Geochemical Characteristics Of Trace Elements And Rare Earth Elements In The Sediments Of Lake Ah

With the rapid growth of population and the acceleration of urbanization in the world,trace elements and rare earth elements are widely used in industrial,agricultural and medical industries,resulting in a significant increase in their access to the environment,thus affecting the quality of urban water environment.Aha Lake is an important water source protection area in Guiyang City,and human activities such as coal mining,agricultural activities and urban activities in the basin in recent decades have had a noticeable impact on its water ecological environment.In this study,the sediments of Aha Lake in Guiyang City were taken as the research object,and the surface and columnar sediment samples of Aha Lake were systematically collected.The contents of rare earth elements and trace elements were determined by inductively coupled plasma mass spectrometry（ICP-MS）,and the geochemical analysis was carried out.The results showed that in the surface sediments,Cd exceeded the soil background value of Guiyang by up to 3.63 times,and V,Cu and Pb did not exceed the background value,while the average contents of Co,Zn,As,Mo,Cd and Sb exceeded the background value,indicating that they were jointly affected by natural weathering and human input.The spatial differences of trace elements were obvious,and the overall content was higher in Youyu River,Baiyan River and Jinzhong River.The results of Nemerow index method,geoaccumulation index method,pollution load method and comprehensive potential ecological risk assessment showed that Cd was the most polluted element,and the trace element pollution in the inflow area of Youyu River tributary was the most serious.In the columnar sediments,the contents of trace elements in the inflow areas of the Jinzhong River and Youyu River increased from deep to shallow,which was consistent with the gradual increase of human activities in the two tributaries in recent decades.The accumulation and ecological risk of trace elements in sediments of20～30 cm were the highest,which was consistent with the relative enrichment of trace elements in this sedimentary period,which was related to the strong coal mining activities in the same period.The contents of 14 rare earth elements in the surface sediments of Aha Lake varied greatly,ranging from 0.15 to 99.20 mg/kg,while∑REE ranged from 69.55 to258.21 mg/kg.The rare earth element distribution patterns of surface sediments and each sedimentary column were basically the same,showing a right-leaning distribution pattern of relatively enriched light rare earth elements（LREE）,relatively depleted heavy rare earth elements（HREE）and weak Eu negative anomaly.The standard distribution pattern of chondrite,geochemical parameters of rare earth elements and discriminant function DF analysis showed that the weathering of soil and bedrock in the basin was the main contribution of rare earth elements in the sediments of Aha Lake.Tracer analysis based on LREE/HREE,（La/Yb）_CN,Ce_anomaly,（La/Gd）_CNand（Gd/Nd）_CNshowed that LREE was more enriched in the sediments of Jinzhong River and Yahe River which were greatly affected by urban wastewater,while MREE was more enriched in the sediments of Youyu River and Baiyan River which were affected by coal mine wastewater.These parameters may have the potential to indicate that the sediments of Aha Lake were affected by human activities such as urban wastewater and coal mine wastewater.In addition,∑REE,Ce_anomalyand Eu_anomalywere correlated with total trace element content and accumulation index of trace elements,which could be used as indicators of trace element pollution in sediments of Aha Lake.This study can provide basic data for future studies using rare earth element parameter tracing,and is of great significance for formulating corresponding pollution prevention and control measures and protecting water resources of Aha Lake.