Spatiotemporal Patterns and Environmental Associations of Zooplankton Community Structure and Functional Groups in Guanyinge Reservoir, Northeast China

In northern deep-water drinking-water reservoirs, determining whether the taxonomic and functional structures of zooplankton respond consistently to environmental gradients is important for understanding seasonal community variation and evaluating the complementary ecological information provided by taxonomic and functional-group metrics. Seasonal surveys were conducted in Guanyinge Reservoir across four seasons, different horizontal regions, and water layers. Using community-structure analysis, functional-group classification, Mantel test, Pearson permutation correlation analysis, and redundancy analysis (RDA), we examined the spatiotemporal patterns of zooplankton communities and functional groups and their associations with environmental variables. Both aquatic environmental variables and zooplankton community characteristics exhibited stronger seasonal than spatial differentiation, and the reservoir remained within the mesotrophic range during the four seasonal surveys. A total of 98 zooplankton species were identified, belonging to 68 genera across five taxonomic groups. Species richness peaked in autumn and was the lowest in spring, whereas zooplankton abundance and biomass reached their maximum values in summer and minimum values in winter. This asynchronous variation indicated that seasonal changes in species richness did not parallel those in zooplankton abundance and biomass. Abundance- and biomass-based patterns also differed at both the dominant-species and functional-group levels. Specifically, relative abundance was dominated by PF, RF, and PC, whereas LCF, SCF, RC, and RF accounted for most of the relative biomass, indicating that numerical dominance did not correspond to biomass contribution. Further environmental response analysis revealed that water temperature (WT) and total nitrogen (TN) were strongly correlated with the overall characteristics of zooplankton communities. Nitrate nitrogen (NO3−-N) showed significant independent explanatory effects across the abundance- and biomass-based dominant-species and major functional-group RDA analyses and was the most consistent nitrogen-related explanatory variable across these analytical levels. In contrast, water temperature (WT), nitrite nitrogen (NO2−-N), transparency (SD), and total phosphorus (TP) showed level-specific associations with different components of zooplankton structure. Overall, the spatiotemporal variation in zooplankton communities in Guanyinge Reservoir was primarily associated with seasonal environmental variation. Moreover, taxonomic and functional-group structures, as well as abundance- and biomass-based patterns, showed non-congruent associations with environmental gradients. Combining taxonomic metrics with abundance- and biomass-based functional-group metrics can more comprehensively characterize seasonal community variation and environmental associations in northern deep-water reservoirs. This study provides complementary ecological information for ecological monitoring, protection, and ecological status assessment of drinking-water source reservoirs.