Variacions estacionals en la salinitat del subsòl a les basses litorals de nova creació a la Pletera

Abstract

The study area is located within the wetlands of the Baix Empordà, where the old mouth of the River Ter, has led to the formation of a lagoon system that from 1992 is considered an Area of Natural Interest (EIN). The present documented, focuses on the lagoon of Fra Ramon and L04, with the objective of characterizing the seasonal variations in the salinity of the soil. From the data collected seasonally during the period between February 2016 and April 2017, have developed a study of the levels of resistivity electrical resistivity tomography to determine the levels of soil salinity. The ERT (Electrical Resistivity Tomography) has served to create a 2-D model with the distribution of resistivity values in depth, allowing to study the variations of the results among the different campaigns, "Time-lapse", either in % of variation between campaigns, % accumulated or median values of resistivity in depth. These parameters have been related to external data such as the water levels of the lagoons, records of surveys and excavations, and hydro-meteorological and maritime values to determine the temporal variation of salinity and check what are the values that affect in these variations. The resistivity data observed, both by data collected externally and the calculated data in the laboratory, show a clear variation linked on weather conditions depending on the season of the year, having regard to the higher values of salinity in times with the presence of precipitation and an increase in the level of the lagoons and the sea. These conditions would increase the saturation of the material on the top layer of the profile. As has also been observed, there is a relationship between soil moisture and salinity, confirming the reason that soil resistivity increases in time with a high contribution of water in the area, considering the balance between fresh and saline water at each particular time. While in the absence of water and drying of the top layer of the profile would be a decrease in the levels of soil resistivity. On the other band resistivity values in lower layers are related to the intrusion of sea water. With an increase of the effect of the sea water, the levels of resistivity lower and therefore increase the salinity values. On the other band, high resistivity values, will be related to the presence of fresh water