The Pantanal () is a natural region encompassing the world's largest tropical wetland area, and the world's largest flooded grasslands. It is located mostly within the Brazilian state of Mato Grosso do Sul, but it extends into Mato Grosso and portions of Bolivia and Paraguay. It sprawls over an area estimated at between . Various subregional ecosystems exist, each with distinct hydrological, geological and ecological characteristics; up to 12 of them have been defined.
Roughly 80% of the Pantanal floodplains are submerged during the rainy seasons, nurturing a biologically diverse collection of aquatic plants and helping to support a dense array of animal species.
Etymology
The name "Pantanal" comes from the Portuguese word pântano that means "swamp", "wetland", "bog", "quagmire" or "marsh" plus the suffix -al, that means "abundance, agglomeration, collection"; By comparison, the Brazilian highlands are locally referred to as the planalto, that means "plateau" or, literally, "high plain".
Geography and geology
The Pantanal is about , gently-sloped basin that receives runoff from the upland areas (the Planalto highlands) and slowly releases the water through the Paraguay River and tributaries. The formation is a result of the large, concave pre-Andean depression of the Earth's crust, related to the Andean orogeny of the Tertiary. It constitutes an enormous internal river delta, in which several rivers flowing from the surrounding plateau merge, depositing their sediments and erosion residues, which have been filling, throughout the years, the large depression area of the Pantanal. This area is also one of the distinct physiographic provinces of the larger Parana-Paraguay Plain area, which encompasses a total of .
The Pantanal is bounded by the Chiquitano dry forests to the west and northwest, by the Arid Chaco dry forests to the southwest, and the Humid Chaco to the south. The Cerrado savannas lie to the north, east and southeast. The Pantanal is a tropical wet and dry region with an average annual temperate of and rainfall at a year. Throughout the year, temperature varies about with the warmest month being November (with an average temperature of ) and the coldest month being June (with an average temperature of ). Its wettest month is January (with an average of ) and its driest is June (with an average of ).
Hydrodynamics
Floodplain ecosystems such as the Pantanal are defined by their seasonal inundation and desiccation. They shift between phases of standing water and phases of dry soil, when the water table can be well below the root region. Soils range from high levels of sand in higher areas to higher amounts of clay and silt in riverine areas.
Elevation of the Pantanal ranges from above sea level. Annual rainfall over the flood basin is between , with most rainfall occurring between November and March. Annual average precipitation ranged from 920 to 1,540 mm in the years 1968-2000. In the Paraguay River portion of the Pantanal, water levels rise between two meters to five meters seasonally; water fluctuations in other parts of the Pantanal are less than this. Flood waters tend to flow slowly ( per second) due to the low gradients and high resistance offered by the dense vegetation.
When rising river waters first contact previously dry soil, the waters become oxygen-depleted, rendering the water environs anoxic. Many natural fish kills can occur if there are no oxygenated water refuges available. The reason for this remains speculative: it may be due to the growth of toxin-producing bacteria in the deoxygenated water rather than as a direct result of lack of oxygen.
Flora
The vegetation of the Pantanal, often referred to as the "Pantanal complex", is a mixture of plant communities typical of a variety of surrounding biome regions: these include moist tropical Amazonian rainforest plants, semiarid woodland plants typical of northeast Brazil, Brazilian cerrado savanna plants and plants of the Chaco savannas of Bolivia and Paraguay. Forests usually occur at higher altitudes of the region, while grasslands cover the seasonally inundated areas. The key limiting factors for growth are inundation and, even more importantly, water-stress during the dry season.
According to Embrapa, approximately 2,000 different plants have been identified in the Pantanal biome and classified according to their potential, with some presenting significant medicinal promise.
Fauna
The Pantanal ecosystem is home to some 463 species of birds, 269 species of fishes, more than 236 species of mammals, 141 species of reptiles and amphibians, and over 9,000 subspecies of invertebrates.