Biodiversity of macro-benthic and physicochemical quality (IRWQIsc) and toxic (IRWQIst) indices in the rivers of the Maharloo wetland basin

The Maharloo Wetland in the Fars Province has a great ecosystem and socio-economic importance for the city of Shiraz. The two rivers, Chenarrahdar and Khoshk River, as well as some springs in this basin, are the main suppliers of water to the wetland. These two rivers originate upstream of Shiraz city and, after passing through Shiraz city and receiving various wastewaters and pollutants, reach the Maharloo Wetland in the southeast of Shiraz city. This study was conducted to investigate the biodiversity of benthic organisms and the physicochemical and toxicity status of the rivers in the Maharloo watershed. Water and benthic organisms were sampled from 12 stations from the two rivers and springs, and the biological indices of benthic organisms, water quality, and water toxicity were evaluated in four seasons. According to the results, in all four sampling seasons, the water quality index (IRWQIsc) and toxicity index (IRWQIst) were suitable at the upstream stations and before the rivers enter the city of Shiraz, due to the entry of various types of domestic, agricultural, industrial and surface sewage of the city, these two indices are severely reduced and reach a severely polluted and critical ecosystem eutrophication condition. For studies of the benthic fauna of the rivers of the Maharloo watershed, sampling was performed at the stations. Then the benthic biodiversity indices, including HFBI, BMWP, ASPT, and Shannon-Wiener, were examined and evaluated. Based on the results of the biological indices, the biological communities in the rivers are completely different before entering the city of Shiraz and after that, and in parts of both rivers in the downstream stations, anaerobic conditions are created, and the possibility of life for benthic fauna is lost. The dominant benthic communities at the sampling stations before entering Shiraz city were mainly from the families Caenidae, Tipulidae, Baetidae, Gammaridae, Hydropsychidae, and Dytiscidae, but at the downstream stations within Shiraz city and the entrance to Maharloo Wetland, the dominant benthic communities were mainly from the families Naididae, Culicidae, Staphylinidae, Erpobdellidae, and Tubificidae. According to the results, the need to develop a comprehensive quality management program for basin entering the two rivers of Shiraz, Chenarrahdar and Khoshk, is essential to improve the ecosystem of the rivers in the basin and the Maharloo Wetland.