The Pantanal is a tropical wetland and one of the world's largest wetland of any kind. 80% of it lies within the Brazilian state of Mato Grosso do Sul but extends into Mato Grosso as well as into portions of Bolivia and Paraguay, sprawling over an area estimated at between 140,000 square kilometres (54,000 sq mi) and 195,000 square kilometres (75,000 sq mi). Various sub-regional ecosystems exist, each with distinct hydrological, geological and ecological characteristics; up to twelve of them have been defined (RADAMBRASIL 1982).
80% of the Pantanal floodplains are submerged during the rainy seasons, nurturing an astonishing biologically diverse collection of aquatic plants and helping support a dense array of animal species.
The name "Pantanal" comes from the Portuguese word pântano, meaning wetland, bog, swamp or marsh. By comparison, the Brazilian highlands are locally referred to as the planalto, plateau or, literally, high plain.
Geology, geography and ecology
The Pantanal is a huge 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.
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 has an average yearly rainfall of 1,000–1,400 mm (39–55 in), but is fed by the upper Paraguay River. Its average temperature is 25 °C (77 °F), but temperatures can fluctuate from 0 to 40 °C (32 to 104 °F).
During the rainy season the water in the Pantanal basin rises between two and five meters. Just as the Nile delta is fertile farmable land, so too are the Pantanal plains. The dramatic increase of water during the rainy season nourishes the producers of Pantanal, which in turn nourishes all the other species as well. Humans have taken advantage of this so much that it has become a problem.
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 80 to 150 m (260 to 490 ft) above sea-level. Annual rainfall over the flood basin is between 1,000 to 1,500 mm (39 to 59 in) with most rainfall occurring between November and March. 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 (2 to 10 cm (0.79 to 3.9 in) per second) due to the low gradients and high resistance offered by the dense vegetation.
When rising river waters first contacts 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 de-oxygenated water rather than as a direct result of lack of oxygen (McClain 2002)).
The vegetation of the Pantanal is often referred to as the "Pantanal complex" and is a mixture of plant communities typical of a variety of surrounding biome regions: these include moist tropical Amazonian rainforest plants, semi-arid 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. The Pantanal ecosystem is home to 3500 known plant species.
The Pantanal ecosystem is also thought to be home to 1000 bird species, 400 fish species, 300 mammalian species, 480 reptile species and over 9000 different subspecies of invertebrates.
Among the rarest animals to inhabit the wetland of the Pantanal are the Marsh Deer (Blastocerus dichotomus) and the Giant River Otter (Pteroneura brasiliensis). Parts of the Pantanal are also home to the following endangered or threatened species: the Hyacinth Macaw (Anodorhyncus hyacinthinus) (a bird endangered due to smuggling), the Crowned Solitary Eagle, the Jaguar (Panthera onca), the Maned Wolf (Chrysocyon brachyurus), the Bush Dog (Speothos venaticus), the Capybara (Hydrochoerus hydrochaeris), the South American Tapir (Tapirus terrestris), the Giant Anteater (Myrmecophaga tridactyla) and the Yacare Caiman (Caiman yacare). The Pantanal is home to one of the largest and healthiest Jaguar populations on Earth.
Most fish are detritivores, primarily ingesting fine particles from sediments and plant surfaces. This is characteristic of fish living in South American flood-plains in general. Fish migration between river channels and flood-plain regions occurs seasonally. These fish have many adaptations that allow them to survive in the oxygen-depleted flood-plain waters.
In addition to the caiman, the following reptiles inhabit the Pantanal: the yellow anaconda (Eunectes notaeus), the Gold tegu (Tupinambis teguixin), the red-footed tortoise (Geochelone carbonaria) and the Green Iguana (Iguana Iguana).