Research On Soil Conservation Services Considering Erosion Sediment Yield And Delivery Processes

Soil conservation service is one of the services provided by ecosystems.It can play a role in reducing sediment accumulation and improving human well-being.The ability of ecosystems to provide soil conservation services is determined by two key processes,one is the process of inhibiting soil erosion and sand production by ecosystems through vegetation roots,the other is that after local soil erosion occurs,the sediment produced by erosion is transported and exported to rivers,lakes and reservoirs,and some of this sediment is intercepted by ecosystems on other plots.Based on the perspective of sediment reduction,this study evaluated soil conservation services during erosion sediment yield and delivery.The part of the Yongding River National Key Soil and Water Loss Control Area located in the Beijing-Tianjin-Hebei urban agglomeration was used as the research area,and the RUSLE-SDR combination model and alternative cost method were used to evaluated soil conservation services.Soil conservation services and their value were assessed from 2005 to 2020,including soil conservation services provided by ecosystems during erosion and sediment yield which characterized by "the reduction of soil erosion" and soil conservation services provided by ecosystems during sediment delivery which measured by "the retention of sediment".On this basis,areas with strong or weak soil conservation service supply capacity in this study area had identified,and key areas for sand production and transport had also identified,which aimed to help the key soil and water loss control areas to formulate scientific and accurate governance solutions and zonal,classified and hierarchical treatment strategies.The main results of the study are as follows:(1)From 2005 to 2020,the main type of ecosystem in this study area are grassland,cropland and forest.The slope of the plateau area in the northern is gentle,and the grassland and cropland are evenly distributed,but the terrain and slope of the area in the southern varies greatly,and the ecosystem types are diverse.With the continuous advancement of urbanization and ecological construction,the area of urban land has been expanding year by year,and the area of forest land has also shown an expanding trend.(2)From 2005 to 2020,the sediment connectivity index(IC)and sediment delivery ratio(SDR)in this study area decreased year by year.Meanwhile,the high-value area was shrinking,and the IC and SDR in the southern were significantly higher than those in the northern area.The average SDR in this area is 43.65%,which is still higher than most river basins in China,meaning the sediment generated by soil erosion has a greater probability of entering rivers,lakes and reservoirs.There are large differences in SDR between regions,mainly related to slope,ecosystem type,vegetation cover and distance from sediment sinks.(3)From 2005 to 2020,in the process of soil erosion and sediment yield,the soil conservation service characterized by "the reduction of soil erosion" provided by the ecosystem in this study area was much lower than the average level of the Beijing-Tianj in-Hebei urban agglomeration.Fortunately,the soil conservation service was constantly improving,the gap with the average level of the Beijing-Tianjin-Hebei urban agglomeration is narrowing,which means that the overall trend of regional soil conservation services is improving.Better soil conservation services in the region were concentrated in the south rim and north rim of the study area,followed by the east,which are areas that need key protection.The soil conservation services of forests and shrubs were significantly better than those of other ecosystem types.Therefore,they are the types of ecosystems that can be considered for increasing in ecological construction.(4)From 2005 to 2020,the actual amount of soil erosion in the study area was relatively large,which was ten times the average level of the Beijing-Tianjin-Hebei urban agglomeration,but showed a trend of erosion mitigation.The most severe erosion is mainly concentrated in the northern plateau area,although the area of these heavily eroded areas is small,but it contributes most of the soil erosion,and its area continues to expand during the study period.Therefore,these areas are key areas that require rational allocation of human,material and financial resources to carry out priority governance.(5)From 2005 to 2020,the soil conservation services measured by "the retention of sediment" provided by the ecosystems in this study area fluctuated less and weakened.Overall,the distribution area of cropland and grassland with gentle slope had significantly higher soil conservation service.The soil conservation services provided by the northern plateau area with a large area of cropland and grassland were generally higher than those in the southern area with dense hills and undulating slopes.(6)From 2005 to 2020,the sediment delivery(SD)in this study area decreased,and the area of the high-value area decreased significantly year after year.These high-value areas are mainly distributed in the transition area between forset and cropland,and grassland,in which the slope is steep.The SDs of water,grassland and barren land were much higher than other ecosystem types,and their SDs increased during the study period.(7)From 2005 to 2020,in the case of comprehensive consideration of the process of sediment yield and delivery,the total amount and value of soil conservation services in this study area increased significantly year by year,with the average values being 62.96 million t/a and 843 million yuan/a,respectively.The soil conservation services provided by ecosystems in the process of sediment yield(the average proportion was 94.02%)were much higher than those provided by ecosystems in the process of sediment delivery.The number of small watersheds with high levels of soil conservation services and high value was increasing,and it was mainly located in the southern and eastern regions where forest was concentrated.