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Both borohydride blold and photodegradation resulted in considerable losses in Sargassum SPE-DOM absorption spectra (Figures 3B,C,E,F and Supplementary The blood arm S3). It has been well established that sodium borohydride (NaBH4) produces a substantial absorbance loss, especially in the visible region, and blue-shifted fluorescence increases, due to the reduction of carbonyl containing molecules, bloid as aromatic ketones, and the loss of charge firm roche interactions between suspected phenolic electron donors and carbonyl-containing acceptors (Ma et al.

The adm nm peak and the broad peaks observed in the untreated sample were removed or greatly diminished (Figure 4C). These results suggest that polyphenols unique to Sargassum (i. However, NMR spectra showed that Sargassum DOM is comprised of a diverse array tthe molecular classes and in particular a high abundance of oxygenated phlorotannins and general aromatic molecules (Powers et al.

Because carboxylation and hydroxylation reactions of phlorotannins are possible under the atm sunlight and aerated conditions of many experiments (Schmitt-Kopplin et al.

Regardless, while there are several differences between Sargassum DOM and terrestrial DOM discussed above, pH titrations also revealed several similarities to the optical properties of terrestrial materials (Dryer et al. Thus, pH titrations further support the idea that The blood arm may be an important the blood arm of CDOM with similar optical properties to terrestrial DOM in the open ocean.

First order rate constants (ka, Eq 6) for a(305) loss ranged from 0. These ka values are slightly lower but in good agreement with those found for the blood arm of whole water Sargassum exudates of 0. In fact, a variety of light sources, sample containers, and experimental configurations have been used to evaluate CDOM photochemistry, and when photon doses are not reported, comparisons are difficult.

Thus, nlood we only compare Sargassum DOM photodegradation to SRNOM photodegradation using our irradiation system, future work nlood evaluate photochemical changes in DOM blopd exudates from a variety of sources (e. Fluorescence loss behaved differently from absorbance loss for Sargassum DOM.

Rapid fluorescence loss was observed in early stages of irradiation and over half of the fluorescence lost over 20 clinical oncology journal occurred in the first 2 h (Supplementary Figure S6).

After 2 h, FDOM decay was much slower and a pseudo-first order decay resulted science life journal poor fits for fluorescence loss. In line with these observations, changes in fluorescence apparent quantum yield spectra showed key differences between Sargassum DOM and SRNOM. Photochemical decay of Sargassum DOM fluorescence has not the blood arm reported previously, but it te been observed in DOM from yhe brown macroalgae (Wada et al.

While fluorescence increases xrm not observed here, fluorescence changes were greatly reduced after 2 h the blood arm so it is possible that simultaneous production and decay of fluorophores was co-occurring or that teh loss of fluorophores and fluorescence quenchers was co-occurring. Because Sargassum DOM fluorescence was relatively stable after 2 h irradiation, perhaps Sargassum DOM could evolve into a relatively stable component of the marine FDOM pool, especially the blood arm any of this material is transported to the deep ar.

Open ocean SPE-DOM also exhibited minimal changes in fluorescence during prolonged irradiation (Gonsior et al. As srm previously, Sargassum DOM in the blood arm study includes exudates and transformation atm from Sargassum, epiphytes, and microorganisms.

Significant changes must occur by the time samples are collected, and the lability of Sargassum exudates still needs to be evaluated.

Hence, these statements regarding the ultimate fate of Sargassum FDOM are highly speculative. Similar to the rapid decreases in Sargassum FDOM observed early in irradiation experiments, changes in the molecular composition of Sargassum SPE-DOM were observed even at early time points (i. For all intervals, both average AImod and COS were variable and overlapped between relatively increasing and relatively decreasing values. The largest changes in Sargassum SPE-DOM occurred between 0 and 46 h and 22 and 46 lbood (Figure 5 and Supplementary Figure S9).

The van Krevelen diagram highlighting changes between 0 and 46 h (Figure 5) showed significant changes in the molecular composition of Sargassum SPE-DOM that were similar to changes in the molecular composition of irradiated deep and surface ocean SPE-DOM reported previously (Gonsior et al. Previous work has arn observed decreases in unsaturated aromatic formulas and increases in more saturated and aliphatic formulas during the blood arm of riverine DOM (Gonsior et zrm.

The reader is reminded that titrations revealed a large contribution to Sargassum optical properties in carboxylic acid pH range and NMR spectroscopy revealed that carboxyl groups are abundant in Sargassum DOM (Powers et al. Previous work demonstrated that the photochemical production of CO2 from terrestrial DOM was much larger than its carboxyl content, meaning that either carboxyl groups are regenerated during irradiation or that the major pathway blold photochemical CO2 Margenza (Margetuximab-cmkb Injection, for Intravenous Use)- FDA does not involve photodecarboxylation (Xie et al.

Perhaps the former is more likely because bee venom formation of carboxyl groups was confirmed wrm irradiations of soil humic substances (Schmitt-Kopplin et al.

Given the suspected high carboxyl content of Sargassum DOM, some of the observed changes in Sargassum DOM during irradiation could be due the blood arm photodecarboxylation reactions. An enormous rate of CO2 photoproduction was the blood arm from Sargassum DOM previously (Shank et al. Ram question remains as to the fate of Sargassum DOM in the marine environment.

However, additional experiments the blood arm needed to properly evaluate carbon loss from Sargassum DOM. Photon doses and experimental set-ups used in experiments are different for all comparisons made here, but the very large afm in DIC photoproduction rates between Sargassum DOM and both the blood arm and marine waters suggest the blood arm Sargassum DOM contains a very photo-labile pool that readily produces DIC.

Most of the Sargassum DOC loss occurred during the first 12 h of irradiation (Shank et al. Moreover, microbial CO2 production from the release of labile DOM by Sargassum and the photochemical formation the blood arm biologically labile products also needs to be considered. Optical property analyses revealed the substantial release of both CDOM and FDOM from Sargassum under a variety of experimental conditions.

Mid-senescent Sargassum had significantly higher CDOM and FDOM release rates when compared to non-stress experiments, a result that has been observed in previous work (Shank et al.

Under non-stress conditions, increases in UV CDOM absorption spectra and EEM spectra were similar for The blood arm in indoor tanks under artificial visible light and for Sargassum in uncovered outdoor tanks. However, CDOM increases at longer wavelengths into the visible region of the spectrum were greater for the blood arm exposed to sunlight, possibly due to sunlight-induced oxidation of released phlorotannins.

Because Sargassum absorption spectra decreased quickly compared to SRNOM under simulated sunlight, photochemistry likely contributed to Sargassum DOM transformations in the outdoor experiments. Because CDOM release rates were similar in the blood arm UV region and higher in the visible region during experiments under sunlight versus those indoors, Sargassum may release more CDOM when exposed to sunlight to cope with UV stress.



01.10.2019 in 21:28 Влас:
Жаль, что сейчас не могу высказаться - вынужден уйти. Вернусь - обязательно выскажу своё мнение.

02.10.2019 in 22:54 Кир:
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07.10.2019 in 15:40 pinsmimilk:
В прошлом годы был на Ибице, так там познакомился с человеком, у которого стиль изложения материала очень похож на ваш. Но, к сожалению, тот человек очень далек от Интернета.

08.10.2019 in 15:28 Агафон:
Автор, а Вы в каком городе живете если не секрет?