Identification of key environmental factors and intelligent ecological zoning in the upper Yangtze basin

Ecological zoning is indispensable for delineating heterogeneous environmental regimes and informing targeted basin management. To elucidate the drivers of phytoplankton community structure, we analyzed water chemistry and phytoplankton data from 26 sites in the upper Yangtze River using random forest modeling. We identified total nitrogen, total phosphorus, water temperature, and pH as primary determinants, enabling the delineation of three distinct ecological zones. These zones exhibit significant geographical variations in physical profiles and species richness. Niche analysis revealed a positive correlation between species niche breadth and overlap. Importantly, the nitrogen-to-phosphorus ratio emerged as the critical regulator of spatial differentiation and niche characteristics. Regulating these nutrient ratios is vital for maintaining ecosystem stability. This predictive framework clarifies the mechanisms shaping phytoplankton distribution and provides a quantitative basis for region-specific conservation and nutrient-management strategies in large river systems.