Spectral Characteristics of Dissolved Organic Matter (DOM) Releases from Soils of Typical Water-Level Fluctuation Zones of Three Gorges Reservoir Areas:UV-Vis Spectrum

Abstract

Water-level fluctuation zone is an important area in Three Gorges Reservoir areas, because dissolved organic matter (DOM) releases from submerged soils is a crucial source of DOM in overlying waters when flooding occurs. But there was little qualitative and quantitative analysis for DOM. In this study, soils of four typical water-level fluctuation zones were selected to conduct simulated flooding experiment. Also, UV-Vis spectroscopy was utilized to investigate the DOM spectral characteristics in two individual flooding sets including ambient (open air) and anoxic conditions. The results showed, for all soils, the DOM release patterns all showed a "rapid release, then decrease, and final dynamic equilibrium" trend. Also, through calculations of DOM releasing rates and fluxes, DOM releases clearly showed a feature of "source-sink dynamic exchange". By comparison between two flooding treatments, although DOC and CDOM didn't show any significant differences, but higher aromaticity (SUVA280) was observed in anoxic experiment. In contrast, spectra slope ratio (SR) was insensitive to redox conditions of different flooding. Meanwhile, correlation between DOC and CDOM in anoxic was also higher than that in ambient flooding. Additionally, obvious differences among soils from different sampling sites were observed, Shibao Zhai (SB) of which showed the greatest releasing potential. Considering the various soil properties, soil organic matter amounts in soils is one of the key factors to explain the differences among sampling sites, but other geochemical factors should also be considered in the processes of DOM releases. Summarily, only focusing on the changes of DOC concentrations in submerging process is not enough to comprehensively describe the DOM release characteristics.