柴达木盆地大气降尘可溶盐物源探讨及其资源与环境影响

Sources of soluble salts in dustfall and their impact on resources and environment in the Qaidam basin

位于干旱和半干旱地区的湖泊,在气候变化和人为干扰作用下大片干涸湖床暴露出来成为重要的粉尘源区,引发了一系列的生态环境和健康问题,引起了广泛的关注。青藏高原在全球气候和生态环境变化中具有重要作用,柴达木盆地是青藏高原重要组成部分,盆地内气候干旱,多风少雨,盐湖众多,盐渍化和盐漠化表土极为发育,是青藏高原沙尘暴频发地区之一。同时柴达木盆地沙尘气溶胶中可溶盐含量较高,这些高含盐粉尘不仅会造成盆地表土盐渍化范围扩大,而且还会通过影响盆地上空云的形成进而对气候产生重要作用。进一步,这些细颗粒粉尘在进行远距离输送的过程中,还可能会影响到青藏高原乃至全球的气候及生态环境变化。为此,本研究拟对柴达木盆地南部大气降尘中可溶盐组分及时空分布规律开展研究,以期理解含盐降尘对区域盐类资源的富集与生态环境的影响。在柴达木盆地南部大致沿着主导风向自西向东共安置8个集尘装置,并对收集的降尘中盐类矿物和化学成分开展分析,同时结合盆地不同表土类型的可溶盐组成、空间分布特征及格尔木市、都兰县后向轨迹分析开展进一步讨论。研究结果表明,降尘中主要的可溶盐成分(Na^(+)、Cl^(-)、Ca^(2+)、SO_(4)^(2-)、Mg^(2+)、K^(+)、NO_(3)^(-)、Li^(+)、B^(3+)(B_(2)O_(3))、Sr^(2+)等)含量介于2.27%~20.92%之间,其中,Na^(+)、Cl^(-)、Ca^(2+)、SO_(4)^(2-)这四种离子占全部水溶性离子的74%~95%,主要以石盐和石膏的形式存在。在空间分布上,可溶性矿物和水溶性离子含量均表现为:在河西八连和巴隆乡含量较高,在诺木洪含量达到最低值。2020年1~4月,盆地主要受偏西气流的影响,并且大部分气流经过位于中东部的一里坪、台吉乃尔湖区和盆地南缘昆仑山北麓。对比研究区表土和降尘化学组分得到,盆地南部降尘中的水溶性离子主要来源于自然表土,Mg^(2+)、K^(+)、Li^(+)、B^(3+)(B_(2)O_(3))这些离子在个别采样点明显富集,除了受到附近高含盐表土的影响外,盐湖区也会对其产生一定的贡献;而NO_(3)^(-)主要受人为污染源的影响。综合分析认为,在潜在物源、风动力条件和地形地貌等因素的影响下,分布在盆地内的沙漠和盐化草原释放的盐尘仅对局部范围造成影响,并且沙漠对盐尘的贡献相对微弱,而盆地中东部广泛分布的雅丹、盐滩释放的盐尘影响范围较大。此外,本研究还对盐沉积通量、钾盐沉积通量进行了粗略的评估,得到每年降尘至少贡献各类可溶盐组分约为28108多t,钾离子703多t。因此,初步认为大气降尘可作为盐湖成盐物质的补给源之一,具有明显的资源与环境效应。

In arid and semi-arid areas,due to climate change and human disturbance,lakes have gradually shrunk,exposing large areas of dry lakebeds that become important dust sources,triggering a series of ecological environment and health problems causing widespread concern.The Qinghai-Tibet Plateau plays an important role in global climate and ecological environment changes.Strong winds prevail in the arid Qaidam basin,an important part of the Qinghai-Tibet Plateau that hosts numerous salt lakes,with well developed topsoil salinization.It is one of the areas with frequent sandstorms on the Qinghai-Tibet Plateau.At the same time,the dust aerosol in the Qaidam basin has a relatively high soluble salt content,which will not only cause the expansion of the surface salinization,but also have an important effect on the climate by affecting cloud formation over the basin.Furthermore,the long distance transport of these fine particles may have an important impact on the Qinghai-Tibet Plateau,and even affect the global climate causing ecological environment changes.Therefore,the characterization and temporal-spatial characteristics of soluble salts of dustfall were analysed in the southern Qaidam basin.The objectives were to estimate the impact of soluble salts of dustfall on the enrichment of regional salt resources and the ecological environment.A total of 8dust collection devices were installed in southern Qaidam basin from west to east along the dominant wind direction.The collected dustfall was analyzed for salt minerals and chemical composition.At the same time,the soluble salt composition and spatial distribution characteristics of different surface soil types were combined with the distribution characteristics of the backward trajectory in Golmud City and Dulan County for further discussion.The results show that the soluble salt of dustfall(Na^(+)、Cl^(-)、Ca^(2+)、SO_(4)^(2-)、Mg^(2+)、K^(+)、NO_(3)^(-)、Li^(+)、B^(3+)(B_(2)O_(3))、Sr^(2+) etc.)were in the range of 2.27%~20.92%,of which these four ions(Na^(+),Cl^(-),Ca^(2+),SO_(4)^(2-))account for 74%to 95%of all water-soluble ions.These four ions mainly exist in halite and gypsum.In terms of spatial distribution,the content of soluble minerals and water-soluble ions are both higher in Hexi Balian and Balong Townships,and the lowest in Nomhon.From January to April in 2020,the basin was mainly affected by the westward airflow,most of which passed through the Yiliping,Taijinar Lake area in the middle east and the northern foothills of the Kunlun Mountain on the southern margin of the basin.Comparing the surface soil and dust fall chemical composition in the study area indicates that the water-soluble ions of the dustfall are mainly derived from the natural topsoil.Mg^(2+),K^(+),Li^(+)and B^(3+)(B_(2)O_(3))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 provides some contribution.The NO3-is mainly affected by man-made pollution sources.Comprehensive analysis suggests that under the influence of factors such as potential sources,wind conditions,topography and geomorphology,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 the Qaidam basin has a relatively large impact.In addition,this study also conducted a rough assessment of salt deposition flux and potassium salt deposition flux,and found that at least 28108tons of various soluble salt components and more than 703tons of potassium ions are contributed by the annual dust fall.Therefore,it is hypothesized 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 impact.