Contributions for the Understanding of the São Pedro do Sul (North of Portugal) Geohydraulic and Thermomineral System: Hydrochemistry and Stable Isotopes Studies

Solange Almeida,Paula Carreira,Alcino Oliveira,Luís Gomes

doi:10.3390/geosciences12020084

Solange Almeida, Paula Carreira + Show 2 more

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https://doi.org/10.3390/geosciences12020084

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Abstract

São Pedro do Sul thermomineral aquifer system is located in the North of Portugal. Hydrogeochemistry and isotopic studies were conducted in order to improve knowledge of this groundwater system, known since ancient Roman times for their therapeutic properties. One thermomineral spring (NT) and three boreholes (AC1, SDV1 and SDV2) have a mean temperature around 68 °C. Currently, these waters are mainly used in thermal spas and for geothermal energy supply. Major cations and anions were used to identify and characterize different water types and sub-systems. Stable isotopes composition, δ18O and δ2H, have been used to determine the origin and have been used as a first approach to estimate the mean preferential recharge altitude of thermomineral water. The results suggest a single aquifer system with a relative composition of cations and anions and similar mineralization values. δ18O and δ2H values indicate a meteoric origin with no significant evaporation before infiltration. Besides, the isotopic composition points to recharge areas located at altitudes of about 1000 m a.s.l. This suggests a recharge area in the Freita/Arada mountains located NW of the thermomineral poles.

Highlights

Since the Roman occupation, spas have been a tradition in Portugal, owing mainly to the great diversity in the chemistry of its natural mineral waters, which reflect the geological and structural diversity of the territory
Groundwater samples were collected from boreholes and springs in order to obtain a representative composition of the thermomineral and cold shallow aquifer systems of the São Pedro do Sul region (Figure 2)
The selected cold springs intend to represent the shallow groundwater of the region, characterized by the low mineralization, low temperature, and pH values around 5 to 6

Summary

Introduction

Since the Roman occupation, spas have been a tradition in Portugal, owing mainly to the great diversity in the chemistry of its natural mineral waters, which reflect the geological and structural diversity of the territory. The research region is located near the village of São Pedro do Sul, district of Viseu, central Portugal (Figure 1), where this thermomineral aquifer system represents one of the most important sites of thermomineral waters of Portugal. The economic importance of spas for regional development can be inferred by the number of visitors every year to these facilities. According to [1], in 1998, the number of spa users amounted to 20,012. Due to the above reasons (health and economics), protection areas are of vital importance to guarantee the quality of the mineral water and to prevent contamination problems.

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