WATEM/SEDEM框架下的土壤保持效益传输研究

Assessing the delivery of soil erosion control benefits at the watershed level following the WATEM/SEDEM concept

土壤侵蚀是陆地生态系统中广泛存在的地表过程,具有当地和异地两方面的生态环境和社会经济影响。土壤保持为人类社会提供防止土壤肥力下降和减少库塘淤积等效益。当前对异地土壤保持效益的计算大多基于当地土壤保持量、采用单一的泥沙输移比,忽视了泥沙输移比的尺度效应及其与流域特征和降雨等因素的时空变异相关的事实,缺乏对土壤保持效益空间传输的定量和显式表达。本文基于WATEM/SEDEM模型框架,通过流域侵蚀产沙和泥沙传输模拟,建立了评估当地和异地土壤保持效益的方法,量化了碾庄沟流域不同土地利用类型区土壤保持效益的输入和输出及其空间格局。该方法能识别土壤保持效益净供给区和净受益区,可建立起供给区和受益区之间定量化、空间直观的土壤保持效益传输联系,可为实施空间位置明确的生态补偿决策服务。

Soil erosion and sediment delivery occurs widely in terrestrial environments. It has onsite and off-site environmental and social-economic effects. Soil erosion control provides various benefits for human beings, such as prevention of soil productivity loss, and reducing impoundment of reservoirs. For a land plot, the off-site benefits of soil erosion control is equal to the reduction of sediment export. Previously, assessments of off-site benefits of soil erosion control mostly rely on estimation of on-site soil retention, which is equal to the difference between estimated actual soil erosion and soil erosion without any prevention measures, and an invariant sediment delivery ratio （SDR）. The scale effect of SDR and its correlation with the spatial and temporal variation of watershed characteristics and driven factors, such as spatial variation of rainfall regime, are often ignored. Consequently, quantitative and spatially explicit evaluations of soil erosion control benefits （SECB） and delivery across space are missing. For these reasons, an approach following the framework of WATEM/SEDEM model combining soil erosion and sediment delivery was developed to assess SECB provision and delivery over watershed. This approach integrates the on- site soil erosion prevention and reduction of sediment delivery. A case study was conducted in the Nianzhuang Watershed on the Loess Plateau. The SECB balance and spatial pattern in this loess watershed in the Hilly and Gully Area of the Loess Plateau was assessed. Based on the grid-cell- based modelling, the SECB import and export for each land use type were quantified and mapped. This approach identifies SECB supply areas and external beneficiary areas. In addition, it has potential to link SECB supply areas with beneficiary areas of SECB in a quantitative and spatially explicit way. Thanks to its spatial explicit feature, this approach is capable of serving the location- specific payments for ecosystem services provision.