Molecular Level Analysis Reveals Changes in Chemical Composition of Dissolved Organic Matter From South Texas Rivers After High Flow Events
Molecular Level Analysis Reveals Changes in Chemical Composition of Dissolved Organic Matter From South Texas Rivers After High Flow Events
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DOI：
10.3389/fmars.2019.00673
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发表时间：
2019-11
影响因子：
3.7
通讯作者：
Kaijun Lu;Zhanfei Liu
中科院分区：
文献类型：
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作者：
Kaijun Lu;Zhanfei Liu
河流溶解有机质（DOM）是陆地向海洋环境输出还原性碳的主要来源，河流有机质的流入极大地影响了河口和海湾的生物地球化学循环。因此，DOM组成的任何变化，例如由风暴和飓风引起的洪水引起的变化，都可能随后影响河口环境。为了研究高流量事件对河流DOM的影响，利用高分辨率离子迁移率四极杆飞行时间液相色谱质谱法（IM Q-TOF LCMS）获取了德克萨斯州南部四条河流（Aransas河、Lavaca河、Mission河和Nueces河）DOM的多维分子水平信息。基流样本采集于2016年5月、7月、10月、2017年6月、2018年3月，高流样本采集于2017年9月、2018年6月、9月。根据IM Q-TOF LCMS给出的分子式，高流量事件中H/C比值降低（ESI+为1.52 ~ 1.51，ESI-为1.19 ~ 1.07），O/C比值升高（ESI-为0.31 ~ 0.33）。此外，根据质谱和串联质谱数据，DOM从基流条件下的蛋白质和脂类结构为主的群落转变为高流量事件下的木质素、单宁和凝聚芳香结构为主的群落。高流量河流DOM的这些变化表明陆地信号的增加，这可能是洪水从流域动员陆地有机质的结果。这些被动员的DOM虽然在河流的高流量条件下是难降解的，但当条件发生变化时，它们可能在沿海地区发生反应，从而可能为下游的微生物活动提供燃料。此外，在不同的流动条件下，约有3.76 ~ 21.8%的DOM分子含有结构异构体。如此低的异构体百分比表明，作为各种酶生化反应的产物，DOM中异构体的数量受到限制。综上所述，我们的研究揭示了亚热带地区河流DOM的结构变化对极端气候事件的响应，并对理解气候变化下河口生物地球化学变化具有重要意义。
Riverine dissolved organic matter (DOM) is a major source of reduced carbon exported from land to marine environments, and the inflow of riverine organic matter greatly affects biogeochemical cycling in estuaries and bays. Thus, any change in DOM composition, such as changes caused by flood waters as a result of storms and hurricanes, can subsequently affect estuarine environments. To investigate the impact of high flow events on riverine DOM, multidimensional molecular level information of DOM from four south Texas Rivers (Aransas, Lavaca, Mission, and Nueces Rivers) was acquired using high-resolution Ion Mobility Quadrupole Time of Flight Liquid Chromatography Mass Spectrometry (IM Q-TOF LCMS). Base-flow samples were collected in May, July and October of 2016, June of 2017, and March of 2018, while high-flow samples were collected in September of 2017, and June and September of 2018. Based on the molecular formula assigned from IM Q-TOF LCMS, H/C ratio decreased during high-flow event (1.52 to 1.51 in ESI+; 1.19 to 1.07 in ESI-), while O/C ratio increased (0.31 to 0.33 in ESI-). Furthermore, DOM shifted from a protein-like and lipid-like dominated community at base flow condition, to a lignin, tannin and condensed aromatic structure dominated one during high flow event based on MS and tandem MS data. These changes in high-flow riverine DOM indicate an increase of terrestrial signal, which likely is a result of mobilization of terrestrial organic matter from the watersheds by flooding. These mobilized DOM, though refractory at high-flow condition in rivers, could be reactive in coastal regions when condition changes, and thus potentially fuel microbial activities downstream. In addition, about 3.76 – 21.8% of DOM molecules contain structural isomers among different flow conditions. This low number of isomer percentages suggests that as the products of various enzymatic biochemical reactions, the number of isomers in DOM is constrained. Taken together, our study provides insights into structural changes of riverine DOM in response to extreme climate events in subtropical regions and have implications in understanding biogeochemical changes in estuaries under a changing climate.