| The concept of ecosystem services has become a key issue in the international discussion on climate change impact assessment,landscape management and biodiversity conservation.Land use change,as the focous of global change reaserch,has an important effect on ecosystem services,such as soil erosion,and carbon and nitrogen cycles.The Loess Plateau is a transitional zone from semi-humid to arid desert climate.The hilly and gully region of the Loess Plateau that district serious soil erosion and serious damaged ecosystem.Therefore,it is particularly important to accurately assess the ecosystem services such as soil convervation and carbon and nitrogen sequestrations,as well as quantitatively analyze the trade-off relationship between ecosystem services to procide scientific decision-making for comprehensive management of Nangou Basins.This study selected Nangou Basin as the research object,which has implemented the background of the“Grian for Green”project and‘Filling Gullies’project.The research adopted the methods of grid sampling,experimental observation and collection of meteorological data,biology and soil data,topographic data,model simulation and spatial image in the process of ecological restoration,and combined with GIS technology,to explore the relationship between landscape pattern and soil quality,clarify the distribution and influencing mechanisms soil aggregate stability,soil carobon and nitrogen storages and soil erosion,treveal the ecosystem service emergy values and trade-off relationships such as carbon fixation and oxygen release,soil carbon pool,soil structure and soil erosion and visualized the results.These results provided a scientific basis for vegetation construction and soil and water conservation in the Nangou basin,and lay the foundation for future ecological security of the basin and sustainable restoration of the vegetation ecosystem.The main results are as follows:（1）The spatial distribution characteristics of soil quality in basin landscape were clarified.The land use types in Nangou basin are mainly grassland and forest,the slope is mainly 15°-25°;soil quality of orchard and forest is higher than that of grassland,the slope has no significant effect on soil quality,and the soil quality is reduced with the altitude increase;LSI,LJI,SPLIT and AI have siginificant effects on soil quality,and LSI,SPLIT and AI have a significant negative correlation with soil quality.The results can provide a scientific basis for basin vegetation restoration and soil and water conservation management,thus ensuring soil quality improvement in the basin.（2）The distribution and influencing factors of soil aggregate stability under the change of basin land use are clarified.Soil aggregate stability of grassland is the largest,followed by forest,orchard and farmland.Due to the cultivation of orchard,soil aggregate stability is seriously destroyed,however,it can be restored quickly after orchard abandonment.Soil clay,soil bulk density,soil carbon,soil nitrogen and soluble carbon and nitrogen have significant effects on soil aggregate stability.Soil aggregate stability is significantly positively correlated with soil nitrogen in the surface soil,while soil aggregate had a negative effect on soil nitrogen in deep soil.The results indicated that vegetation restoration played a better role in improving the stability of soil aggregates.（3）The sequestration rate,sequestration potential and influencing factors of soil carbon and nitrogen in the different land use types were elucidated.The carbon sequestration rates of orchard,grassland and forest were 0.1,0.4 and 0.4 Mg hm-2 yr-1,respectively,and the carbon sequestration potential were 1.9,86.8 and 164.6 Mg yr-1,respectively.The nitrogen sequestration rates of orchard,grassland and forest were 6.1×10-3,17.2×10-33 and 6.9×10-3 Mg hm-2 yr-1,and nitrogen sequestration potential were 0.2×10-3,5.1×10-3 and 2.7×10-3 Kg yr-1.Soil carbon and nitrogen storages and carbon and nitrogen sequestration of farmland and orchard are mainly affected by soil particles and soil bulk density,while grassland and forest are mainly affected by soil aggregate stability and C:N ratio.Soil bulk density and soil carbon and nitrogen storages were significantly positively correlated.Soil aggregate atability were also positively correlated with soil carbon storage.Soil particles were negatively correlated with soil carbon storage and positively correlated with soil nitrogen storage.The results suggest that forest should be the main restorsed vegetation in the area to increase carbon storages and prevent soil and nutrient loss.（4）The spatial distribution of soil erosion in the basin was revealed,and the characteristics of soil erosion under different land use types and topographic factors were discussed.Soil and water conservation in Nangou basin is significant,but the potential for soil erosion is still high.The range of soil erodibility in the basin is 0.108-0.118 t ha h MJ-1 ha-1 mm-1,and the maximum soil erosion modulus is 5625 t km-2 a-1,the average soil erosion modulus is 1008.4 t km-2 a-1,the total soil erosion modulus is 7.31×106 t km-2 a-1.Soil erosion is mainly micro-degree and lightness,and soil erosion sensitivity is mainly sensitive and midly sensitive in Nangou basin.In addition,soil erosion in grassland,orchard and 8°-25°slope is the most serious.The results indicated that soil and water conservation is significantly improved,but the potential for soil erosion is still high.Ecological restoration and soil and water conservation projects aere needed for the slope of 8°-25°to increase the ecological benefits of the basin.（5）Based on the emergy analysis and visualization analysis to evaluate the material quality,emergy value and ecosystem service values of Nangou basin.The total emergy value of Nangou basin is 1.49×1022 sej,in which the carbon sequestration emergy value is37.71×1010 sej,the oxygen release emergy value is 21.49×1015 sej,the nutrient retention emergy value is 17.01×1018 sej,the soil conversation emergy value is 36.69×1013 sej,the soil structure emergy value is 1.30×1010 sej and the soil carbon pool emergy value is 37.45×1013sej.The total value of Nangou basin is 20.4×106 yuan,of which soil conservation service value is 16.2%,soil carbon pool service value is 75.5%,grassland ecosystem services value is23.4%,forest ecosystem services value is 62.9%.Soil conservation and nutrient rentention service of farmland,orchard and grassland are more prominent,while carbon fixation and oxygen release service,soil carbon pool service and soil structure service of forest are more prominent.（6）It revealed the trade-off relationships between different ecosystem services under different land use types and slopes.There is zero trade-off between soil conservation service and nutrient rentention service,and there is near-zero trade-off between NPP service and soil carbon pool service.Soil structure service and NPP service,soil carbon pool and soil structure service are also close to zero trade-odds.In addition,trade-off between soil conservation service and soil structure service>trade-off between soil conservation service and NPP service>trade-off between soil conservation service and soil carbon pool service.The ecosystem service trade-off degree of diferenrt land use types was orchard>farmland>grassland>forest,and with the increase of slope,the trade-off degree of ecosystem services was also gradually increased.Forest and grassland benefit from soil structure services and soil carbon pool services,while cropland and orchard benefit from more soil and nutrient conservation services.This study considered that the improvement of soil organic carbon storage is the basis of improving soil function in the Nangou basin,however,the primary of improving soil organic carbon is to control soil and nutrient loss. |
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