[Changes in Epilithic Algae Community and Its Relationship with Environmental Factors in the Meixi River, a Tributary of the Three Gorges Reservoir].

To explore the relationship between the community of epilithic algae and environmental factors in tributaries of the Three Gorges Reservoir region, the epilithic algae and related environment factors were investigated from 26 sampling sites in Meixi River, a tributary of the Three Gorges Reservoir region, during flood period (August 2016), drought period (November 2016), and normal water period (March 2017). Results showed that 106 species (including varieties) belonging to 47 genera and 5 families were identified from 26 sampling sites during the three periods. Among these, 73 species belonged to 38 genera and 5 families in the flood period, 67 species belonged to 36 genera and 4 families in the drought period, and 63 species belonged to 33 genera and 4 families in the normal water period. Nineteen, 17, and 18 dominant species were identified during the flood period, drought period, and normal water period, respectively. The main dominant species were Achnanthes sp., Aphanizomenon sp., and Phormidium sp. in the flood period; Achnanthes sp., Gomphonema sp., and Microcystis sp. in the drought period; and Gomphonema sp., Nitzschia sp., and Chroococcus sp. in the normal water period. Moreover, species such as Cocconeis placentula, Achnanthes sp., Gomphonema subclavatum, G. parvulum, Navicula parva, and G. constrictum were determined to be the common dominant species during the three periods. Redundancy analysis revealed that the changes in the relative abundance of dominant species in the backwater sections were significantly related to the electrical conductivity, dissolved oxygen, pH, total phosphorus, and total nitrogen, and the relative abundance of dominant species in the natural sections was mainly related to the electrical conductivity, pH, total phosphorus, temperature, and velocity. Moreover, a different relationship with the environmental factors was determined among the three periods. However, a negative correlation between total phosphorus and the relative abundances in G. parvulum, G. constrictum, and Achnanthes sp. and a positive correlation between pH and the relative abundances in G. parvulum, G. constrictum, and Achnanthes sp. were found during the three periods. These results indicated that the differences in the hydrological regime and environmental factors in the Three Gorges Reservoir played an important role on the composition of epilithic algae community and led to a significant change in the community structure of epilithic algae.

[Benthic Diatom Communities in the Main Stream of Three Gorges Reservoir Area and Its Relationship with Environmental Factors].

In order to study changes in benthic diatom communities and their relationships with environmental factors during different hydrological periods, 32 sites were sampled in the main stream of the Three Gorges Reservoir during the non-storage period (July 2015 to September 2015) and the storage period (December 2015 to March 2016). Results showed that there were significant differences in water temperature (WT), underwater light intensity (PAR), pH, conductivity (Spc), dissolved oxygen (DO), redox potential (ORP), turbidity (Tur), transparency (SD), flow rate (v), and permanganate index between the storage and non-storage periods. Ninety-six species of benthic diatoms, belonging to 28 genera, were identified during the two hydrological periods. Thirteen dominant species and three dominant species were identified during the non-storage period and the storage period, respectively, suggesting that some differences existed in the composition and distribution of dominant species between the two periods. However, Melosira varians, an α-polluting and eutrophic species, was dominant during both of the hydrological periods. Redundancy analysis (RDA) found that pH, flow rate, and orthophosphate (PO43--P) were the main environmental factors affecting the composition of benthic diatom communities, and a significant difference was found between up- and down-stream areas during the non-storage period. In comparison, water temperature, turbidity, permanganate index, and dissolved oxygen (DO) were the main environmental factors influencing the patterns of benthic diatoms communities, for which an insignificant difference was observed between up- and down-stream areas during the storage period. These results suggest that water storage in the Three Gorges Reservoir has an important impact on the composition of benthic diatom communities, and that this results in a change in community structure.