Study of abundance and identification of benthic invertebrate in the Kamal Saleh Dam Lake, Arak

Benthic macroinvertebrate communities are inhabited in the lentic sediment; they can used as an indicator for evaluation the quality of aquatic environment. In order to assess the benthic communities of Kamal Saleh Dam Lake, seasonal sampling at 5 stations was performed. The sampling was carried out by the sediment sampler with the dimensions of 20cm×20cm. The lake showed minimum 7. 6 and maximum 21. 2 water temperature in winter and summer, respectively. The concentration of dissolved oxygen in the surface water was fluctuated with an average of 8. 07 ± 1. 5 (mg/l) within the range of at least 6. 44 (mg/l) and up to 10. 12 (mg/l) respectively in summer and winter, respectively. The maximum, minimum and average depth of the water was 18. 2, 14 and 16. 8 meters in winter and fall, respectively. In this study the genus of families Naididae ،Chironomidae، Viviparidae، Valvatidae، Coenagrionidae and Lymnaeidae was observed. Tubifex was the dominant genus in all stages. The maximum and minimum density of benthic was reported 115. 64±18. 39 (N/ M2) of 34. 22 ± 13. 63 in spring and autumn, respectively. The values of diversity index were between 0. 29 and 0. 88. The highest and lowest values of Shannon diversity species index were in spring and winter respectively. Simpson's dominance index and Margalef's richness index also measured in autumn and winter for Simpson index and in summer and winter for Margalef index respectively. The low abundance of the benthic fauna of lake can be related to not suitable bed for establishment and deficiency of nutrients in this young lake. It seems that the structure of substrate, the amount of nutrients and grazing pressure are the most important environmental factors that affect benthic community in the Kamal Saleh Dam Lake, Arak.