Rull cave is a karstic cave located in Vall d’Ebo (Alicante, Southeast of Spain) developed in massive Miocene conglomerates and Cretaceous limestones. Processes in soil above Rull cave and outdoor atmosphere directly influence the underground environment of the cave. Continuous and discrete monitoring of cave atmosphere and soil (from 2012 to 2022) allows to characterise the spatial distribution and temporal variations of the gaseous concentration (²²²Rn and CO₂) and understand the relationship between the processes which occurred in the 3-component system (soil-cave-atmosphere). Besides the presence of visitors, Rull cave maintains stable values of mean temperature (16.2 °C) and relative humidity (97.6%). In an annual cycle the cave presents two different gaseous stages (stagnation and ventilation). Maximum average values of CO₂ and ²²²Rn concentration are reached within the stagnation stage, in the warmest period of the year. On the contrary, in the ventilation stage (in the coldest months) the cave reaches the lowest concentrations in its inner atmosphere. For the study period, daily average CO₂ and ²²²Rn concentrations are 2008 ppm and 1745 Bq/m³, respectively. Results show that the dynamics of ²²²Rn and CO₂ in the cave air follow different patterns defined by the complex relationships between external and internal factors. Findings from this study provide substantial information about the environmental situation of the cave atmosphere in terms of air quality for visitors and workers.

Groundwater plays a key role in the subsistence of people and their activities throughout the globe, particularly in arid zones. In the highly dynamic context of the Mediterranean landscape, a deep understanding of aquifer systems is essential for their optimal management. The aim of this study was to estimate the influence of land cover on recharge in the Almudaina-Segaria aquifer, through the simulation of different land cover scenarios. The results showed a 32% decrease in the total water volume + entering the aquifer when extensive agriculture was replaced by natural forests, with a remarkable drop in the water table elevation for a large portion of the aquifer, depending on geology and topography. Considering the demographic evolution and ongoing climatic changes, it is fundamental to incorporate a management perspective where surface and underground processes are integrated as a fundamental part of a sustainable system.

The Santo Domingo Diocesan School (Orihuela, SE Spain) is a singular case study that relates air quality monitoring and stone conservation. The monument suffers severe damage due to salt crystallization by rising damp, which is related to the indoor environment dynamics, high groundwater salt content, and microstructure, the building’s porous stone (biocalcarenite). Results revealed that ²²²Rn concentration in indoor air is low due to the building’s high ventilation rate, despite the medium-low geogenic radon potential in the area. Wavelets analysis showed that ventilation is caused by outdoor and indoor temperature variations and directly affects the ²²²Rn and CO₂ dynamics inside the church. CO₂, as well as relative humidity (RH), presented periodicities with intermediate frequencies (5–8 days) related to visits. These RH and temperature (T) variations intensified the salt damage by increasing the frequency of dissolution-crystallization cycles. The mineralogical characterization and geochemical calculations concluded that chlorides (halite and sylvite), sulfates (thenardite, epsomite, hexahydrite and aphthitalite) and nitrates (niter) present from dissolution forms to whiskers and hopper-type morphologies. This indicates high saturation values and, therefore, higher crystallization pressure values within the porous media of the biocalcarenite. On the contrary, the near-equilibrium crystal shape and incongruent precipitation reaction for humberstonite suggest a lower alteration for this salt on the building stone.

Our research aims to assess the complex interactions between the elements that constitute and influence a cave system through the analysis of an extensive dataset of climatic and environmental parameters (²²²Rn, CO₂, drip rates, chemical composition, and environmental isotopes) measured in air, water, and solid in the Rull Cave (southeastern Spain). Of particular importance is understanding the effect of rainfall and temperature on water and gas transport through the epikarst and the involved processes. Our results show that the cave gaseous concentration patterns do not only depend on the temperature-caused movement of air masses, but they can also be affected by abundant rainfall. The δ¹⁸O and δD composition of cave water also relies on such precipitations for the effective transfer of the rainfall signal into the cave, which can take between 3 and 7 days. The elemental ratios (Sr/Ca and Mg/Ca) show high responsiveness to the water drip rate, hinting that enhanced prior calcite precipitation (PCP) occurs at slower drip rates. Despite this, and regardless of drip rates, calcite saturation indices follow a seasonal variation pattern inversely proportional to the cave air CO₂ concentration, while δ¹³C-DIC is proportional. Our results show how the interlinkage between these multiple components defines the dynamics of the atmosphere-soil-cave system. Cave monitoring is then essential to understand the karstic vadose zone, which is highly sensitive to climatic influence and its changes.

In poor-ventilated caves, indoor gases can seasonally reach concentrations much higher than normal atmospheric values, which may become a critical health risk. In this study, we investigate the cave atmosphere of the Rull cave in terms of assessing the cave air quality and understanding the cave dynamics. Rull cave is located in Vall d’Ebo (Alicante, southeast Spain). It is a karstic cave developed in massive Miocene conglomerates and Cretaceous limestones. Above the cave, the silty-silty loam soil profile has a thickness below 1 m. Inside the cave, calcite speleothems and cave sediments are widely present. The uranium and thorium concentrations are higher for the soil and cave sediments, and minor for host-rock, and lower for speleothems. Moreover, both soil and cave sediments are powder materials, and the emanation is enhanced in comparison to host-rock and speleothems, although their volume in the cave is higher than soil and cave sediments.At the cave location and for a decade-long monitoring period (November 2012 - July 2022), the prevailing meteorological conditions in terms of temperature and relative humidity were 16.1 ºC and 69.9%, respectively, on daily average values. The average annual precipitation is 553 mm. In the cave interior and besides the presence of visitors (15000 visitors/year), mean temperature (16.2 °C) and relative humidity (97.6%) maintain stable values.In an annual cycle, the cave presents two different gaseous stages (stagnation and ventilation). Maximum average values of CO2 and 222Rn concentration (3966 ppm and 4185 Bq/m3) are reached within the stagnation stage (April/May to September). On the contrary, in the ventilation stage (October to March/April) the cave reaches the lowest concentrations in its inner atmosphere (478 ppm and 404 Bq/m3).The spatial distribution of gases in the cave is dependent on the air density gradient between the cave and the outer atmosphere and controls the seasonal variations of both gases. The emanation of 222Rn from cave sediments, host-rock, and speleothems, contributes to increasing and maintaining a nearly 222Rn cave concentration during the stagnation stage. Dripping water degassing might also contribute to raising gas concentrations in caves. However, in Rull cave dripping waters are not abundant and thus the contribution of CO2 or 222Rn degassing from seepage waters to increase cave gaseous concentration might be low.The continuous monitoring of Rull cave provides substantial information about the environmental situation of the cave atmosphere in terms of air quality for visitors and cave guides. The maximum average concentrations of CO2 and 222Rn in Rull cave and exposition times and doses comply with the recommendations of the legislation. Considering 222Rn, accurate planning of the cave guides and visitors during the stagnation stage is recommended to be less exposed to ionizing radiation due to the presence of radon gas.