مرضیه رشیدی گل رویه

The purpose of this research was to determine the concentration of poly aromatic hydrocarbons (PAHs) in the surface sediments during four seasons at different transects of the southern basin of the Caspian Sea and to investigate the causes of their temporal and spatial changes, to compare with the standard limits, and to find the origin of these compounds. The samples from the surface sediments were collected using a grab (van Veen grab) from depths of 10 and 30 m in the coasts of Guilan, Mazandaran, and Golestan provinces at eight transects (Astara, Anzali, Sefidroud, Ramsar, Nowshahr, Babolsar, Amirabad, and Torkaman) during the autumn and winter seasons of 2018, spring and summer of 2019. The sediment samples were prepared in order to investigate PAHs using a standard method (extraction with organic compounds by the Soxhlet apparatus). The results showed that the mean (±SE) annual concentration of PAHs in the four seasons of autumn, winter, spring, and summer was 29.6±11.5, 2125±611, 4.2±3.0, and 5.3±3.1 µg/kg dry weight, respectively, and the maximum concentration of PAHs was recorded in the Nowshahr transect in the winter season. The results of the current research showed that 2 and 6 rings compounds had a low percentage of abundance in the sediments and the mean concentrations of PAHs and BaP in most of the samples were lower than the international threshold standards. The origin of PAHs compound in the sediment was recorded in more pyrogenic sources based on the diagnostic ratio (LMW/HMW=0.3).

Heavy metals are among the pollutants that cause many problems for aquatic organisms and, ultimately, for humans in aquatic ecosystems. Sediments serve as a reservoir for metal pollutants from both natural and anthropogenic sources. Therefore, the purpose of this study is to investigate the concentrations of both resistant and non-resistant forms of the metals Cu, Cd, Pb, and Hg in surface sediments at depths of 10 and 30 meters along eight transects from the fall and winter of 2018 to the spring and summer of 2019 in the southern Caspian Sea. The results showed that the mean concentration (±SE) of Cu, Pb, Cd (mg/kg dw), and Hg (µg/kg dw) in the resistant fraction were (17.08 ± 1.37), (867.80 ± 8.96), (4.82 ± 0.64), and (5.42 ± 0.05), while the non-resistant fractions were (3.09 ± 0.66), (22.80 ± 1.23), (9.70 ± 0.16), and (8.13 ± 0.05), respectively. When comparing the concentrations of non-resistant forms accessible to living organisms with international standards, it was found that the concentrations of Cu and Hg were lower than the standards, while the concentrations of Pb and Cd slightly exceeded the international standards, suggesting a man-made origin for Pb and Cd. The results of measuring heavy metals in sediments indicated that the contribution of anthropogenic sources to the origin of these metals is greater than that from natural and geochemical sources.

The Zhaveh dam is located on the Sirvan River containing two main branches of Gaveh Rood and Qeshlaq. The dam was designed for industrial and agricultural use. Surface sediment samples were collected at 5 selected stations in the two branches of the Sirvan River, Qeshlaq and Gaveh, as well as in the dam reservoir. In this study, nine sediment parameters (different forms of nitrogen and phosphorus, TOC, pH, Eh) were investigated to determine the quality and the prediction of the eutrophication trend of the Zhaveh Dam. The quality of sediments in different stations showed that they contain high organic and mineral pollution. Based on the TOC% of the sediment, the region was considered as slightly to highly polluted, especially in stations 2 and 3, but station 4 (Gaveh Rood branch) was classified as moderate quality. The changes in the OPI and ONI indices and comparison with the organic index standard also indicated the high pollution of the sediments in this region. These conditions are due to the high mean concentration of total phosphorus (2075±178 mg/kg.dw) and bioavailable phosphorus (666±142 mg/kg.dw) in the rivers feeding the dam, which deal with a high risk of eutrophication. In addition, after the water intake of the Zhaveh Dam and the high concentration of organic and mineral pollutants during the retention time of the water, it will be difficult to control the eutrophication