The molecular composition of dissolved organic matter (DOM) is increasingly recognized as fundamentally important to mercury transport and transformations, with numerous approaches undertaken to examine DOM characteristics beyond dissolved organic carbon concentrations. In this study, we use a high-resolution mass spectrometry approach, Fourier-transform ion cyclotron resonance mass spectrometry, to characterize DOM compound classes, DOM aromaticity (AI_mod), and the nominal oxygenation state of carbon (NOSC) across thirteen small boreal forest streams in central Canada. We then relate the relative abundance of hundreds of different DOM molecules with inorganic mercury and methylmercury (MeHg) concentrations across late spring and fall seasons. The number of significant correlations and the classes of DOM compounds significantly correlating with inorganic mercury and MeHg concentrations differs substantially across seasons and between mercury forms. For inorganic mercury, the abundance of nitrogen and sulfur containing DOM are most often positively correlated (mean ρ = 0.80) in the late spring, whereas during the fall, the abundance of low-oxidized lignins is more important, though with weaker correlations (mean ρ = 0.51). For MeHg, low-oxidized lignins and hydrolysable tannins, likely sourced from conifer throughfall and litter, account for up to 83% of all DOM-MeHg correlations regardless of season. Further network analyses reveal that the strongest and most significant inorganic mercury-DOM correlations are found across a wide range of NOSC values, indicating that DOM involved with the transport of inorganic mercury encompasses a wide range of polarities and thermodynamic stabilities. In contrast, DOM molecules exclusively correlated with MeHg concentrations have more positive NOSC and AI_mod values, implying the preferential transport of MeHg with more thermodynamically stable and aromatic DOM molecules. DOM molecules significantly correlated with both inorganic mercury and MeHg concentrations are found exclusively in the late spring. Overall, this non-targeted approach may help to inform further targeted investigations, especially as it relates to the underrepresented importance of plant biomolecules in facilitating mercury transport.

Graphical abstract

中文翻译：

---

加拿大北方河流中溶解有机物与无机汞和甲基汞的分子相关性

溶解有机物 (DOM) 的分子组成越来越被认为对汞的运输和转化至关重要，人们采用了许多方法来检查溶解有机碳浓度以外的 DOM 特性。在这项研究中，我们使用高分辨率质谱方法，傅里叶变换离子回旋共振质谱，来表征 DOM 化合物类别，DOM 芳香性（AI _mod)，以及加拿大中部 13 条北方小森林溪流中碳的标称氧合状态 (NOSC)。然后，我们将数百种不同 DOM 分子的相对丰度与晚春和秋季的无机汞和甲基汞 (MeHg) 浓度联系起来。显着相关性的数量和与无机汞和甲基汞浓度显着相关的 DOM 化合物类别在不同季节和不同汞形态之间存在显着差异。对于无机汞，含氮和硫的 DOM 的丰度在晚春最常呈正相关（平均 ρ = 0.80），而在秋季，低氧化木质素的丰度更为重要，尽管相关性较弱（平均ρ = 0.51)。对于甲基汞、低氧化木质素和可水解单宁，可能来自针叶树的落叶和枯枝落叶，占所有 DOM-MeHg 相关性的 83%，无论季节如何。进一步的网络分析表明，在广泛的 NOSC 值中发现了最强和最显着的无机汞-DOM 相关性，表明与无机汞运输有关的 DOM 包含广泛的极性和热力学稳定性。相比之下，仅与 MeHg 浓度相关的 DOM 分子具有更积极的 NOSC 和 AI 表明与无机汞运输有关的 DOM 包含广泛的极性和热力学稳定性。相比之下，仅与 MeHg 浓度相关的 DOM 分子具有更积极的 NOSC 和 AI 表明与无机汞运输有关的 DOM 包含广泛的极性和热力学稳定性。相比之下，仅与 MeHg 浓度相关的 DOM 分子具有更积极的 NOSC 和 AI_mod值，意味着甲基汞优先传输具有更热力学稳定和芳香的 DOM 分子。与无机汞和甲基汞浓度显着相关的 DOM 分子仅在晚春发现。总体而言，这种非针对性的方法可能有助于为进一步的针对性调查提供信息，特别是因为它涉及植物生物分子在促进汞运输方面未被充分代表的重要性。

图形概要