[Ultraviolet-visible (UV-Vis) spectral characteristics of dissolved organic matter (DOM) in soils and sediments of typical water-level fluctuation zones of Three Gorges Reservoir areas].

Dissolved organic matter (DOM) is a very important component in terrestrial ecosystem, which also plays a key role in geo-environmental chemistry. A number of DOM samples were extracted from soils and sediments samples obtained from typical water-level fluctuation zones of Three Gorges reservoir areas. Ultraviolet-visible (UV-Vis) absorption spectra were recorded for unveiling the geochemical characteristics of DOM based on specific absorption parameters and fitting models. Through the results of specific absorption parameters, it was suggested that the aromaticity, hydrophobicity and humification degree were lower in soils than in the surface sediments, which were also independent of the sampling location height and land-use types. Among the four absorption models selected, model 2 was the optimal. Meanwhile, different models and fitting wavelengths also significantly affected the absorption spectral slope (S value): S increased with the decreasing wavelength. Additionally, the correlation among different S values obtained from different fitting wavelength ranges was significantly different suggesting that the S values in various wavelength ranges only indicated the tip of the iceberg of DOM characteristics instead of the entirety. Furthermore, the ratio of specific spectral slope (S(R)) indicated lower degradation (photo-bleaching or microbial degradation) degree in the surface sediments as compared to those in soils and older sediments. The surface sediments had higher aromaticity, hydrophobicity, molecular weight and photochemical/ biodegradation activity potentials, suggesting fresher DOM, lower effect of photobleaching and microbial degradation activities.