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Biodegradation of CO2, CH4 and volatile organic compounds (VOCs) in soil gas from the Vicano-Cimino hydrothermal system (central Italy)
Language
English
Obiettivo Specifico
6A. Geochimica per l'ambiente
Status
Published
JCR Journal
JCR Journal
Title of the book
Issue/vol(year)
/86(2015)
Pages (printed)
81-93
Issued date
2015
Abstract
We investigated the effect of microbial activity on the chemistry of hydrothermal fluids related to the
Vicano–Cimino system, central Italy. The database included the composition and d13C CO2 and d13C
CH4 values for soil gas from an area characterized by intense degassing of fluids having a deep origin.
The d13C CH4 values along vertical profiles in the soil indicated that CH4 was controlled by microbial
oxidation occurring at shallow (<50 cm) depth, where free O2 was available. This was consistent with
the vertical gradients of CH4, H2S and O2 concentrations. The d13C CO2 values in soil gas, characterized
by a composition similar to that of the hydrothermal fluids, were not significantly influenced by
biodegradation. On the contrary, gas strongly affected by air contamination showed a significant d13C
CO2 fractionation. Microbial activity caused strong consumption of hydrothermal alkanes, alkenes, cyclics
and hydrogenated halocarbons, whereas benzene was recalcitrant. Oxygenated compounds from
hydrocarbon degradation consisted of alcohols, with minor aldehydes, ketones and carboxylic acids. A
predominance of alcohols at a high rate of degassing flux, corresponding to a short residence time of
hydrothermal gas within the soil, indicated incomplete oxidation. N-bearing compounds were likely produced
by humic substances in the soil and/or related to contamination by pesticides, whereas a-pinene
traced air entering the soil. The study demonstrates that microbial communities in the soil play an important
role for mitigating the release to the atmosphere of C-bearing gases, especially CH4, through diffuse
soil degassing, a mechanism that in central Italy significantly contributes to the discharge of CO2-rich gas
from deep sources
Vicano–Cimino system, central Italy. The database included the composition and d13C CO2 and d13C
CH4 values for soil gas from an area characterized by intense degassing of fluids having a deep origin.
The d13C CH4 values along vertical profiles in the soil indicated that CH4 was controlled by microbial
oxidation occurring at shallow (<50 cm) depth, where free O2 was available. This was consistent with
the vertical gradients of CH4, H2S and O2 concentrations. The d13C CO2 values in soil gas, characterized
by a composition similar to that of the hydrothermal fluids, were not significantly influenced by
biodegradation. On the contrary, gas strongly affected by air contamination showed a significant d13C
CO2 fractionation. Microbial activity caused strong consumption of hydrothermal alkanes, alkenes, cyclics
and hydrogenated halocarbons, whereas benzene was recalcitrant. Oxygenated compounds from
hydrocarbon degradation consisted of alcohols, with minor aldehydes, ketones and carboxylic acids. A
predominance of alcohols at a high rate of degassing flux, corresponding to a short residence time of
hydrothermal gas within the soil, indicated incomplete oxidation. N-bearing compounds were likely produced
by humic substances in the soil and/or related to contamination by pesticides, whereas a-pinene
traced air entering the soil. The study demonstrates that microbial communities in the soil play an important
role for mitigating the release to the atmosphere of C-bearing gases, especially CH4, through diffuse
soil degassing, a mechanism that in central Italy significantly contributes to the discharge of CO2-rich gas
from deep sources
Type
article
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