بررسی لیمنولوژی رودخانه بهمنشیر

Bahmanshir River derived from Karoon River and finally connected to Arvandrood that passed from Abadan and then flow intothe Persian Gulf. Because of low slope of Bahmanshir River from Ahwaz to Abadan, tidal flow intrusion long distance in Bahmanshir, Arvandrood and Karoon. Sampling from physical and chemical parameters and phytoplankton were done by Nansen sampler, benthic sampling, heavy metals, TOM and grain size sampling were done by grab. Samplings of zooplankton were done by filtering 20 liters water in 100 mesh size net from mid-depth of river water. Fish sampling were done by gill net, Trawl net, sobor gill net and stable net with 20, 27, 30, 35, 39, 40 mesh sizes. Physical and Chemical parameters were more similar from station one to four but there were some differences with station five in mouth of river in the sea. Nitrate showed same variations in all studied stations and maximum concentration of nitrite was observed in station five in June and July. The highestvalue of Total hardness and salinity were observed in station five . The range of pH was 7.2 to 8.5. Cd and Zn were found to be the lowest and the highest concentration in sediments respectively. Annual average following as: Cd < Co < Cu < Pb = Ni < Zn According to ISQGs and river water quality standards, chemical and physical parameters and sediment heavy metals werein acceptable range. Only Cd and Zn values were found higher than acceptableranges. No significant difference was observed between stations for heavy metal concentrations. In general, 44 phytoplankton species were identified Bacillariophycea (77.74%), Cyanophycea( 10.39%), (Chlorophycae 8.88%) and (Dinophycea 2.99%) were the dominant phytoplankton classes in this study. Shannon index have shown the highest species diversity during one year in January and the lowest was in fourth station. 110 Phytoplankton species composition inBahmanshir have shown that Bacillariophycea became higher from river to estuary and among zooplanktons Rotifera and Tintinida were the most frequentgroups in estuary region with 83% of total abundance. Copepoda, Rotifera and Protozoa (especiallyTintinida) were the most frequent zooplankton groups. The highest frequency of zooplankton with 40.6% was observed in the station one in Khoramshahr. 16 macrobenthic groups were identified during the study. Polycheate worms, Isopoda and Oligocheate worms have shown the 83.5% , 5.4% and 3% frequencies respectively. 43 fish species that included in 26 families were identified. Cyprinidae with 12 species and Clupeidae with 2 species were the highest and the lowest species frequencies respectively. Among the identified fish species Hypophthalmichthys molitrix, Barbusesocinus , Crrassius auratuswere exotic species and rest of them were local species. Seasonal changes were affected directly by quantitative and qualitative variations in Karoon water and planktonic species composition in estuary region were affected by tidal flow and advances of seawater. Cyprinidae and Barbus geniuses were the most frequent fresh water fish species. Migrant species like Johnius dussumeieri, Acanthophagus latus, Hilsa ilishawere captured in most stations and months, presence of these species is important for reproduction. Fish species of this river have different diet that included soft sediments, planktons, benthos, macroscopic plants, small fishes and shrimps.

Keywords:

دریاچه شناسی , رودها , رودخانه بهمنشیر , ترکیب شیمیایی