EXPLORING CLIMATE CHANGE IMPACTS AND GROUNDWATER CONTAMINATION DYNAMICS IN A WEST-MEDITERRANEAN COASTAL BASIN

Groundwater represents approximately 30% of Earth's total freshwater reserves, playing a key role in sustaining ecosystems, supporting agriculture, and providing potable water for millions of people worldwide. However, its long-term availability and utilization are threatened by various natural and anthropogenic factors, including climate change and human-induced contamination. This thesis investigates such impacts in the coastal basin of Garraf (Spain), located in the heart of the Mediterranean climatic hotspot and dotted with detrimental anthropogenic activities that have resulted in significant degradation of groundwater quality, such as agriculture and waste disposal sites. The karstic nature of this basin represents an intriguing and complex setting for the study of underground dynamics due to the numerous subterranean water flows that discharge freshwater into the sea, a phenomenon known as submarine groundwater discharge (SGD). The study employs historical climate data from the Catalan Meteorological Service to assess the impact of climate change on the region, focusing on temperature and precipitation trends over the past seven decades, and evaluating the main adverse effects on groundwater resources in the region. The noticeable increase in temperature and the variability of the precipitation regime are consistent with the projections of the IPCC for the Mediterranean basin. Additionally, a comprehensive analysis of the groundwater hydro-chemical status is conducted using both primary data collected firsthand and secondary data from the Catalan Water Agency. Spatially mapping the contaminant distribution facilitates the identification of critical hotspots and the prediction of groundwater quality in unsampled regions. The basin exhibits high concentrations of nutrients (DIN, DIP, DSi), especially agriculture-derived nitrates in the western sector. On the other hand, seawater intrusion (SWI) affects the eastern portion, as evidenced by the significant presence of chlorides in groundwater samples. Moreover, high concentrations of anthropogenic nitrogenous compounds (NO3, NO2, NH₄⁺) are found within the SGD fluxes measured on the beach of Sitges, suggesting an impact that extends far beyond local communities, affecting coastal and marine ecosystems. Ultimately, the research explores the interplay between climate change and groundwater contamination, discussing how these factors may interact to exacerbate adverse effects in the target area. This study highlights the urgent need for sustainable groundwater management practices, as the subject under investigation transcends the mere environmental dimension, affecting local communities with significant anthropological, social, and economic repercussions.