Effect of freezing-thawing on dissolved organic matter in water

摘要

The aim of this study was to investigate the effect of freezing-thawing on the content, spectroscopic characteristics, and chlorine reactivity of dissolved organic matter (DOM) and its fractions in water. DOM was fractionated using XAD resins into five fractions: hydrophobic acid, hydrophobic neutral, transphilic acid, transphilic neutral, and hydrophilic fraction. The bulk DOM showed DOC variation rates ranging from -2.65 to 26.94%, and the five DOM fractions exhibited DOC variation rates ranging from -22.48 to 78.16%, after freeze-thaw treatments. DOC of water samples were significantly affected by freezing and thawing temperatures, times of freeze-thaw cycles, and freezing time. The aromaticity of DOM and its fractions decreased as a result of freezing-thawing. Both freezing and thawing temperatures had a significant impact on aromatic substances contained in DOM, while the times of freeze-thaw cycles and freezing time made a relative slight influence on them. The freeze-thaw treatments reduced the chlorine reactivity of DOM and its fractions. The freezing temperature and freezing time were significant factors influencing the reactivity of DOM. The freeze-thaw treatments led to an increase in the contents of four types of fluorescent materials contained in DOM. The effect of freezing-thawing was most significant on aromatic protein- and SMP-like fluorescent materials, secondary significant on humic acid-like fluorescent materials, and slightly on fulvic acid-like fluorescent materials.