Alfredo Seritti

DOC, absorption and fluorescence properties of estuarine and coastal waters of the Northern Tyrrhenian Sea

AbstractEstuarine and coastal waters of a selected area of the Tyrrhenian Sea were analysed for dissolved organic carbon (DOC), absorption and fluorescence properties. Coastal DOC values ranged from 0.88 to 1.37 mg L−1 with an average of 1.1 mg L−1. Absorption coefficients measured at 280 nm (a280) and 355 nm (a355) were in the range 0.95–2.3 m−1 (average 1.52 m−1) and 0.14-0.57 m−1 (average 0.27 m−1), respectively. The slope of the log-linearized absorption spectra, S, ranged from 0.012 to 0.029 nm−1 with a mean value of 0.019 nm−1. Normalized fluorescence, excited at the same wavelengths of the absorption measurements, Fn(280) and Fn(355), exhibited mean values of 0.07 and 0.77 N.Fl.U., and the quantum yields, Ф280 and Ф355, had mean values of 0.0014 and 0.0065, respectively. The chromatographic behavior of a riverine and a coastal sample, compared with that of a solution of commercial humic acid, used as standard, shows a variation in the chromatographic signature to which corresponds a decrease in the...

Organic carbon dynamics in the Mediterranean Sea: An integrated study

[1] Total (TOC) and dissolved (DOC) organic carbon vertical profiles were analyzed from 11 stations located in various regions of the Mediterranean Sea, together with the distribution of other physical, chemical and biological parameters. TOC showed the highest concentrations (68–83 mM) above the pycnocline, followed by a marked decrease to values of 45–48 mM at 100–200 m. Below 200 m, values of 40–45 mM were observed. The excess TOC and DOC occurring at each station was calculated by subtracting 48 mM from the observed concentrations. The stock of the excess TOC and DOC increased eastward; while surface DOC mineralization rates decreased from 1.5 m Md 1 to 0.26 m Md 1 eastward. The integrated average of the biological parameters in the above-pycnocline layer showed a bacterial production versus particulate primary production (BP/PPP) ratio ranging from 22% in the Ionian Sea (MIO station) to 31% in the Ligurian Sea (Dyfamed station), while bacterial carbon demand versus PPP was higher than 100%, considering a bacterial growth efficiency of both 15% and 30%. The data here reported indicate various scenarios of carbon dynamics. At the stations west of the Sardinian Channel, the microbial loop was very active, and a high flux of carbon to the microbial loop (large bacterial and protist abundance) may be hypothesized, which would result in a low DOC concentration. At the stations east of the Sardinian Channel, no significant longitudinal variation was found in DOC and BP. DOC accumulated at these stations, possibly due to bacteria P-limitation, to DOC chemical composition and/or to the occurrence of different prokaryotic populations with a different ability to consume the available DOC.

Production of hydrophobic fluorescent organic matter by the marine diatom Phaeodactylum tricornutum

Abstract A fluorescence-chromatography cross-investigation on C-18 Sep-Pak extractable organic matter produced by a laboratory culture of Phaeodactylum tricornutum (SPE-POM) is presented. A comparison with the fluorescence and chromatographic characteristics of the Sep-Pak extractable dissolved marine organic matter (SPE-MOM) is also described. The results show that Phaeodactylum tricornutum excretes two main groups of fluorescent compounds consisting of protein material and flavins, which are very quickly degradated to simplier structures which can be considered a part of the starting reagents of humification reactions in the sea. Reverse phase high performance liquid chromatography (RP-HPLC) allowed two degradation products of riboflavin to be isolated.

Ethylenediamine in the voltammetric determination of copper in sea water at a rotating mercury film electrode

Abstract The use of ethylenediamine in the voltammetric study of copper in natural sea water was evaluated for applicability with rotating thin mercury film electrodes. It was shown that this method increases the analytical sensitivity for copper at such electrodes by at least a factor of 4, and improves the detection of pH 8 labile copper.

Use of Synchronous Scan Excitation Spectra to Detect Fluorescent Metal Organic Ligands Produced by the Marine Diatom Phaeodactylum Tricornutum

The use of synchronous scan excitation spectra (SSES) for investigating the fluorescence characteristics of the Sep-Pak extractable phytoplanktonic organic matter (SPE-POM) produced by the marine diatom Phaeodactylum tricornutum under (SPE-POM∗) and without (SPE-POM) metal stress is proposed. A Δλ of 70 nm was found suitable to detect the fluorophores occurring in such samples. A proteinaceous, lumichrome and lumiflavin contributions together with that of a degradation and/or condensation product were observed. The fluorescence quenching technique applied to SSES enabled detection of the contribution of each group of fluorophores to the copper complexation. The log K of complexes were in the range 5–6. A comparison with the Sep-Pak extractable marine organic matter (SPE-MOM) from seawater shows a relationship between the proteinaceous material produced by Phaeodactylum tricornutum and that occurring in seawater.

Fluorescence characteristics of reverse phase HPLC fractionated marine organic matter

Abstract Fluorescence emission spectra, recorded at different excitation wavelengths (λex), and synchronous‐scan excitation spectra of Sep‐Pak extractable marine organic matter (SPE‐MOM) and its reverse phase HPLC fractions were used to describe the fluorescence characteristics of such naturally occurring organic compounds. Sep‐Pak extractable soil fulvic acid (SPE‐SFA) and its Chromatographic fractions were used as reference material. The results show a different distribution of fluorescent material with respect to the chromophoric one in the HPLC fractions of SPE‐MOM with a higher concentration of the shortest wavelength emitting fluorophores in the most hydrophobic fraction. No apparent correlation with polarity was observed for the SPE‐SFA sample. Synchronous‐scan excitation spectra indicate a higher presence of the shorter λex fluorophores in SPE‐MOM whereas SPE‐SFA exhibits a remarkable presence of longer λex fluorophores. Hence, a younger formation of marine organic matter with a lower structural c...

Copper binding ability of the extracellular organic matter released by Skeletonema costatum

AbstractThe copper complexing ability of the exudates produced during the exponential growth phase by Skeletonema costatum has been investigated by a ligand-competition technique involving copper sorption onto C-18 Sep-Pak cartridges. Two ligands with different affinity for copper were required for the best fit of the copper complexation data in seawater with and without exudates: a strong ligand with a log K close to 13 and a weaker ligand with a log K close to 9. The culture increased both L1 and L2 ligand concentrations, already present in seawater, by a factor close to 4 after the first 72 hours of growth. The presence of class 1 stronger ligands in copper binding organics produced by the diatom is discussed in relation to natural copper speciation in the sea.