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Abstract: This study tests the hypothesis that the degree of moisture in the soil pore system determines gas exchange processes (ventilation/charge) between the outer atmosphere and the karst-epikarst during the warm, dry period (summer). These processes explain “anomalous” CO2 fluxes measured over this and other ecosystems. Emission of CO2 by ventilation of cavities requires an open double membrane system (host rock and soil) through which air movement can take place (H2Ovapour, CO2, 222Rn, etc.). An experimental study on the behavior of the soil and host rock porous system under changing air humidity conditions, coupled with a broad analytical approach addressing CO2 fluxes using the eddy-covariance technique and monitoring of the cave microclimate serves to define the suitable environmental conditions favoring air transfer between the cave atmosphere and exterior. This study shows the correlation between evapotranspiration, CO2 emissions, and cave ventilation processes due to the daytime opening of the soil membrane. Thus, the role of the soil as a membrane/interface or transfer medium can be observed, and it is directly dependent on weather conditions (temperature, humidity, wind). [Copyright &y& Elsevier]

Abstract: Castañar de Ibor (Caceres, Spain) is a low energy cave showing very high micro-environmental stability throughout the annual cycle and minimum rates of energy exchange with the atmosphere. The radon (222Rn) levels monitored inside Castañar cave reached 50,462Bqm−3 in April 2005 and had an annual average of 32,246Bqm−3. Annual variations in Rn concentration seem mainly related to differences in internal and external temperature. The highest values of 222Rn concentration occur during winter and early spring when air-cave temperature surpasses the external air temperature, evidencing very low air exchange rate. These values are the highest recorded in any Spanish cave, either natural or show, and are much higher than the average in most caves around the world. The calculation of the effective dose received by guides during 2004 showed values higher than the maximum effective dose recommended by authorities. Two management measurements were applied to reduce these doses: reduction of the time of visit to a maximum of 60min, and opening the cave door 1hour before the entrance of the guides and visitors. These management measures were effective, as they led to a decrease of 10–12% in 222Rn in the cave atmosphere during visits and prevented the guides from being exposed to higher than recommended doses of radiation. [Copyright &y& Elsevier]