title: Geosphere-biosphere interactions in bio-activity volcanic lakes: evidences from Hule and Rìo Cuarto (Costa Rica).
abstract: Hule and Río Cuarto are maar lakes located 11 and 18 km N of Poás volcano along a 27 km long fracture zone, in the Central Volcanic Range of Costa Rica. Both lakes are characterized by a stable thermic and chemical stratification and recently they were affected by fish killing events likely related to the uprising of deep anoxic waters to the surface caused by rollover phenomena. The vertical profiles of temperature, pH, redox potential, chemical and isotopic compositions of water and dissolved gases, as well as prokaryotic diversity estimated by DNA fingerprinting and massive 16S rRNA pyrosequencing along the water column of the two lakes, have highlighted that different bio-geochemical processes occur in these meromictic lakes. Although the two lakes host different bacterial and archaeal phylogenetic groups, water and gas chemistry in both lakes is controlled by the same prokaryotic functions, especially regarding the CO2-CH4 cycle. Addition of hydrothermal CO2 through the bottom of the lakes plays a fundamental priming role in developing a stable water stratification and fuelling anoxic bacterial and archaeal populations. Methanogens and methane oxidizers as well as autotrophic and heterotrophic aerobic bacteria responsible of organic carbon recycling resulted to be stratified with depth and strictly related to the chemical-physical conditions and availability of free oxygen, affecting both the CO2 and CH4 chemical concentrations and their isotopic compositions along the water column. Hule and Río Cuarto lakes were demonstrated to contain a CO2 (CH4, N2)-rich gas reservoir mainly controlled by the interactions occurring between geosphere and biosphere. Thus, we introduced the term of bio-activity volcanic lakes to distinguish these lakes, which have analogues worldwide (e.g. Kivu: D.R.C.-Rwanda; Albano, Monticchio and Averno: Italy; Pavin: France) from volcanic lakes only characterized by geogenic CO2 reservoir such as Nyos and Monoun (Cameroon).
authors: Dipartimento di Scienze della Terra, University of Florence, Florence, Italy.
authors: Jacopo
authors: J
authors: Cabassi
authors: Dipartimento di Scienze della Terra, University of Florence, Florence, Italy; CNR - Istituto di Geoscienze e Georisorse, Florence, Italy.
authors: Franco
authors: F
authors: Tassi
authors: Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
authors: Francesca
authors: F
authors: Mapelli
authors: Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
authors: Sara
authors: S
authors: Borin
authors: Dipartimento di Scienze della Terra e del Mare, University of Palermo, Palermo, Italy.
authors: Sergio
authors: S
authors: Calabrese
authors: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna, Bologna, Italy.
authors: Dmitri
authors: D
authors: Rouwet
authors: Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy.
authors: Giovanni
authors: G
authors: Chiodini
authors: Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
authors: Ramona
authors: R
authors: Marasco
authors: Department of Food, Environmental and Nutritional Sciences, University of Milan, Milan, Italy.
authors: Bessem
authors: B
authors: Chouaia
authors: Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy.
authors: Rosario
authors: R
authors: Avino
authors: Dipartimento di Scienze della Terra, University of Florence, Florence, Italy; CNR - Istituto di Geoscienze e Georisorse, Florence, Italy.
authors: Orlando
authors: O
authors: Vaselli
authors: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, Italy.
authors: Giovannella
authors: G
authors: Pecoraino
authors: Dipartimento di Scienze della Terra, University of Florence, Florence, Italy; CNR - Istituto di Geoscienze e Georisorse, Florence, Italy.
authors: Francesco
authors: F
authors: Capecchiacci
authors: Dipartimento di Scienze della Terra, University of Florence, Florence, Italy.
authors: Gabriele
authors: G
authors: Bicocchi
authors: Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy.
authors: Stefano
authors: S
authors: Caliro
authors: Centro de Investigaciones en Ciencias Geológicas, Escuela Centroamericana de Geología, Red Sismológica Nacional, Universidad de Costa Rica, San Jose, Costa Rica.
authors: Carlos
authors: C
authors: Ramirez
authors: Centro de Investigaciones en Ciencias Geológicas, Escuela Centroamericana de Geología, Red Sismológica Nacional, Universidad de Costa Rica, San Jose, Costa Rica.
authors: Raul
authors: R
authors: Mora-Amador
mesh_terms: D001105:Archaea / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D001419:Bacteria / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D002245:Carbon Dioxide / Q000737:chemistry; D003364:Costa Rica; D016172:DNA Fingerprinting; D006863:Hydrogen-Ion Concentration; D060086:Hydrothermal Vents / Q000737:chemistry / Q000382:microbiology; D060106:Lakes / Q000737:chemistry / Q000382:microbiology; D008697:Methane / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics*; D018707:Volcanic Eruptions
chemical_list: D012336:RNA, Ribosomal, 16S; D002245:Carbon Dioxide; D008697:Methane; D010100:Oxygen