No abstract

The temperature distribution of shallow sectors of coastal aquifers are highly influenced by the atmospheric temperature and recharge. However, geothermal heat or vertical fluxes due to the presence of the saline wedge have more influence at deeper locations. In this study, using numerical models that account for variable density, periodic oscillations of temperature have been detected, and their origin has been attributed to the influence exerted by recharge and tides. The combined analysis of field data and numerical models showed that the alternation of dry and wet periods modifies heat distribution in deep zones (>100 m) of the aquifer. Oscillations with diurnal and semidiurnal frequencies have been detected for groundwater temperature, but they show differences in terms of amplitudes and delay with electrical conductivity (EC). The main driver of the temperature oscillations is the forward and backward displacement of the freshwater–saltwater interface, and the associated thermal plume generated by the upward flow from the aquifer basement. These oscillations are amplified at the interfaces between layers with different hydraulic conductivity, where thermal contours are affected by refraction.

Environmental tracers were used to characterize the origin and determine the age of the groundwater in the Motril-Salobreña aquifer (south-eastern Spain). The stable isotope concentrations (δ 18 O/δ 2 H), compared to the results obtained in previous studies, indicate that most of the recharge during the sampling period was from irrigation return flow and the carbonate Escalate aquifer. The combined dating of 3 H, 3 He, 4 He, 85 Kr, and 39 Ar allowed establishing the presence of modern water throughout the aquifer, although with different mixing percentages. Thus, there is a large zone characterized by a fluvial domain with 100% young waters (< 5 years) due to the circulation of water through an area of high permeability sediments. In the discharge zone of the aquifer, older water is located (age > 170 years), and the percentage of young water is reduced (22.5%). This is explained by the greater distance that groundwater travels (aquifer thicknesses is over 250 m) and the lower permeability of the aquifer in the deeper sectors.

La Charca de Suárez (LCS) is a Protected Nature Reserve encompassing 4 lagoons located 300 m from the Mediterranean coast in southern Spain. LCS is a highly anthropized area, and its conservation is closely linked to the human use of water resources in its surroundings and within the reserve. Different methodologies were applied to determine the hydrodynamics of the lagoons and their connection to the Motril-Salobreña aquifer. Fieldwork was carried out to estimate the water balance of the lagoon complex, the groundwater flow directions, the lagoons-aquifer exchange flow and the hydrochemical characteristics of the water. The study focussed on the changes that take place during dry-wet periods that were detected in a 7-month period when measurements were collected. The lagoons were connected to the aquifer with a flow-through functioning under normal conditions. However, the predominant inlet to the system was the anthropic supply of surface water which fed one of the lagoons and produced changes in its flow pattern. Sea wave storms also altered the hydrodynamic of the lagoon complex and manifested a future threat to the conservation status of the wetland according to predicted climate change scenarios. This research presents the first study on this wetland and reveals the complex hydrological functioning of the system with high spatially and temporally variability controlled by climate conditions and human activity, setting a corner stone for future studies.