Photobleaching of chromophoric dissolved organic matter (CDOM) in the Yangtze River estuary: kinetics and effects of temperature, pH, and salinity

Song, Guisheng; Li, Yijie; Hu, Suzheng; Li, Guiju; Zhao, Ruihua; Sun, Xin; Xie, Huixiang

doi:10.1039/c6em00682e

Cited by 26 publications

(16 citation statements)

References 89 publications

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“…The time‐course CDOM and humic‐like FDOM data are best fit to the equation of

Y = R_{0} + R_{p} * ((), - k_{lab} * X),

where X (day) stands for irradiation time, Y for a CDOM (330), or C h normalized to the time‐zero value, R 0 for the photobleaching‐resistant fraction of CDOM or humic‐like FDOM, R p for the photobleachable fraction of CDOM or humic‐like FDOM, and k lab (day −1 ) for the photobleaching rate constant of the photobleachable fraction. A similar approach has been used to estimate the photobleachable and photobleaching‐resistant fractions of CDOM in the Yangtze River estuary (Song et al, 2017) and the bio‐labile and bio‐refractory fractions of DOM in coastal oceans (Lønborg & Álvarez‐Salgado, 2012).…”

Section: Resultsmentioning

confidence: 99%

“…The Napierian absorption coefficient at wavelength λ (nm), a CDOM ( λ ) (m −1 ), was calculated as 2.303 times the measured absorbance at λ divided by the path length of the cuvette (0.1 m). The detection limit, defined as three times the standard deviation of eight Nanopure water blank measurements, was 0.018 m −1 in the wavelength range from 300–500 nm (Song et al, 2017). The spectral slope coefficient between 275 and 295 nm, S 275–295 (nm −1 ), was calculated according to the method of Helms et al (2008).…”

Section: Methodsmentioning

confidence: 99%

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Depth‐Resolved Photochemical Lability of Dissolved Organic Matter in the Western Tropical Pacific Ocean

et al. 2020

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Water samples collected from various depths of the offshore South China and Philippine Seas were exposed to solar‐simulated radiation. Photomineralization of dissolved organic carbon (DOC) and photobleaching of chromophoric dissolved organic matter (CDOM) and its humic‐like fluorescent constituent (FDOM) were observed in all samples. Protein‐like FDOM was, however, either photo‐decomposed or photo‐produced, depending on the sample's depth. The photobleaching of CDOM and humic‐like FDOM was much faster in deep than in shallow water samples while photomineralization displayed a weaker vertical zonation. Prior‐irradiated deep water inoculated with surface‐water bacteria showed enhanced microbial DOC removal but CDOM production. Results from this study suggest that deep‐ocean CDOM and FDOM can barely survive photobleaching during one ocean mixing cycle, but photochemical turnover of the bio‐refractory deep DOC is considerably longer than its average radiocarbon age. Coupled photochemical‐microbial processes can not only remove part of the bio‐refractory deep DOM but also regenerate part of it during ocean overturning circulation.

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“…The time‐course CDOM and humic‐like FDOM data are best fit to the equation of

Y = R_{0} + R_{p} * ((), - k_{lab} * X),

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Depth‐Resolved Photochemical Lability of Dissolved Organic Matter in the Western Tropical Pacific Ocean

et al. 2020

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“…The analytical uncertainty of a CDOM measurement was assessed by analyzing six replicates of the sample collected at station M01 from the August cruise, arriving at a standard deviation of 0.06 m −1 or 1.3 % at 330 nm, with the mean a CDOM at 330 nm (a 330 ) being 4.37 m −1 . In this study we choose a 330 as an indicator of the CDOM abundance, given that this variable has been frequently used for this surrogate role (e.g., Osburn et al, 2009;Gareis et al, 2010;Mann et al, 2012;Song et al, 2017) and that the wavelength of 330 nm is where many aquatic CDOM photoreactions, including photobleaching, exhibit maximum rates in surface water under solar radiation (e.g., Vähätalo et al, 2000;Zhang et al, 2006;White et al, 2010;Xie et al, 2012a). CDOM absorption coefficients at other commonly used wavelengths and the spectral slope coefficient between 300 and 500 nm are presented in Table S2.…”

Section: Dom Analysismentioning

confidence: 99%

Distribution, seasonality, and fluxes of dissolved organic matter in the Pearl River (Zhujiang) estuary, China

Song

Massicotte³

et al. 2019

Biogeosciences

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Abstract. Dissolved organic carbon (DOC) concentration in the Pearl River estuary (PRE) of China was measured in May, August, and October 2015 and January 2016. Chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) in the latter three seasons were characterized by absorption and fluorescence spectroscopy. CDOM and FDOM exhibited negligible seasonal variations, while DOC displayed a significant seasonality, with the average concentration being highest in May (156 µmol L−1), lowest in November (87 µmol L−1), and comparable between January (118 µmol L−1) and August (112 µmol L−1). Although DOC, CDOM, and FDOM in surface water were generally higher than in bottom water, the difference between the two layers was statistically insignificant. DOC showed little cross-estuary variations in all seasons, while CDOM and FDOM in January were higher on the west side of the estuary than on the east side. All three variables showed rapid drawdowns in the head region of the estuary (salinity <5); their dynamics in the main estuary were primarily controlled by conservative mixing, leading to linearly declining or relatively constant (for DOC in May and November only) contents with increasing salinity. The decrease in FDOM with salinity was 5 %–35 % faster than that of CDOM, which in turn was 2–3 times quicker than that of DOC. Salinity and CDOM absorption coefficients could serve as indicators of DOC in August and January. Freshwater endmembers in all seasons mainly contained fresh, protein-rich DOM of microbial origin, a large part of it likely being pollution-derived. Protein-like materials were preferentially consumed in the head region but the dominance of the protein signature was maintained throughout the estuary. Exports of DOC and CDOM (in terms of the absorption coefficient at 330 nm) into the South China Sea were estimated as 195×109 g and 266×109 m2 for the PRE and 362×109 g and 493×109 m2 for the entire Pearl River Delta. The PRE presents the lowest concentrations and export fluxes of DOC and CDOM among the world's major estuaries. DOM delivered from the PRE is, however, protein-rich and thus may enhance heterotrophs in the adjacent coastal waters. Overall, the PRE manifests lower abundance and smaller spatiotemporal variability of DOM than expected for a sizable estuary with a marked seasonality of river runoff due supposedly to the poorly forested watershed of the Pearl River, the rapid degradation of the pollution-derived DOM in the upper reach, and the short residence time of freshwater.

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“…The rest was unresolved. Studies on environmental grab samples are mixed; some report no consistent effect, others rate enhancement, and still others rate suppression with increasing salinity (see [ 76 , 77 ]).…”

Section: Involvement Of Halogen Species In Organic Matter Processimentioning

confidence: 99%

Participation of the Halogens in Photochemical Reactions in Natural and Treated Waters

Yang

Pignatello

2017

Molecules

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Halide ions are ubiquitous in natural waters and wastewaters. Halogens play an important and complex role in environmental photochemical processes and in reactions taking place during photochemical water treatment. While inert to solar wavelengths, halides can be converted into radical and non-radical reactive halogen species (RHS) by sensitized photolysis and by reactions with secondary reactive oxygen species (ROS) produced through sunlight-initiated reactions in water and atmospheric aerosols, such as hydroxyl radical, ozone, and nitrate radical. In photochemical advanced oxidation processes for water treatment, RHS can be generated by UV photolysis and by reactions of halides with hydroxyl radicals, sulfate radicals, ozone, and other ROS. RHS are reactive toward organic compounds, and some reactions lead to incorporation of halogen into byproducts. Recent studies indicate that halides, or the RHS derived from them, affect the concentrations of photogenerated reactive oxygen species (ROS) and other reactive species; influence the photobleaching of dissolved natural organic matter (DOM); alter the rates and products of pollutant transformations; lead to covalent incorporation of halogen into small natural molecules, DOM, and pollutants; and give rise to certain halogen oxides of concern as water contaminants. The complex and colorful chemistry of halogen in waters will be summarized in detail and the implications of this chemistry for global biogeochemical cycling of halogen, contaminant fate in natural waters, and water purification technologies will be discussed.

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Photobleaching of chromophoric dissolved organic matter (CDOM) in the Yangtze River estuary: kinetics and effects of temperature, pH, and salinity

Cited by 26 publications

References 89 publications

Depth‐Resolved Photochemical Lability of Dissolved Organic Matter in the Western Tropical Pacific Ocean

Depth‐Resolved Photochemical Lability of Dissolved Organic Matter in the Western Tropical Pacific Ocean

Distribution, seasonality, and fluxes of dissolved organic matter in the Pearl River (Zhujiang) estuary, China

Participation of the Halogens in Photochemical Reactions in Natural and Treated Waters

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