运用紫外光谱、 三维荧光光谱技术结合平行因子分析法(PARAFAC)探讨了pH值对滇池水体环境中溶解性有机质(DOM)光化学降解特性(紫外光谱特征、 荧光组分及其荧光强度)的影响。 掌握了不同pH值条件下DOM光化学降解特性及其差异性, 可为DOM的生物地球化学循环基础数据提供有利支撑, 同时对富营养化湖泊水质改善和有效控制具有重要的启示作用。 结果表明, 在光降解发生过程中(0～30 d), DOM被识别出具有三个主要荧光组分, 分别为长波类富里酸组分C1(325, 425 nm), 类蛋白类组分C2(295, 390 nm)和具有高芳香度特性的类腐殖质组分C3(260/350, 360/450 nm); pH值的变化对DOM光降解过程中的紫外光谱和三维荧光光谱特征均产生重要影响; 当pH值从4.0增加到9.0, DOM的紫外吸光系数随pH值增大而增大, 总荧光强度随pH值增加而逐渐下降; 类蛋白组分C2从降解的第8天开始, 其荧光强度也表现出随pH值增加逐渐下降的趋势, 这表明高pH值能够促进水体DOM的光降解作用。 鉴于pH值能够对DOM光降解过程及其紫外光谱和三维荧光光谱特征产生重要影响, 研究认为, 对比不同来源DOM(自然水体、 DOM提取物等)的紫外光谱、 三维荧光光谱和平行因子分析结果时, 应监测并报告DOM溶液的pH值, pH值应尽量保持一致, 以保证结果的可比性。

The effects of pH values on the characteristics of photochemical degradation of dissolved organic matter (DOM) from Dianchi Lake by using UV-Visible absorption and three-dimensional excitation-emission matrix fluorescence spectroscopy (EEMs) combined with parallel factors analysis (PARAFAC) were investigated in the present study. The photochemical degradation characteristics and differences of DOM under different pH values can provide useful support for the basic data of biogeochemical cycle of DOM, and have important enlightenment for the improvement and effective control of water quality in eutrophic lakes. Three fluorescent components were identified during the process of photo-degradation of DOM (30 days), based on the split-half validation procedure. The three components identified from the fluorescence spectra were a fulvic-like fluorescence component C1 (325, 425 nm), a protein-like component (C2) (295, 390 nm) and a humic-like component (C3) (260/350, 360/450 nm)with high aromaticity. The change of pH values had important influences on the characteristics of absorption and EEM spectra of DOM in the process of photo-degradation. The results showed that the absorption coefficients of DOM increased and total fluorescence intensity decreased gradually with the increase of pH value from 4.0 to 9.0. During the 8～30 days incubation period, the intensity of fluorescent component C2 showed a trend of gradually decrease with the shift of pH value from 4.0 to 9.0, which suggested that high pH value can potentially promote photodegradation of DOM. The influences of pH values on the photo-degradation, absorption and fluorescence spectra emphasize the need for pH to be monitored and accurately controlled. It is also highly recommended that when we contrast the absorption and fluorescence data or constructing PARAFAC models among samples with different origins, the pH should be held constant to remove any potential interference of data.