CHARACTERISTICS AND MAIN INFLUENCING FACTORS OF PLANKTON FUNCTIONAL GROUPS IN SUMMER AND AUTUMN OF CHANGHU LAKE

Changhu Lake, is a typical eutrophication shallow lake in Jianghan Plain, Hubei Province, with comprehensive functions such as flood storage, irrigation, aquaculture and navigation, higher productivity, rich fishing. Plankton can reflect the water quality, the primary productivity of ecosystem, the fishing productivity, feeding pressure, and so on. By plenty of rainfall, the conditions of water temperature and light are suitable, the biomass and population density of plankton are the highest in the whole year in summer and autumn. The division of plankton into functional groups is one of the hot topics at present. To explore the characteristics of plankton functional groups and their main influencing factors, two sample surveys were conducted in Changhu Lake, in July (summer) and October (autumn) 2017. The main influencing factors were analyzed by RDA analysis and Pearson correlation analysis. The results showed that 95 species, 49 genera and 7 phyla of phytoplankton were identified, which were divided into 25 functional groups with an average density of 5.12×10⁶ ind./L and an average biomass of 1.663 mg/L. There were 59 species in 41 genera, 3 phyla, which were divided into 8 zooplankton functional groups with an average density of 3.76×10³ ind./L and an average biomass of 2.803 mg/L. The average density and biomass of plankton functional groups were significantly higher in summer than those in autumn (P＜0.01), and the highest density was at H1station in summer, the highest density and biomass were at Y4 station in autumn; and from summer to fall the function groups A and LCF are inherited by E and K. From the perspective of dominant functional groups, the dominant functional groups were B, D, J, L₀, MP, P, T_C, PF, RF and SCF in two seasons, among which functional groups L₀, T_C, RF and PF were the absolute dominant groups. Redundancy analysis showed that TN, TP and DO were the main environmental factors affecting plankton functional groups, and water temperature and pH were positively correlated with most of the functional groups. Pearson correlation analysis showed the phytoplankton functional groups B, D, J, L₀, Y and zooplankton PF, RF, SCF were significantly correlated with each other (P<0.01), and competition and predation and other biological activities had significant effects on the functional group characteristics. It is concluded that the feeding pressure of fishes to plankton is high and the water quality is still in the state of eutrophication in Changhu Lake. This study provides theoretical basis and reference for the subsequent assessment of the ecological restoration effect, artificial regulation, natural proliferation and sustainable development of large-surface fishery resources.