As a water storage lake for the South-to-North Water Diversion Project, it is crucial to examine changes in aquatic ecosystem structures in Lake Luoma, Jiangsu province. Field sampling was carried out in Lake Luoma monthly from 2014 to 2018 to study the relationship between the phytoplankton community structure and environmental factors. During the studied period, total nitrogen, permanganate index, and electrical conductivity in water column gradually increased, whereas fluoride content declined. The pattern of total phosphorus and dissolved oxygen was not distinct. A total of 71 genera of phytoplankton were identified from 2014 to 2018, and the average monthly biomass variation ranged from 0.16 to 5.51 mg·L-1. Bacillariophyta and Chlorophyta were the dominant phyla in the four years, followed by Pyrrophyta and Cryptophyta. The dominant genera were Synedra sp., Chroomonas spp., Aulacoseira spp., Dinobryon sp., Scenedesmus spp. , Fragilaria spp., Mougeotia sp. , Ankistrodesmus sp. , and Euglena spp. The results showed that the phytoplankton community structure significantly changed in the four years, which was mainly ascribed to the redistribution of biomass. Specifically, in addition to the dominance of Bacillariophyta and Chlorophyta, the dominance of Pyrrophyta and Cyanophyta increased during the last two years. Non-metric multidimensional scaling analysis showed that variation of the phytoplankton community in Lake Luoma was mainly related to total nitrogen, fluoride, water temperature, total phosphorus, dissolved oxygen, pH, conductivity, and permanganate index, among which the total nitrogen, water temperature, and fluoride concentration dominated the phytoplankton community change after the generalized additive model test. Water temperature is the driving factor affecting seasonal changes of the phytoplankton community. Total nitrogen and fluoride concentrations are the driving factors affecting the interannual variation in the phytoplankton community. Our study indicated that in recent years, the implementation of the ban on sand mining and demolition of the enclosed aquaculture in Lake Luoma has affected the water environment, resulting in a significant succession of the phytoplankton community.
Keywords: community structure; generalized additive models; non-metric multidimensional scaling; nutrient; phytoplankton; shallow lake.