Spatial and temporal changes of water environmental factors and water quality assessment in coastal waters of Jiangsu Province

This study aims to explore the temporal and spatial changes in water environmental factors and seawater quality in the near-shore waters of Jiangsu Province. From 2017 to 2023, the single-factor evaluation method and the comprehensive pollution index evaluation method were employed to assess water environmental factors and water quality, and the correlations between water ecological factors were analyzed. The results indicated that the overall levels of dissolved oxygen (DO), chemical oxygen demand (COD), and petroleum were satisfactory. The pollution levels of the main pollutants, inorganic nitrogen (IN) and reactive phosphate (RP), showed a downward trend, and the overall water quality improved after 2019. There was a significant positive correlation between IN and RP, suggesting they might share the same source. In terms of spatial distribution, each factor exhibited certain regularities: DO was higher in the north than in the south; the pH value was higher in the north and south than in the central area; the concentrations of IN and petroleum were higher near the shore; COD was higher in the northern and near-shore regions; and RP was more concentrated in the central and near-shore areas. Moreover, research revealed that seawater quality was influenced by various factors, including natural and human-induced ones. As a unique phenomenon in the Yellow Sea waters, green tides had a disruptive effect on the content changes of water quality factors during their formation and disappearance in different years, particularly on DO. Special events such as coastal industries, the COVID-19 pandemic, and marine projects affected the discharge and input of pollutants. Policies implemented in different periods were crucial for optimizing water quality. • Spatial and temporal changes of water environmental factors and water quality. • Single factor evaluation method; Comprehensive pollution Index evaluation method; Spearman's rank correlation coefficient. • The marine environment has improved from 2017 to 2023. • Factors affecting water quality: green tide distribution, land-based inputs, Policy correlation and so on. • Provide decision-making support for the protection of the marine ecological environment.