18. Spectral Analysis of Time Series of Carbonate Aquifer of Sierra Gorda

Both Moon and Sun induce Earth tides. Signatures of the Earth’s crustal tides could be recorded in the groundwater in the form of rise and fall of its piezometric surface. In relationship with this phenomenon, there is a scarcity of these kinds of studies in carbonate aquifers. Spectral analysis has been applied in Sierra Gorda aquifer located in the southern of Spain in order to determine the presence and statistical significance of cycles from different time data series like air temperature, barometric pressure, electrical conductivity, pH and piezometric level located in the north border of the aquifer. Diver and Hidrolab sensors to collect data every 1 and 6 h were installed in some of these springs and piezometric borehole. The piezometric data series have more than 25,000 hourly data. The period studied start in November 2010 and end in September 2013. In this site, it has been observed some spectral peaks that could be linked with crustal tides related to cyclic movement of Moon and Sun around Earth. The most significant peaks in piezometric levels that could be related to Moon and Sun show values of 12 h, 1 day, 14 days and 28 days. On the other hand, similar signal is recorded by pH and conductivity temporal data. The influence of Earth tides on pH and conductivity is less studied and would be necessary new investigations on this aquifer to confirm this possibility. The spectral signature of temperature and barometric data is quite different to others variables studied.