Spatiotemporal Tradeoffs And Synergy Of Watershed Ecosystem Services

As a typical mountainous watershed,the Bailongjiang Watershed of Gansu is located in the transition zone between the Qinghai-Tibet Plateau,the Qinba Mountain and the Loess Plateau.It is an important water conservation area and ecological barrier in the upper reaches of the Yangtze River.However,its terrain is variable and geological disasters are frequent,which have been seriously threatening the ecological security and socioeconomic development of the watershed.At the same time,it is located in the concentrated area of national-level poverty-stricken counties(Qinba Mountain Area)and the key area of rural poverty alleviation in the “13th Five-Year Plan” of Gansu Province.This basin is facing the severe challenge of accelerating the transformation of economic development mode and gradually lifting people out of poverty.Therefore,four typical Ecosystem services(ES)(food supply,soil conservation,water conservation and habitat quality)from 1990 to 2016 were evaluated with the support of the GIS spatial analysis and InVEST model.And through the methods of radar map,spatiotemporal correlation analysis and cluster analysis,the spatiotemporal changes of ES structure,spatiotemporal tradeoff and ecological function zoning ware studied at the basin,county,topography(landform or elevation)and major land use types.The main conclusions were as follows:(1)The spatiotemporal changes in ES structure.From 1990 to 2016,except for the continuous increase of food supply,the other three services(soil conservation,water conservation and habitat quality)in the watershed all showed a trend of decreasing first and then increasing around 2002.The ES structure in the four years was successively shown as “water and soil conservation supply” type,“unsustainable supply” type,“habitat friendly supply” type and “sustainable supply” type.Affected by the spatiotemporal differences in the natural processes and socioeconomic activities of the watershed,the food supply was concentrated in the lower slope and valley agricultural area of Tanchang and Wudu,while the other three services were mainly distributed in the forest and grass areas.Among them,the soil conservation as a whole,which was weakened with the elevation of the landform,while the water conservation and habitat quality increased first and then decreased,and the changes of the four services were also different in time and space.(2)The spatiotemporal correlation between ES.In the watershed,the annual food supply was statically and significantly negatively correlated with the other three services,and the other three services showed static significant positive correlation with each other.Water conservation and soil retention during the first two periods(1990-2002,2002-2010)showed a dynamic significant positive correlation with the increase in degree,and then(2010-2016)suddenly became a dynamic significant negative correlation,and the relationship between water conservation and food supply was opposite.There was a dynamic significant negative correlation between food supply and soil conservation in the middle period(2002-2010),but no significant correlation between the first and the last period(1990-2002,2010-2016),and the relationship between food supply and habitat quality was reversed.From the first two periods to the last period,the relationship between soil conservation and food supply changed from non-obvious to dynamic weak positive correlation,the dynamic significant positive correlation between water conservation and habitat quality gradually changed to the weak negative correlation as a whole.Compared with the watershed,the spatiotemporal correlation between services has certain differences in county,landform and land use types,which obviously reflected on the direction and degree of relationship.(3)The spatialtemporal tradeoff and synergy of ES.In the watershed,the tradeoff intensity between food supply and soil conservation,food supply and water conservation increased first and then decreased around 2002.The tradeoff strength between food supply and habitat quality and the synergistic strength between soil conservation,water conservation and habitat quality decreased first and then increased.In terms of spatial distribution,the high-intensity areas of the first two pairs of services were mainly concentrated in the agricultural farming areas on the northern part of Tanchang and the banks of the Bailongjiang in the Zhouqu-Wudu-Wenxian section,the high-value areas of the last four pairs were distributed in the forests and grass area.The change in the degree of relationship between services on most spatial units took 2002 as the inflection point,and the degree of relationship between units and its comparison with the degree of watershed were quite different.Which shown that the degree of spatiotemporal tradeoff and synergy among services at various scales was the unity of global consistency and local difference.(4)The ecological function zoning.Based on the ES cluster,the watershed was divided into five ecological functional areas,included the downstream ecological conservation area of Baishuijiang River,the downstream ecological conservation area of Datuanyu River,the water source and habitat conservation area of Bailongjiang River,the ecological agriculture area of Bailongjiang River and the core agricultural area of Bailongjiang River.In addition,this study further synthesized the differences of social ecological factors and the influence factors of “comprehensive ecological benefits” in various functional areas,and put forward suggestions on regional ecological system management,so as to provided scientific instructions for the socioeconomic development and ecological civilization construction in the watershed.