Based On InVEST Model Evaluating Ecosy Stem Services In Watershed Scale

The Qilian Mountains is the birthplace of the three major inland rivers in the Hexi Corridor area,and has an irreplaceable role in the economic development and ecological security of the northwest China.The quality of the ecosystem services of them affect the ecological environment quality of the river basins directly.In this paper,the water supply,carbon storage and sediment delivery ratio modules of the In VEST model are used to the evaluate the ecosystem services comprehensively in the Tianlaochi catchment,which is a typical small catchment in the upper reaches of the Heihe River located in the middle of the Qilian Mountains.At the same time,three different scenarios were set up to simulate the possible changes in the future watershed and to evaluate the change of ecosystem services in order to provide theoretical basis and guidance for ecological management and environmental protection policy formulation in Qilian Mountains.The main research results are as follows:(1)In the natural development priority scenario,the total amount of carbon storage in the catchment is 62319.70 tons,and the natural forest is the main body of the carbon storage service in the catchment,accounting for 78.93% of the carbon storage in the watershed.The Picea crassifolia is the largest carbon storage,accounting for 55.23% of the carbon stocks in the basin.In the economic development priority scenario,the carbon storage of the basin is 33638.53 tons,the carbon storage is reduced by about 46.02%,and the carbon storage services to reduce.In the ecological protection priority scenario,the total amount of carbon storage is 62319.70 tons,and the carbon storage service is increased.Thus,when only the maximum the carbon storage service is considered,the afforestation activities should be vigorously carried out in the watershed.The total carbon storage of understory vegetation in the watershed is 1917.94 tons,among which the carbon storage capacity of Picea crassifolia,Sabina przewalskii and bush wood are 1368.30,158.68 and 390.96 tons respectively.When neglecting forest carbon storage,Basin carbon stocks could cause some errors.(2)In the natural development priority scenario,the simulation of water supply in the catchment is 2.51 × 106 m3 and the high value area is mainly concentrated in the area of snow and bare rock and bush wood,accounting for 79.73% of them.Compared with the observations,the relative error is 7.52%,which indicates that the In VEST model water supply module has good applicability in the study area.In the economic development priority scenario,the water supply of the catchment is 3.16 × 106 m3,the increase is about 25.78%,and water supply services are on the rise.In the ecological protection priority scenario,the water supply is 2.18 × 106 m3,the decrease is about 13.37%,and the water supply service decline.Thus,only to maximize the supply of water resources,the basin should be based on the cultivation of alpine meadow.(3)In the natural development priority scenario,simulated total soil conservation of 1331832.26 tons,soil erosion amount of 2206.70 tons,and erosion is compared to observed value,the relative error of 8.20%,which indicated that the soil conservation module of In VEST model had good applicability in the study area.In the three different scenarios,the total gap between soil conservation in the basin is small.Under the economic development priority scenari,the soil conservation amount was 1330153.73 tons,down by 1678.53 tons,and soil conservation services are reduced.In ecological protection priority scenari,soil conservation capacity of 1333162.87 tons,an increase of 1330.61 tons,and soil retention capacity improved.In the case of extremely high vegetation coverage,the change of the vegetation in the catchment will not affect the soil maintenance service too much.(4)There is no correlation between soil conservation service and water storage service and carbon storage service.Well,there is a strong negative correlation between water supply and carbon storage service.According to the ecosystem services from low to high,divided into level 1,2,3 and 4 function area.In the natural development priority scenario,Carbon storage services accounted for 21.34%,3.99%,35.89% and 38.78% of the level 1,2,3 and 4 function area.In economic development priority scenario,level 1 and 2 area unchanged,level 4 area all degraded to level 3 area.In ecological protection priority scenario,level 1 and 2 area unchanged,part of the level 3 area convert to the level 4 area.In natural development priority scenario,water supply service level 1,2,3 and 4 function area accounted for 23.40%,26.29%,25.27% and 25.04% respectively.In the economic development priority scenario,level 1 and 2 are transitioned to level 3 and level 4,and most of level 3 and part level 4 are transitioned to level 1 and level 2 in the ecological protection priority scenario.In the natural development priority scenario,21.16%,57.02%,13.88% and 7.49% of the level 1,2,3 and 4 function area of the soil maintenance service respectively.Under the economic development priority,level 2,3 and 4 area are all converted to level 1 area.In ecological protection priority scenario,soil conservation function area has not changed.In the natural development priority scenario,level 1,2,3 and 4 function area of the integrated ecosystem services accounted for 24.27%,24.43%,26.56% and 24.74% respectively.In the economic development priority scenario and environmental protection priority,level 1 and 2 area are all converted to level 3 and 4 area,and level 4 area is 2.52 and 1.64 times than the natural development priority scenario,respectively.In the economic development priority scenario,the level 3 and level 4 areas reach the maximum value of the three scenarios,which is the maximum value of the three ecological service of the Tianlaochi catchment.However,due to the fragmentation of the soil conservation service distribution,the integrated functional area can be considered only a superposition of carbon storage services and water supply services.As we all know,Tianlaochi catchment ecosystem services are numerous,so the results may be misleading in the guidance of the development of the basin.