GEOCHEMICAL FEATURES OF RARE EARTH ELEMENTS IN SEDIMENTS OF THE CHAOHU LAKE AND ITS ENVIRONMENTAL IMPLICATIONS

A sediment core (named CHX hereafter) was collected from the center of the western Chaohu Lake. The concentrations of rear earth elements (REEs) in different layers of the core were analyzed using ICP-MS. The results show that the mean concentration of REE in the samples is (234.7±17.9) μg/g (n=71), slightly greater than that of the average crust. It is also found that the light REE concentrations in the sediments are evidently higher than the heavy REE, and the ratio of light REE to heavy REE (ΣLREE/ΣHREE) averages 9.7. In addition, the feature of Eu shows obviously negative anomaly, but Ce shows slightly positive anomaly in the core CHX. Chondrite normalized REE distribution pattern of the sediments is characterized by the enrichment of light REE. The lake deposits can be divided into two sedimentary layers. For the sediments below the depth 30 cm, the contents of REE and clay minerals are significantly and positively correlated. It is identified that grain size is the controlling factor for REE distribution, and this reflects the control of natural factors on the REE concentrations. In contrast, REE contents and ΣLREE/ΣHREE values in the sediments above 30 cm depth are significantly higher than those below, and the level of REE is no longer controlled by clay concentration. In combination with ²¹⁰Pb-dating, it is found that the content of REE have been increasing over the last 200 years. This may reflect the increasing impact of modern human activities on the sediments, and the decrease in ΣREE in most recent sediments is perhaps caused by optimization of energy structure and dramatic increasing of fishery catches.