# Radon Dynamics in Granite and Calcareous Soils: Long-Term Experiments in a Semi-Arid Context
## 5 Conclusions  
Long-term monitoring of loamy sand and silty clay loam soils highlights the importance of soil texture and weather parameters on radon dynamics. Rainfall plays a key role due to its direct impact on soil water content in the context of a warm semi-arid climate. Statistical analysis of the time series reveals that radon activity undergoes strong seasonal variations related to rain and soil water content. For both soils, at the study depth of 90-100 cm, radon activity is above the average level during rainy periods, mainly in spring, whereas it is below these levels during dry periods, particularly in summer (4215 \(\pm\) 960 Bq m\({}^{-3}\) and 1363 \(\pm\) 814 Bq m\({}^{-3}\), in granite and calcareous soils, respectively). An increase in soil water content (SWC) enhances radon emanation. However, if this increase in SWC is high enough, the topsoil layer becomes saturated and impedes radon movement, causing a significant increase in radon activity. For SWC to be significantly affected at a depth of 90-100 cm, there must be heavy and/or prolonged rainfall. Given these conditions, a measurable increase in SWC will occur much faster in the loamy sand soil compared to the silty clay loam soil. Radon increments due to SWC variation can be measurable within hours or days, depending on soil texture. Our artificial water experiments, which forced SWC to be higher than those usual in the studied region, demonstrate that humid climates with greater rainfall would result in soils with higher radon activities (for a given radium concentration). Multivariate analysis reports how weather parameters determine the radon dynamics. SWC is likely to exert the most significant influence on radon in soil. However, its response to rainfall events and variability within the soil depth depends on the soil type. Barometric pressure, temperature, and wind also affect radon activity in soil, although their impact is less significant in the studied soils. Loamy sand soil shows statistically more robust results than silty clay loam soil. Thus, radon is positively related to SWC and negatively related to temperature, evapotranspiration, and pressure for both soils, while wind speed is only negatively associated with the loamy sand soil. Wavelet analysis confirms the  
Figure 9: Analysis of the impact of water content and soil texture on radon activity, gas permeability (\(\
u k_{g}\); (**a–c**)), and radon potential (RP; (**d–f**)). This comparative analysis contemplates four soil textures (clay, silt, loam, sandy) and three \({}^{226}\)Ra concentrations (50–100–200 Bq kg\({}^{-1}\)). interrelation in the time-frequency domain of SWC and radon in loamy sand soil. In this soil, wavelet analysis also highlights the effect of variations in pressure and wind speed on radon activity. However, wavelet results for the silty clay loam are less decisive, probably due to the absence of rainfalls in the monitoring period, and also due to the inherent properties of the soil. Finally, the analysis of the radon potential (RP) for the studied soils under a warm semi-arid climate is classified as low risk due to low \({}^{226}\)Ra concentration. The response of radon activity to changes in the environment has been parametrised to model RP variations under different soils and climate conditions. Thus, theoretical RP analysis confirms the significant radon fluctuations recorded in the long-term radon series. Small fluctuations in water content at low soil VWC have a large impact on radon concentration, and afterwards, the activity remains stable. Water saturation influences RP evolution by changing radon activity and permeability applied to local soil texture heterogeneity and \({}^{226}\)Ra concentration. Continuous monitoring is proven to be crucial for understanding seasonal radon changes, especially regarding the estimation of RP.