Suchergebnisse

Castañar cave contains the highest radon gas (222Rn) concentration in Spain with an annual average of 31.9 kBq m−3. Seasonal variations with summer minimums and maximum values in fall were recorded. The reduction of air-filled porosity of soil and rock by condensation or rainfalls hides the radon exchange by gas diffusion, determining this seasonal stair-step pattern of the radon activity concentration in underground air. The effective total dose and the maximum hours permitted have been evaluated for the guides and public safety with a highly detailed radon measurement along 2011 and 2012. A network of 12 passive detectors (kodalphas) has been installed, as well as, two radon continuous monitoring in the most interesting geological sites of the subterranean environment. ; A follow up of the recommended time (max. 50 min) inside the underground environment has been analysed since the reopen to public visitors for not surpassing the legal maximum effective dose for tourists and guides. Results shown that public visitors would receive in fall a 12.1% of the total effective dose permitted per visit, whereas in summer it is reduced to 8.6%, while the cave guide received a total effective dose of 6.41 mSv in four months. ; The spatial radon maps allow defining the most suitable touristic paths according to the radon concentration distribution and therefore, appropriate fall and summer touristic paths are recommended. ; This research was funded by the Regional Government of Extremadura (Spain) through EAFRD Axis 2 "Improving the environment and the countryside" and the Spanish Ministry of Economy and Competitiveness through project CGL2013-43324R and the programme Torres Quevedo (PTQ 13-06296 and PTQ 12-05601). ; A.F-C is funded by an IEF Marie Curie Action (FP7/2007–2013) under REA grant agreement n° 624204 ; Peer reviewed

This study is based on field monitoring of a cave-soil-atmosphere system validated with laboratory experiments. CO and Rn dynamics in the cavity are dependent on climatic parameters, mainly on the differences between the outdoor and indoor temperature. The annual cycles in the cave are characterized by two outstanding phenomena: cave gas recharge and ventilation when the cave acts as a gas sink or source. A permanent relationship with soil above the cave exists. The soil temperature and moisture are responsible for CO production on various time scales. Soil CO at the Rull site reaches values higher than 3000Â ppm in April–May, but falls to nearly 1000Â ppm during the summer. Maximum CO values in the cave are reached in the warmest months and are in accordance with soil CO values. The maximum CO concentration in the cave is 3470Â ppm on average, while the minimum is 623Â ppm. To describe the field findings, CO production and diffusion experiments related to the soil behaviour were developed. The results show that the soil CO production increases as the soil temperature and moisture increase according to a calculated logarithmic equation until the soil water content exceeds the saturation value. The soil-produced CO reaches the Rull cave by diffusion, which in Rull soil is reduced to approximately 60% when the soil water content increased from 0 to 30%. We estimated that 57Â kg of CO was emitted from the cave to the atmosphere in an annual cycle, considering a cave volume of 9915Â m. Finally, projections of the future climate at the study site confirm a general tendency for annual-mean conditions to be warmer and drier, which will directly affect the soil CO production. In this situation, the Rull cave will experience changes in the stored and subsequently exchanged annual amount of CO. ; This research was funded by the Spanish Ministry of Economy and Competitiveness projects CGL2011-25162 and CGL2013-43324-R and its programme Torres Quevedo (PTQ 13-06296 and PTQ 12-05601). A pre-doctoral research fellowship (BES-2012-053468) was awarded to C. Pla for the project CGL2011-25162. ; Funding was also provided by the People Programme (Marie Curie Actions—Intra-European Fellowships, call 2013) of the European Union's Seventh Framework Programme (FP7/2007-2013) under the REA grant agreement n624204 ; Peer Reviewed

This study characterizes the processes involved in seasonal CO exchange between soils and shallow underground systems and explores the contribution of the different biotic and abiotic sources as a function of changing weather conditions. We spatially and temporally investigated five karstic caves across the Iberian Peninsula, which presented different microclimatic, geologic and geomorphologic features. The locations present Mediterranean and Oceanic climates. Spot air sampling of CO (g) and δCO in the caves, soils and outside atmospheric air was periodically conducted. The isotopic ratio of the source contribution enhancing the CO concentration was calculated using the Keeling model. We compared the isotopic ratio of the source in the soil (δC–soil) with that in the soil-underground system (δC–system). Although the studied field sites have different features, we found common seasonal trends in their values, which suggests a climatic control over the soil air CO and the δCO of the sources of CO in the soil (δC–soil) and the system (δC–system). The roots respiration and soil organic matter degradation are the main source of CO in underground environments, and the inlet of the gas is mainly driven by diffusion and advection. Drier and warmer conditions enhance soil-exterior CO interchange, reducing the CO concentration and increasing the δCO of the soil air. Moreover, the isotopic ratio of the source of CO in both the soil and the system tends to heavier values throughout the dry and warm season. We conclude that seasonal variations of soil CO concentration and its C/C isotopic ratio are mainly regulated by thermo-hygrometric conditions. In cold and wet seasons, the increase of soil moisture reduces soil diffusivity and allows the storage of CO in the subsoil. During dry and warm seasons, the evaporation of soil water favours diffusive and advective transport of soil-derived CO to the atmosphere. The soil CO diffusion is enough important during this season to modify the isotopic ratio of soil produced CO (3–6‰ heavier). Drought induces release of CO with an isotopic ratio heavier than produced by organic sources. Consequently, climatic conditions drive abiotic processes that turn regulate a seasonal storage of soil-produced CO within soil and underground systems. The results here obtained imply that abiotic emissions of soil-produced CO must be an inherent consequence of droughts, which intensification has been forecasted at global scale in the next 100 years. ; This research was funded by the Spanish Ministry of Economy and Competitiveness projects CGL2016-78318-C2-1R and CGL2016-78318-C2-2R AEI/FEDER/UE and its programme Torres Quevedo (PTQ 13-06296). Funding was also provided by the People Programme (Marie Curie Actions-Intra-European Fellowships, call 2013) of the European Union's Seventh Framework Programme (FP7/2007-2013) under the REA grant agreement nº 624204. ; Peer Reviewed

11 páginas.-- 6 figuras.-- 64 referencias.-- Supplementary Information accompanies this paper at http://www.nature.com/naturecommunications http://www.nature.com/ncomms/2015/150427/ncomms8003/extref/ncomms8003-s1.pdf ; Las figuras que no se encuentran en el Preprint son de acceso libre en el enlace al texto original. ; © 2015 Macmillan Publishers Limited. All rights reserved. In recent years, methane (CH4) has received increasing scientific attention because it is the most abundant non-CO2 atmospheric greenhouse gas (GHG) and controls numerous chemical reactions in the troposphere and stratosphere. However, there is much that is unknown about CH4 sources and sinks and their evolution over time. Here we show that near-surface cavities in the uppermost vadose zone are now actively removing atmospheric CH4. Through seasonal geochemical tracing of air in the atmosphere, soil and underground at diverse geographic and climatic locations in Spain, our results show that complete consumption of CH4 is favoured in the subsurface atmosphere under near vapour-saturation conditions and without significant intervention of methanotrophic bacteria. Overall, our results indicate that subterranean atmospheres may be acting as sinks for atmospheric CH4 on a daily scale. However, this terrestrial sink has not yet been considered in CH4 budget balances. ; This research was funded by the Spanish Ministry of Economy and Competitiveness project CGL2013-43324-R and its programme Torres Quevedo (PTQ 13-06296 and PTQ 12-05601). Funding was also provided by the People Programme (Marie Curie Actions—Intra-European Fellowships, call 2013) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement nº 624204 and by CSIC funds (PIE project 201230E125). We thank cave managers for their collaboration throughout the entire investigation ; Peer Reviewed

A comprehensive environmental monitoring program was conducted in the Ojo Guareña cave system (Spain), one of the longest cave systems in Europe, to assess the magnitude of the spatiotemporal changes in carbon dioxide gas (CO2) in the cave–soil–atmosphere profile. The key climate-driven processes involved in gas exchange, primarily gas diffusion and cave ventilation due to advective forces, were characterized. The spatial distributions of both processes were described through measurements of CO2 and its carbon isotopic signal (δ13C[CO2]) from exterior, soil and cave air samples analyzed by cavity ring-down spectroscopy (CRDS). The trigger mechanisms of air advection (temperature or air density differences or barometric imbalances) were controlled by continuous logging systems. Radon monitoring was also used to characterize the changing airflow that results in a predictable seasonal or daily pattern of CO2 concentrations and its carbon isotopic signal. Large daily oscillations of CO2 levels, ranging from 680 to 1900 ppm day−1 on average, were registered during the daily oscillations of the exterior air temperature around the cave air temperature. These daily variations in CO2 concentration were unobservable once the outside air temperature was continuously below the cave temperature and a prevailing advective-renewal of cave air was established, such that the daily-averaged concentrations of CO2 reached minimum values close to atmospheric background. The daily pulses of CO2 and other tracer gases such as radon (222Rn) were smoothed in the inner cave locations, where fluctuation of both gases was primarily correlated with medium-term changes in air pressure. A pooled analysis of these data provided evidence that atmospheric air that is inhaled into dynamically ventilated caves can then return to the lower troposphere as CO2-rich cave air. ; This research was funded by the Agreement between Fundación Patrimonio Natural (Regional Government of Castilla y León) and CSIC and by the Spanish Ministry of Economy and Competitiveness (MINECO) project CGL2013-43324-R and in collaboration with project CGL2011-25162-BTE. ; Funding was also provided by the People Programme (Marie Curie Actions—Intra-European Fellowships, call 2013) of the European Union's Seventh Framework Programme (FP7/2007–2013) under REA grant agreement no. 624204, and the MINECO programme Torres Quevedo (PTQ 13-06296 and PTQ 12-05601). ; Peer reviewed

Subterranean ecosystems play an active role in the global carbon cycle, yet only a few studies using indirect methods have focused on the role of the cave microbiota in this critical cycle. Here we present pioneering research based on in situ real-time monitoring of CO2 and CH4 diffusive fluxes and concurrent δ13C geochemical tracing in caves, combined with 16S microbiome analysis. Our findings show that cave sediments are promoting continuous CH4 consumption from cave atmosphere, resulting in a significant removal of 65% to 90%. This research reveals the most effective taxa and metabolic pathways in consumption and uptake of greenhouse gases. Methanotrophic bacteria were the most effective group involved in CH4 consumption, namely within the families Methylomonaceae, Methylomirabilaceae and Methylacidiphilaceae. In addition, Crossiella and Nitrosococcaceae wb1-P19 could be one of the main responsible of CO2 uptake, which occurs via the Calvin-Benson-Bassham cycle and reversible hydration of CO2. Thus, syntrophic relationships exist between Crossiella and nitrifying bacteria that capture CO2, consume inorganic N produced by heterotrophic ammonification in the surface of sediments, and induce moonmilk formation. Moonmilk is found as the most evolved phase of the microbial processes in cave sediments that fixes CO2 as calcite and intensifies CH4 oxidation. From an ecological perspective, cave sediments act qualitatively as soils, providing fundamental ecosystem services (e.g. nutrient cycling and carbon sequestration) with direct influence on greenhouse gas emissions. ; This work was supported by the Spanish Ministry of Science, Innovation through project PID2019-110603RB-I00, MCIN/AEI/FEDER UE/10.13039/501100011033 and with collaboration of projects RTI2018-099052-B-I00 and PID2020-114978GB-I00. This research has also received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 844535 — MIFLUKE. ; Peer reviewed

The soils above caves represent a membrane that regulates the connection between the underground environment and the outside atmosphere. In this study, soils from two different field sites (Cueva de Altamira and Cueva del Rull in Spain) are investigated. Field results are analysed and linked to laboratory tests. Several laboratory experiments are performed to quantify CO diffusion coefficients and water infiltration rates in these soils under different degrees of soil water saturation and compaction. Tests confirm that the grain size distribution, organic matter content, mineral composition and water content of soils affect gas transport through the soil pore network. Both field and lab results reveal that Altamira soil has a coarser texture and therefore has higher CO diffusion coefficients, infiltration rates and hydraulic conductivity values than Rull soil. Rull soil contains a higher proportion of fine particles and organic matter, which explains the lower fluid transport coefficients. When soils are near saturation, fluid transport does not depend on the physical properties of soil but depends on the soil water content. In this state, liquid transport regulates the available space within the soil pores, which leads to a reduction in the gaseous diffusion coefficient of the soil. After rainfall episodes, the connection between the exterior atmosphere and underground cavities is hindered due to a rise in the soil water content, which is responsible for the closure of the overlying membrane. This study demonstrates that soil-produced CO reaches the underground atmosphere through diffusion processes that are controlled by the intrinsic properties of soil (porosity, grain size distribution, texture, mineralogy and organic matter content) and soil water content. ; This research was funded by the Spanish Ministry of Economy and Competitiveness projects CGL2011-25162 and CGL2013-43324-R and its programme Torres Quevedo (PTQ 13-06296). A pre-doctoral research fellowship (BES-2012-053468) was awarded to C. Pla for the project CGL2011-25162. Funding was also provided by the People Programme (Marie Curie Actions Intra-European Fellowships, call 2013) of the European Union's Seventh Framework Programme (FP7/2007–2013) under the REA grant agreement n° 624204. ; Peer Reviewed

El Sidrón Cave is an archaeological and anthropological reference site of the Neanderthal world. It shows singular activity related to cannibalisation, and all existing processes are relevant to explain the specific behaviour of the concerned individuals. This paper presents geoarchaeological data, primarily based on mineralogical and petrographic techniques, from an investigation of the nature of the encrustations or hard coatings that affect a large part of the Neanderthal bone remains and their relationship with the depositional and post-depositional processes at the archaeological site. Crusts and patina were found to be numerous and diverse, mainly composed of calcite and siliciclastic grains, with different proportions and textures. The analysis indicated different origins and scenarios from their initial post-mortem accumulation to the final deposit recovered during the archaeological work. The presence of micromorphological features, such as clotted-peloidal micrite, needle-fibre calcite (NFC) aggregates, clay coatings, iron–manganese impregnation, and/or adhered aeolian dust may indicate that a significant proportion of the remains were affected by subaerial conditions in a relatively short period of time in a shelter, cave entrance, or shallower level of the karstic system, prior to their accumulation in the Ossuary Gallery. ; This work has been supported since 1999 through different research contracts between the Government of the Principality of Asturias, the University of Oviedo, the University of Alicante, the National Museum of Natural Sciences (CSIC, Madrid), and the University of Salamanca. ; Peer reviewed