Unveiling the spatiotemporal dynamics of planktonic communities in Juam Lake: insights from eDNA metabarcoding

Freshwater ecosystems are highly dynamic environments where plankton communities are essential indicators of ecological health and function. This study investigated the seasonal and spatial dynamics of phytoplankton and zooplankton communities in Juam Lake, a significant reservoir in South Korea, across multiple sampling periods (spring and autumn 2021–2022). Physicochemical parameters, including water temperature, dissolved oxygen, and nutrient concentrations, exhibited distinct seasonal patterns, ranging from 13–15 °C in spring to 26–27 °C in autumn. Amplicon sequence variant (ASV) analysis revealed clear seasonal succession in dominant plankton groups. Phytoplankton communities shifted from Chlorophyta dominance in spring 2021 to Cryptophyceae prominence in spring 2022, while Bacillariophyceae and Chrysophyceae increased in autumn 2022. Zooplankton communities displayed alternating dominance patterns, with rotifers prevalent in spring seasons and Copepoda dominating autumn samples. Multivariate analysis demonstrated that water temperature (p < 0.0001) and dissolved oxygen (p = 0.001) strongly influenced community structure, while water depth was not a significant factor (p = 0.73). Alpha diversity indices revealed higher diversity metrics in middle and outflow sites, with benthic zones consistently exhibiting the highest Shannon diversity for both plankton groups. Correlation analysis identified key indicator taxa with distinct environmental preferences, such as Stephanodiscus showing strong negative relationships with water temperature (−0.66) and total organic carbon (−0.70), while Trichocerca displayed positive correlations with water temperature (0.55). The sampling investigation of the plankton community in Juam Lake using eDNA provides valuable insights into the complex spatiotemporal dynamics, and highlights that seasonality is more important than spatial factors (flow point and water depth) in structuring these aquatic communities in a controlled Juam Lake. In particular, the absence of spatial differences following water depth in shallow lakes may be reflected in establishing more efficient lake sampling plans in the future.