| The gully control and land consolidation project is another important land regulation and ecological management project implemented on the Loess Plateau after "Grain for Green"project.The Loess Plateau has a very important position in the ecological protection and high-quality development strategy of the Yellow River Basin.Finding a balance between food security and ecological environment and promoting land remediation and ecological construction in the Loess Plateau is an inevitable requirement for national strategic development.The gully control and land consolidation project can increase cultivated land area,improve cultivated land quality and ensure food security,but its impact on the regional ecological environment has not been determined.It is of great theoretical and practical significance to study the ecological and environmental effects of gully control and land consolidation project to promote the synergistic and high-quality development of ecology,economy and society on the Loess Plateau.This study combines field monitoring,spatial analysis of remote sensing information and model analysis to analyze the spatial and temporal characteristics of soil properties,soil moisture and vegetation cover in gully of typical projects in Yan’an City.Based on the land use data,the In VEST model and the coupling degree model were used to quantitatively analyze the change characteristics of land use,ecosystem service value and the coupling evolution trend of agro-ecological and economic system in Yan’an before and after the project,to clarify the impact of the project on the ecological environment,and to scientifically evaluate the ecological and environmental effects of the project.These were expected to provide a scientific basis for improving the utilization rate of regional soil and water resources,the ecological protection and high-quality development of similar regions on the Loess Plateau.The main research results of the paper are as follows:(1)The spatial and temporal variation characteristics of soil properties in the gully before and after the implementation of the project were analyzed,and through comprehensive evaluation,it was found that the soil properties in the gully recovered faster.The variation coefficient of soil bulk density and pH in the gully is below 0.1,which belongs to weak variation and the coefficients of variation of other physical and chemical properties were between 0.10 and 0.77,which belongs to moderate variation degree.After the project,the variation coefficients of each indicator in the gully tended to decrease.All physical and chemical property indexes changed significantly in 2-3 years after the project.Among the different locations of the gully,the differences in soil bulk,texture,conductivity,organic matter and total nitrogen were significant.The soil quality index was the highest in the third year after the project.(2)The spatial and temporal variation characteristics of soil moisture in the gully were analyzed,revealing the formation mechanism and the mechanism of akinetic regulation of soil flow in the gully on the Loess Plateau.Soil moisture in gully was significantly 5%higher than that in control slope,and its seasonal variation was slightly behind that of rainfall.The advantage of soil moisture content in the deep layer is more obvious.The soil moisture variation coefficient is between 0.131-0.234,with strong spatial heterogeneity of soil moisture below the surface layer and active variation of soil moisture in the soil layer below 100 cm.The soil moisture content at the gully exit was significantly higher than that at the gully head,and the relative soil moisture content below 40 cm reached 1.According to the temporal and spatial distribution characteristics of gully soil water,the mechanism of flow formation and non-dynamic control in gully soil on the Loess Plateau was revealed by using the gully water control technique of "integrated drainage and drainage".(3)The spatial and temporal variability of the vegetation cover in the watershed was elucidated,the driving factors were identified.It is pointed out that the gully control and land consolidation project has a positive influence on the vegetation cover change in the whole watershed.The vegetation cover in the watershed is generally good,and the spatial distribution shows a trend of "low in the gully and high on the slope".From 2010 to 2019,the vegetation index showed a significant increase trend with the growth rate is 0.004/a,and the significant change area was concentrated in the gully.Among the drivers of vegetation cover change in the watershed,climatic and non-climatic factors are 14.05%and 85.92%respectively,and the area affected by human activities is much larger than that climatic factors.The gully control and land consolidation project is the main reason for the vegetation cover change in the watershed.(4)The spatial and temporal variation characteristics of land use,ecosystem service value and trade-off/synergistic relationships before and after the gully control and land consolidation project in Yan’an city were analyzed,and the relationship between them and the project was analyzed,and puts forward the coordinated development strategy between the project and the ecological environment in each county.From 2010 to 2018,the land use type of Yan’an city maintained a relatively stable state,mainly cultivated land,forest land,grassland conversion to each other.The total value of ecosystem services increased 0.28%.Among the four typical ecosystem service values,soil conservation,carbon sequestration and habitat quality decreased by 7.7%,0.16%and 1.4%respectively,while water production services increased by 0.56%,and their spatial aggregation tended to disperse.The ecological environment is developing towards a balanced,and the four ecosystem services show synergistic relationship,among which the synergistic relationship between soil conservation service and water production service,carbon sequestration service and habitat quality are significant.Gully control and land consolidation project has a negative impact on ecosystem services in Yan’an city,and has a significant impact on carbon sequestration services.(5)The index system of agro-eco-economic system in Yan’an city was established,and the coupling evolution trend of agro-eco-economic system before and after gully control and land consolidation project was revealed by coupling degree model.From 2010 to 2018,both the comprehensive evaluation index of agro-ecosystem and agro-economic system in Yan’an city showed S-shaped growth curve,and the coupling coordination degree index of agro-eco-economic system increased from 0.51 to 0.72.The coupling coordination state develops from primary coordination level to good coordination level.The system coupling trend has experienced the stages of "decay coupling-coordination coupling-repair coupling-coordination coupling".In 2018,the coupling relationship is in the stage of coordinated development with rapid economic growth.Gully control and land consolidation project promoted the coupling and coordinated development of agricultural eco-economic system.In conclusion,gully control and land consolidation projects have certain negative effects on regional ecological environment,but the negative effects are short-term and partial,and long-term and overall positive effects are larger.Gully control and land consolidation project can maintain the stability of regional land use and ecosystem service value,promote the coordinated development and optimal balance of regional ecosystem service,and realize the win-win situation of ecological security and food security. |
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