Oral Presentation World Lake Conference 2025

Seasonal Reversal in Phytoplankton Assembly Mechanisms: Stochastic Dominance in Autumn vs. Deterministic Control in Spring within the middle and lower reaches of the Yellow River (#109)

Dahai Zeng 1 2 3 , HouKuan Ding 1 2 3 , Yuanyuan Tang 1 2 3 , Yunni Gao 1 2 3 , Jialin Jin 1 2 3 , Xiaofei Gao 1 2 3 , Jingxiao Zhang 1 2 3 , Huatao Yuan 1 2 3 , Jing Dong 1 2 3 , Xuejun Li 1 2 3
  1. College of Fisheries, Henan Normal University, Xinxiang, Henan, China
  2. Research Station on Water Ecosystem in Danjiangkou Reservoir of Henan Province, Nanyang, Henan, China
  3. The National Ecological Quality Comprehensive Monitoring Station (Hebi Station), Hebi, Henan, China

This study investigated seasonal variations in phytoplankton community structure and assembly mechanisms in a riverine environment with high silt loads. Phytoplankton and physicochemical water quality factors were analyzed in the middle and lower reaches of the Yellow River during two seasons: November 2023 (autumn) and April 2024 (spring). A total of 110 algal species from seven phyla were identified, with green algae being predominant in richness and cyanobacteria in abundance. Both richness and abundance was lower in autumn than in spring. The α-diversity analysis revealed that the Pielou evenness index was significantly higher in spring compared to autumn. Non-metric multidimensional scaling (NMDS) based on Bray-Curtis distances  showed significant seasonal differences in phytoplankton community composition. Furthermore, β-diversity decomposition analysis revealed that turnover was dominant component in both seasons, but the proportion of nestedness was significantly higher in spring compared to autumn. Based on the analyses of the Dispersal-Niche Continuum Index (DNCI) and the Modified Stochasticity Ratio (MST), this study reveals significant seasonal differences in the assembly mechanisms of phytoplankton communities in high-sediment regions: stochastic processes dominated by dispersal prevail in autumn, whereas deterministic processes governed by niche selection dominate in spring. The community structure of phytoplankton in this region is shaped by the combined effects of geographical factors, altitude, and environmental variables, with particularly pronounced seasonal variations in environmental drivers—total nitrogen (TN) emerges as the primary factor influencing autumn community assembly, while spring community structure is mainly regulated by silica (SiO₂) and pH. This study deepens the understanding of phytoplankton assembly mechanisms in sedimnet-rich rivers and provides fundamental data for phytoplankton construction mechanisms and aquatic biodiversity conservation in the middle and lower reaches of the Yellow River.