Diatoms as indicators of organic pollution and nutrient enrichment in the Damavand River, Central Alborz, Iran

Diatoms are well-known indicators of water quality in rivers. Therefore, the composition and abundance of diatoms are used as a tool to monitor rivers in different countries. In Iran, few studies have been conducted on biomonitoring the rivers using diatoms. For diatom-based water quality assessment, it is necessary to determine the characteristic diatom species and the pollution tolerance level of the species. The present study investigates the indicator diatom assemblage from upstream (least polluted) to downstream (most polluted) stations along the Damavand River at different seasons from 2017 to 2019. The study of relative abundance and presence of species along the river showed that several species, sensitive to pollution, were dominant upstream. However, they were present as rare species and disappeared at high pollution levels in downstream stations. Several species had moderate resistance to pollution. Therefore, they reached the highest abundance in the river's middle course, and their abundance was highly reduced downstream. The most resistant species appeared in the lower reaches of the river, which had a very high level of pollution. This research introduces the indicator species of diatoms and their pollution tolerance in the Damavand water basin. Thus, this study can be a baseline for diatom-based water quality monitoring at aquatic resources in Central Alborz.