Effect of freezing–thawing on dissolved organic matter in water

Abstract

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.

Keywords:

• Freezing–thawing
• Dissolved organic matter
• Water
• Fractionation
• Chlorine reactivity

Acknowledgments

The work was supported by the National Natural Science Foundation of China (No. 21107039), the Science and Technology Research Project of Liaoning Provincial Education Department (No. L2011002), the Science and Technology Plan Project of Liaoning Province (No. 2011230009).