Landscape dynamics facilitated non-point source pollution control and regional water security of the Three Gorges Reservoir area, China

Abstract

Land use changes would significantly affect the hydrologic process at the regional scale, bringing both positive and negative ecological impacts. Estimating landscape dynamics and their effects on non-point source pollution are critical for understanding the magnitude and direction of ecological effects caused by various human demands, which is beneficial for relevant authorities to get more useful information on regional water security and provide practical guidance for land use planning. In this paper, the InVEST model was used to estimate the nitrogen loss during 1990–2015 of the Three Gorges Reservoir (TGR) area in China, and the driving mechanism of non-point source pollution was explored by spatial analysis. Meanwhile, we designed three scenarios to dissociate the impacts of afforestation and urbanization on water quality in the reservoir area. The results documented that the nitrogen loss rate of the TGR area decreased from 171.09 kg/km2 in 1990 to 108.81 kg/km2 in 2015. The nitrogen loss reduced significantly after the implementation of the reforestation project in particular. The spatial analysis demonstrated that the variation of nitrogen loss was positively related to annual total precipitation, annual mean temperature, the proportion of developed land, elevation and slope, but was negatively related to the surface height fluctuation and soil pH. The scenario analysis showed that the land use changes in the TGR area effectively control the non-point source pollution, which could provide some references for the watershed management of water sacurity. Forest restoration would reduce the nitrogen loss by 3.76 × 106 kg, while urbanization would aggravate the nitrogen loss with the annual amount of 0.20 × 105 kg for the whole TGR area. These results demonstrated significant differences in the impact of various land use patterns on nonpoint source pollution and regional water security, providing a theoretical basis for policy decisions and regional ecosystem management. To properly handle the relationship between environmental protection and economic development in ecologically fragile areas, we made some land use proposals such as reducing the discharge of industrial wastewater and the abuse of high nitrogen fertilizers. We also designed a landscape planning scheme regarding revegetation in the intermittent streams and water-level-fluctuation zone, thus improving regional water security in the TGR area.