Abstract: Currently, the water supply source is complex, and the trend of water quality changes in the receiving reservoir is unclear. To evaluate the ecological health of the water body, it is important to quantify and determine the impact of the phytoplankton community in the water supply on the growth of phytoplankton in the receiving water. In this study, the physic-chemical factors of the water in the supply and receiving reservoirs were measured during different seasons of water transfer period. The changes in cell density and community structure of phytoplankton in the mixed water treatment of different ratios of the supply and receiving water were compared and analyzed by using the algae growth potential test. The results show that the concentrations of nitrogen and phosphorus nutrients in the receiving reservoir did not change significantly during the water transfer period (P＞0.05). The algae growth potential tests conducted in different seasons showed that the peak time of phytoplankton cell density in the treatment groups of summer and winter was 4 days earlier than that in the control group, and the peak density increased with the increase of the mixing ratio. However, the density of phytoplankton in the treatment group in the end of the summer cultivation period (20 days) was lower than that in the control group. Additionally, the actual peak density of phytoplankton in the treatment groups in summer, autumn and winter was 10%, 17%-24%, and 31% lower than the theoretically estimated value, respectively. The changes in community structure in the treatment group show that the absolute dominant species in the receiving reservoir during summer was replaced by the dominant species in the input water, and the relative abundance of the dominant species in autumn and winter increased with the increase of the water mixing ratio, indicating that they were significantly affected by the growth of the dominant species in the supply water. Overall, the difference in nutrient concentrations between the supply and receiving water bodies is the main factor affecting the growth of phytoplankton. Continuous water transfer significantly affects the community structure of phytoplankton in the receiving water body but also reduces the risk of algal blooms to some extent.

Key words: water transfer, physic-chemical factors, phytoplankton, community structure, algal growth potential test