A ssessing the water quality of Zayandeh Rud River affected of drough period using BMWP, ASPT and Hilsenhoff biological indices

Identification the extent of water pollution provides useful information for aquatic ecosystems assessment using biological indices, especially benthic macroinvertebrates. This study aimed to evaluate the water quality of Zayandeh-Roud River due to its importance for agriculture, urban and industry sectors. Water samples were collected from Baghbadoran, Falavarjan Bridge, Ghadir Bridge, Freeway Bridge(Chum) and Ziar Bridge stations in 2013 on a monthly basis. BMWP, ASPT and Hilsenhoff as biological indices of river water quality were compared with the same period in2007(before the drought). Results of indices water quality of Freeway Bridge(Chum) and Ziar Bridge stations was very bad. The values of BMWP and ASPT in this time period (2007-2013) of water quality were decreased. Results showed a negative significant correlation between these indices and EC, BOD5, COD, phosphate and temperature of river water. According to the results the water quality of Zayandeh-Roud river has classified in bad to very bad due to frequent drought events.