HYDROCHEMICAL-ISOTOPIC STUDY OF PRECIPITATION, SURFACE, AND GROUNDWATER IN MOUNTAIN AREAS: THE EXAMPLE OF THE CHIMBORAZO PROVINCE (ECUADOR) AND AOSTA VALLEY (ITALY)

This thesis presents a detailed hydrochemical and isotopic study of precipitation, surface water and groundwater in two different mountainous regions: Chimborazo Province in Ecuador and Valle d'Aosta in Italy. The main objective is to understand the recharge patterns and hydrochemical characteristics of the water resources of these regions, which are crucial for sustainable water management. The Chimborazo Province of Ecuador is located in the central highlands and includes the basins of the Chibunga and Guano Rivers at altitudes ranging from 2754 to 6270 meters above sea level, including the Chimborazo Volcano. The region experiences significant climatic variability influenced by the Intertropical Convergence Zone and the El Niño-Southern Oscillation (ENSO). The Aosta Valley in Italy is located in the north-western part of Italy, bordering France and Switzerland, and is a highly mountainous region nestled in the Alps. The Perrot Spring, a key focus of the study, is in the Chalamy Valley at an altitude of 1300 meters above sea level. The study uses a combination of field sampling, laboratory analysis and data interpretation. Water samples were collected from a variety of sources including rainfall, rivers, springs and wells. Hydrochemical analyses included measurements of pH, electrical conductivity (EC), major ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl-, SO₄²-, HCO₃-) and isotopic ratios (δ¹⁸O and δ²H). Continuous monitoring programs have been established to track hydrochemical and isotopic parameters, providing insights into recharge dynamics and water quality variations across different seasons and climatic conditions. In the Chimborazo province, recharge zones were identified between 3800 and 4500 m asl, influenced by rainfall and volcanic meltwater. Seasonal isotopic variations were observed, with isotopic depletion during the rainy season and enrichment during the dry season. Groundwater showed significant variability in electrolytic conductivity (EC) and pH, influenced by volcanic and sedimentary formations. Elevated levels of bicarbonates and sulphates indicated interaction with volcanic rocks and anthropogenic activities. The recharge area for the Perrot Spring was identified between 1990 and 2210 m asl. Seasonal variations in isotopic composition were influenced by both Atlantic and Mediterranean air masses. Samples showed low EC and slightly alkaline pH, typical of interactions with carbonate and metamorphic rocks. The water chemistry of the Perrot Spring indicated minimal water-rock interaction, with low ion concentrations. This work provides a comprehensive analysis of the hydrochemical and isotopic characteristics of water resources in the Chimborazo Province and the Aosta Valley, highlighting the importance of understanding recharge patterns for sustainable water management. By implementing the proposed strategies and addressing the potential challenges, local authorities can ensure the long-term sustainability of their groundwater resources.