Characterizing the photochemical degradation of aquatic humic substances from a dystrophic lake using excitation-emission matrix fluorescence spectroscopy and parallel factor analysis

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• 作者：Yukiko Senga ; Satoshi Moriai ; Chika Naruoka ; Ryoma Nedachi ; Shigeharu Terui
• 关键词：EEM–PARAFAC ; Aquatic humic substances (AHS) ; Photochemical degradation ; Solar radiation ; Wetland
• 刊名：Limnology
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：18
• 期：1
• 页码：97-110
• 全文大小：
• 刊物类别：Biomedical and Life Sciences
• 刊物主题：Ecology; Environment, general; Freshwater & Marine Ecology;
• 出版者：Springer Japan
• ISSN：1439-863X
• 卷排序：18

文摘

Three-dimensional excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC) were used to monitor composition and reactivity changes caused by the photochemical degradation of aquatic humic substances (AHS) from a dystrophic lake in Kushiro Wetland, Japan. AHS-rich lake water was exposed to three treatments in summer and winter 2014: radiation with the full solar wavelength range, radiation with the >320-nm solar wavelength range, and no solar radiation. Irradiation caused AHS-like peaks to shift to shorter wavelengths in the EEM contour plots, implying that AHS photodegradation caused the formation of lower-molecular-weight fractions or more simply structured components. Three components were identified from PARAFAC analyses: AHS-1 (excitation/emission wavelengths of maxima: <252 and 315 nm/426 nm), AHS-2 (360 and 261 nm/489 nm), and AHS-3 (276 nm/403 nm). These components had different photosensitivities. AHS-1 was most sensitive to full solar radiation, while AHS-2 was most sensitive to >320-nm radiation. More photodegradation of these components occurred in the summer than in the winter, indicating that photodegradation depended on light intensity. AHS-3 was photoresistant. The different characteristics of the components reflected the in situ dynamics of the components. The AHS-3 fluorescence intensity was positively correlated with the dissolved organic carbon concentration but the AHS-1 and AHS-2 fluorescence intensities were not. The EEM–PARAFAC method was found to be a good tool for tracing AHS-like materials in situ and in the laboratory.