Unraveling nitrogen evolution characteristics and driving mechanisms of estuarine alluvial islands

Nitrogen pollution has long been a major threat to river and estuarine ecosystems around the world. However, at present, most of the research focuses on rivers and attached freshwater lakes, and the research on the nitrogen evolution characteristics and driving mechanisms of estuarine alluvial islands at river estuaries remains poorly understood. In this study, four cross-sections in Chongming District from 2021 to 2023, including Qixiaogang West Bridge, Qianweicun Bridge, Wuxiao, and Sanshahong Intersection were Sampled. Using Pearson correlation analysis, regression analysis and other methods to explore the correlation and trend of water quality indicators, and then reveal the spatiotemporal changes of nitrogen and its influencing factors. Our results showed that the statistical analysis revealed no significant fluctuations in ammonia nitrogen (NH₄⁺) and total nitrogen (TN) during the study period; specifically (NH₄⁺ reached 0.65 mg/L in June, while TN reached 4.36 mg/L in December). Correlation analysis revealed a negative correlation between TN, NH₄⁺, and pH, a positive correlation with dissolved oxygen (DO), and notable correlations between NH₄⁺ and turbidity and electric conductivity (EC). In addition, natural factors (rainfall) and human activities were important factors affecting nitrogen, with agricultural cultivation leading to a reduction of 78.92 km² in the study area. These results will help reveal the characteristics and driving mechanisms of nitrogen concentration in estuarine alluvial islands, propose targeted measures for future water pollution control, and provide valuable references for similar studies.