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).