The inputs of solutes through SGD over a tidal cycle in a coastal system
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A study of the influence of continental groundwater discharge during a tidal cycle (semidiurnal mesotidal) in a large coastal inlet surrounded by a crystalline drainage basin (Ría de Vigo, NW Iberian Peninsula) during two contrasting climatic and oceanographic periods in July 2023 (dry period) and March 2024 (wet period) has been carried out. In order to monitor this, three Time Series stations were located through the system under study: the first and the second ones in the inner ría (Cobres) and outer ría (Baiona), were increased subterranean waters discharge were already detected, and the third one in the middle ría (Toralla), where the contribution of the continental groundwater discharge was low according to previous studies. 222Rn and 226Ra activity was measured in seawater as tracers of the subterranean waters in order to characterize its temporal variation in different sectors of the Ría over a tidal cycle. Moreover, geochemical parameters e.g. trace metals and several chemical elements, organic matter, optical properties of the DOM, nutrients, stable isotopes and rare earth elements were analysed. Variations in the salinity values were correlated with changes in the sea level due to the semidiurnal regime as well as 222Rn activity and redox sensitive metals as Fe and Mn. Lower salinity levels occurring during low tide and increased 222Rn activity, mainly during the wet period, correlates with higher values of the geochemical parameters, e.g. DOM, Fe and Mn. This fact emphasizes the importance and the contribution of the groundwater waters into the Ría seawater, and the needing of these high frequency studies on a temporal scale.