Research on spatio-temporal distribution characteristics of urban river water quality based on principal component analysis: a case study of Cangzhou City

Comprehensive and objective evaluation of the pollution status of urban river water quality is of great significance to the precise prevention and control of urban river water pollution. Based on the data of 7 water quality indicators of pH, dissolved oxygen (DO), permanganate index (COD_Mn), chemical oxygen demand (COD_Cr), total phosphorus (TP), ammonia nitrogen (NH₃-N) and fluoride (F⁻) of 13 important rivers in Cangzhou City in 2022, the principal component analysis (PCA) method was employed to extract the leading indicators causing changes in river water quality and to diagnose the pollution status of the rivers. Subsequently, the weights of water quality indicators were used to calculate the comprehensive scores for each river monitoring section and different seasons and analyze the spatial and temporal distribution characteristics of river water quality. The results showed that : (1) The overall water quality of the 13 rivers in Cangzhou City was relatively good in 2022, with most water bodies meeting the Class Ⅲ water standards of Environmental Quality Standards for Surface Water (GB 3838-2002), while a few rivers reached the Class Ⅳ water standards in terms of COD_Mn and COD_Cr indicators. (2) The application of the PCA method allowed the transformation of the 7 water quality indicators into 2 principal components, with a cumulative variance contribution rate of 78.492%. Among them, the water quality indicators, COD_Mn, COD_Cr, TP, and F⁻, were significantly correlated with the first principal component and dominated the water quality changes in the study area. Moreover, these four indicators showed a significant positive correlation between each other. (3) The spatial analysis revealed that Canglang Channel was the most polluted among the 13 monitored rivers, and the river pollution in the northeast of Cangzhou City was worse than that in the northwestern and southern areas. (4) The seasonal analysis indicated that the seasonal variation for water pollution in urban rivers was in the following order: summer>spring>winter>autumn. The analysis results could provide reference for the control strategy of urban river water pollution in Cangzhou City.