Limnological survey on the most important rivers in the Iranian Southern Coasts of the Caspian Sea in the Guilan province with emphasize on the pollutants(Hevigh, Karkanrud and Shafarud rivers)

Abstract

In order to create a reliable ecological database for Guilans running waters(north Iran near the Caspian sea), at the first step 3 important rivers containing Hevigh, Karkanrud and Shafarud, were selected and limnological survey, during autumn 1380 and summer1381 were seasonally carried out for them. Results showed that the key physico-chemical parameters such as dissolved O2, BOD5, pH, Phosphate, Nitrate, Nitrite, ammonium and in all of the three rivers water were in their normal range suggesting good water quality. Chrysophyta, Chlorophyta, Cyanophyta and Euglenophyta were respectively the most prevalent phytoplankton taxa and Zooplankton fauna of the rivers were fixed and sessile species belong to Protozoa and Rotatoria. 42 benthic macroinvertebrates taxa(Hevigh:36,Karkanrud:22 and Shafarud:30) were identified in these 3 rivers which individuals belong to order Diptera compromise the most divers and frequent one. Regarding macroinvertebrates diversity and indicator groups, it seems that Hevigh river has relatively better water quality than the two other. 23 fish species belong to 9 family,7 order and 2 class , were identified in these rivers during the study period which cyprinid were the most diverse and prevalent of them. Albornoides sp., Capoeta capoeta and Neogobios sp. were the most widespread and frequent species of the identified fishes in all of them. Bacteriological survey including Coliform and E.Colie count showed that the lower parts of the rivers near the estuaries were more infected and the bottom sediments had more bacterial count during the all sampling period. However the total coliform count never exceed of 200 colonies per 100cc , suggesting no risk for direct contact (swimming and washing), according to EPA standards. Chromium, Cadmium and Mercury had very low concentrations in the rivers water but Cupper had relatively high concentration (up to 1.788 mg/l in Hevigh river) amongst the studied heavy metals. The maximum and minimum concentrations of detergent materials or surfactant (LAS) were respectively observed in Shafarud (0.047 mg/l) and Hevigh (0.014 mg/l). According to the results of the study even though all the three rivers water had an overall reasonable quality, but some signs of destructions and degradations such as sedimentation, relatively increase of nutrient, increased concentrations of some pollutants, which all results in the low diversity of macroinvertebrates and prevents migration of anadromous fishes, calls for a continuing monitoring program and precise control for these regions.