The Río de la Plata Estuary, Argentina-Uruguay

Abstract

The Río de la Plata is an extensive and shallow coastal plain estuary on the western South Atlantic coast (35–36°S). The estuary receives freshwater from South America’s second largest basin (about 3.2 million km²) through the Paraná River, one of the longest in the world, its main tributary, the Paraguay River, and the Uruguay River. The funnel of the Río de la Plata estuary extends for over 280 km from the head (25 km wide), at the confluence of the Paraná and Uruguay rivers, to the 230-km-wide mouth between Punta Rasa and Punta del Este. A submerged shoal, the Barra del Indio, represents a geomorphological barrier and divides the Río de la Plata estuary into an inner and an outer system (Fig. 13.1). The inner fluvial system under strong tidal influence, with a depth between 1 and 5 m, is about 180 km long and up to 80 km wide and extends over 13,000 km². In the outer mixohaline brackish system with an area of about 22,000 km², both depths (5–25 m) and section width increase concomitantly (Fig. 13.1). However, the mixohaline area increases to about 38,000 km² if based on the mean position of the 30 isohaline (Guerrero et al. 1997a,b). The limit between mixohaline waters and continental shelf waters depends on the dynamics of the estuary. The main characteristics of the Río de la Plata estuary are its large spatial scale and the occurrence of a quasi-permanent salt wedge regime, which generates a border system (bottom and surface salinity fronts) which plays an important role in the reproductive processes of fish species and where high zooplankton biomass concentrates.