ANALYSIS ON THE ECOSYSTEM STRUCTURE AND FUNCTION OF LAKE QIANDAO BASED ON ECOPATH MODEL

To explore the current status and historical change of the Lake Qiandao ecosystem, the Ecopath model of the Lake Qiandao ecosystem was constructed based on the survey data of fishery resources and water environment in Lake Qiandao in 2016. And the trophic level structure, energy flow and ecosystem characteristics were analyzed based on this model. The Ecopath pedigree index (P index) was 0.54, with high data reliability. Ecopath model was consisted of 18 functional groups, and the fractional trophic levels ranged from 1 to 3.14. Energy flow of Lake Qiandao ecosystem was dominated by grazing food chain, which accounted for 56% of the energy source. Parameters reflected the complexity of the ecosystem, For example, the system connectance index (CI), the omnivory index (SOI), the Finn cycling index and the Finn mean path length were 0.26, 0.13, 5.15% and 2.46, respectively. Compared with other reservoirs, it showed that the functional groups of Lake Qiandao ecosystem had a higher polymerization, a closer connection, a higher rate of material recycling and the ecosystem was more mature. However, the total system throughput of Lake Qiandao in 2016 was low with 24698.27 t/(km²·a), and the total primary production was 6.51 folds of the total respiration, which indicate that the scale of Lake Qiandao ecosystem was small and still in a developmental stage. According to the historical analyses of the Lake Qiandao ecosystem, the scale of this ecosystem has become larger, and the stability and complexity have been enhanced, but the nutrient interaction relationship was weakened, and the ability of the ecosystem to resist external interference was still weak. At the same time, the conversion efficiency of primary producers of Lake Qiandao ecosystem was low, and the food web was simple. So appropriate management measures should be taken to ensure healthy development of Lake Qiandao ecosystem.