| The water and soil erosion is very serious in hilly region of the Loess Plateau in China,a large-scale artificial shrub-grassland system has been established in this region since the 1980s,which has achieved good ecological,economic and social benefits.Therefor the evaluation of service function of shrub-grassland system has important theoretical and practical significance for the protection and construction of the Loess Plateau ecosystem.This study took Anding district,Dingxi city,Gansu province as an example,and used InVEST model to evaluate the water conservation function of the artificial shrub-grassland system in Anding district in 2017.In addition,it classified the cold and hot spots and the importance of water conservation and water quality purification function,and made quantitative spatial analysis.Based on the evaluation results,the existing problems and future development priorities of the ecosystem in the hilly region of the Loess Plateau were put forward.The main conclusions are as follows:Firstly,The water yield per unit area in the Anding area is 292.67 m~3/hm~2,the average water yield of grid unit is 0-460.825 mm,and the total annual water yield is3.41×10~8 m~3.According to the assessment results of water yield,it is calculated that the water conservation per unit area of the Anding area in 2017 is 102.13 m~3/hm~2,the average water conservation of grid unit is between 0-364.541 mm,and the total water conservation assessment is 1.19×10~8 m~3.The spatial distribution of water yield and water conservation is higher in the southwest and lower in the northeast.Using Gi*statistical method,the spatial distribution characteristics of cold and hot spots for ecosystem services in the stable region are as follows:hot spots are mostly distributed in the southwest region,while cold spots are mainly distributed in the east-central region.Secondly,the output and retention of P per unit area in the Anding area are 0.51kg/hm~2 and 1.59 kg/hm~2 respectively,and the total output and retention of P are 172.7t and 564.6 t respectively.The output and retention of N per unit area are 2.44 kg/hm~2and 7.22 kg/hm~2 respectively,and the total output and retention of N are 838.87 t and2586.92 t respectively.The water purification function is higher in the Xihe and Chenggou River basins and lower in the eastern regions.The spatial distribution characteristics of cold and hot spots of ecosystem services in Anding district are as follows:the distribution of cold and hot spots output by N and P has a small difference and a lot of overlaps,and the distribution characteristic is decreasing gradually from southwest to northeast,which is consistent with the distribution characteristics of water conservation function.Thirdly,combine the land use type map to analyze the water conservation and water purification functions of Anding district in 2017.Among different land use types,the water conservation functions per unit area are ranked by size as follows:grassland>artificial irrigated grassland>cultivated land>forest land>unused land>construction land.The artificial shrub-grassland system have a capacity of 369.25 m~3/hm~2 per unit,it was ranked second.The purification rate of N in the water purification function is in order from high to low:forest land(85.85%)>grassland(72.24%)>artificial irrigated grassland(72.21%)>unused land(68.92%)>construction land(65.24%)>water area(61.51%)>cultivated land(59.47%).The purification rate of P from high to low was as followed:forest land(79.13%)>grassland(72.26%)>artificial irrigated grassland(71.07%)>water area(69.32%)>unused land(69.06%)>cultivated land(68%)>construction land(65.52%).Among them,the net rates of nitrogen and phosphorus in the artificial shrub-grassland system are 72.21%and 71.07%respectively,ranking the third from high to low.The evaluation results showed that the artificial shrub-grassland system in the hilly region of the Loess Plateau has greatr water conservation and water purification function.Fourthly,using the Reclassify tool of ArcGIS software(10.5)to classify the water conservation and water purification functions in the Anding district.The output results showed that the grade distribution of water conservation and water quality purification functions is very different.In addition,the spatial superposition analysis of water conservation and water purification function divided it into five levels.The evaluation results showed that the extremely important area and highly important area of the artificial shrub-grassland system have a high proportion,accounting for 51%and 44%of the total land area respectively.Among seven different land use types,the artificial shrub-grassland system have the best water conservation and water quality purification function. |
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