Massive nutrient inputs from different land uses have caused eutrophication in the Yangtze River. River sediment, as a sink for terrestrial nutrients, can sustain eutrophication for a long time. To further improve water quality, sediment organic carbon (TOC), nitrogen (TN), phosphorus (TP), and the impact of land use composition were investigated in the Tuojiang River watershed, once the most polluted tributary of the Upper Yangtze River. Results showed that the average TOC, TN, and TP contents were, respectively, 11.4 g/kg, 1078 mg/kg, and 1170 mg/kg higher than the local soil background value or the ecologically safe level limit. Due to the spatial layout of agriculture and industry, sediment nutrients were higher in the tributaries and the upper reaches of the main stream of the Tuojiang River. Regression analysis identified that TN was primarily affected by the composition of the dry-farm field within the 500 m zone along the river system, and TOC was affected by 1000 m of dry-farm field and 100 m of paddy field, while TP was related to the distribution of the phosphate chemical industry. It also enhances the urgency of reducing nutrient loss from agricultural non-point sources and mitigating residual nutrients in river sediment.
Bao et al. (Sat,) studied this question.