Absorption and fluorescence spectroscopy laser photobleaching experiments were employed to probe the origins of optical properties humic substances (HS). Luminescence quantum yields wavelengths maximum emission acquired for Suwannee River acid (SRHA) fulvic (SRFA) at an extensive series excitation across ultraviolet visible. Laser irradiation a wavelength visible was further destroy selectively chromophores absorbing specific wavelengths, using absorption follow losses with time. The results...

The spectral dependencies of absorption and fluorescence emission (emission maxima (λmax), quantum yields (ϕ), mean lifetimes (τm)) were acquired for a commercial lignin, Suwannee River humic (SRHA) fulvic (SRFA) acids, series solid phase extracts (C18) from the Middle Atlantic Bight (MAB extracts). These parameters compared with relative average size total lignin phenol content (TLP). TLP was strongly correlated at 280 355 nm MAB extracts, SRHA, SRFA. dependence λmax, ϕ, τm very similar all...

The mechanism(s) by which hydrogen peroxide (H(2)O(2)) is photoproduced humic substances and chromophoric dissolved organic matter was probed examining the dependence of initial H(2)O(2) photoproduction rate (R(H(2)O(2))) apparent quantum yields on dioxygen concentration for both untreated borohydride-reduced samples. Although borohydride reduction substantially reduced light absorption, R(H(2)O(2)) values were largely unaffected. Apparent monochromatic polychromatic thus increased following...

To probe the mechanism of photosensitized loss phenols by humic substances (HS), dependence initial rate 2,4,6-trimethylphenol (TMP) (R(TMP)) on dioxygen concentration was examined both for a variety untreated as well borohydride-reduced HS and C(18) extracts from Delaware Bay Mid-Atlantic Bight. R(TMP) inversely proportional to at [O(2)] > 50 μM, consistent with reaction triplet excited states, but not (1)O(2) or RO(2). Modeling provided constants TMP reaction, O(2) quenching, lifetimes...

Treatment of Suwanee River humic (SRHA) and fulvic (SRFA) acids, a commercial lignin (LAC), series solid phase extracts (C18) from the Middle Atlantic Bight (MAB extracts) with sodium borohydride (NaBH4), selective reductant carbonyl-containing compounds including quinones aromatic ketones, produces preferential loss visible absorption (≥50% for SRFA) substantially enhanced, blue-shifted fluorescence emission (2- to 3-fold increase). Comparison results those obtained model hydroquinones...

The distribution of chromophoric‐dissolved‐organic‐matter (CDOM) was investigated in the western tropical North Atlantic Ocean (WTNA) during low and high flow periods Amazon River. A strong correlation observed between situ CDOM absorption at 490 nm diffuse attenuation coefficient (K490) period (ratio 0.7). SeaWiFS monthly composites K490 showed (1) very values over most WTNA, with higher restricted to continental shelf season (2) much WTNA extending offshore >1000 km from river mouth...

The molecular basis of the optical properties chromophoric dissolved organic matter (CDOM) and humic substances (HS) remains poorly understood yet to be investigated adequately. This study evaluates relative contributions two broad classes carbonyl-containing compounds, ketones/aldehydes versus quinones, absorption emission a representative suite HS as well lignin sample. Selective reduction quinones hydroquinones by addition small molar excesses dithionite these samples under anoxic...

Abstract Dissolved organic carbon (DOC) plays critical roles in marine cycling, but its sources and sinks remain uncertain. In this study, we monitored DOC exudation rates of Sargassum natans under visible light (λ > 390 nm) solar radiation. release ranged from 7 to 10 μg C g −1 biomass hr (wet weight) light, increased 23 41 when exposed natural sunlight. Results indicate that released by could amount 0.3 1.2 Tg C/year, potentially contributing significantly the pool Gulf Mexico Western...

The mass spectra acquired by ESI FT-ICR MS of untreated, borohydride-reduced, and borodeuteride-reduced samples Suwannee River fulvic acid (SRFA) a C18 extract from the upper Delaware Bay were compared to one another. Treatment these with sodium borodeuteride was shown produce unique labels for species which contain or two ketone/aldehyde moieties. Approximately 30% all identified peaks in comprise ketone/aldehyde-containing species. molecular formulas majority had O/C H/C molar ratios...

The combined effects of pH and borohydride reduction on the optical properties a series humic substances lignin model were examined to probe molecular moieties interactions that give rise observed these materials. Increasing from 2 12 produced significantly enhanced absorption across spectra all samples, with distinct spectral responses over ranges attributable deprotonation carboxylic acids phenols. Borohydride substantially attenuated broadband enhancements pH, clearly indicating loss due...

Addition of a series phenol electron donors to solutions humic substances (HS) enhanced substantially the initial rates hydrogen peroxide (H2O2) photoproduction (RH2O2), with enhancement factors (EF) ranging from low ∼3 for 2,4,6-trimethylphenol (TMP) high ∼15 3,4-dimethoxyphenol (DMOP). The substantial inhibition RH2O2 following borohydride reduction HS, as well dependence on and dioxygen concentrations are consistent mechanism in which phenols react triplet excited states (aromatic)...

Sodium borohydride (NaBH4) selectively reduces ketones/aldehydes to alcohols and quinones hydroquinones has been used reduce these carbonyl moieties within humic substances (HS) chromophoric dissolved organic matter (CDOM) gain insight into their contributions the optical/photochemical properties of materials. To further investigate effects reduction on absorption emission HS develop a standard protocol for this reduction, increasing concentrations were examined over course 96 h. Time...

Published algorithms were employed to convert SeaWiFS images of normalized water‐leaving‐radiance absorption CDOM (chromophoric dissolved organic matter). The best performing algorithm was produce decadal time‐series monthly composites from 1998 through 2007. Deficits in coefficient for surface waters across the shelf over summer then acquired relative uniformly mixed prior and following stratification (spring fall, respectively). Estimates attained photochemical oxidation carbon CO 2 on...

AbstractAbstractEstuarine and coastal waters of a selected area the Tyrrhenian Sea were analysed for dissolved organic carbon (DOC), absorption fluorescence properties. Coastal DOC values ranged from 0.88 to 1.37 mg L−1 with an average 1.1 L−1. Absorption coefficients measured at 280 nm (a280) 355 (a355) in range 0.95–2.3 m−1 (average 1.52 m−1) 0.14-0.57 0.27 m−1), respectively. The slope log-linearized spectra, S, 0.012 0.029 nm−1 mean value 0.019 nm−1. Normalized fluorescence, excited same...

Chromophoric dissolved organic matter (CDOM) is the dominant absorber of ultraviolet radiation in ocean, but its sources within as well chemical composition, remain uncertain. One source marine CDOM Sargassum, an epipelagic macro brown alga common to Gulf Mexico, Caribbean, and Western North Atlantic. Furthermore, Sargassum contains phlorotannins, a class polyphenols that may have similar optical properties terrestrial polyphenols. Here, we analyze properties, acquired from absorption...