[Vertical Distribution Characteristics of Dissolved Organic Matter in Groundwater and Its Cause]

Dissolved organic matter (DOM) can change the species, migration and transformation of foreign pollutants in groundwater, and the investigations of its composition and distribution characteristics play a role in environment protection. The groundwater DOMs were obtained at the depths of 1.2, 1.5 and 1.8 m, and its origin, composition, concentration, distribution characteristics and influencing factors were studied using UV-Vis and fluorescence spectra combined with parallel factor analysis and principle components analysis. The results showed that, DOM in the groundwater originated from both terrigenous input and microbial activities, and was comprised of humic-like matter, heterogeneous component, and protein-like matter. Humic-like matter and heterogeneous components showed a high concentration at 1.5 m and a low one at 1.2 m, whereas the protein-like matter exhibited a low concentration at 1.5 m and a high one at 1.2 m. The groundwater DOM at 1.5 m exhibited the highest aromaticity, humification, molecular weight and polar functional group content, while that at 1.2 m depth showed the lowest aromaticity, humification, molecular weight and polar functional group content. The vertical distribution of DOM in groundwater was related to aromaticity, humification, molecular weight and polar functional group, and the DOM with high aromaticity, humification, molecular weight and polar functional group resisted to biodegradation, and could easily enter into the bottom layer groundwater.