Spatial And Temporal Evolution Of Ecosystem Services In The Shule River Basin Based On InVEST Model

Ecosystem services are of great importance to human well-being and the sustainable development of social economy.Located at the westernmost tip of the Hexi Corridor,the Shule River Basin is characterized as small annual precipitation,large evaporation,low vegetation coverage and fragile ecosystem.By adopting GIS and InVEST models,this paper quantitatively evaluates water conservation,soil conservation,carbon storage,habitat quality services,spatiotemporal distribution of habitat quality service and their influencing factors.Meanwhile,the importance level and spatial distribution of ecosystem services are classified so as to provide scientific suggestions for watershed ecosystem protection.The main conclusions are as follows:Firstly,the water conservation function of Shule River Basin is enhanced,and the total amount of water conservation in general increases by 371.44 million m3.The spatial distribution trend is high in southeast and low in northwest.The water conservation of different land types is low-coverage grassland,medium-coverage grassland,glacial snow,cultivated land,high-coverage grassland,woodland,rivers and lakes by descending order.Topographic and meteorological factors have an impact on water conservation.The average amount of water conservation capacity increases with altitude and slope.The amount of water conservation capacity in different slopes is shady slope,semi sunny slope,semi shady slope,sunny slope in descending order.The spatial distribution of water conservation and annual precipitation tends to be consistent,which is contrary to the spatial distribution trend of potential evapotranspiration and annual average temperature.Secondly,the function of soil conservation was in general enhanced,and the amount of soil conservation increased by 288.355116 million tons.The spatial distribution trend is high in southeast and low in northwest.The soil conservation of different land types are low coverage grassland,medium coverage grassland,unused land,high coverage grassland,forest land,glacial snow,cultivated land,urban and construction land,rivers or lakes,rural residential areas by descending order.The high values of soil retention amount and average value are distributed in the area with an altitude of 2800 to 4800 meters.There is a great difference between soil texture and soil types in different slope ranges,hence soil retention and average value increase with elevation.The terrain fluctuation is less than 300 meters,the soilretention and average value increase with fluctuation,while the fluctuation is more than 300 meters,they start to decrease.With the increase of precipitation,the vegetation coverage and the soil retention are increased.The retention of different soil types varies greatly,among which cold calcium soil,cold calcium soil,chestnut soil,brown calcium soil and coarse bone soil have higher soil retention,while brown desert soil,gray brown desert soil and other soil types have lower soil retention.Thirdly,the carbon storage function of the basin was enhanced,with a total increase of 14.96 million tons.The areas with high carbon reserves are mainly distributed in the oasis areas in the middle of the basin,while the carbon reserves in the north of the basin are relatively low,and the carbon reserves in the south of the basin are at a medium level.The carbon storage of different land types is unused land,low coverage grassland,medium coverage grassland,cultivated land,forest land,high coverage grassland,river or lake,rural residential area,urban and construction land,glacial snow by descending order.The unused land is transformed into cultivated land,forest land and grassland.The vegetation coverage increases the aboveground and underground carbon reserves of soil and vegetation,resulting in the increase of carbon reserves in the Shule River Basin.Fourthly,the function of habitat quality has been strengthened year by year.In1990,2000,2010,and 2017,the average habitat quality index of the basin was 0.2685,0.2682,0.2691,and 0.2704,which indicates a decreasing to increasing trend.The index also shows an alternating from high to low in spatial distribution,and the high value gradually concentrated from north to south.The average index of habitat quality of different land types in each year is high coverage grassland,medium coverage grassland,forest land,low coverage grassland,cultivated land,river or lake,rural residential area,urban and construction land,unused land,glacial snow in descending order.From 1990 to 2017,78.83% of the regional habitat quality index of the basin remained unchanged,while 11.35% of the regional habitat index increased,and9.82% of the regional habitat quality index decreased.Fifthly,the Shule River Basin is divided into four types of ecosystem service function areas,of which the minimum area of the most important area is 433.8 km2,accounting for only about 0.48%.The maximum area of the general important area is13042.9 km2,accounting for about 10.01% of the basin.The areas of the medium important area and the important area account for 11.15% and 2.44% respectively of the total area.