Estudi de l'evolució hidroquímica i isotòpica de la llacuna de Fra Ramon: la Pletera, Baix Ter – Origen de l’aigua com a base per a la seva gestió

Abstract

The study area is located within the wetlands of Baix Empordà, where the ancient mouth of the River Ter caused the formation of a lagoon system that since 1992 is considered Natural Interest Space. This document focuses on the lagoon Fra Ramon with the aim of characterizing their hydrodynamic spatially and temporarily. From the data collected during a year (November 2014-October 2015) has developed a conceptual mass balance that allows us to evaluate the importance of groundwater flows to maintain the level of the lagoon. So far, only has been contemplated the difference between precipitation (460.09 ± 185.55 m3 / month) and average annual evaporation (792.81 ± 80.00 m3 / month). However, it was found that the volume of the lagoon is also dependent on the inputs and outputs of groundwater as the annual mass balance conducted indicates a gain of 20.10% in volume. Nutrients data allowed the observation of a clear horizontal stratification in the lagoon for density effect, being the bottom layer a reduction zone that may contain toxic species. The evolution of ions observed was useful in identifying the ammonium and bicarbonate as indicators of the entrances of groundwater in the lagoon, while decreasing the concentration of other ions such as Cl- for effect of dilution. Mixture, evaporation and reverse models were used to simulate the chemical composition of the lagoon and its evolution. Contrary to what was known, the aquifer represents between 40 and 80% the water of the lagoon and this can evaporate between 50 and 60% in July, whereas the first and second campaigns are not affected by this process. This causes an increase in the concentration of ions with an even higher rate of salinity than in the sea and values of δ18O and δD above 12 and 35‰ respectively. The inverse model and saturation indices have verified the conceptual model and have identified other processes such as calcite precipitation. The processes described control water fluxes and the salinity of the wetland area and consequently, its ability to preserve the existing biodiversity. This study shows the importance of taking knowledge of hydrochemical processes for any purpose relating to the management and preservation of these environments