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PhD Thesis Defence by Sonia Valdivielso

19 July 2022 @ 11:00 am - 1:00 pm

The PhD student Sonia Valdivielso Mijangos, from the Groundwater and Hydrogeochemistry research group, will defend her thesis on 19th July at 11h in the Sala de Juntas of the Faculty of Earth Sciences at the Universitat de Barcelona. The PhD defence will be also streamed following this link.

Title: Isotopic characterization of precipitation and its relationship with groundwater in the Central Andes

Directors: Enric Vázquez-Suñé and Emilio Custodio

Thesis Committee: Albert Soler, Christian Herrera Lameli, Josep Mas Pla

Abstract:

The availability of water resources is increasingly limited worldwide. Therefore, optimal and sustainable management is necessary to ensure a balance between ecosystems and human rights and activities. In the arid Central Andes, there is a great demand for water for different uses, including domestic consumption, intensive mining and, in some areas, livestock and emerging ecotourism. These human activities must respect and conserve the lagoon systems of the salt flats, on which the fauna depend. Understanding the hydrological and hydrogeological functioning of basins is essential for the optimal and sustainable management of water resources. To address this issue, the objective of this thesis is to advance the knowledge on the isotopic composition of precipitation and its relationship with groundwater in the Central Andes, particularly in the Salar de Atacama basin (Chile).

This thesis contributes to the (1) understanding of the origin of precipitation in the Central Andes and reviews how it varies isotopically (δ18O and δ2H) throughout the Amazon basin and in the Central Andes between 14°S and 28°S, (2) identification of the factors that control the isotopic composition of precipitation in areas with scarce isotopic and meteorological data and estimation of the meteorological and isotopic variables of precipitation, (3) characterisation of precipitation and identification of the recharge zone of the Salar de Atacama basin using stable isotopes, and (4) quantification of the contribution of snowmelt to the recharge of the aquifer of the basin.

Through an exhaustive review of the literature, precipitation in the Central Andes has been characterised. Precipitation occurs mainly during the austral summer. The masses of humidity have different origin: (1) from the North Atlantic Ocean through the Amazon basin, (2) from the South Atlantic Ocean through the Plate River basin and the Gran Chaco in summer, and (3) the Pacific Ocean in winter. The processes involved in the isotopic evolution of summer convective precipitation in the Eastern Cordillera are known. However, there is no consensus on the factors that control the isotopic variation in the Western Cordillera.

To identify the processes that determine the precipitation isotopy in the Cordillera Occidental, a statistical analysis is carried out between geospatial, meteorological and isotopic variables. The result indicates that temperature is controlled by altitude and latitude, while relative humidity is controlled by latitude, and summer precipitation is controlled by altitude and latitude. The stable isotopes of precipitation are controlled by temperature, altitude, latitude, longitude, and precipitation. Finally, based on these relationships, these variables are estimated by independent models throughout the study area and three isotopic models (summer, winter and annual).

The isotopic compositions of the surface water and groundwater indicate the presence of evaporation and that they are similar to each other in each subbasin, both in the Salar de Atacama and in the Altiplano-Puna. Finally, the meteoric source of the waters of the Altiplano-Puna basins is more depleted of heavy isotopes than are the waters of the peripheral subbasins of the salar. Therefore, these results show that there is no hydraulic connection between basins and that there is no significant transfer of water from the Altiplano-Puna to the peripheral aquifer of the Salar de Atacama.

This thesis presents a first view of the behavior of snow in the Toconao subbasin (subbasin east of the Salar de Atacama) through physical models. The total average precipitation was 139 mm/year in 2017, of which a third was in the form of snow. In summer the snow was above 4500 m asl and it melted in 10 days. In winter, when the temperature is lower, the snow cover covered much of the basin and slowly melted for a month.

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Details

Date:
19 July 2022
Time:
11:00 am - 1:00 pm
Event Category:
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