Milstead Reid P, Horvath Emma R, Remucal Christina K
Environmental Chemistry and Technology Program, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
Department of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
Environ Sci Technol. 2023 Aug 15;57(32):11876-11885. doi: 10.1021/acs.est.3c01500. Epub 2023 Jul 31.
Dissolved organic matter (DOM) plays an important role in carbon cycling within inland surface waters. Under sunlight irradiation, DOM undergoes complete photooxidation to produce carbon dioxide (CO) and partial photooxidation that alters the molecular composition of DOM. However, a mechanistic understanding of the relationship between DOM composition and its susceptibility to partial and complete photooxidation in surface waters is currently lacking. This work combines light exposure experiments with high-resolution mass spectrometry to investigate DOM photooxidation using two DOM isolates and DOM from 16 lakes that vary in trophic status and size. High ratios of oxygen consumption to dissolved inorganic carbon (DIC) production demonstrate that all samples undergo extensive partial photooxidation. At the molecular level, more oxidized, aromatic DOM formulas are associated with oxygen consumption and DIC production. Bulk level measurements indicate that DOM becomes less aromatic and lower in apparent molecular weight following partial photooxidation, and there is molecular level evidence of oxygen addition and loss of CO in all samples. However, formulas most susceptible to photooxidation vary depending on the initial DOM composition. Collectively, this work provides insights into the relationship between DOM composition and photooxidation, which has important implications for carbon cycling in diverse surface waters.
溶解有机物（DOM）在内陆地表水的碳循环中起着重要作用。在阳光照射下，DOM会发生完全光氧化生成二氧化碳（CO₂），以及改变DOM分子组成的部分光氧化。然而，目前缺乏对地表水DOM组成与其对部分光氧化和完全光氧化敏感性之间关系的机理理解。这项工作将光照实验与高分辨率质谱相结合，使用两种DOM分离物以及来自16个营养状态和大小各异湖泊的DOM来研究DOM光氧化。高的耗氧量与溶解无机碳（DIC）生成量之比表明所有样品都经历了广泛的部分光氧化。在分子水平上，氧化程度更高、芳香性更强的DOM分子式与耗氧量和DIC生成相关。总体水平测量表明，部分光氧化后DOM的芳香性降低，表观分子量减小，并且在所有样品中都有分子水平上氧添加和CO₂损失的证据。然而，最易发生光氧化的分子式因初始DOM组成而异。总的来说，这项工作为DOM组成与光氧化之间的关系提供了见解，这对不同地表水的碳循环具有重要意义。
