Molecular dissolved organic matter composition in lakes across Sweden as relative intensities of FT-ICR-MS peaks and PARAFAC components and optical indices

Whether intrinsic molecular properties or extrinsic factors such as environmental conditions control the decomposition of natural organic matter across soil, marine and freshwater systems has been subject to debate. Comprehensive evaluations of the controls that molecular structure exerts on organic matter's persistence in the environment have been precluded by organic matter's extreme complexity. Here we examine dissolved organic matter from 109 Swedish lakes using ultrahigh-resolution mass spectrometry and optical spectroscopy to investigate the constraints on its persistence in the environment. We find that degradation processes preferentially remove oxidized, aromatic compounds, whereas reduced, aliphatic and N-containing compounds are either resistant to degradation or tightly cycled and thus persist in aquatic systems. The patterns we observe for individual molecules are consistent with our measurements of emergent bulk characteristics of organic matter at wide geographic and temporal scales, as reflected by optical properties. We conclude that intrinsic molecular properties are an important control of overall organic matter reactivity.在土壤、海洋与淡水生态系统中，究竟是内在分子属性，还是环境条件等外在因素主导天然有机质（Natural Organic Matter, NOM）的分解过程，长期以来学界对此一直存在争议。由于天然有机质本身极为复杂，此前学界始终无法全面评估分子结构对其环境持久性的调控机制。本研究针对瑞典109个湖泊的溶解性有机质（Dissolved Organic Matter, DOM），采用超高分辨质谱（Ultrahigh-resolution Mass Spectrometry）与光学光谱技术开展分析，以探究其环境持久性的制约因素。研究结果显示，降解过程会优先去除氧化态芳香族化合物；而还原态脂肪族化合物与含氮化合物要么具备抗降解性，要么处于紧密循环状态，因此能够在水生生态系统中持续留存。我们在单分子层面观测到的变化规律，与通过光学特性所反映的、大地理范围与长时间尺度下有机质整体涌现特征的测量结果高度一致。综上，本研究得出结论：内在分子属性是调控天然有机质整体反应活性的重要因素。