Leyva Dennys, Jaffé Rudolf, Courson Jessica, Kominoski John S, Tariq Muhammad Usman, Saeed Fahad, Fernandez-Lima Francisco
Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA.
Institute of Environment, Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA.
Aquat Sci. 2022 Oct;84(4). doi: 10.1007/s00027-022-00887-y. Epub 2022 Sep 23.
Understanding dissolved organic matter (DOM) export to the ocean is needed to assess the impact of climate change on the global carbon cycle. The molecular-level characterization of DOM compositional variability and complexity in aquatic ecosystems has been analytically challenging. Advanced analytical studies based on ultra-high resolution mass spectrometry (FT ICR MS) have proven highly successful to better understand the dynamics of DOM in coastal ecosystems. In this work, the molecular signature of DOM along a freshwater-to-estuarine gradient in the Harney River, Florida Everglades was analyzed for the first time using a novel approach based on tandem high resolution ion mobility and ultra-high resolution mass spectrometry (ESI-TIMS-FT ICR MS). This method enhances traditional DOM molecular characterization by including the molecular isomeric complexity. An average of six and up to 12 isomers were observed per chemical formula and characteristic isomers to each section of the freshwater-to-estuarine gradient were successfully identified. We measured a decrease in the chemical complexity and diversity (both in the number of molecular formulas and number of isomers per chemical formula) with increasing salinity; this trend is representative of the biogeochemical transformations of DOM during transport and along source variations, showing both clear degradation products and formation of new components along the salinity transect. The inclusion of the isomeric content at the molecular formula allowed to differentiate isomeric species that are present along the transect (mainly lignin-type components) and responsible for the DOM refractory nature. DOM isomeric fingerprints characteristic of the molecular variability along the Everglades freshwater-to-estuarine gradient are also described.
要评估气候变化对全球碳循环的影响，就需要了解溶解有机物（DOM）向海洋的输出情况。对水生生态系统中DOM组成的变异性和复杂性进行分子水平的表征在分析上具有挑战性。基于超高分辨率质谱（FT ICR MS）的先进分析研究已被证明在更好地理解沿海生态系统中DOM的动态方面非常成功。在这项工作中，首次使用基于串联高分辨率离子淌度和超高分辨率质谱（ESI-TIMS-FT ICR MS）的新方法，分析了佛罗里达大沼泽地哈尼河中从淡水到河口梯度上DOM的分子特征。该方法通过纳入分子异构体复杂性增强了传统的DOM分子表征。每个化学式平均观察到六种异构体，最多可达12种，并且成功鉴定出了淡水到河口梯度各部分的特征异构体。我们测量到随着盐度增加，化学复杂性和多样性（包括分子式数量和每个化学式的异构体数量）均降低；这种趋势代表了DOM在运输过程中以及沿源变化时的生物地球化学转化，显示出沿盐度断面既有明显的降解产物，也有新成分的形成。纳入分子式中的异构体含量能够区分沿断面存在的异构体种类（主要是木质素类成分），这些异构体是DOM难降解性质的原因。还描述了沿大沼泽地淡水到河口梯度的分子变异性所特有的DOM异构体指纹图谱。
