Dynamic impacts of changes in river structure and connectivity on water quality under urbanization in the Yangtze River Delta plain

The deterioration of river water quality in urbanized areas is getting more serious, and affects the regional ecology and development of social economy; however, its mechanisms of dynamic variation is still an open question. In this study, we detected the dynamics of water quality and its driven mechanisms in the Yangtze River Delta plain, one of the most developed areas in China. The results showed that the spatial agglomerations of dissolved oxygen (DO), ammonia nitrogen (NH3-N), and total phosphorus (TP) presented seasonal differences, which exhibited a trend of shifting from west to east and then to west from spring to winter. Further, the relative contribution rates of the river network characteristics affecting water quality were quantified on the basis of backpropagation artificial neural networks. We found that the average contribution rates of river structure (more than 60%) were higher than that of river connectivity, and the dominant factors influencing water quality were water surface ratio (W-P) and multifractal indices (Delta a, Delta f). Specifically, the average relative contribution rates of W-P, Delta a and Delta f were 18.72%, 15.03%, and 14.52% during the flood season, respectively, and 15.83%, 16.58%, and 14.54% during the non-flood season. The functional connectivity influenced by obstruction of sluices also influences water quality, which accounting for 11.15% and 12.85% in the flood and non-flood seasons, respectively.

Automated summary

The study found seasonal variations in water quality in the Yangtze River Delta plain, where river structure has a greater impact on water quality than river connectivity. Factors such as water surface ratio and multifractal indices play a significant role in influencing water quality.