| As the zone where the transition between land and water converges, the water-level-fluctuating zone (WLFZ) has a sensitive and fragile ecosystem. This could result in a series of ecological and environmental problems in the WLFZ as well as the Three Gorges Reservoir (TGR). Dissolved organic matter (DOM) plays an important role in the migration and transformation of pollutants. DOM may interact with trace heavy metal ions, influencing their migration and transformation at the land and water interface, their toxicity and their bio-availability. Therefore, the study on physical and chemical characteristics of DOM in the WLFZ soil is the important part of prevention and control of ecological environmental problems in the WLFZ, TGR. So in this paper, the author selects soil samples in the WLFZ of Kai County, from the analysis of Three-dimensional fluorescence spectral of soil DOM, making conclusions as follows:(1) Extraction of soil DOM used freeze-drying soil samples, and samples were shaken for 16 h. Samples were kept in a refrigerator at 4°C.(2) Soil DOM from the WLFZ of Kai County was found to contain four fluorescence peaks: peaks A and C, which represent humus-like fluorescence, and peaks B and D, which represent tryptophan-like fluorescence. Two additional peaks, E and F, which represent tyrosine-like fluorescence, were only present in certain soils. Analysis of location of the soil DOM fluorescence peaks showed that the fluctuations of the position of peak A, B, D, F varied greatly, and that of peak C, E was not large. Analysis of soil DOM fluorescence intensities showed that soil humus was the main source of soil DOM, and the humus-like material in the soil DOM from the WLFZ was mainly humic substances of large molecular weight.(3) Analysis of soil DOM collected from January to July, 2009 showed that the humic-like substances increased, tryptophan-like and high-wavelength tyrosine-like substances reduced in the studing period, and low-wavelength tyrosine-like substances had no change. This indicated the potential ability of release in to the overlying water of humic-like substances were stronger.(4) Analysis of soil DOM from the WLFZ along the flow of XiaoJiang showed the changing trend of Peak A, C, D fluorescence was similar; Peak B, E and F had no obvious rule. Analysis of soil DOM from the six towns showed that the changing trends of fluorescence intensity of humic-like in the six towns were the same, and there was no obvious difference between the content of humic-like in the six towns; The changing trends of fluorescence intensity of tryptophan-like and tyrosine-like in the six towns were different, and there was significantly difference between the content of that in the six towns. The comparison of the fluorescence intensities of soil DOM in submerged soil and in exposed soil showed that the fluorescence intensities of peaks C and D were greatly influenced by the water level fluctuations, and there was more DOM in the exposed soil than the submerged soil of the WLFZ. Analysis of the HIX values in submerged and exposed soil DOM indicated that the soil DOM in exposed areas had a higher degree of humification and aromaticity, and periodic submerging and exposure of soil had an impact on the humification of DOM.(5) The fluorescence intensity ratios of soil DOM in the WLFZ showed that WLFZ soil was not polluted badly, and the soil DOM contained at least two types of humus-like fluorescence groups and two types of protein-like fluorescence groups. Analysis of the correlations between the fluorescence intensities of the different peaks showed that the fluorescence intensities of peaks A and C had a good correlation, the tryptophan-like fluorescence peaks B and D had a poor correlation and tyrosine-like fluorescence peaks E and F had some correlation. A good correlation between the humic-like fluorescence peak A and the protein-like fluorescence peaks E and F. The intensities of fluorescence peaks of soil DOM and SOM had some correlation.(6) The humic-like and protein-like fluorescence matter of soil DOM were strong organic ligands of Cd (Ⅱ), Pb (Ⅱ) in the WLFZ, and the ability that Cd(Ⅱ) and Pb(Ⅱ) combined with fulvic acid (small molecular weight) was stronger than that of humic acid (large molecular weight). The combined ratio of fluorophores between Pb(Ⅱ) and soil DOM was larger than that of Cd(Ⅱ) in Zhenan town, indicating that Pb(Ⅱ) could easily migrate and convert with the purple soil DOM. Cd(Ⅱ) could easily combine with humic-like fluorescence matter of sandy soil DOM, and Pb(Ⅱ) could easily combine with protein-like fluorescence matter. In the sandy soil of the WLFZ, Cd(Ⅱ) and Pb(Ⅱ) could easily migrate or proliferate to the water environment. The ability that Cd(Ⅱ) and Pb(Ⅱ) combined with protein-like fluorescence matter was stronger than that of humic-like fluorescence matter in the sandy soil of the WLFZ.The research results of the paper can provide the basic data and theoretical basis for the study of the characteristics and the migration and transformation of the DOM in the WLFZ of the TGR. It can also provide a theoretical basis for control ecological and environmental problems in the WLFZ. |
