Department of Civil, Environmental, and Architectural Engineering, USA.
Environmental Engineering Program, University of Colorado, Boulder, CO, USA.
Environ Sci Process Impacts. 2024 Oct 16;26(10):1663-1702. doi: 10.1039/d4em00183d.
Dissolved organic matter (DOM) is ubiquitous in aquatic environments and challenging to characterize due to its heterogeneity. Optical measurements (, absorbance and fluorescence spectroscopy) are popular characterization tools, because they are non-destructive, require small sample volumes, and are relatively inexpensive and more accessible compared to other techniques (, high resolution mass spectrometry). To make inferences about DOM chemistry, optical surrogates have been derived from absorbance and fluorescence spectra to describe differences in spectral shape (, E2:E3 ratio, spectral slope, fluorescence indices) or quantify carbon-normalized optical responses (, specific absorbance (SUVA) or specific fluorescence intensity (SFI)). The most common interpretations relate these optical surrogates to DOM molecular weight or aromaticity. This critical review traces the genesis of each of these interpretations and, to the extent possible, discusses additional lines of evidence that have been developed since their inception using datasets comparing diverse DOM sources or strategic endmembers. This review draws several conclusions. More caution is needed to avoid presenting surrogates as specific to either molecular weight or aromaticity, as these physicochemical characteristics are often correlated or interdependent. Many surrogates are proposed using narrow contexts, such as fractionation of a limited number of samples or dependence on isolates. Further study is needed to determine if interpretations are generalizable to whole-waters. Lastly, there is a broad opportunity to identify why endmembers with low abundance of aromatic carbon (, effluent organic matter, Antarctic lakes) often do not follow systematic trends with molecular weight or aromaticity as observed in endmembers from terrestrial environments with higher plant inputs.
溶解有机质（DOM）在水生环境中普遍存在，由于其异质性，难以进行特征描述。光学测量（吸收和荧光光谱学）是常用的特征描述工具，因为它们是非破坏性的，需要的样品体积小，与其他技术（如高分辨率质谱）相比，成本相对较低，更容易获得。为了推断 DOM 的化学性质，已经从吸收和荧光光谱中推导出了光学替代物，以描述光谱形状的差异（如 E2:E3 比、光谱斜率、荧光指数）或定量碳归一化的光学响应（如比吸收值（SUVA）或比荧光强度（SFI））。最常见的解释是将这些光学替代物与 DOM 的分子量或芳香度联系起来。本综述追溯了每一种解释的起源，并在可能的情况下，讨论了自成立以来，利用比较不同 DOM 来源或战略端元的数据集发展起来的其他证据。本综述得出了几个结论。需要更加谨慎，避免将替代物作为分子量或芳香度的特定指标，因为这些物理化学特性通常是相关的或相互依存的。许多替代物是在狭隘的背景下提出的，例如对有限数量的样品进行分级，或依赖于分离物。需要进一步研究以确定这些解释是否可以推广到整个水体。最后，有一个广泛的机会来确定为什么芳香碳丰度低的端元（如废水有机物、南极湖泊）通常不遵循与分子量或芳香度的系统趋势，而与具有较高植物输入的陆地环境中的端元不同。
