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Assessing the prevalence, products, and pathways of dissolved organic matter partial photo-oxidation in arctic surface waters.
Environmental Science: Processes & Impacts ( IF 4.3 ) Pub Date : 2020-02-11 , DOI: 10.1039/c9em00504h
Collin P Ward 1 , Rose M Cory
Affiliation  

In sunlit waters, photodegradation of dissolved organic matter (DOM) yields completely oxidized carbon (i.e., CO2) as well as a suite of partially oxidized compounds formed from oxygen incorporation (i.e., partial photo-oxidation). Of these two groups of DOM photo-products, more studies focus on CO2 (a greenhouse gas) than on partially oxidized DOM, which is likely a diverse group of compounds with poorly constrained roles in aquatic carbon cycling or biogeochemistry. The objective of this study is to address knowledge gaps on the prevalence, products, and pathways of DOM partial photo-oxidation. Here we traced the photochemical incorporation of isotopically labelled 18O2 into DOM isolated from Alaskan Arctic surface waters using high-resolution mass spectrometry. Complete and partial photo-oxidation of DOM was also quantified as CO2 production and O2 consumption. The majority of 18O-containing partial oxidation photo-products were classified as carboxylic rich alicyclic molecules (CRAM) and overlapped in composition with previously reported photo-products known to result from the oxidation of DOM by singlet oxygen. These results support a previously proposed hypothesis that photo-oxidation by singlet oxygen may contribute to the formation of CRAM, a compound class of DOM ubiquitously observed in surface waters. The novel application of an isotopic tracer for oxygen incorporation with a mass balance approach to quantify complete and partial photo-oxidation of DOM revealed that less than one mol of O2 is required to produce one mol of CO2. A sensitivity analysis based on this new knowledge demonstrated that the magnitude of DOM partial photo-oxidation may be underestimated by up to four-fold. Consequently, partial photo-oxidation likely plays a more prominent role in shaping DOM composition in sunlit waters of the Arctic than previously understood. Therefore, partial photo-oxidation should be increasingly incorporated into the experimental framework of studies focused on DOM composition in surface waters.

中文翻译:

评估北极地表水中溶解有机物部分光氧化的发生率,产物和途径。

在阳光照射的水中,溶解有机物(DOM)的光降解会产生完全氧化的碳(即CO2)以及通过掺入氧而形成的一组部分氧化的化合物(即部分光氧化)。在这两类DOM光产物中,更多的研究集中于CO2(一种温室气体),而不是部分氧化的DOM,这可能是在水生碳循环或生物地球化学中受约束作用较弱的多种化合物。本研究的目的是解决DOM部分光氧化的发生率,产物和途径方面的知识空白。在这里,我们使用高分辨率质谱分析法将同位素标记的18O2光化学结合到从阿拉斯加北极地表水中分离出的DOM中。DOM的全部和部分光氧化也被量化为CO2产生和O2消耗。大部分含18O的部分氧化光产物被归类为富含羧基的脂环族分子(CRAM),其组成与先前报道的由单线态氧氧化DOM导致的光产物重叠。这些结果支持了先前提出的假说,即单线态氧的光氧化作用可能有助于CRAM的形成,CRAM是在地表水中普遍观察到的DOM化合物类别。同位素示踪剂与质量平衡方法结合用于氧结合的定量定量DOM的完全和部分光氧化的新颖应用表明,生产一摩尔CO2所需的氧气少于一摩尔。基于这一新知识的敏感性分析表明,DOM部分光氧化的幅度可能被低估了多达四倍。因此,与以前所了解的相比,部分光氧化在塑造北极阳光照射的水中的DOM组成中可能起更重要的作用。因此,部分光氧化应越来越多地纳入以地表水中DOM组成为重点的研究实验框架中。
更新日期:2020-02-11
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