Spectral Characteristics And Photodegradation Of Soil Dissolved Organic Matter In The Small Watershed Of The Central Dianchi Lake

Dissolved organic matter(DOM) is an organic compound with different structure and molecular weight. It was universal in the natural environment and played an important role in the energy cycle and the migration of pollutants.Ultraviolet-visible(UV-vis) and the three-dimensional excitation emission matrix fluorescence (3D-EEM spectroscopies, combined with parallel factor analysis(PARAFAC) were conducted to investigate the structure and origin of 72 DOMs extracted from upper soils around Dianchi lake basin, Kunming. The results showed that the characters of all samples' UV-visible spectra were similar. The absorption coefficient of DOM samples decreased gradually with the wavelength increasing. There was an obvious shoulder absorption peak in the 250-280nm band.Additionally, in Chaihe reservoir and the east of Dianchi lake, the aromaticity(A250/A365), molecular weight(SR), humification degree(SUVA254) and hydrophobicity(SUVA260) of soil's DOM were all much higher than those at other three sampling sites. The 3D-EEM spectrum revealed that all DOM samples around Dianchi lake had four special peaks, which were UV fulvic-like fluorescence, visible fulvic-like fluorescence and two humic-like fluorescences. Fluorescence index(FI)and Autochthonous index(BIX) were suggested that soil's DOM were main from the external import and had low protein-like components and bioavailability. Four fluorescence components were dentified by parallel factor analysis and showed significant correlation(P<0.01),which were illustrated that the four fluorescence components had a similar source. In addition, the contribution rates of fulvic-like fluorescence component was the highest, which was suggested that the content of fulvic acid material was relatively higher in soil's DOM.Three upper soil's DOMs around Dianchi lake basin were conducted in laboratory to investigate the degradation of matter and structure under three light illuminations by using UV-vis and 3D-EEM spectroscopies. The results showed that:(1)the absorption coefficient,concentration(DOC) and four fluorescence peaks intensity(Peak A,C,D and E) of soil's DOMs were degraded under UV-light illumination;(2)fulvic-like and humic-like materials' degradation degree were higher because they were colored macromolecule components and more sensitive to UV-light;(3) the spectral slope ratio (SR) were increased and humification degree(SUVA254) were decreased under UV-light illumination,Which can be used as important indicators for DOM's structure changes;(4)the rise of BIX values suggested that the terrigenous characteristics of soil's DOMs transferred to autochthonous characteristics due to UV-light illumination;(5) owing to the original structure and optical properties, the FI values of soil's DOMs had no obvious change under the UV-light illumination;(6)the photodegradation of DOM had a significant positive correlation with ammonium concentration;(7)all indexes were not significantly changed under dark condition.