Epiphytic algae communities and their relationship with environmental factors in the "One River and Two Streams" Basin in Xizang

Due to the uniqueness of natural environment and ecosystem on the Qinghai-Tibet Plateau, the plateau algal community structure and its relationship with environmental factors have received unprecedented attention. In order to explore the epiphytic algae communities and their relationship with environmental factors in the "One River and Two Streams" Basin in Xizang, a total of 7 sampling sites were investigated in four quarters. Water quality evaluation of the study area was based on both hydrochemistry and epiphytic algae. The results showed that a total of 97 species from 60 genera belonging to five phyla were detected. The community was dominated by Bacillariophyta (48 species from 25 genera), Chlorophyta (17 species from 13 genera), and Cyanophyta (26 species from 18 genera), with average annual relative abundances of 88.5%, 6.7%, and 3.6%, respectively. Nitzschia sp. of Bacillariophyta was the dominant species. Significantly higher water temperature (WT) but lower pH was seen in summer than in other seasons. Water turbidity in autumn and ammonia nitrogen (NH3-N) concentration in winter were significantly higher than in other seasons. Total phosphorus (TP) did not change much across seasons. A water quality evaluation based on both hydrochemical parameters (single-factor analysis and comprehensive pollution index, CPI) and the biological index of epiphytic algae (diversity index, pollution indicator species, and index of biotic integrity, IBI) indicated that water quality was mostly at good or medium status. Redundancy analysis (RDA) indicated that the measured environmental factors had no significant effect on the relative abundance and the dominance of pollution indicator species. Dominant species were positively correlated with photosynthetically active radiation (PAR) and ultraviolet A (UVA), and turbidity had a significant negative effect on the number of species. By combining a hydrochemical and biological index, this study emphasizes the importance of water quality monitoring from both a short-term transient as well as a long-term comprehensive perspective. This approach can provide comprehensive and systematic reflections on the health status of waterbodies.