Soil erosion dynamic changes and its impact factors in Zhifanggou watershed of the Loess Plateau, China

In order to explore the soil erosion rules in loess hilly-gully area of the Loess Plateau, Zhifanggou Watershed was selected to evaluate the soil erosion dynamic changes and its impact factors from 1938 to 2010. Based on GIS technique, the revised universal soil loss equation (RUSLE) was used to evaluate spatial and temporal change of soil erosion and the effect of terrain and land use on soil erosion in the past 70 years. The results showed that 1) soil erosion modulus increased significantly from 7584.39 t.km(-2).a(-1) in 1938 to 46,392.56 t.km(-2).a(-1) in 1958, and it decreased to 5150.80 t.km(-2).a(-1) in 2010; 2) the area of moderate erosion and below accounted for 52.99% of the whole area in 1938; during the period from 1958 to 1978, severe erosion become the dominant pattern which was up to 67.05% of area in whole watershed, and the most severe erosion accounting for 78.61% happened in 1958; soil erosion declined slightly during the period from 1979 to 1998, and this decreasing trend continued until 1999 in which severe erosion area only occupied 8.96%. 3) Soil erosion intensity and quantity increased significantly with the slope increasing, area of the slope steeper than 15 took up 81.95%, but disproportionally contributed 96.76% of the total soil erosion amount, while slope steeper than 25 degrees contributed nearly 80%. Soil erosion intensity at sunny and half sunny slope was higher than that at shady and half shady slope, sunny and half sunny slope covered 48.25% of the total area, but contributed 52.42% of the soil erosion amount. 4) Soil erosion intensity of forestland was slightest while strongest in unutilized land. Farmland was the major source of soil erosion during 1958-1998, and grassland was the major source of soil erosion in the following period. With persistent ecological management and protection over past 30 years, the eco-environment in Zhifanggou watershed was improved remarkable, but soil erosion needs to be paid more attention in the future conservation, especially in the steep slope and gullies areas.