Abstract

The South American rivers discharging to the Southern Pacific are located between 30° and 54° latitude South, encompass a wide range of climates and ecoregions, and are characterized by highly endemic flora and fauna (DGA, 2016). These river systems are influenced by marked climatic and geographic drivers, such as the cold-water masses of the Humboldt Current and the Southern Pacific High anticyclone to the west and the high Andes Mountains to the east (BCN, 2021; Luebert and Pliscoff, 2018). Southern Pacific rivers are characterized by marked gradients of urbanization. Large cities are in the northern zone with the Chilean capital Santiago (~7 million inhabitants) in the Maipo River basin, and two coastal cities each with ~1 million inhabitants, Valparaíso-Viña del Mar near the Aconcagua River mouth and Concepción-Talcahuano at the mouth of the Biobío River. Urbanization coincides with a high deterioration of the ecological state of rivers in the northern zone as a result of multiple anthropogenic activities in river basins. As such, extraction of water for human consumption and industrial uses as well as irrigation of agricultural lands are the most frequent uses of river water in this zone. Further South, many installed and planned hydropower dams fragment rivers (Díaz et al., 2019). Toward the southern austral zone (Patagonia), anthropogenic activities are less intensive, with low levels of urbanization, but aquaculture focused on salmonids has grown exponentially since early 1990, causing marked environmental impacts in rivers and fjords. Most of the Southern Pacific river basins are located in Chile with some basins shared with neighboring Argentina (e.g., Valdivia and Baker rivers). The Maule and Biobío rivers in the Mediterranean zone and the Baker and Serrano rivers in the southern Patagonian zone are among the South Pacific river basins with the largest surface area (>20,000km2). In addition to the Andean rivers, the southern Pacific Coast also receives many smaller Coast Range rivers. The Andean basins of the Biobío, Valdivia, Puelo, Baker and Serrano rivers cover the latitudinal and climatic gradient of the southern Pacific region and have marked ecological, cultural, and economic importance.