Contributions of Fe(III) to UV–Vis absorbance in river water: a case study on the Connecticut River and argument for the systematic tandem measurement of Fe(III) and CDOM
Contributions of Fe(III) to UV–Vis absorbance in river water: a case study on the Connecticut River and argument for the systematic tandem measurement of Fe(III) and CDOM
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DOI：
10.1007/s10533-022-00937-5
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发表时间：
2022-05
期刊：
影响因子：
4
通讯作者：
L. Logozzo;Joseph W. Martin;J. McArthur;P. Raymond
中科院分区：
文献类型：
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作者：
L. Logozzo;Joseph W. Martin;J. McArthur;P. Raymond
溶解有机物(DOM)影响着水生生态系统的结构和功能。DOM吸收紫外光和可见光(UV-Vis)波长的光，从而影响光衰减。由于DOM的吸收取决于其组成，因此使用UV-Vis吸光度来限制DOM的组成、来源和数量。铁，Fe(III)，也吸收在UV-Vis中；当Fe(III)存在时，DOM属性的吸光度被高估。在这里，我们探索DOM和Fe(III)在流域尺度上的不同行为如何影响UV-Vis吸收，并评估系统特定的变异性如何影响温带流域现有Fe(III)校正因子的有效性。我们在 ~ 1.5年期间每两周对康涅狄格河干流中的5个站点进行采样，并在2019年夏季对康涅狄格河流域的7个站点进行一次采样。我们利用粒度分离来分离DOM和Fe(III)对吸光度的影响，并表明Fe(III)对254 nm(A254)和412 nm(A412)吸光度的不同贡献使Fe(III)的校正复杂化。我们证明，Fe(III)对DOM属性吸光度的高估与Fe(III)：溶解有机碳浓度比有关；因此，即使在Fe(III)较低的情况下，高估也可能很高。即使在单个系统中，254高估也是高度可变的，但可能高达53%。最后，我们说明UV-VIS高估可能会对DOM质量的季节、流量和土地利用趋势产生偏差。综上所述，这些发现认为，为了估计CDOM的组成或数量，应同时测量Fe(III)和UV-Vis吸光度。
Dissolved organic matter (DOM) impacts the structure and function of aquatic ecosystems. DOM absorbs light in the UV and visible (UV–Vis) wavelengths, thus impacting light attenuation. Because absorption by DOM depends on its composition, UV–Vis absorbance is used to constrain DOM composition, source, and amount. Ferric iron, Fe(III), also absorbs in the UV–Vis; when Fe(III) is present, DOM-attributed absorbance is overestimated. Here, we explore how differing behavior of DOM and Fe(III) at the catchment scale impacts UV–Vis absorbance and evaluate how system-specific variability impacts the effectiveness of existing Fe(III) correction factors in a temperate watershed. We sampled five sites in the Connecticut River mainstem bi-weekly for ~ 1.5 years, and seven sites in the Connecticut River watershed once during the summer 2019. We utilized size fractionation to isolate the impact of DOM and Fe(III) on absorbance and show that variable contributions of Fe(III) to absorbance at 254 nm (a254) and 412 nm (a412) by size fraction complicates correction for Fe(III). We demonstrate that the overestimation of DOM-attributed absorbance by Fe(III) is correlated to the Fe(III):dissolved organic carbon concentration ratio; thus, overestimation can be high even when Fe(III) is low. a254overestimation is highly variable even within a single system, but can be as high as 53%. Finally, we illustrate that UV-Vis overestimation might impart bias to seasonal, discharge, and land-use trends in DOM quality. Together, these findings argue that Fe(III) should be measured in tandem with UV–Vis absorbance for estimates of CDOM composition or amount.