黄土丘陵区坡改梯生态经济耦合效应

坡改梯是黄土丘陵区提高农作物单产和控制水土流失的有效措施。基于坡改梯内生和外延效应的学术思路,构建了能定量刻画坡改梯生态经济耦合状况的数学模型;以位于黄土丘陵区腹地的延安燕沟流域为例,利用土地利用和数字地形等空间数据、作物产量和土壤侵蚀模拟数据以及监测和调查数据,定量评价分析了燕沟流域坡改梯的生态经济耦合效应。结果表明:地形坡度越大,坡改梯的生态经济耦合效应越显著;地形坡度5°和15°是两个重要阈值,5°以下不必进行坡改梯,5°—15°之间应作为坡改梯的重点对象,15°以上宜退耕还林还草。坡改梯使燕沟流域农耕地的生态经济耦合程度得到了显著提高,坡改梯前生态经济耦合指数为1.805t/100元,坡改梯后下降为0.853t/100元,下降幅度达52.73%。随着坡改梯和植被覆盖率的提高,流域的洪水径流量和输沙模数均大幅度下降。

Ecological-economic coupling effects of transforming slope farmland to terraces in the hilly-gully region of Loess Plateau

Transforming slope farmland to terraces has been an effective measure to improve crop yield per unit and control soil and water loss. Based on the theory of internal and external effects of transforming slope farmland to terraces, this paper constructs the mathematical model for quantitatively evaluating ecological-economic coupling status. Taking the Yangou watershed of Yan''an city which is located in the core area of the hilly-gully region of Loess Plateau as a case, using spatial data of land use and DEM, crop yield and soil erosion modeling data, and monitoring and survey data, this paper quantitatively assesses and analyzes ecological-economic coupling effects of transforming slope farmland to terraces. The results show that: (1) it is feasible to evaluate ecological-economic coupling effects of transforming slope farmland to terraces from the internal and external aspects. Soil erosion cost per economic yield unit (Ecological-economic coupling index) can quantitatively and effectively reflects ecological-economic coupling level. (2) Assuming beans and corn are cultivated on the slope farmland, the changing trend of ecological-economic coupling index shows that it ascends as the topographic gradient rises. This indicates that the higher topographic gradient, the more soil erosion cost of per economic yield unit. Topographic gradient 5° and 15° are two important thresholds. There is no need to transform slope farmland below 5°. However, slope farmland between 5° and 15° should be the key object of transformation to terraces. Slope farmland above 15° needs to be converted to forest and grassland. (3) Transforming slope farmland to terraces has dramatically enhanced ecological-economic coupling level of cultivated land in the Yangou watershed. Before and after transforming slope farmland to terraces, the ecological-economic coupling index is 1.805 t/100 yuan, 0.853 t/100 yuan, respectively, decreased by 52.73%. As the transformation from slope farmland to terraces and the enhancement of vegetation coverage rate, the flood runoff and sediment transport modulus have sharply declined, and the soil and water loss situation has been obviously improved.