River Runoff And Dissolved Carbon Transport Process In Qinghai Lake Basin

The water and carbon transport processes,take part in the exchange of matter and the cycle of energy among various ecosystems of the earth,affect the function of ecosystems,respond to the climate change,control the formation and evolution of many natural processes in the various layers of the surface on earth,and play a key role in the exist of human beings,the development of society and the stability of the ecological environment.The river is called the earth's artery,it's the main channel that connecting the ocean and the land ecosystems,also the important link between the land and sea carbon pools,and the most important link that constitutes the water and carbon transport process.The hydrogen-oxygen stable isotope and hydrochemistry method is the effective means to clarify the interaction and transformation relationship between river water and various water bodies,to reflect the water-rock interaction in the basin,and to explore the contribution rate of material energy and influence mechanism of each tributary to the main river.The dissolved carbon component is the important indicator to reveal the leaching and compensation mechanism of chemical ions in river water,the process of mineral leaching and weathering,and the biological activity of aquatic organisms.Qinghai Lake Basin is the important water source in the northeast Qinghai-Tibet Plateau and plays an irreplaceable role in maintaining the ecological security of this area.However,the fragile natural environment and the scarce hydrological monitoring sites made it difficult to establish a complete research framework of the water and carbon transport process.This paper combines the meteorological,hydrological,geological topographic data of Qinghai Lake Basin with the hydrogen and oxygen stable isotopes,hydrochemical ions and dissolved carbon components of river water to study the process of river runoff and dissolved carbon transport in Qinghai Lake Basin from August 2017 to July 2018.The results show that the annual mean values of?¹⁸O and?²H in the precipitation in Qinghai Lake Basin are-11.72‰and-77.15‰,respectively.The Local Meteoric Water Line(LWML)shown as ?²H=7.86?¹⁸O+15.01,the precipitation process is affected by the secondary evaporation and the temperature effects.The annual mean values of?¹⁸O and?²H in river water are-7.60‰and-48.07‰,respectively.The local evaporation line(LEL)is ?²H=5.77?¹⁸O-3.97,showing a strong evaporation during the runoff process and showing the similar characteristics with the precipitation in seasonal variation because most of the river are supplied by the precipitation.The average value of the Total Dissolved Solids(TDS)in Qinghai Lake Basin is 350.76mg/L,and the average value of the electricity conductivity(EC)is 338.68?S/cm.The anion and cation are dominated by HCO₃^-and Ca²⁺,respectively,and the hydrochemical type in the basin is Ca-Mg-HCO₃.The major chemical process of river water is controlled by rock weathering.Daotang river has the highest value of the?¹⁸O,TDS and EC among all the rivers in Qinghai Lake Basin.The stable isotope and the TDS values of the tributaries in Buha River and Shaliu River all higher than their main stream,the main cause is that the tributary flow is smaller,the flow rate is slower and the environment background is more complex than the main stream,thus the evaporation intensity is stronger.Moreover,the larger flow of the main river which has a certain dilution effect on the dissolved matter in the water.The flow of the upper reaches of Buha River occupied for about 56.81%of the total flow that Buha River floe into Qinghai Lake.The average Dissolved Inorganic Carbon(DIC)concentration of river water in Qinghai Lake Basin is about 42.68 mg/L,showing the seasonal characteristics that high in winter and low in summer.The average Dissolved Organic Carbon(DOC)concentration is about 4.55 mg/L,and present the opposite seasonal characteristics with DIC.The concentrations of DIC and DOC show the same characteristics with the stable isotope and hydrochemistry that Daotang river has the highest concentration among all rivers,and the concentrations of tributaries higher than their main stream in Buha River and Shaliu River.Soil erosion and rock weathering are the main sources of the DIC in river water,and runoff is the key factor that controlling the DOC concentration.There is a significant positive correlation between dissolved carbon flux and the runoff which affected by the climatic factors.Buha River has about 940.94×10⁸g C and Shaliu River has about 194.05×10⁸g C flowing into Qinghai Lake every year,of which June to September can account for more than 79.15%.This study would provide important theoretical and practical value for the study of water and carbon transport process in Qinghai Lake Basin,and scientifically evaluate the impact of surface water environment evolution on the ecological function of the Qinghai-Tibet Plateau,as well as provide realistic reference to the effectively promote ecological environment protection and rational development of water resources in the Qinghai-Tibet Plateau.