Correlation analysis between pH value of Yingna River with environmental factors and phytoplankton in China based on multivariable statistics analysis

Abstract

The Yingna River flows through Dalian and Dandong, China, before emptying into the Yellow Sea, where the pH value in some areas exceeds the standard limits. To investigate the key factors and mechanisms driving pH variation, the Yingna River, Xiaosi River, and Zhuang River were selected as the study subjects. Results indicate that phytoplankton in all three rivers primarily belong to Chlorophyta and Bacillariophyta, with Chlorella, Cyclotella, and Navicula as dominant species. The Yingna River also has unique dominant species such as Scenedesmus quadricauda, Scenedesmus spinosus and Chroococcus. Its main functional groups are B, J, L0, X1, X2. Environmental factor analysis shows that the pH value of the Yingna River was significantly higher than that of the other two rivers (P < 0.05). Carbonates(CO₃^2‐)was present in the water, while total alkalinity (TA), bicarbonate(HCO₃^‐, and active phosphorus (PO₄-P) concentrations were significantly lower than those in the Xiaosi River (P < 0.05). A generalized additive model (GAM) was constructed for pH with HCO₃^‐, Chemical Oxygen Demand (COD), CO₃^2‐, and Ammonia nitrogen (NH₄-N), achieving an Akaike information criterion (AIC) of ‐22.98, with an explanatory power of 99.79%. The Mantel test demonstrated that pH value, HCO₃^‐, NH₄-N, and N:P ratio were the primary factors influencing the phytoplankton diversity indices. Redundancy analysis (RDA) indicated that pH value, HCO₃^‐, NH₄-N, and N:P ratio were the main factors affecting the dominant species of phytoplankton. This study aims to analyze the relationship between pH and other environmental factors, as well as phytoplankton, providing a reference for the ecological protection and restoration of the Yingna River.