Characterization of a karstic aquifer using magnetic resonance sounding and electrical resistivity tomography: a case-study of Estaña Lakes (northern Spain)Caractérisation d’un aquifère karstique par sondage par résonance magnétique et tomographie par résistivité électrique : une étude de cas, les Lacs d’Estaña (Espagne du Nord)Caracterización de un acuífero kárstico usando sondeos de resonancia magnética y tomografía de resistividad eléctrica: un caso de estudio de los lagos de Estaña (norte de España)利用磁共振测深及电阻率断层扫描刻画喀斯特含水层:以西班牙北部Estaña湖为例Caraterização de um aquífero cársico através de métodos de ressonância magnética e tomografia de resistividade elétrica: um caso de estudo nos Lagos de Estaña (norte de Espanha)

The geophysical characterization of a previously unstudied endorheic karstic system is presented. The studied area, known as the Estaña Lakes, is located in the Pyrenean Marginal Sierras, northern Spain. The Estaña Lakes are a set of natural water ponds on a bedrock of Triassic evaporites, lutites and carbonates. This wetland is included in the Natura 2000 European network of nature protection areas as a “Site of Community Importance”. Two geophysical techniques were used, magnetic resonance sounding (MRS) and electrical resistivity tomography (ERT), to map the subsurface geology and characterize the aquifer layers and the hydraulic links between the aquifers and lakes. The geophysical data were integrated with the surface geology and data from six boreholes. Ten electrical profiles were performed to identify the thickness of the units and lithological changes, whereas the MRS was used to determine the top of the saturated zone. As result, the aquifer in the Estaña Lakes system and surrounding area has been identified as Middle Triassic carbonates, which does not correspond with the regional aquifer in the area (Upper Cretaceous and Eocene). This work shows the power of geophysical methods in poorly understood and tectonically complex areas in addition to the standard aquifer tests to evaluate hydraulic properties.