Liu, Guo, and Wu (2017) report that groundwater samples were taken from five couple wells of salty-mixed irrigation (SMI), Hengshui test site (HTS) wells and surface drainage, in order to characterize REE geochemistry of different waters and determine mixing ratio of deep groundwater to shallow groundwater. Results showed that shallow groundwater had similar total REE concentrations (58.8-167.1 ng/L, average 119.1 ng/L) to deep groundwater (48.0-216.1 ng/L, average 107.9 ng/L), while surface waters generally showed higher values (162.4-257.7 ng/L, average 193.3 ng/L). Fractionation between light and middle REEs (R(M/L)) and between middle and heavy
REEs (R(H/M)) showed that all groundwater samples were consistently depleted in light REEs, with the largest enrichment in middles REEs (0.68<R(M/L)<0.92, average 0.82) being observed in surface waters, followed by shallow groundwater (0.55<R(M/L)<0.75, average 0.75) and deep groundwater (0.35<R(M/L)<0.66, average 0.55), although comparable enrichment in heavy REEs was found in shallow (0.37<R(H/L)<0.50, average 0.44) and deep groundwater (0.29<R(H/L)<0.55, average 0.43).
The variations in aqueous REE patterns demonstrated that surface water was preferentially accumulated in middle and heavy REEs over light REEs; shallow groundwater increasingly enriched in heavy REEs was possible due to interactions with aquifer sediments during infiltration; deep groundwater showed decreasing enrichment in middle REEs when receiving recharges from shallow groundwater, although heavy REEs enrichment degree exhibited different trends, likely because of difference in solution
complexation. Mixing calculation showed that shallow groundwater recharge consisted of about 40% of deep groundwater. This investigation would help in effectively managing groundwater resources for sustainable development in the NCP under the great influence of human activities.
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