[Temporal and Spatial Variation Patterns of Picophytoplankton and Their Correlations with Environmental Factors During the Wet Season in East Lake Dongting].

Picophytoplankton (<3 μm), comprising picocyanobacteria (PCY) and photosynthetic picoeukaryotes (PPEs), are considerably important in the material circulation and energy flow of aquatic ecosystems. To explore the temporal and spatial variation patterns of picophytoplankton and their correlations with environmental factors in lotic Yangtze-connected lakes, field investigations were performed on a monthly basis during the wet season (May to August) in 2019 in East Lake Dongting, a Yangtze-connected lake. The results indicated that both the Chla biomass and abundances of picophytoplankton exhibited significant spatial and temporal variability (<0.05). The picophytoplankton Chla biomass showed an average concentration of 8.52 μg·L and accounted for 41.6% to total phytoplankton on an average. From May to August, Chla biomass of picophytoplankton kept increasing with increasing temperature, especially in the north and south of the lake, and it was the lowest in the east of the lake. PCY dominated picophytoplankton abundance in East Lake Dongting and was 3.4 times the abundance of PPEs on an average. Similar spatial and temporal variation patterns were observed between PCY and PPEs. The abundances of PCY and PPEs both increased first and then decreased during the wet season. Spatially, picophytoplankton showed a trend to migrate from the northern lake to the southern lake from May to July, and the abundance significantly declined in August and peaked mainly in the north of the lake. The analysis results showed that picophytoplankton in East Lake Dongting exhibited significant spatial and temporal variability during the wet season; the water level and N：P ratio were determined to be the most important factors explaining the variation of the abundance proportion of PCY and PPEs.