Changes in the soil erosion status in the middle and lower reaches of the Yangtze River basin from 2001 to 2014 and the impacts of erosion on the water quality of lakes and reservoirs

The revised universal soil loss equation (RUSLE) was used to obtain the soil erosion intensity distribution in the middle and lower reaches of the Yangtze River basin (MLYB), where the input data included a digital elevation model (DEM) and Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing products. Changes in the soil erosion intensity throughout the MLYB were analysed from 2001 to 2014, and the potential influences of these changes on the local water quality of lakes and reservoirs were revealed. This investigation is the first to reveal the spatial and temporal changes in soil erosion throughout the MLYB. The results indicated that from 2001 to 2014, most of the MLYB was characterized by slight and light soil erosion levels, whereas relatively few areas exhibited intensive to severe soil erosion. Soil erosion in the MLYB displayed a decreasing trend from 2001 to 2014; over 80% of the region displayed a decreasing soil erosion intensity change rate, indicating that soil conservation in most of the MLYB has improved over the past 14 years. However, 12.8% of the area presented an increasing change rate, and the region with the maximum increasing change rate was located mainly in the lower Yangtze basin. Furthermore, spatial heterogeneities were found in the soil erosion intensities throughout the MLYB: soil erosion improved in the upper and middle regions of the MLYB, whereas soil erosion worsened in the lower regions of the MLYB. Among the sub-basins of the MLYB, obvious soil erosion occurred most frequently in the Hanjiang basin and least frequently in the Taihu basin. A driving force analysis showed that the influence of precipitation on soil erosion is more evident than that of human activities in all sub-basins except the Dongting basin. A correlation analysis between soil erosion and water turbidity/water transparency showed that 45.9% of the decreasing water turbidity is correlated with decreasing soil erosion and that 42.5% of the increasing water turbidity might be influenced by increasing soil erosion. Decreased soil erosion might be responsible for the improved water transparency for 50% of the lakes, whereas increased soil erosion is correlated with a decrease in water transparency for over 50% of the lakes.