Increase in rare earth element concentrations controlled by dissolved organic matter in river water during rainfall events in a temperate, small forested catchment

Matsunaga, Takeshi; Tsuzuki, Katsunori  ; Yanase, Nobuyuki; Kritsananuwat, R.*; Hanzawa, Yukiko  ; Naganawa, Hirochika  

In a temperate, forested river catchment, distribution of dissolved rare earth elements (REE) during rainfall events was studied as analogues elements for transuranic nuclides. Concentrations of dissolved REE showed almost concurrent increases and decreases with the river water discharge during rainfall events. The concentration variations were tightly coupled with those of optical properties related to humic substances of dissolved organic matter (DOM). An ultrafiltration analysis revealed that colloidal REE present in 10 k - 30 kDa size fraction was the chief component for dissolved REE increase in high water flow condition. Shale-normalized concentration patterns of REE suggest an involvement of humic substances of DOM. A high correlation between size fractioned REE concentrations and specific ultraviolet absorbance suggests that aromaticity would be an essential property of DOM in regard to its complexation with dissolved REE in the studied river water.