Spatial distributions of nitrogen and phosphorus losses in a basin and responses to best management practices — Jialing River Basin case study

Abstract

Tracing the main sources and spatial distributions of pollutants and quantifying the effects of various factors on soil erosion and pollution loads are important to allow appropriate management systems to be developed for large complex watersheds and allow water pollution to be controlled efficiently and economically. A distributed water, sediment, and pollutant model was used to qualitatively and quantitatively assess temporal and spatial variations in water and sediment characteristics and nitrogen (N) and phosphorus (P) loss distributions in a basin from a macroscopic point of view and to trace the sources of pollutants, using the Jialing River Basin as an example. Changes in N and P losses in the basin caused by various management practices were assessed. The results indicated that the average annual water and sediment yield in the study area were 103–857 mm and 2.4–1274.1 t/ha, respectively. The loss of total N and P were 1.1–21.6 kg/ha and 0.01–11.2 kg/ha. The spatial distribution varied greatly, but the annual variation trend was relatively stable. The contribution of N from industrial point sources reached 1973 tons, which was dominant. And the total N distribution in the watershed was closely related to woodland. Total P pollution was most severe for cultivated land. The P load caused by fertilization reached 805 tons, which was significantly more than the point source discharge. Assessments of the effects of implementing various management practices in the watershed indicated that N losses would be decreased more effectively by filter belt in woodland than by other practices. The total N loss would be reduced by 4.4% for every 0.5 m filter belt added to woodland. The losses would be decreased more effectively by a cultivated land filter belt and controlling fertilizer application than by other practices. The 0.5 m filter belt of cultivated land can reduce total P by 5%, and reducing fertilization by 5% can reduce total P by 7.3%. Understanding the temporal and spatial distributions of pollutant sources in a river basin and tracing pollutant sources will allow appropriate management practices to be implemented in key areas to effectively control pollutants.