Temporal And Spatial Distribution Characteristics And Discussion On Provenance Of Soluble Salt In Atmospheric Dustfall In The South Of Qaidam Basin

In arid and semi-arid areas,due to climate change and human disturbance,lakes have gradually shrunk,exposing large areas of dry lake beds and becoming important dust sources,triggering a series of ecological environment and health problems,which have aroused widespread concern.The Qaidam Basin is located in the northern part of the Qinghai-Tibet Plateau.In the Qaidam Basin,there have an arid climate and numerous salt lakes.Meanwhile,the topsoil salinization and salinization are extremely developed.It is one of the areas with frequent sandstorms on the Qinghai-Tibet Plateau.For one thing,the dust aerosol in the Qaidam Basin contains a relatively high soluble salt content,which will cause the expansion of the surface salinization.For another thing,these fine-particle dusts are easily suspended above the atmospheric boundary layer,the moisture-absorbing particles(chloride and sulfate of sodium,potassium,calcium and magnesium,etc.)in which can act as cloud condensation nuclei or ice nuclei,indirectly affecting the local climate by affecting the formation of cloud droplets and ice.Meanwhile,when these fine dusts are transported over long distances,they may also affect the climate and ecological environment changes in the Qinghai-Tibet Plateau and even the world.However,few people pay attention to and study this phenomenon.Therefore,it is necessary to understand the temporal and spatial distribution characteristics and main sources of soluble salts in atmospheric dustfall in the southern Qaidam Basin.First and foremost,this study analyzes the spatial distribution characteristics of soluble salts in the topsoil of the Qaidam Basin and the temporal and spatial distribution characteristics of soluble salt components(salt minerals and water-soluble ions)in the atmospheric dustfall in the southern Qaidam Basin.Secondly,compare and analyze the characteristics of water-soluble ions in the surface soil and atmospheric dust in the study area.Third and last,combining the backward trajectory distribution characteristics of Golmud City and Dulan County,further discussion on the sources of water-soluble ions in atmospheric dustfall in the basin was carried out,got the following conclusions:(1)The main salt minerals in the topsoil of the Qaidam Basin include halite,gypsum and a small amount of thenardite;the average content of the main water-soluble ions(Na⁺,Cl^-,Ca²⁺,SO₄^2-,Mg²⁺,K⁺,NO₃^-,Li⁺,B³⁺(B₂O₃),Sr²⁺etc.)is 9.7566(Wt%);the high-salt areas are concentrated in the vicinity of the salt lake area and gradually decrease to the surrounding area in the Qaidam Basin.At the same time,the salt content of different topsoil in the basin is in order of playa,Yardang,saline meadow,Gobi Desert and desert.Combining the resistance to wind erosion of various types of topsoil,the distribution areas of playa and Yadan are initially obtained,which are the main source areas for the release of salty dust;(2)The soluble minerals in the dustfall of the Qaidam Basin mainly include halite and gypsum.The soluble salt of dustfall(Na⁺,Cl^-,Ca²⁺,SO₄^2-,Mg²⁺,K⁺,NO₃^-,Li⁺,B³⁺(B₂O₃),Sr²⁺etc.)were in the range of 2.27(Wt%)?20.92(Wt%),of which these four ions(Na⁺,Cl^-,Ca²⁺,SO₄^2-)account for 74%to 95%of all water-soluble ions.These four ions mainly exist in the form of halite and gypsum.In terms of spatial distribution,the content of soluble minerals and water-soluble ions are both higher in HXB and BLX,and the lowest in NMH;(3)Comparing the surface soil and dust fall chemical composition in the study area,the water-soluble ions of the dustfall mainly from natural topsoil.Mg²⁺,K⁺,Li⁺and B³⁺(B₂O₃)were obviously abundant in individual monitoring points,indicating that in addition to the influence of the nearby high-salt surface soil,the salt lake area also has certain Contribution.The NO₃^-is mainly affected by man-made pollution sources;(4)The basin was mainly affected by the westward airflow,and most of the airflow mainly passed through the salt lake area in the middle east and the northern foot of Kunlun Mountain on the southern margin of the basin.Combining factors such as the erodibility level of various types of topsoil,meteorological conditions and topography,comprehensive analysis suggests that the salt dust released by the deserts and saline meadow will only affect a local area,and the desert's contribution to the salt dust is relatively weak.However,the salt dust from Yardang and playa widely distributed in the Middle East of Qaidam Basin has a relatively large impact;(5)In addition,this study also conducted a rough assessment of salt deposition flux and potassium salt deposition flux,and found that at least 28,108 tons of various soluble salt components and more than 703 tons of potassium ions are contributed by the annual dust fall.Therefore,it is preliminarily believed that atmospheric dust can be used as one of the replenishment sources of salt-forming substances in salt lakes,which has obvious resource and environmental effects.