Dynamics Of Water Yield And Carbon Sequestration Capacity And The Impacts By Grazing In The Upper Reaches Of Zhuanglang River Basin

Rapid climate change and grazing activities have significantly affected the dynamics of water yield and carbon sequestration capacity of the ecosystem in the upper reaches of the Yellow River basin.As an important water source,and vegetation carbon sequestration area in the upper reaches of the Yellow River,Qilian Mountain is widely distributed with alpine ecosystem of human and land combination.The water yield and vegetation carbon sequestration capacity of these alpine ecosystem of human and land combination is very important for their downstream ecological security and water resources protection.However,under the dual influence of climate change and grazing activities,the dynamics and interaction mechanism of water yield and vegetation carbon sequestration capacity of these alpine ecosystems of human and land combination are not clear.At present,it is urgent to explore these dynamics and their interaction mechanism,so as to provide scientific support for the implementation of the major strategy of ecological protection and high-quality development in the Yellow River Basin and the realization of the"double carbon"goal.Zhuanglang River,located in the eastern part of Qilian Mountains,is the first-class tributary of the Yellow River.The ecosystem of Zhuanglang River basin is a typical representative of the alpine ecosystem of human and land combination in the Qilian Mountains.This paper selected the upper reaches of Zhuanglang River basin as the study area,took net primary productivity(NPP)and water yield depth as the measurement indicators of water yield and vegetation carbon sequestration capacity of regional ecosystem,compiled and integrated the grazing impacts module based on the ecosystem process model IBIS_i,to realize the interactive simulation of"water-carbon-grazing"of alpine ecosystem of human and land combination.At the same time,combined with the NPP remote sensing data and the runoff observation data of hydrological stations in the study area,the model accuracy is verified,and then the dynamics of water yield depth in the upper reaches of Zhuanglang River basin from2001 to 2020 is simulated.Then,using the simulation results of water yield depth and NPP remote sensing results,this paper explored the dynamics,interaction and spatial differences of ecosystem water yield and vegetation carbon sequestration capacity in the study area in the past 20 years.On this basis,the influence mechanism of grazing on grassland water yield and vegetation carbon sequestration capacity was analyzed by simulating the grassland ecosystem status in the study area from 2001 to 2020under the actual grazing and non grazing conditions,outputting the simulation results of water yield depth and NPP,as well as the key ecological process quantities.The water yield and vegetation carbon sequestration capacity of grassland under the influence of climate change and grazing in the next 30 years were predicted.The following conclusions were drawn:(1)From 2001 to 2020,the relationship between water yield and vegetation carbon sequestration capacity was synergistic,and both had been enhanced.For each land cover type,the order of water yield increase from large to small was forest land>grassland>cultivated land,and the order of vegetation carbon sequestration capacity increase from large to small was cultivated land>grassland>forest land.From the average state,the order of water yield and carbon sequestration capacity of vegetation from strong to weak was forest land>grassland>cultivated land.(2)Grazing activities mainly enhanced the surface evaporation process,weakened the canopy interception evaporation process and vegetation transpiration process,resulting in the enhancement of the water yield and the weakening of the vegetation carbon sequestration capacity of the grassland ecosystem in the upper reaches of Zhuanglang River.(3)In the combined scenario simulations of different climatic conditions and grazing intensities,maintaining the current(2011?2020)average climate state,the increase of grazing intensity gradient will lead to the enhancement of water yield and the weakening of vegetation carbon sequestration capacity.Keeping the current grazing intensity unchanged,the increase of precipitation will lead to the improvement of water yield and carbon sequestration capacity of vegetation.