Distribution Characteristics Of Uranium And Thorium Isotopes In Different Salinity Waters In Qinghai Lake Area With Its Environmental Significance

Radioactive isotopes of uranium series with different half-life are widely used in marine sediments,corals,and Cave Stalagmite,which is a timer in the global climate and environment process.Uranium nuclides in the lake water continuously release energy to carry out radioactive decay.This fractionation feature is not only affected by the water environment in the lake area,but also affected by exogenous substances.Through its distribution characteristics in water,it can indicate the changing process of climate and environment,which is of great value.This study investigated lakes with different salinities in the Qinghai Lake area,finally,lake waters on the horizontal and vertical scales of Qinghai Lake,Tuosu Lake and Gahai Lake were chosen as the research object.After obtaining uranium and thorium elements through enrichment,purification,separation and other chemical processes,isotope analysis was carried out using multi-receiver inductively coupled plasma mass spectrometer.The uranium content and isotope distribution in different salinity waters were shown:?1?The range of uranium content in 45 samples from horizontal and spatial scale at three vertical depth sections was 12.36¹4.14?g/L,with the mean value of 13.59?g/L,and(²³⁴U/²³⁸U)A.R was 1.876¹.892,and the mean value was 1.887.The range of uranium content of the 9 samples from Tuosu Lake was 35.15³5.77 ?g/L,the mean value was 35.48?g/L,and(²³⁴U/²³⁸U)A.R was 1.460¹.464,the mean value was 1.462.The range of uranium content of 10 samples from different station of Gahai Lake was 18.23¹8.53?g/L,with the mean value of 18.34?g/L,and(²³⁴U/²³⁸U)A.R was 1.791¹.796,with an average of 1.793.In the same lake,there is almost no difference that uranium content and(²³⁴U/²³⁸U)A.R at spatial scale and depth scale,as the distribution of uranium elements in the seawater,it presents a uniform state.Through the analysis of the correlation between the uranium content?TDS value,salinity and p H value of lake water,the content of uranium in the same lake has a positive correlation with TDS value and salinity,but the content of uranium in lake water is negatively correlated with p H value.?2?The overall distribution of uranium content in Qinghai lake is uniform,but there is a weak difference between the North Lake area,the South Lake area and the West Lake area.The relationship between uranium content is North Lake area > the South Lake area > the West Lake area.The relation of(²³⁴U/²³⁸U)A.R is the West Lake area > South Lake area > North Lake area.It shows that there are differences in the runoff,oxidation conditions and the lithology of the recharge area in the lake environment,it indicates that the Northwest Lake area has the best oxidation conditions and the strongest runoff conditions,and the source conditions of the Triassic strata are the most abundant,in contrast,the Southwest Lake area has poor oxidation conditions and runoff conditions,weak carrying conditions of provenance in Silurian strata.?3?Compared with three lakes,the TDS value?salinity and p H value at Lake Tuosu are not the highest,but the uranium content is about twice of the Qinghai Lake and Gahai Lake,it may be related to the uranium mine and high uranium minerals in mud volcanoes around the lake.Under high temperature and high pressure,the high uranium deposits were brokren up in the stratum and transported to the lake in the pores with groundwater,at the same time,in the condition of high dissolved oxygen in lake water,the content of uranium is high.The distribution of ²³²Th,total dissolved ²³⁰Th and ²³⁰Thxs in lake water were shown:?1?The content range of ²³²Th in Qinghai lake was 0.27¹5 pmol/kg,with an average of 2.21 pmol/kg,and the total dissolved ²³⁰Th was 0.07²0.55micro-Bq/kg,the mean was 8.95micro-Bq/kg.The content range of ²³⁰Thxs was 0.08²0.31 micro-Bq/kg and the mean was 7.59 micro-Bq/kg.The content range of the ²³²Th in Tuosu Lake was 0.64¹1.71 pmol/kg,with an average value of 9.03 pmol/kg,and the total dissolved ²³⁰Th was 10.55¹4.53micro-Bq/kg,with the mean of 12.53micro-Bq/kg,and the content range of Tuosu Lake ²³⁰Thxs was 4.29¹1.52micro-Bq/kg,and the mean value was 6.23 micro-Bq/kg.The content range of Gahai Lake ²³²Th was 8.33⁴4.94 pmol/kg,with an average value of 13.82 pmol/kg,the total dissolved ²³⁰Th in the range of 8.58⁴1.06micro-Bq/kg,the mean was 15.09micro-Bq/kg,and the content range of ²³⁰Thxs was 2.76⁹.65micro-Bq/kg,with the mean value of 5.44 micro-Bq/kg.In the three lakes,the relationship between ²³²Th content is Gahai Lake > Tuosu Lake > Qinghai Lake,the relationship between ²³⁰Thxs content is Qinghai Lake> Tuosu Lake > Gahai Lake.The more content of the ²³²Th from terrestrial clastic material,the content of total dissolved ²³⁰Th in the the lake is much higher than autogenic ²³⁰Thxs??2?The ²³⁰Thxs content of 107 and 123 stations in three depth sections of Qinghai Lake shows an upward trend of fluctuation with water depth,which is similar to that of ²³⁰Th in ocean water and indicates that there are certain particulate matter purification and scavenging effects in the lake.However,the ²³⁰Thxs content of the 131 station located in the southern area of the lake area fluctuated downward with the water depth,and the mean ²³⁰Thxs content was 11.89micro-Bq/kg,which was significantly higher than average content of ²³⁰Thxs at 107 and 123 stations.It shows that the scavenging effect of particles in the lake area is very weak or there is a rapid removal of large particles,so it is mainly influenced by the particle properties of the lake water in the region.?3?The ²³²Th content of Qinghai Lake,Tuosu Lake and Gahai is related to salinity.It can be pointed out that the climate drought and weathering degree are strong or weak.The more the ²³²Th in the exogenous clastic rock is brought into the lake,the more arid the climate is,the higher the amount of evaporation and weathering.Qinghai Lake has the highest precipitation amomg the three lakes,with the lowest evaporation capacity and weathering degree,and the drought and weathering degree of the Gahai and Tuosu lake in Delingha basin is higher than that in Qinghai Lake.Around the Buha river estuary in the northwest of Qinghai Lake has higher content of ²³²Th,and the ²³⁰Thxs content may from Quaternary loose clastic rock in the south of the lake area is obviously higher,which indicated that under the prevailing northwest wind,the weathering degree of the surrounding rock in the Northwest-southeast Lake region is higher.