Spatiotemporal Change and Source Apportionment of Non-point Source Nitrogen and Phosphorus Pollution Loads in the Three Gorges Reservoir Area

Abstract

The Three Gorges Reservoir area (TGRA) is a critical water source protection area in China and one of the regions with rapid economic development in the Yangtze River basin. Non-point source pollution is the leading cause of the deterioration of the water environment in the TGRA; therefore, studying the non-point source pollution status in the TGRA is of great significance to the regional ecological security and sustainable development. The improved export coefficient model was used to estimate the total non-point source nitrogen and phosphorus pollution loads in the TGRA from 1990 to 2015, the spatial and temporal characteristics of the non-point source nitrogen and phosphorus pollution were analyzed, and the primary sources of pollution were determined by calculating the contribution rate of each pollution source. The results concluded that the nitrogen and phosphorus pollution loads were highest in the hinterland of the reservoir, followed by the end of the reservoir, with the lowest in the head of the reservoir, showing significant spatial heterogeneity in the TGRA. The total loads of nitrogen and phosphorus pollution increased firstly and then decreased, which reached the highest value in 2000 and the lowest value in 2015. The contribution rate of each pollution source to the nitrogen and phosphorus pollution loads, from highest to lowest, were land use, rural life, livestock, and poultry farming. Among them, the land use type of dry land was the predominant source of non-point source nitrogen and phosphorus pollution.