Abstract: Submarine groundwater discharge is a significant source of the rare earth elements (REEs) in the coastal waters, studies on the geochemistry of REEs in the groundwater are very limited. In this study, the distribution, influencing factors and complex speciation of dissolved REEs in the groundwater of Dagu River Basin in Shandong Province were examined by field investigation and simulation. The conclusions have been obtained as follows: the distribution of REEs in groundwater has a great spatial variation, pH and the reductive dissolution of Fe, Mn oxides/hydroxides may be the important factors affecting the concentration of rare earth elements. The REEs speciation mainly exists as LnCO+3 and Ln(CO3)-2. However light rare earth elements are more likely to form LnSO+4 than middle rare earth elements and heavy rare earth elements in the case of high sulfate. And the patterns of the REEs generally show heavy rare earth elements enrichment in groundwater, the preferential adsorption of LnCO+3 by electronegative particles in the aquifer may be the reason for heavy rare earth elements enrichment. Affected by surrounding refineries, all samples have positive lanthanum anomalies. The proportion of anthropogenic lanthanum in fresh groundwater and recirculated seawater are 34%-75% and 42%-57%, respectively.

Key words: Dagu River Basin, groundwater, rare earth elements, anomalies