Origin of dissolved organic matter in deep groundwater of marine deposits and its implication for metal binding

海洋堆積物由来の深部地下水中の溶存有機物の起源と金属結合への影響

斉藤 拓巳*; 西 柊作*; 天野 由記   ; 別部 光里*; 宮川 和也   

Saito, Takumi*; Nishi, Shusaku*; Amano, Yuki; Beppu, Hikari*; Miyakawa, Kazuya

Dissolved organic matter (DOM) plays important roles for the fate of contaminants and nutrients in the nature. Nevertheless, our understanding on DOM in deep groundwater is limited. This study tackled this issue by intensive groundwater sampling at various depths of an underground research laboratory. The origin and the binding properties of different fluorescent DOM components against Eu(III) were studied by fluorescence emission-excitation-matrices (EEMs) and parallel factor analysis (PARAFAC). Four components with distinctive fluorescent properties were obtained by PARAFAC: one marine humic-like component, two terrestrial humic-like components, and one protein-like component. It was revealed that Eu(III) strongly bound to the terrestrial humic-like components but less so to the marine humic-like component. The partial least squares (PLS) regression further revealed the origin and distributions of the components. It was suggested that microbial decomposition of the DOM components, the input of marine humic-like component from sedimentary rocks and mixing of fossil meteoric and sea waters determined their spatial distributions and affinities to Eu(III). These results indicated the dynamic nature of DOM in deep groundwater of marine deposits and provided an important insight to discuss their impacts on the migration of contaminants and nutrient in deep underground environments.