To reasonably evaluate the eco-environmental health of the Tangwang River, which is a tributary of the Songhua River in China, community structures of periphyton and cleanliness of the benthic diatom at 24 sampling sites were investigated using McNaughton's dominance index, clustering, and ecotype analysis, while the relationship between the environmental factors and the diatom communities were studied by principal component analysis, Spearman correlation test, and redundancy analysis, in August 2018 (flood season). A total of 99 species or variants of benthic diatoms have been identified, indicating that there were abundant diatoms in the Tangwang River. Achnanthidium minutissimum and other diatoms that can be used as clean water indicators were dominant species in the Tangwang River, which indicates that the eco-environmental quality of the Tangwang River was relatively healthy in the flood season. Of these, the dominant degree of A. minutissimum was 0.32, making it the absolute dominant species in Tangwang River. Sampling sites can be divided into three groups based on clustering analysis. The dominant species of group 1 and group 2 were mainly clean species, indicating that the two groups were in a relatively healthy state. Nitzschia palea, Ulnaria ulna, and other diatoms that can be used as eutrophication indicators were the dominant species of group 3, indicating that group 3 was less healthy than the other two groups. From groups 1 and 2, the results from ecotype analysis showed a decrease in the proportion of polyoxybiontic diatoms and an increase in the proportion of α-mesosaphrobe diatoms, polysaprobe diatoms, oligo-mesotrophic diatoms, mesotrophic diatoms, meso-eutrophic diatoms, and eutrophic diatoms. Compared to the other two groups, the results from ecotype analysis showed a significant increase in the proportion of α-mesosaphrobe diatoms, polysaprobe diatoms, eutrophic diatoms and hypereutrophic diatoms in group 3. The predominant aquatic influencing factors of diatom community structures for the Tangwang River were permanganate index, total nitrogen (TN), and ammonia nitrogen (NH4+-N), of which permanganate index was the main factor for group 2, while TN and NH4+-N were the main factors for group 3. As a result, the eco-environmental quality of the Tangwang River was good, and the benthic diatom was found to be an effective indicator of the nutritional conditions and saprophytic status.
Keywords: Achnanthidium minutissimum; Tangwang River; benthic diatom; ecological type; saprobic.