Assessing the soil erosion control service of ecosystems change in the Loess Plateau of China

Soil erosion in terrestrial ecosystems, as an important global environmental problem, significantly impacts on environmental quality and social economy. By protecting soil from wind and water erosion, terrestrial ecosystems supply human beings with soil erosion control service, one of the fundamental ecosystem services that ensure human welfare. The Loess Plateau was one of the regions in the world that suffered from severe soil erosion. In the past decades, restoration projects were implemented to improve soil erosion control in the region. The Grain-to-Green project, converting slope croplands into forest or grasslands, launched in 1999 was the most massive one. It is needed to assess the change of soil erosion control service brought about by the project. This study evaluated the land cover changes from 2000 to 2008 by satellite image interpretation. Universal Soil Loss Equation (USLE) was employed for the soil erosion control assessment for the same period with localized parameters. Soil retention calculated as potential soil erosion (erosion without vegetation cover) minus actual soil erosion was applied as indicator for soil erosion control service. The results indicate that ecosystem soil erosion control service has been improved from 2000 to 2008 as a result of vegetation restoration. Average soil retention rate (the ratio of soil retention to potential soil loss in percentage) was up to 63.3% during 2000-2008. Soil loss rate in 34% of the entire plateau decreased, 48% unchanged and 18% slightly increased. Areas suffering from intense erosion shrank and light erosion areas expanded. Zones with slope gradient of 8 degrees-35 degrees were the main contribution area of soil loss. On average, these zones produced 82% of the total soil loss with 45.5% of the total area in the Loess Plateau. Correspondingly, soil erosion control capacity was significantly improved in these zones. Soil loss rate decreased from 5000 t km(-2) yr(-1) to 3600 t km(-2) yr(-1), 6900 t km(-2) yr(-1) to 4700 t km(-2) yr(-1), and 8500 t km(-2) yr(-1) to 5500 t km(-2) yr(-1) in the zones with slope gradient of 8 degrees-15 degrees, 15 degrees-25 degrees, and 25 degrees-35 degrees respectively. However, the mean soil erosion rate in areas with slope gradient over 8 degrees was still larger than 3600 t km(-2) yr(-1), which is far beyond the tolerable erosion rate of 1000 t km(-2) yr(-1). Thus, soil erosion is still one of the top environmental problems that need more ecological restoration efforts. (C) 2011 Elsevier B.V. All rights reserved.