This study focused on the correlation between river sinuosity and self-purification capacity, using the Shiwuli River in Hefei, China as a case. Through field monitoring, the reduction rate of each pollutant per unit length of river reach and its correlation with the corresponding sinuosity were analysed. The results show that river sinuosity has different degrees of positive correlation with the growth rate of dissolved oxygen (DO) and the reduction rates of total nitrogen (TN), ammonia nitrogen (NH₃-N) and total phosphorus (TP). River sinuosity needs to be above 1.42 to ensure the river's basic self-purification capability. We also discuss the mechanism of river sinuosity on water body self-purification and propose the increase in river sinuosity to improve the river's capacity to purify water from pollutants. This measure could enhance the growth rate of DO, the longitudinal hyporheic exchange flow, and the action time of other basic self-purification factors of the river. This study could help scientific decision-making in the river reconstruction planning in the process of urbanization in the middle and lower reaches of the Yangtze River in China.

River pollution is a significant problem within the urbanization process in China. Nitrogen is one of the most important pollutants in rivers, and the nitrogen purification capacity of rivers can be affected by their sinuous morphology. In this study, a set of sandy circulating water test models was constructed, consisting of four river channel simulation models with sinuosities of 1.0, 1.4, 1.8, and 2.2. Each model was then infused with the same concentration of nitrogen-polluted water, which circulated for 52 h. The nitrogen reduction processes of rivers with different sinuosities were studied through water quality monitoring. The positive correlation between river sinuosity and nitrogen purification capacity was verified in physical laboratory test models. The effect of sinuosity on the spatiotemporal distribution of total nitrogen in pore water was confirmed. Additionally, the near-shore substrate was more involved in the process of river self-purification than the far-shore substrate. The concave bank of the sinuous rivers was more prone to pollutant accumulation and had a higher purification capacity than the convex bank. After the polluted water entered the sinuous channel systems, pollutant concentration differed within the convex bank between the more polluted upstream section and the less polluted downstream section. This study lays a foundation for studying the mechanism by which river sinuosity influences self-purification capacity.

River pollution is a major issue in China’s urbanization process. Understanding the effects of river morphology and constructed wetlands on the self-purification capacity is crucial for water quality improvement. This study takes the Shiwuli River, a main tributary of Chaohu Lake, as an example. By monitoring the concentration changes of five water quality indicators—total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH₃-N), chemical oxygen demand (COD), and dissolved oxygen (DO)—in the river section for the years 2017 and 2024, we conducted a comparative analysis of the relationship between river morphology and self-purification capacity, as well as influencing factors. The results show that meandering rivers possess self-purification capabilities under natural conditions. There is a positive correlation between river sinuosity and the reduction rates of TP, TN, NH₃-N, and COD, as well as the increase rate of DO—the greater the sinuosity, the stronger the purification capacity. Wetlands enhance both the self-purification capacity and the purification rate of river channels, reducing the required sinuosity for effective self-purification from 1.49 to 1.30. This study also discusses the mechanisms by which meandering rivers influence water self-purification, and proposes that increasing river sinuosity and constructing wetlands can enhance the self-purification capacity. This measure will increase the length and width of the river, prolong the purification time, improve the DO level, and enhance the exchange between the riverbed and groundwater. The findings of this study can provide a reference for river restoration and management in the context of urbanization.

The connectivity of the stream network plays an important role in water-mediated transport and river environments, which are threatened by the rugged development process in China. In this study, based on graph theory, a connectivity evaluation index system was built, which includes the Edge Connectivity, Edge-Node rate, Connectivity Reliability, and Edge Weight. The new evaluation standard and calculation method of each index is presented. The river-lake system of Fenhu industrial park in Jiangsu China is simplified to an Edge-Node graph and evaluated by the index system as a case study. The results indicate that the river-lake system of the research area has low Edge Connectivity, a high Edge-Node rate, and high reliability in the current connectivity level. In addition, the Edge Weight index of several channels does not satisfy the standard of the Basic Edge Weight. To solve the connectivity problems, specific project plans include broadening the unqualified channel and building canals linked with the low-connectivity lakes. The results show that, after the planning, the connectivity of the stream network in Fenhu industrial park will increase, and the connectivity evaluation index system is useful in the study area.

River morphological changes significantly influence water purification functions; however, systematic research on the evolution of natural river morphology and its underlying mechanisms remains insufficient. This study investigates the Shiwuli River, a typical tributary of Chaohu Lake, by quantitatively analyzing its morphological evolution characteristics based on high-resolution satellite imagery from 2014 to 2024. Combined with field monitoring data from all four seasons of 2024, the study explores the influence mechanisms of river sinuosity, cascade flow, and wetlands on water purification. The results indicate significant morphological changes in the Shiwuli River: the total length decreased by 3.95 km, sinuosity decreased by 0.22, and the average width increased by 27.85 m. The comprehensive attenuation coefficient of pollutants in the monitored sections was consistently greater than zero, demonstrating the self-purification capacity of the natural meandering river, with the highest purification capacity observed in summer and the weakest in winter. Dissolved oxygen (DO) content was generally higher in concave banks than in convex banks, and the rate of increase in DO per unit length rose with increasing sinuosity. The cascade flow formed by rolling dams significantly enhanced DO concentration (by 19.23–26.25%), with average pollutant reduction rates ranging from 12.64% to 33.76%. The wetland sections exhibited average reduction rates of 79.07% for total phosphorus (TP), 39.33% for total nitrogen (TN), 47.43% for ammonia nitrogen (NH₃-N), and 45.67% for chemical oxygen demand (COD), demonstrating significantly better purification effects compared to the main river channel. This study reveals that the synergistic interaction among river sinuosity, cascade flow, and wetland systems enhances the water body’s self-purification capacity, providing a scientific basis for river ecological restoration and sustainable utilization of water resources.