Evaluation of water quality pollution and analysis of vertical distribution characteristics of typical Rivers in the Pearl River Delta, South China

Abstract

Water quality comprehensive evaluation is an essential technical measure for water environment management and treatment. The previous research methods were often insufficient for studying black-sticking water bodies' formation and transformation mechanisms. In view of this, the single pollution index method and the comprehensive water quality identification index method (Iwq) were used to evaluate the pollution characteristics of rivers; the main pollution factors and sources of the watershed were determined by principal component analysis (PCA), and the vertical stratification characteristics of the water bodies were analyzed. The results showed that the total nitrogen (TN) values of pollutants in typical rivers in the Pearl River Delta were higher than the class V water quality standard, and the ammonia nitrogen (NH3−N) pollution level was the second-highest. TN concentration ranges from 4.27 to 19.83 mg/g, and NH3-N concentration ranges from 2.44 to 15.37 mg/g. In addition, in the monitoring of 15 rivers, 11 of them were the inferior V surface water, including five rivers' comprehensive water quality categories for black-stinking water bodies. This may be related to the process of water self-purification and pollutant transport, and rivers in densely populated areas are often subject to discharge from domestic sewage and industrial sewage. The results of the PCA extracted three principal components (PC), accounting for 88.825% of the total variance, with the first and third PCs controlled by human activities and the second PC influenced by natural sources. There is a more apparent vertical stratification of water bodies here in the typical rivers of the Pearl River Delta, and DO was an important factor affecting the vertical distribution of chemical oxygen demand (COD), NH3-N, TN, total phosphorus (TP), sulfide, Ferrum (Fe), and manganese (Mn). The severe lack of DO in deep water bodies led to elevated levels of NH3-N, Fe, and Mn, and gases such as hydrogen sulfide was released under anaerobic conditions, resulting in eutrophication and black-sticking levels in water bodies.