Occurrence, fractionation characteristics and human activities impact of rare earth elements in the water and sediment of coal mining subsidence lakes in eastern China.

Surface water and sediment rare earth elements (REEs) concentrations can reflect the impact of human activities on aquatic ecosystems. Variations in formation time may result in changes in the geochemical characteristics of REEs in the water‒sediment system of coal mining subsidence lakes. However, our understanding of this phenomenon is limited. The spatial distribution, coexistence patterns, and fractionation characteristics of REEs were investigated in coal mining subsidence lakes with different subsidence times in the Huainan coalfield in eastern China. The results indicate that REEs concentrations in lake water are relatively low. Both compartments are enriched in light rare earth elements (LREEs), and the degree of enrichment increases with time, which can be attributed to the combined influences of natural processes and human activities. Under alkaline water conditions in the study area, LREEs are preferentially removed from the aqueous phase, leading to their enrichment in sediments. The anomalous behavior of Ce is associated with the oxidative environment under alkaline conditions, whereas the Eu anomaly is influenced primarily by the dissolution of feldspar minerals. Agricultural activities result in significant inputs of light rare earth elements (La) to farmlands each year through the application of rare earth fertilizers. These elements are ultimately released into coal mining subsidence lakes, resulting in noticeable anomalies of La in the majority of lakes within the study area. These findings indicate that the lakes in the subsidence area are strongly affected by agricultural activities. The difference between lakes with different numbers of sinking years is reflected mainly in the degree of enrichment of LREEs, and the older the lake is, the greater the degree of enrichment of LREEs. These research results provide a scientific basis for the treatment and protection of the water environment in coal mining subsidence lakes influenced by anthropogenic activities. Through this series of studies, we will improve our understanding of the behavior of REEs in the aquatic environment under the influence of human activities and to provide support for sustainable mineral resource development and environmental protection policy formulation. [ABSTRACT FROM AUTHOR]