Mechanisms regulating CO2 and CH4 dynamics in the Azorean volcanic lakes (São Miguel Island, Portugal)

Bio-geochemistry of volcanic lakes in the Azores, Portugal

  • Franco Tassi | University of Florence, Italy.
  • Jacopo Cabassi University of Florence, Italy.
  • Cesar Andrade Universidade dos Açores, Portugal.
  • Cristiana Callieri CNR-ISE, Italy.
  • Catarina Silva Universidade dos Açores, Portugal.
  • Fatima Viveiros Universidade dos Açores, Portugal.
  • Gianluca Corno CNR-ISE, Italy.
  • Orlando Vaselli University of Florence, Italy.
  • Enrico Selmo University of Parma, Italy.
  • Andrea Gallorini University of Florence, Italy.
  • Andrea Ricci University of Florence, Italy.
  • Luciano Giannini University of Florence, Italy.
  • Josè V. Cruz Universidade dos Açores, Portugal.


Chemical and isotopic vertical profiles from the volcanic lakes of Sete Cidades, Santiago, Fogo, Congro and Furnas (Island of São Miguel, Azores Archipelago, Portugal) were studied to investigate the biogeochemical processes acting at different depths, with a focus on the CO2 and CH4 dynamics. These lakes are fed by meteoric water affected by seawater spray and interacting with volcanic rocks at a relatively low extent. In addition to volcanogenic gas inputs, the biogeochemical processes are influenced by microbial activities since the lakes offer specialized ecological niches for oxic and anoxic metabolism. The lakes were sampled in two extreme conditions of (partial) mixing (winter) and stratification (summer), respectively. The seasonal thermal stratification favored the development of anaerobic hypolimnia, showing relatively high concentrations of NH4+, NO3-, P and other minor species (Fe, Mn, Zn, As) controlled by microbial activity and minerogenetic processes occurring within the lake sediments. The strongly negative d13C-TDIC values measured in almost all the studied lakes suggest dominant contribution of organic carbon. Dissolved gases were mostly consisting of atmospheric compounds with significant concentrations of CO2 and CH4. The d13C-CO2 values were intermediate between those measured in the hydrothermal fluids and those typical of biogenic CO2. Dissolved CH4, which was the most abundant extra-atmospheric gas in the anoxic waters, was measured at significant concentrations even in the aerobic layers, especially in the winter season. This unexpected feature may tentatively be explained by admitting i) convective mixing of shallow and deep waters, and/or ii) aerobic CH4 production. Further investigations, focusing on the recognition of microbial populations able to produce CH4 at different redox conditions, may be useful to corroborate these intriguing hypotheses.



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Author Biography

Franco Tassi, University of Florence
Department of Earth Sciences, Associate Professor
Original Articles
Supporting Agencies
no funding
Volcanic lake, methane paradox, lake stratification, dissolved gas reservoir, microbiological activity, Azores.
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How to Cite
Tassi F, Cabassi J, Andrade C, Callieri C, Silva C, Viveiros F, Corno G, Vaselli O, Selmo E, Gallorini A, Ricci A, Giannini L, Cruz JV. Mechanisms regulating CO2 and CH4 dynamics in the Azorean volcanic lakes (São Miguel Island, Portugal): Bio-geochemistry of volcanic lakes in the Azores, Portugal. J Limnol [Internet]. 2018Jul.24 [cited 2021Apr.22];77(3). Available from:

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