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13 results on '"De Nobili, Maria"'

12. Electrochemical and Structural Modifications of Humic Acids in Aerobically and Anaerobically Incubated Peat.

Author

Bravo, Carlo, Toniolo, Rosanna, Contin, Marco, and De Nobili, Maria

Subjects
HUMIC acid, ELECTROPHILES, PEAT mosses, FLUORESCENCE spectroscopy, SULFONIC acids, GREENHOUSE gases & the environment
Abstract

Exposure to oxygen and aerobic biological activity during drought periods alters the availability of terminal electron acceptors (TEA) in the peat catotelm layer. We investigated the changes in the electrochemical and chemical characteristics of humic acids (HA) induced by subjecting air-dried sphagnum peat to biological oxidation or reduction during a 90-day incubation experiment. Structural modifications of HAs from anaerobically (HAred) and aerobically (HAox) incubated peat were investigated by ATR-FTIR, UV-vis, and EEM fluorescence spectroscopy. Number and strength of acid groups were characterized by titration, while changes in redox properties were characterized by cyclic voltammetry and quantified by coulometry with mediated electrochemical oxidation (MEO). Exposure to oxygen had small effects, but compared to anaerobic incubation, decreased by 20% the capacity of HA to reduce the radical ion of 2,2'-Azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS·-), passing from 2.77 ± 0.13 mmole- gHA-1 in HAred to 2.21 ± 0.10 mmole- gHA-1 in HAox. Pseudo-first-order electron transfer kinetic constants were 13.3 ± 1.2 s-1 for HAox and 16.7 ± 1.4 s-1 for HAred. Alterations in the hydrological status of the catotelm have minor effects on the actual in situ availability of organic TEA, but if coupled to intensified biological activity they may result in significant variations of greenhouse gases emissions. [ABSTRACT FROM AUTHOR]

Published
2021
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13. Electron donating properties of humic acids in saltmarsh soils reflect soil geochemical characteristics

Author

Carlo Bravo, Rosanna Toniolo, Elisa Pellegrini, Christian Millo, Stefano Covelli, Marco Contin, Ladislau Martin-Neto, Maria De Nobili, Bravo, Carlo, Toniolo, Rosanna, Pellegrini, Elisa, Millo, Christian, Covelli, Stefano, Contin, Marco, Martin-Neto, Ladislau, and De Nobili, Maria

Subjects
Salt marshes, Redox, Humic substance, Soil Science, ABTS, EDC, Humic substances, Salt marshe, BIOGEOQUÍMICA MARINHA
Abstract

n saltmarsh soils, humic acids (HA) are involved in geochemically important redox processes. The electron donating capacity (EDC) of HA depends on their molecular structure, but also reflects the intensity of biological reduction in tidal environments. We examined twelve soils in three saltmarshes located along a geographical gradient and applied a specific sequential extraction procedure for the isolation of HA fractions bound (BHA) or not (FHA) to the mineral matrix by Ca2+ bridges, and investigated the relationships of their properties, in particular their EDC, with the biogeochemical characteristics of the soils. Spectroscopic assessment was carried out by UV–vis, FTIR and 13C NMR, quantification and characterization of radicals was performed by electron paramagnetic resonance (EPR) spectroscopy. The EDC was determined by using the 2,2′ -azinobis-(3-ethyl-benzothiazolinesulfonic acid) (ABTS) decolorization assay and experimental data were fitted to a biphasic model to calculate the contributions of the fast and slow reactions to electron transfer. The results confirmed that the two HA fractions possess different structural characteristics and that BHA present higher EDC values compared to FHA. The EDC of both fractions is strongly related to the geochemical characteristics of soils, and represents an easily measured and highly informative parameter to understand mechanisms affecting redox processes in transitional environments

Published
2022

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