Multimedia Nitrogen and Phosphorus Migration and Source Control Using Multivariate Analysis and XGBoost: The Case Study in a Typical Agricultural Basin, Danjiangkou Reservoir

Abstract

Preventing eutrophication requires a deep understanding of nutrient sources and migration processes. The Guanshan River in the Danjiangkou Reservoir was selected as a typical agricultural basin. River water, sediment, and soil samples were collected to determine nitrogen (N) and phosphorus (P) contents and forms. Multivariate statistical analysis, buffer analysis, and extreme gradient boosting regression (XGBoost) were used to investigate the nutrient sources, the sources’ scale effects, and migration. The results showed that the exogenous sources of river nutrients were fertilizer (provided phosphate (PO4-P) and ammonium (NH4-N)), domestic wastewater (provided nitrate (NO3-N) and organic nitrogen), and natural soil and rock leaching (provided PO4-P and organic phosphorus). Fertilization within 300–1200 m and domestic wastewater discharge within 150 m of the river affected the contents of the river nutrients significantly (with R ranging between 0.40 and 0.73, p ≤ 0.01). The sediment was the N source and P sink of the overlying water. With NH4-N/PO4-P compound fertilization, the NO3-N and calcium-bound phosphorus (Ca-P) exhibited co-enrichment. Appropriately increasing NH4-N application could stimulate P biological uptake, thus inhibiting P emigration from agricultural soil under N-limited states. In conclusion, this study effectively recognized river nutrient sources and their scale impacts and also explored more effective fertilization strategies, which are beneficial for the optimized management of agricultural activities.