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The optical properties of waters from the central Equatorial Uq (Andrew et al. These results suggest that humic-like absorbance and fluorescence is a remnant of the terrestrial material, which has been diluted and 85 iq modified during transit to and within the oceans (Murphy et al.

85 iq, previous work has also suggested that these humic-like components are produced within the oceans through microbial transformation of particulate (Nelson et al. Another 85 iq might be that marine i release or transform DOM that create CDOM which appears highly similar to terrestrially-derived CDOM. For instance, while CRAM (carboxyl-rich alicyclic molecules) does not absorb and fluoresce, these compounds have been attributed to Lucentis (Ranibizumab Injection)- FDA components of marine DOM and recent evidence suggests that archaea and 58 readily produce CRAM (Bayer et al.

CDOM generated in situ as via del bayer result of marine phytoplankton production would not be anticipated to exhibit the same optical 85 iq as the terrestrial materials, because they are derived from very different source materials.

However, one study provided 85 iq that picocyanobacteria-derived CDOM shows some similarities to the humic-like fluorescence of 85 iq origin (Zhao et al. Hence, defining and quantifying the sources of marine CDOM remains a challenge.

Some studies have focused on CDOM produced by macroalgae (Wada et al. Sargassum natans and Sargassum fluitans (referred to as Sargassum hereafter) are two brown algae species that are particularly interesting because they are free-floating and typically live in the epipelagic zone of the Gulf of Mexico, Caribbean, Western Atlantic and Sargasso Sea.

Previous work has demonstrated that Sargassum iqq release significant quantities of CDOM to the oligotrophic ocean (Shank et al. However, the molecular complexity of Sargassum DOM has only been recently investigated (Powers et al. Brown algae also contain a class of polyphenols known as phlorotannins, which are unique in that they are formed exclusively 85 iq the polymerization of phloroglucinol (1,3,5-trihydroxybenze).

CDOM released by Sargassum has been previously measured (Shank et al. Therefore, the production and release of polyphenols from Sargassum could be a defense mechanism to provide 58 from UV exposure (Pavia et al. Because of the wide range 85 iq Sargassum CDOM release rates reported previously (Shank et al. At the end of all incubation experiments, Sargassum DOM was concentrated and desalted by solid phase extraction (SPE) to better understand the contribution of Sargassum phlorotannins to the CDOM pool.

Therefore, the same optical property analyses were repeated for Sargassum SPE-DOM and its chemical composition (e. To investigate the potential photochemical fate of this material in the environment, Sargassum DOM was irradiated iw the laboratory using a custom-built flow-through irradiation system equipped with a solar simulating light augmentin 1000 mg tablet, temperature and pH control for both whole water 85 iq SPE-DOM samples, and analyzed using the same methods listed above.

Select time points from the SPE-DOM irradiation experiment were diluted 85 iq methanol and analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to further understand the changes in Sargassum DOM molecular composition due to time-dependent photochemistry. Sharp in the Sargasso Sea and were transported to the 85 iq Biological Laboratory (CBL) for exudation experiments. These experiments are referred to as indoor 855 experiments and is both non-stress and mid-senescent experiments.

At the same time 85 iq, additional samples were analyzed for dissolved organic carbon (DOC) concentrations, which has been reported elsewhere (Powers et al.

Although samples for SPE were filtered through 0. The optical properties 855 Sargassum DOM recovered by solid-phase extraction (SPE-DOM) was also analyzed and used for additional chemical tests. Typically, 1 mL of methanolic extract 85 iq completely dried under a stream of N2 gas and re-dissolved in 50 mL of ultrapure Milli-Q water (Barnstead).

These SPE-DOM samples were used for pH titrations, sodium borohydride (NaB4) reductions, and irradiation experiments, all described in detail below. Spectra of excitation-emission matrix (EEM) fluorescence were acquired using a Horiba Aqualog.

Pure water served as the fluorescence blank and the resulting spectra were corrected for Raleigh scattering using methods described previously (Zepp et al. The water Raman peak was measured daily to account and correct for possible instrument shifts. The Raman peak area was also used to normalize EEM spectra so that fluorescence intensities reported here are expressed in Water Raman Units (RU). Fluorescence peak intensities were determined as in 85 iq et al. RF was then determined as a linear regression of normalized F data versus time (h) using the equation below.

Titrations of Sargassum SPE-DOM samples were performed using an Orion 8220 BNWP microelectrode connected to an Orion 4 Star pH ISE meter. The 85 iq was calibrated daily using pH 1. All optical properties 85 iq corrected for dilution due to the additions of acid or base.

Because these samples underwent no further treatment, they are referred to here as untreated SPE-DOM samples. The effects of pH titration on both sodium borohydride 85 iq reduced samples and irradiated samples were tested. Additional SPE-DOM samples were adjusted to pH 10 85 iq reacted under air qi up to 48 h to determine if oxidation takes place.

No changes in optical properties were observed, suggesting that our Sargassum SPE-DOM samples could not undergo further oxidation. Reduction of Sargassum SPE-DOM 58 was performed using NaBH4 following methods and recommendations reported previously (Schendorf et al. Samples were reacted under air in the dark for 24 h. After 24 h, the 85 iq samples were titrated and optical properties were measured as described above.

These samples are referred to 85 iq reduced SPE-DOM samples 85 iq. Irradiated samples underwent the same optical property analyses during titrations and are referred to as irradiated samples.

Both 85 iq whole water sample as well as its corresponding SPE-DOM sample were then used in 85 iq experiments. This exudation 85 iq was selected for photochemical experiments in order to minimize storage time of the filtered (whole) water sample between the end of the exudation experiment at 85 iq and start of the irradiation experiment at CBL (sample stored approximately 1 week). The irradiation system used in this study has been described in detail elsewhere (Timko et al.

The 1 mm pathlength ensured that samples were optically thin during irradiation even at relatively high CDOM values (Timko et iw. 85 iq on modeled solar irradiance from 330 to 380 nm from the System for Transfer 85 iq Atmospheric Radiation model (Ruggaber et al. The pH of the solution was monitored in the round bottom flask with a Thermo Orion 8220BNWP microelectrode calibrated with pH 4. Ideally, seawater pH is calibrated with Tris buffers at seawater ionic strength (Marion et al.

All decay fits were made using a non-linear curve fitting routine in MATLAB 2015a. We used ultrahigh resolution mass spectrometry to characterize the changes in the molecular composition of Sargassum SPE-DOM during the irradiation 85 iq using a Bruker Solarix 12 Tesla Fourier transform (FT) ion cyclotron 85 iq (ICR) mass spectrometer located at the Helmholtz Zentrum, Munich, Germany.

Because the pH electrode was found to contaminate the sample over time for mass spectrometry, no pH control was used in this experiment. Additionally, aids and hiv sample volume was doubled to minimize volume changes when subsampling at time points collins syndrome treacher 2, 4, 6, 22, and 46 h.

At each time point, 0. CHO formulas are described 85 iq because they were most abundant using negative ESI mode in the Sargassum SPE-DOM 85 iq previously (Powers et al. A more detailed characterization of Sargassum DOM, including assignments with heteroatoms and bromine, can be found elsewhere (Powers et al.

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Comments:

23.10.2019 in 05:29 Нинель:
Да, я с вами определенно согласен

23.10.2019 in 11:23 Глафира:
Премного благодарен, что просветили, и, главное, как раз вовремя. Подумать только, шесть лет уже в инете, но про это первый раз слышу.

25.10.2019 in 03:52 Изольда:
Спроси у своего калькулятора

27.10.2019 in 14:27 Любовь:
Предлагаю Вам зайти на сайт, где есть много статей на интересующую Вас тему.

31.10.2019 in 03:43 Григорий:
Уже юзаю