小球藻来源溶解有机质的光化学降解特性

利用三维荧光光谱-平行因子分析(EEM-PARAFAC)手段结合吸收光谱分析,研究了小球藻指数期和稳定期培养液中溶解有机物(DOM)在秋季天然太阳辐射作用下的光降解动力学特征.结果表明,小球藻生长过程中除能产生短波激发类腐殖质组分C1(其荧光峰的激发/发射波长位置为240,335 nm /406 nm)及类蛋白质组分C3(225,275 nm/334 nm)外,还会形成长波激发类腐殖质组分C2(260,395 nm /502 nm),表明C2组分并非仅有传统认为的陆源属性,同时也具有自生源属性.稳定期培养液的吸收光谱在250~300 nm范围内出现的肩峰,可用于指示水环境中现场自生源的贡献.不同生长时期培养液中DOM的吸收系数和荧光组分的降解动力学都符合一级反应方程.稳定期类腐殖质荧光组分(C1和C2)的光降解程度略高于指数期,但指数期类色氨酸组分(C3)的光降解程度略高于稳定期.经太阳辐照6 d后,小球藻培养液的吸收系数a₃₅₀及各荧光组分的平均损失率分别达到83.0%、84.0%、64.8%和80.0%,对应的半衰期只有1.6~5.0 d,揭示出藻类自生来源的DOM具有很强的光化学降解活性.

Photochemical degradation of autochthonous dissolved organic matter from the culture media of Chlorella spp.

Fluorescence excitation-emission matrix spectroscopy (EEM) and absorption spectroscopy were applied to study the photobleaching of dissolved organic matter (DOM) from the culture media of Chlorella spp. during a six day natural solar radiation in October 2008. Samples from both exponential and stationary phases of algal growth were collected for the photodegradation experiment. The purpose was to investigate the photoreactivity of autochthonous DOM in aquatic environments. Parallel factor analysis (PARAFAC) revealed two humic-like (C1:240, 335 nm/406 nm; C2:260, 395 nm /502 nm) and one protein-like (C3: 225, 275 nm/334 nm) fluorescent components in the culture media. The presence of longer-wavelength-excited humic-like component C2 indicated that this typical ‘terrestrial’ component may also be derived from biological origin. The short-wavelength shoulders at 250~300 nm in the absorption spectra of stationary phase sample may be used as an indicator of in-situ chromophoric DOM (CDOM) production in aquatic environments. The photodegradation dynamics of absorption coefficient and all fluorescent components of DOM from both growth phases followed the first-order reaction process. The loss of humic-like components for stationary phase samples was slightly higher than those of exponential phase samples, while the protein-like component showed the reverse trend. After the six-day natural solar irradiation, the average loss of a350 and fluorescence intensity for C1, C2 and C3 was 83.0%, 84.0%, 64.8% and 80.0%, respectively, corresponding to a half-time between 1.6~5.0 days. These results demonstrated that algal-derived DOM is highly photoreactive and susceptible to photochemical degradation.