Dissolved organic matter (DOM) is recognized for its importance in freshwater ecosystems, but historical reliance on DOM quantity rather than indicators of DOM composition has led to an incomplete understanding of DOM and an underestimation of its role and importance in biogeochemical processes. A single sample of DOM can be composed of tens of thousands of distinct molecules. Each of these unique DOM molecules has their own chemical properties and reactivity or role in the environment. Human activities can modify DOM composition and recent research has uncovered distinct DOM pools laced with human markers and footprints. Here we review how land use change, climate change, nutrient pollution, browning, wildfires, and dams can change DOM composition which in turn will affect internal processing of freshwater DOM. We then describe how human-modified DOM can affect biogeochemical processes. Drought, wildfires, cultivated land use, eutrophication, climate change driven permafrost thaw, and other human stressors can shift the composition of DOM in freshwater ecosystems increasing the relative contribution of microbial-like and aliphatic components. In contrast, increases in precipitation may shift DOM towards more relatively humic-rich, allochthonous forms of DOM. These shifts in DOM pools will likely have highly contrasting effects on carbon outgassing and burial, nutrient cycles, ecosystem metabolism, metal toxicity, and the treatments needed to produce clean drinking water. A deeper understanding of the links between the chemical properties of DOM and biogeochemical dynamics can help to address important future environmental issues, such as the transfer of organic contaminants through food webs, alterations to nitrogen cycling, impacts on drinking water quality, and biogeochemical effects of global climate change.

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人类如何改变淡水中溶解的有机物成分：与地球生物地球化学的相关性

溶解有机质 (DOM) 因其在淡水生态系统中的重要性而得到认可，但历史上对 DOM 数量而非 DOM 组成指标的依赖导致对 DOM 的理解不完整，并低估了其在生物地球化学过程中的作用和重要性。DOM 的单个样本可以由数万个不同的分子组成。这些独特的 DOM 分子中的每一个都有自己的化学特性和反应性或在环境中的作用。人类活动可以修改 DOM 的组成，最近的研究发现了带有人类标记和足迹的不同 DOM 池。在这里，我们回顾了土地利用变化、气候变化、养分污染、褐变、野火和水坝如何改变 DOM 组成，进而影响淡水 DOM 的内部处理。然后我们描述了人类修改的 DOM 如何影响生物地球化学过程。干旱、野火、耕地利用、富营养化、气候变化驱动的永久冻土融化和其他人类压力因素可以改变淡水生态系统中 DOM 的组成，增加类微生物和脂肪族成分的相对贡献。相比之下，降水的增加可能会将 DOM 转移到更富含腐殖质的外来 DOM 形式。DOM 池的这些变化可能会对碳释放和掩埋、养分循环、生态系统代谢、金属毒性以及生产清洁饮用水所需的处理产生截然不同的影响。更深入地了解 DOM 的化学性质与生物地球化学动力学之间的联系有助于解决未来的重要环境问题，