基于PSR框架,针对土壤侵蚀小流域的土地质量评价

Land quality indictors based on “Press-State-Response” framework at catchment for soil degradation by water erosion

土壤侵蚀与水土流失是我国土地退化的重要形式。建立基于“压力 -状态 -响应 (PSR)”模式的土地质量指标体系能够比较明确反映出土地质量变化的因果关系 ,从而有助于决策者采取合适的土地政策和管理措施 ,进行退化土地的恢复重建。在我国水土流失较为严重的黄土高原丘陵沟壑区 ,选取安塞县大南沟小流域进行案例分析 ,分别以栅格 (10 m× 10 m)和小流域整体为评价对象建立起基于 PSR框架 ,针对土壤侵蚀的土地质量指标体系。前者 (以栅格为评价对象 )的压力指标主要为坡度 ,状态指标包括土壤侵蚀强度、土壤肥力和植被盖度 ,响应指标为土地利用类型 ;后者 (以小流域整体为评价对象 )指标包括 3个方面 ,即基于栅格计算的指标、统计指标和格局指标。具体的的压力指标包括地形压力、耕地压力、农作物收入压力以及格局压力等指标 ,状态指标包括土壤侵蚀强度、土壤肥力、植物盖度、流域出口水土流失和格局状态指标 ,响应指标包括非农地面积比重和梯田占农地面积比重等指标。以小流域 1998年土地利用图为基础 ,运用模型模拟和统计分析对小流域整体和小流域内土地质量的相对差异进行了评价。结果表明 ,小流域平均坡度 2 7.85°,最大坡度高达 5 9.39°,耕地平均坡度 2 4 .5 6°,耕地面积比重4 2 .8% ,农作物收入比?

Soil erosion is one of the most important land degradation in China. Land quality indicators based on “Press-State-Response” framework can explore distinctively the reason and the results of land quality changes, which will help administrator to adopt suitable land policy and management measures to rehabillitate degraded land and improve land quality. Respectively taking cell (10m×10m) and whole catchment as evaluation unit, Land quality indicators based on PSR framework for soil degradation by water erosion were build up at Da Nangou catchment, Shaanxi province, hilly area in Loess Plateu. In the former land quality indicator (cell as evaluation unit), slope gradient is used as a press indicator, state indicators include soil erosion intensity, soil fertility and vegetation cover, response indicator is the land use type. As for the latter (whole catchment as evaluation unit), the press indicators include topography, cultivation, crop income and land use pattern; state indicators include soil erosion intensity, soil fertility, vegetation cover and soil and water loss indicators at catchment exit; response indicators include the proportion of the area of non-farmland (forest/shrub + grassland + fallow) to whole land and terrace land to whole farmland. Land qulity status of the catchment were evaluated based on land use in the year of 1998 by the application of model simulating and statistical analysis.Average slope gradient in the small catchment is 27.85°, the maxium gradient is 59.39°, the average gradient for farmland is 24.56°, the proportion of the area of farmland to whole land is 42.8% and the income proportion from crop is about 63%. We divide the land quality of the catchment into six grade and the pressure evaluation is fifth; the average soil erosion intensity and the total erosion is respectively 36.39t/ha and 6.03t/ha at the catchment exit. The average vegetation cover is 2.83%; the state grade is fourth; the area proportion of non-farmland to whole land is 57.2% and the terrace land to whole farmland is 4.01%, the response grade is also fourth. Spatial heterogeneity of land quality at catchment is low, the fourth grade land occupied almost the percent 50 to the total catchment area. Land quality is different among land use types. The order from high to low of land quality is respectively forest/shrub, grassland, orach/economic forest, fallow and farmland. The results will provide some useful information for land planning in valley and land quality comparision among different valleies.