of pollutants, they are also potential sources of pollutants in aquatic ecosystems.
Materials and Methods: In this research, to study the geochemistry of important estuarine areas in the southern Caspian Sea basin, In this study, due to the importance of estuarine areas in terms of environment and fish farming and human activities, one core and 24 Surface sediment samples were collected from 8 rivers as Gorganrood, Qarasu, Tajan, Babolrood, Sardabroud, Safarod, Cheshmeh Kileh, Sefidrud, in three points (upstream, river mouth up to 10 meters depth).Grain size analysis, organic matter content and ICP analyses were performed on the samples.
Results: According to grain size analysis, the mean of gravel, sand, silt and clay was 3.59, 52.46, 41.48 and 2.27%, respectively, indicating that the predominant sediment load in river beds is generally sand. The highest concentrations of iron (45000 ppm), aluminum (74000 ppm), chromium (142.78 ppm), cobalt (33.67 ppm) and lead (56.70 ppm) in Ramsar River (Safarood), arsenic (18.45 ppm) and zinc (110.3 ppm) were observed in Gorganrood river, nickel (60 ppm) in Qarahsoo river and copper (52.63 ppm) in Sefidrood. Also, the lowest concentration of elements in the Gorgan Bay core (K5) at depth 85 cm with an approximate age of 1400 years was obtained, which was used as a baseline reference. Based on different pollution indicators, the degree of pollution (Cd) Babolrud, Cheshmeh Kileh and Sardabrud are in the range of moderate pollution and in the Gorganrud, Qarah Su, Tajan, Ramsar and Sefidrud are in the range of significant pollution. According to the modified degree of pollution index, all rivers are classified in the range of low to medium degree of pollution, and (PLI) in most stations showed in the range of more than 1 (slightly polluted to polluted), but ecological risk (RI) were still in the low risk range. The enrichment factor (EF) in the sediments of the estuarine sections showed that the above rivers are probably enriched (Table.1).
Conclusion: One of the factors for the enrichment of these elements can be the geology of the region. The eastern parts of the Caspian Sea include the Gorgan metamorphic complex and due to the igneous nature of these set, contains a large amount of heavy metals. In addition, another origin of the source rock in this part includes fine materials, especially shale, which has a relatively high ability to absorb heavy metals effects to the presence of clay minerals. Likewise in the central and western parts, ultramafic rocks contain large amounts of iron, chromium, nickel, cobalt and manganese, which are eroded by the hot and humid climate of these areas. According to the sediment quality guidelines of Canada and the United States, it was observed that the amount of these elements in the sediments of the region is less than dangerous and harmful but continuous monitoring of pollution is essential for future decisions and decision-making.