The Plata Basin (Cuenca del Plata) is the largest water system in South America after the Amazon watershed and the fifth largest in the world. Named by Solis in 1516 as “Mar Dulce”, covers an area of more than 3,200,000 square miles, nearly equal to the European Union area. The basin includes important territories belonging to the central and northern Argentina, southern Brazil, southern and eastern Bolivia, most of Uruguay, and the whole territory of Paraguay.
It ranges from the Altiplano of Bolivia to the Atlantic Ocean, and from Chapada de Parecís in the Planalto, which separates it from the Amazon Basin to the Atlantic. Precipitations over the basin meet in five major rivers: Parana, Paraguay, Uruguay, Pilcomayo and Bermejo, flows of which eventually converge in the Rio de la Plata.
These large rivers have a dense network of tributaries, sub-tributaries and minor tributaries like the Iguazú, Salado, Gualeguay, Miriñay, Guaycurú, Pilagá, Guayquiraró and Samborombón, among many others. Different aquatic environments can be found in this vast area, ranging from typical fresh water mixing with seawater in an estuary at the mouth of the Rio de la Plata. The average flow of the basin is 23,000 m³ / s.
Biological and cultural diversity
Given that the basin has its extreme coordinates between parallels 14° and 38° S and meridians 67° and 43° 30′ W, is easy to notice that there is great variation of environmental conditions, in close interaction with a complex mix of cultural, economic and social factors.
The basin includes Andean tributaries that originate in mountainous areas and latitudinal cross the basin dragging sediments, as the Pilcomayo and Bermejo, merging with lowland rivers such as the Paraguay which flows southward collecting filtered water in vast wetlands.
The attractions of the basin go beyond, among others the uncertain flow of the closed basin of the river Parapetí -which is part of the boundary between the Plata Basin and the Amazon, along with other subbasins conditioned to sources of Cordilleran waters.
There are also extensive areas in the basin prone to laminar flooding. The biggest is probably the Pantanal, also known as Gran Pantanal, a network of shallow wetlands covering more than 140,000 km ². The Paraguay River, which gathers the waters of the Pantanal, empties into the Paraná and both feed the largest river wetland system in the planet, about 3,500 kilometers in length free from dams, running north to south from the Pantanal of Mato Grosso to the Rio de la Plata.
The behavior of many of these rivers and wetlands is still poorly understood and have been insufficiently studied and documented in relation to the fish diversity, the reservoirs or breeding sites and the importance of migratory birds, among others.
In summary, the Plata Basin is one of the world’s largest reserves of fresh water, with exceptional cultural and biological diversity -including a major inland fishery and a rich diversity of other aquatic resources that deserve protection. As a whole the rivers and lakes of the basin are also the main system for the Guarani Aquifer, one of the largest groundwater reservoirs in the world.
Transformations and Threats
The Plata Basin is structured along the major population and production demographic group in South America. With almost 130 million inhabitants, some 50 large cities and an economy that represents 70% of GDP per capita of the five countries, is of major economic and social importance. But according to a recent report by Unesco, “the increase of poverty remains the most important social issue facing the countries that comprise it.”
The lower income sector, especially poor people, has a high dependence on natural resources, thus its deterioration provokes losses in household income and diminish of opportunities. To mention only two examples, overfishing at unsustainable rates for export causes a drop of fishery resources in the lower Parana along with negative social impacts, the expansion of clearings and large-scale monocultures impact on family farming and rural emigration aggravating overcrowding in marginal areas of big cities.
At present important anthropogenic changes occur in the watershed. The expansion of the agricultural frontier, inadequate technologies, large projects as poorly planned road connections and waterways, combined with overfishing, overgrazing in the floodplain, deforestation, fires and, generally, the lack of comprehensive management plans for wetland, lead to degradation and loss of ecosystems and their vital resources such as fishing.
Pollutants from mining activities, inadequate treatment of urban waste water and traces of chemicals represent a serious environmental concern in the watershed. Likewise, the illegal trade in endangered species.
In recent decades, rapid population growth, development of road and hydraulic engineering projects such as large scale dams and canals have also led to a decline in environmental quality in the basin, coupled with a intense deforestation, fragmentation and loss of native forests. These impacts and their synergistic effects have meant that in March 2007 the Plata Basin ranked third among the ten most endangered of the world.
The Plata Basin includes key ecosystems. The Gran Chaco is the second largest ecosystem in South America, after the Amazon’s. It corresponds to an alluvial area located to the east of the Andes, formed by deposition of sediments, predominantly of the Bermejo and Pilcomayo. The Bermejo, comes from the Andes to the Paraguay and to the Parana, constituting a natural ecological corridor between Puna ecosystems in the mountains, the foothills of Yungas and dry and humid plains of the Chaco.
The Pantanal, a huge wetland shared by Brazil, Bolivia and Paraguay, in the upper Paraguay basin, is an enormous reservoir of biological value and represents a regulator of the water system of the basin by slowing the arrival of waters of the Paraguay river to the Paraná during four months, thus avoiding the combination of periods of maximum flow of both rivers and by attenuating large floods.
Among large wetlands can be appointed the Bañado La Estrella, connected to the Pilcomayo in territories of Argentina and Paraguay, the Bañados of Izozoc in Bolivia Parapetí linked to the river, and the system of streams, lakes and swamps of the Ibera, in Corrientes, Argentina, a vast wetland of about 7,800 and 12,000 km2, located on a plain of low slope with northeast-southwest direction, fed mainly by rain, which flows into the middle Parana river through the Corriente river.
La Pampa, because of its dimension is the third biome of global importance in the Plata Basin. The most fertile soils of the watershed are located in the plains of the pampas. From early times agricultural production settled there, and it has continued to expand. This bioregion includes the southern Brazilian state of Rio Grande do Sul, the whole Uruguay area, the provinces of Buenos Aires and Entre Rios, southern Santa Fe, Cordoba and Corrientes, part of the province of San Luis and the northern of La Pampa province.
Two other important parts of key ecosystems in South America are in the basin: the Cerrado to the north, which separates the Plata Basin from the Amazon Basin, and the Atlantic rainforest, to the northeast, both having a wide biological diversity. Varied lineage species coexist in the vegetation of the basin, because rivers are like corridors between distant regions, several thousand miles in some cases. For example, most of the gallery forest of the Humid Chaco, while having elements of lineage from Chaco also contains species of Amazonian lineage.
These outstanding data are indicators of the wealth and quality of natural resources, natural productivity, goods and services provided by these ecosystems. It has and will continue to be key for the availability of quality and quantity of water resources and biodiversity for the sustainability of the region.
In summary, the Plata Basin is a region of extraordinary ecological and economic value, with a rich variety in morphology and climate, and in quality of soils, water resources and biological and cultural diversity that make it highly suitable for the implementation of sustainable development strategies. These features simultaneously interacting offer a unique opportunity to enable the implementation of alternative models of sustainability, satisfy human needs in balance with the biological capacity of ecosystems.
© Portal Cuenca del Plata – Gran Chaco, 2009
Spanish version: http://www.cuencadelplata-granchaco.org/cuenca-del-plata/