Optical Properties and Photochemical Transformation of the Dissolved Organic Matter Released by Sargassum

Autoxidized Hydroquinone Mimics the Optical Properties of Chromophoric Dissolved Organic Matter

“…DOM exhibits a number of puzzling spectral properties, a comprehensive explanation for which has not yet been developed. , These properties include DOM’s broadband absorbance extending into the visible, continuously red-shifted emission maxima with an increasing excitation wavelength, low fluorescence quantum yields (Φ f ) that decrease with increasing excitation wavelength, preferential removal of visible absorption, and increasing, blue-shifted fluorescence upon borohydride reduction. , Many of these spectral phenomena are observed not only for aquatic natural organic matter but also for marine DOM, , aged exudates from algae and plankton, soil humic substance extracts, ,, wastewater-derived effluent organic matter, and atmospheric brown carbon. − …”

Carbon Sequestration in the Form of Recalcitrant Dissolved Organic Carbon in a Seaweed (Kelp) Farming Environment

“…For instance, inorganic nutrients were added only at the beginning of degradation, nutrient limitation might occur during the long-term incubation, and the “bottle experiment” affected microbial community succession. Moreover, solar radiation can also degrade DOC molecules, as kelps inhabit in the euphotic zone. , In addition, the commonly used DOC extraction method using SPE-C18 can lead to the loss of some part of the DOC components, as this method has a stronger preference for the mid- to nonpolar molecules, − which usually contain a higher proportion of recalcitrant molecules (e.g., humic substances). ,, This is also evidenced by the relatively higher recovery (35 ± 1 vs 26 ± 1%) of SPE-C18 for the more RDOC (day 360) remaining after the long-term degradation experiment compared to the DOC at the initial stage (day 1) of degradation in this study. Considering these limitations, after the long-term degradation experiment, another 10-day degradation experiment was performed on the remaining RDOC with replenishment of fresh microbial communities and inorganic nutrients, and under solar radiation, as a result, 1.8–3.1% of the remaining RDOC can be further removed (Figure S4), which was consistent with a previous study reporting RDOC removal rates of 0.1–8.7% .…”

“…Moreover, solar radiation can also degrade DOC molecules, as kelps inhabit in the euphotic zone. 73,74 In addition, the commonly used DOC extraction method using SPE-C18 can lead to the loss of some part of the DOC components, as this method has a stronger preference for the mid-to nonpolar molecules, 36−38 which usually contain a higher proportion of recalcitrant molecules (e.g., humic substances). 34,75,76 This is also evidenced by the relatively higher recovery (35 ± 1 vs 26 ± 1%) of SPE-C18 for the more RDOC (day 360) remaining after the long-term degradation experiment compared to the DOC at the initial stage (day 1) of degradation in this study.…”

Changes in light absorption and composition of chromophoric marine-dissolved organic matter across a microbial bloom

“…This behavior is consistent with spectroscopic measurements of microbial growth in laboratory and eld experiments. 40 A distinct peak at 410 nm only appears during and aer the microbial bloom peak, persisting throughout the bloom time course. Absorbance at 410 nm, the A peak, has only infrequently been observed in prior examinations of m-CDOM, and previously only appears aer peak microbial growth, suggesting the associated compounds are likely produced biotically.…”