Characteristics of Dissolved Organic Carbon Revealed by Ultraviolet-Visible Absorbance and Fluorescence Spectroscopy: The Current Status and Future Exploration

Abstract

Dissolved organic carbon (DOC) is an important research subject for various disciplines. The objectives of this chapter are to review and summarize recent advancement in ultraviolet-visible (UV-Vis) and fluorescence spectroscopies and to identify the information gaps for future research. The search for causes of rising DOC in rivers and lakes in Europe and North America has led to no exclusive conclusion, especially from DOC exported from arable land. More studies are still needed in this area. Most of UV-Vis and fluorescence methods developed in the past are still widely used in current studies in the literature, such as specific ultraviolet absorbance (SUVA), spectral slope for UV-Vis, and excitation and emission matrix (EEM), fluorescence indexes (i.e., FI, F eff ) for fluorescence spectroscopy. New methods have been developed and tested, such as ratio of tryptophan-like to fulvic-humic-like, self-organizing map and classification/ regression tree for EEM data analysis, and UV spectral deconvolution. Nevertheless, these new methods are tested in limited sites and studies. Critics on current fluorescence methods can also be found in the literature, such as quenching agents in DOC solutions and interaction of DOC fluorophores. Future research should include standardizing test conditions (e.g., pH, ionic strength, ion composition), as such parameters would affect fluorescence yield of DOC. In addition, new data analysis methods should be developed and tested.

Reduction‐Oxidation Potential and Dissolved Organic Matter Composition in Northern Peat Soil: Interactive Controls of Water Table Position and Plant Functional Groups

“…All data collected using microplates were normalized to data collected with quartz cuvettes (1-cm pathlength). Absorbance indexes used were E2:E3 (λ = 254:365 nm)-an inverse index of both molecular size (De Haan & De Boer, 1987;Helms et al, 2008;Zhang & He, 2015) and electron acceptor capacity (Sharpless et al, 2014)-and E4:E6 (λ = 465:665 nm)-an index of molecular size and/or quinone conjugation (Chen et al, 1977;Senesi et al, 1989;Helms et al, 2008) and fulvic acid content (Blodau & Siems, 2012;Wallage et al, 2006). An increase in E4:E6 is thought to be indicative of DOM containing higher concentrations of carboxylic and ketonic bonds (C═O) in addition to aromatic bonds linked and substituted primarily by oxygen (Chen et al, 2010), because these bonds readily absorb light at λ = 46 5 nm (E4; Uyguner & Bekbolet, 2005;Chen et al, 2010;Hribljan et al, 2014).…”

Impact of Management Practices on Water Extractable Organic Carbon and Nitrogen from 12-Year Poultry Litter Amended Soils

“…In addition, soil WEOM can contribute significant amounts of dissolved organic C and N to surface waters [19] [20]. In recent years, ultraviolet-visible (UV-vis) and fluorescence spectroscopies have been used to characterize WEOM in soil, manure and other environmental samples [11] [21] [22] [23]. These two spectroscopic me-thods for WEOM studies are advantageous because of high sensitivity, relatively simple ease of operation, and the broader instrument availability, compared to some other more sophistic spectroscopic technologies.…”

Quantity and Nature of Water‐Extractable Organic Matter from Sandy Loam Soils with Potato Cropping Management

“…Among these parameters, specific UV absorbance at 254 nm (SUVA 254 ) and specific UV absorbance at 280 nm (SUVA 280 ) can be used as indicators of aromatic and hydrophobic contents, with E4/E6 (ratio of absorbance at 400 nm and 600 nm, or at 465 nm and 665 nm) as the parameter indicative of decomposition and molecular size of the WEOM pool (Jaffrain et al, 2007; Zhang et al, 2011a; Zhao et al, 2013). A humification index using the ratio of fluorescence emission intensity summation from 435 to 480 nm over the emission intensity summation from 300 to 345 with the excitation at 254 nm can be inferred as an indicator of humic material or the degree of decomposition (i.e., more humified organic components) (Cuss and Gueguen, 2015; Zhang and He, 2015). Similarly, a biological index using the fluorescence emission intensity at 380 nm divided by that at 430 nm with the excitation at 310 nm can be referred as an indicator of the presence of autochthonous biological activity (Cuss and Gueguen, 2015; Zhang et al, 2013).…”