Rio de la Plata

GABRIELA PALOMO

Biomes and Ecosystems: An Encyclopedia

Salem Press

Lugar: New Jersey; Año: 2013;

Rio de la Plata is an immense river situated at 35º S on the South West Atlantic Ocean between Argentina to the south and Uruguay to the north. Its funnel shape has 300 km long and 40 km width in the narrower part to 200 km width near the sea. The river received freshwater from Rio Uruguay and Rio Paraná and empties into the Atlantic Ocean. The basin covers 30,000 km2 and is the second largest one of South America, following that of the Amazon, representing an area of 20 % of the continent. The hydrographic system extends from the subequatorial zone through the tropics, and includes part of Bolivia, Paraguay, Uruguay, Brazil and Argentina funneling its numerous tributaries into the La Plata River. The mean annual flow that governs monthly to interannual variations is 25,000 m3s. A submerged shoal, the Barra del Indio represents a geomorphological barrier and defines a salinity front, characterized by strong vertical salinity stratification, with marine waters (saltier and denser) penetrating deeper into the estuary along the bottom, while fresh waters advance oceanward on the surface, forming a salt wedge. The high turbidity front in the inner part of the estuary constrains photosynthesis and food chains are probably detritus based. Immediately offshore the turbidity front, water is less turbid and phytoplankton increased, and all the valuable species for the coastal fisheries concentrate near this area. The physical characteristics of this estuary play a key role in the biodiversity of the benthos, nekton and mammals. Particularly, the reproductive processes of fish species occur in the outer part, being an important area for artisanal and coastal fisheries for both Argentina and Uruguay. The human impact on the estuary through agriculture, cattle raising, industrial and port activities seriously damaged the environment, and threaten the sustainability and existence of this unique place.