| Dissolved organic matter (DOM), which is ubiquitous in almost all of the natural waters (e.g. sea and ocean, river, lake, bog water and ground water), was widely studied because of its significant role in shaping the aquatic environments since last decade. DOM influences a wide variety of physical, chemical and biological processes. Light absorption by DOM has a strong influence on the penetration of ultraviolet and photosynchetically active radiation. DOM mainly comprises organic acids and, therefore, affects pH of the waters and in some acidic waters acts as a buffer. The interactions between DOM and metal ions, organic pollutants influence their concentrations, transportation, toxicity and bioavailability. DOM acts as a large organic carbon reservoir exchanging with the atmosphere, where carbon (as CO2) plays as important role in climate regulation. All of these provide very good reasons for acquiring a better understanding of the origin, composition and structure features of DOM and the role it plays in geochemical processes.In this paper, analytical methods such as three-dimensional excitation emission matrixfluorescence spectroscopy (3DEEM), UV-Vis absorbance, and high performance sizeexclusion chromatography were selected to investigate the physical and chemicalproperties and seasonal variations of DOM in lake waters (Lake Hongfeng, Lake Baihua),lake sediment porewaters and DOM in Nanming River watershed. The complexationbetween DOM and metal ions were also investigated by using 3DEEM and fluorescencequenching titration. The followings summarize the results from this study:1. 3DEEM was; applied to the fluorescence properties of a commercial humic acid fromFluka (Sigma-Aldrich). Results show that EEMs of Fluka humic acid have severaldifferent Ex/Em peaks. Ionic strength in the range of 0~0.05 M KClO4 had littleeffects on the fluorescence spectral characteristics of Fluka humic acid, while theconcentrations of HA (5 mg/L~100 mg/L) and the solution pH (2~12) hadsignificant effects. A red shift in the longer wavelength peak region was observed byincreasing both concentration and pH, respectively. In general, the fluorescence intensity increases with increasing pH, then a slight decrease when pH≥10. For the fulvic-like fluorescence peak B (HA: 50 mg/L or 100 mg/L), the maximum fluorescence was appeared at pH 5.0, which has been previously reported. The calculated protonation constant logK'HL values are 3.57 and 3.13, the r(a/B) values are ranging 0.61 ~ 1.71 and 0.62~2.59, respectively. Also a linear relationship was found between r(A/B) and pH.2. The DOC concentrations, UV-Vis absorbance, fluorescence and molecular weight of sediment porewater DOM in Lake Erhai were investigated. DOC concentration had a high value at the sediment-water interface with a sharp decrease to the depth of 6 cm, and then increases with depth. The vertical distributions of a254, a280 and fluorescence intensity at Ex=335 nm were in agree with the distribution of DOC. The E3/E4 values ranged from 1 to 6 and most of the values were less than 3.5, which meant that the DOM in sediment pore water had relatively high humification, aromaticity and molecular weight. f450/500 values ranged 1.48-1.59, showing the terrestrial nature of the majority of sediment pore water DOM. Of ail the samples analyzed in this study, pore water DOM was found to contain four fluorescence peaks. Peak A and C represent humic-like fluorescence, while peak B and D represent protein-like fluorescence. The fluorescence intensity of these peaks were all strong at the sediment-water interface with a sharp decrease at a depth of 1 cm, then increased with depth. The strong protein-like fluorescence of the porewater DOM increased with depth, suggesting that there had a conservative behavior during early diagenesis. The values of r(A,C) ranged 0.94-1.79, r(D,B) ranged 0.90-1.75. Both r(A,C) and r(D,B) decreased slightly with depth and their close values, indicating that there was a strong relationship between them for the DOM samples from sediment pore wate...
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