In aquatic systems, dissolved organic matter (DOM) has important ecological and biogeochemical functions, where the molecular composition of DOM has larger-scale implications for climate change and global carbon cycles. However, there is limited information about the relationships between landscape characteristics and human disturbance that influence the molecular composition of DOM changes in watersheds. In this study, we collected water samples from 22 sites across a gradient of topographically characterized agricultural land coverage and community infrastructure development in the Kawartha region in Ontario, Canada. We employed a combination of Fourier Transform Ion-Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) and absorbance spectroscopy to investigate changes in the molecular composition of DOM with increasing agricultural and community development disturbance on the optical and molecular characteristics of DOM. We found that dissolved organic carbon (DOC) concentrations in disturbed (>75%) watersheds ranged from 3.67–32.8 mg L⁻¹ and were significantly higher than in watersheds with more abundant forest coverage (3.78–9.13 mg L⁻¹). In addition, watersheds with higher phosphorus concentrations had more negative nominal oxygenation state of carbon (NOSC) values, suggesting biologically processed DOM correlating with increased phosphorus levels in aquatic systems. To relate the molecular properties of DOM to landscape metrics, we used Spearman's correlation analysis to reveal that agriculturally impacted and community developments enhanced the molecular signature of unsaturated hydrocarbon. In addition, we identified 65 dissolved organic phosphorus (DOP) molecules that significantly increased in abundance with disturbance, likely due to microbial mineralization of existing DOM with the addition of phosphorus to form larger, biologically inaccessible molecules. The overall recalcitrance of the identified molecules can serve as molecular signatures when evaluating the level of disturbance of a watershed.

中文翻译：

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新兴研究者系列：土地利用对农业流域溶解有机物质量的影响：分子视角

在水生系统中，溶解有机物（DOM）具有重要的生态和生物地球化学功能，其中DOM的分子组成对气候变化和全球碳循环具有更大规模的影响。然而，关于影响流域 DOM 分子组成变化的景观特征与人类干扰之间关系的信息有限。在这项研究中，我们从加拿大安大略省卡沃萨地区的 22 个地点收集了水样，这些地点具有地形特征的农业土地覆盖和社区基础设施开发。我们采用傅里叶变换离子回旋共振质谱 (FT-ICR-MS) 和吸收光谱相结合的方式来研究随着农业和社区发展对 DOM 光学和分子特性干扰的增加，DOM 分子组成的变化。我们发现受干扰（>75%）流域的溶解有机碳（DOC）浓度范围为3.67–32.8 mg L ^-1，显着高于森林覆盖更丰富的流域（3.78–9.13 mg L ^-1）。此外，磷浓度较高的流域具有更多的负标称碳氧状态（NOSC）值，表明生物处理的 DOM 与水生系统中磷水平的增加相关。为了将 DOM 的分子特性与景观指标联系起来，我们使用 Spearman 的相关分析来揭示农业影响和社区发展增强了不饱和碳氢化合物的分子特征。此外，我们还发现了 65 种溶解的有机磷 (DOP) 分子，这些分子的丰度随着干扰而显着增加，这可能是由于添加磷后现有 DOM 发生微生物矿化，形成更大的、生物上无法接近的分子。在评估分水岭的干扰水平时，所识别分子的总体顽抗性可以作为分子特征。