Water quality monitoring in Karaj River based on benthic bioassay using Hilsenhoff Biological Index (HFBI)

The role and importance of benthic organisms in the food chain and ecological pyramid of aquatic ecosystems is highly recognized. This study was conducted to investigate the benthic population and water quality of Karaj River, located in Alborz Province. In this study, a total of four stations along the river were selected and their benthic fauna were sampled seasonally. Samples were fixed with 4% formalin, isolated, identified, and counted in the laboratory. In the sampling procedure, 24 families, 5 categories and 5 orders were identified. The highest benthic density with 177 specimens (number per square meter) was reported in summer and the lowest benthic density with 105 specimens reported in winter. The benthic population and composition of Karaj River benthic was consisted of two classes of Oligocheata, Platyhelminthes and Coleoptera order and these groups had the highest density in all stations. During this study, the average Shannon-Wiener diversity index was 1.61. The highest Shannon-Wiener diversity index in the first station was 1.92, Based on the Hilsenhof Biological Index (HFBI), resulting that the water quality of Karaj River classified at the levels of good to desirable.