Studies of biotic, quality and pollution parameters of the Karaj protected river

This study was conducted to understand the health status of Karaj River ecosystem as one of the most important rivers in Iran, the physicochemical parameters, toxicity and saprobic indices were analyzed due to sampling from 12 stations in 2021. Identification of benthic organisms and calculation of biological value was performed. Qualitative status, toxicity analysis, measurement of PAHs along with statistical analysis were performed as well. According to the results, the general water quality index decreased in downstream except for the branches. Toxicity had fluctuating and generally decreased from upstream to downstream. The biological value index had the highest rate in Chamran Park and the lowest recorded in Haft Cheshmeh branch. In terms of saprobic index, the river categorized in Oligosaprob, β-mesosaprob and α-amesosaprob classes. Upstream stations had favorable status compared to downstream in both cold and warm seasons. Karaj basin subdivision maps were prepared based on the Munich method, IRWQIsc index and the combination of saprobi map, BOD and land use in the region. The results of the analysis confirmed the important role of human activities in river water quality, especially in rural and garden uses, and in the next stage, roads. From upstream to downstream, the number of pollutant sources has increased and their roles were evident. Development of rural areas negatively increased BOD and benthic index. Therefore, it is necessary to monitor and treat wastewater, to issue the environmental standards for agriculture activities and groundwater uses, as well as deal with violators with the aim of conserving the river.