Temporal and Spatial Dynamics of the Diversity of Small Nanoeukaryotic Plankton in Shallow Lakes in Relation to Different Ecosystem Conditions

Small nanoeukaryotic plankton serve as pivotal ecological indicators in aquatic systems, yet their spatiotemporal patterns in shallow urban lakes under varying ecosystem states remain insufficiently characterized. This study employed single-molecule sequencing to examine these communities in Qingshan Lake and two adjacent enclosures, located in Anhui Province, China, during spring (April) and summer (June) hydrological seasons in 2021. Seasonal comparisons revealed elevated species richness and community evenness during summer relative to spring, with enclosure habitats consistently exhibiting higher values than open-water zones of the main lake. Macrophyte-dominated areas demonstrated peak diversity indices in spring, contrasting with algal-dominated regions showing reduced diversity. The planktonic community exhibited marked seasonal restructuring, transitioning from Cryptomonas curvata dominance in spring to Cyclotella meneghiniana prevalence in summer. These taxa differentially governed spatial patterns, with C. curvata driving spring distributions and C. meneghiniana shaping summer configurations. Structural divergences emerged between macrophyte-dominated and macrophyte-algae transition zones, as well as among distinct algal-dominated areas. Biomarker analysis identified protozoan taxa as hallmarks of macrophyte zones, while algal groups typified phytoplankton-dominated regions. Water temperature, dissolved oxygen and total phosphorus were established as predominant environmental correlates influencing community organization.