基于GIS和RS的退耕还林工程土壤保育价值评估——以陕西吴起县四面窑沟流域为例

在全国退耕还林工程典型地区陕西省吴起县境内，选取四面窑沟流域为研究对象，采用RS和GIS监测退耕还林工程的具体实施方式及其面积，并提出考虑土地覆盖汇流影响的改进坡长因子，利用ArcGIS和RUSLE评估流域在退耕前后的土壤侵蚀强度变化，在此基础上，采用机会成本法和替代价格法评估流域退耕还林工程的土壤保育价值。结果表明：1997-2004年，流域内实际开展退耕还林工程1895．8hm^2,其中，荒山造林369．99hm^2、退耕还林357．48hm^2、退耕还草901．72hm^2、人工封育266．61hm^2；退耕前（1997年）后（2004年）流域土壤侵蚀模数减少了4644．04t／（km^2·a），侵蚀强度由极强度降低为中度；退耕还林工程每年产生土壤保育价值1324．3万元，其中，减少土壤侵蚀效益8．11万元、减少肥力流失效益1180．22万元、减少泥沙淤积效益124．45万元、培育土壤效益11．52万元。

Assessment on soil conservation value of the returning farmland to forestland and grassland project based on GIS and RS: Taking the Simianyaogou Watershed of Wuqi, Shaanxi as the example

The benefit of soil conservation is an important ecological benefit of returning farmland to forestland and grassland.Assessing value of soil conservation can provide an important reference for founding ecological compensation mechanism of returning farmland to forestland and grassland.The Simianyaogou Watershed of Wuqi County,a demonstration area of returning farmland to forestland and grassland in China,was chosen as a study case.The type and area of returning farmland to forestland and grassland were monitored using RS and GIS techniques.The improved L factor of the Revised Universal Soil Loss Equation(RUSLE) was presented,which considers the effect of land cover for erosion.Based on RUSLE and GIS,the dynamic changes of soil erosion were assessed due to returning farmland to forestland and grassland.Then,soil conservation value of returning farmland to forestland and grassland was calculated using method of opportunity cost and replacement price.The results showed that in period from 1997 to 2004,the total area of returning farmland to forestland and grassland was 1 895.8 hm²,of which the afforestation in wasteland was 369.99 hm²,returning farmland to forestland was 357.48 hm²,returning farmland to grassland was 901.72 hm² and closure measure was 266.61 hm>².The annual modulus of soil erosion reduced by 4 644.04 t/(km²·a).The intensity of soil erosion fell from very strong grade into moderate grade.The annual soil conservation value of returning farmland to forestland and grassland was up to 13.24 million yuan,of which 0.08 million yuan for reducing soil loss,11.8 million yuan for reducing fertility loss,1.24 million yuan for reducing sediment deposition and 0.12 million yuan for increasing soil nutrient.