Human activities and climate change threaten water quality in China’s rivers. We simulated the monthly concentrations of riverine total nitrogen (TN), ammonia-nitrogen (NH₃-N), total phosphorus (TP), and chemical oxygen demand (COD_Mn) in 613 sub-watersheds of the nation’s 10 major river basins during the 1980–2050 period based on a 16-year (2003–2018) monitoring dataset using the stacking machine-learning models. The results showed that water quality improved markedly, except for the TN concentration, which was probably due to the lack of a TN control target and assessment system. Quantitative analysis indicated that anthropogenic factors were the primary controls compared with climatic drivers and geographical drivers for TN, TP, and NH₃-N concentrations. On the basis of all 17 sustainable development goals (SDGs) relevant to water quality in China, the water resources, water environment, aquatic ecology and water security should be considered collectively to achieve improvements in the ecological status of China’s rivers.

In this study, the sediment profiles of total organic carbon, total nitrogen, C/N ratios, total phosphorus, N/P ratios, C/P ratios, particle sizes, and stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) were used to investigate natural and anthropogenic impacts on Lake Chaohu over the past 100 years. Before 1960, Lake Chaohu experienced low productivity and a relatively steady and low nutrient input. The increasing concentration and fluxes of total organic carbon, total nitrogen, total phosphorus, together with changes in the δ¹³C and δ¹⁵N of organic material in the sediment cores, suggested that the anthropogenic effects on trophic status first started because of an increase in nutrient input caused by a population increase in the drainage area. With the construction of the Chaohu Dam, an increase in the utilization of fertilizer and the population growth which occurred since 1960, stable depositional conditions and increasing nutrient input resulted in a dominantly algae-derived organic matter source and high productivity. Nutrient input increased most significantly around 1980 following the rapidly growing population, with concomitant urbanization, industrial and agricultural development. This study also revealed that the concentration and distribution of nutrients varied between different areas of sediment within Lake Chaohu because of the influence of different drainage basins and pollution sources.