FRESHWATER RUNOFF FROM PACIFIC-DRAINING CONTINENTAL AND COASTAL BASINS IN PATAGONIA: CHARACTERIZING REGIONAL INPUTS TO CHILEAN FJORDS ASSOCIATED WITH CHANGES IN LAND USE/COVER

The region of west-southern Patagonia (WSP), characterized by its wild and remote landscapes, represents one of the last bastions of pristine natural environments on Earth. With recent colonization and limited human intervention, a significant portion of this territory retains its natural state. WSP boasts mighty rivers, expansive lakes, and the world's largest temperate icefields, making it a geographically distinct area. Unlike the northern Andes, it lacks a central valley, resulting in relatively short linear distances and steep gradients from source to sea. This topography shapes an intricate system of channels and fjords, contributing to one of the world's most extensive coastlines. The freshwater discharges into channels and fjords create a two-layer vertical structure, impacting various environmental parameters such as salinity, temperature, biogeochemistry, light availability, and biological communities. However, the variability of these discharges, influenced by factors like precipitation, temperature, landforms, vegetation, and land use, adds complexity to the system. While the importance of freshwater discharges in Patagonia's coastal ecosystems is recognized, understanding their magnitude, nutrient content, seasonal variations, and responses to climate change remains incomplete. Monitoring is limited to major rivers, with substantial gaps in the archipelago area, which receives higher precipitation. Besides, headwater streams, sensitive to land use and climate changes, have received less attention than larger rivers. This research aims to quantify freshwater coastal discharges in WSP and assess the impacts of land use and cover changes on runoff. Specific objectives include characterizing runoff in terrestrial basins, identifying bioindicators of land use change effects, and exploring relationships between hydrology indicators, land use, and climate variables. The study employs macro-scale and regional approaches across coastal basins and intensive micro-scale investigations in headwater streams. Chapter 1 focuses on estimating freshwater discharges in the entire study area using a hydrological model, considering factors such as soil, geology, land use, and climate. Chapter 2 investigates freshwater inputs into inner fjords, analyzing sources like precipitation, coastal runoff, and glacial ablation. Chapter 3 conducts a micro-scale analysis of headwater streams to detect early effects of land use changes and assess the impact of different hydrological regimes. Additional regional studies in appendices examine the influence of land use change on aquatic macroinvertebrate communities and identify bioindicators for forest degradation in Patagonia's evergreen forests. This research contributes essential insights into the hydrological and ecological dynamics of WSP, a region of global significance for its pristine nature and ongoing environmental changes.