Simulated Study of Water Diversion with Different Trophic Levels Effects on the Water Quality and Phytoplankton Community in Gonghu Bay

To explore the ecological effects of “water diversion project from Yangtze River to Taihu Lake” on the water bodies in the receiving lake area, the simulated indoor experiment was constructed using an aquatic microcosm model in a period of 11 days. The Gonghu Bay area of Taihu Lake was used as the receiving water body, and three groups of Wangyu River water with different nutrient levels O, M, E（Oligotrophic group, Mesotrophic group, Eutrophic group） were introduced to study the dynamic response process of the water ecological environment of the receiving water body under the influence of water diversion at different nutrient levels. The purpose is to provide a basis for the rational formulation of water diversion scheduling plans and the optimization of the scheduling effect of the “water diversion project from Yangtze River to Taihu Lake”. The results showed that: during the experiment, total nitrogen（TN）, nitrate nitrogen（NO3--N）, ammonia nitrogen（NH4+-N）, total phosphorus（TP）, soluble reactive phosphate（SRP） and total organic carbon（TOC） in oligotrophic group and mesotrophic group decreased significantly. The effect of eutrophic water diversion group was worse than that of oligotrophic group and mesotrophic group. Water diversion increased the Shannon-Wiener diversity and Pielou’s evenness index in this water ecosystem. Density of diatoms and other non-cyanobacteria increased. Meanwhile, the growth of cyanobacteria was under competitive stress. The effect of oligotrophic group and mesotrophic group was better than that of eutrophic group. Simultaneously, the results of redundancy analysis showed that: pH, DO, SiO32--Si, TDS, NO3--N, and SRP of the receiving water body were the main environmental factors influencing the distribution of phytoplankton community in this experiment.