Spatio-temporal variations of benthic diatom community in a subtropical river, China Quanfa Zhang, Xiang Tan

Background/Question/Methods

Benthic algae are functioning as important primary producers, chemical modulators, and important habitats for other organisms in aquatic ecosystems. Generally, diatoms (Bacillariophyta) are the dominant taxonomic group in freshwater benthic algae, comprising of more than 80 %of the total abundance and biovolume. Therefore it is vital to study the benthic diatom in aquatic ecosystem with the exacerbation of nutrient pollution from human activities into surface waters. In this study, we investigated the benthic diatom community and physic-chemical variables in China’s upper Han River with a drainage area of 95,200 km² and a length of 925 km. Our objectives were: (1) to determine variabilities in physical and chemical variables in streams; (2) to identify the benthic diatom community structure and succession including dominant species, biomass and biodiversity; and (3) to investigate the main driver for spatio-temporal variations of benthic diatom assemblages. These will be helpful to develop water resource conservation strategy for the upper Han River, China.

Results/Conclusions

There were seasonal variations in physical and chemical variables such as temperature, COD, total nitrogen, DOC, silica, and fluoride. Three species Achnanthidium minutissimum (composed of 10.7 % of the total diatom abundance), A. pyrenaicum (11.9 %), and A. subatomus (12.7 %) were persistently dominant in all seasons, while other two prostrate and motile species Eolimna minima and Nitzschia dissipata also dominated in the base flow season. There were significant differences in the Shannon–Wiener index, evenness index, species richness, and diatom indices between the mainstream and tributary, and diatom indices categorized mainstream as mesotrophic and tributaries as oligo-mesotrophic. Lower water quality in the mainstream led to the dominance of pollution tolerant species Eolimna subminuscula, while tributaries were characterized by Achnanthidium pyrenaicum and A. subatomus. Temporal variation in benthic diatom communities was related to temperature, nitrogen, organic pollutants, and hydrological regime. CCA indicated that spatial patterns of diatom assemblages could be primarily explained by dissolved organic carbon, pH, major ions, and flow velocity. The research demonstrates the applicability of benthic diatoms for water quality and ecohealth assessment in subtropical rivers.