Environment Risk Assessment of Sand and Silt Exploitation from Tonekabon river

This research was carried out during 1382-83 on a monthly scale. The effect of sand and silt mining on Tonekabon river aquatic organisms was studied. One station was selected in sand and silt mining area and two stations were selected in upstream and downstream. The least abundance and biomass of benthic organisms was obtained in station 2 as 5%. This was also observed in estuary, as there were 21% and 74% of benthic organisms respectively in estuary and upstream of the reiver which have lost their habitates due to destruction of this area. Study on fish showed that Cyprinidae had the highest diversity and abundance. Fish abundance was 65% in station 1, 6% in station 2 and 29% in station 3. Station 2 had the least abundance. Migration and artificial propagation of Salmo truta caspius and Rutilus frissii kutum in this river are of high importance. Finally, destabilisation of river substrate and increase of suspended solid have led to reduction in diversity and abundance of species. The negative effects of sand and silt mining were not restricted to the sampling position and have affected other littoral parts of the river. This can result in degredation of river substrate and littoral parts