This enormous tropical wetland, the Pantanal of South America, is approximately the size of the state of Florida and is the fourth largest complex of wetland ecosystems in the world (Keddy 2000). Its basin covers approximately 138,000 km2 in Brazil and 100,000 km2 in Bolivia and Paraguay. It consists of numerous streams, lakes, and seasonally flooded swamps. The basin receives inflows from several large rivers (e.g., Rio Paraguay, Rio Petras, Rio Cuiaba) that flow southward to join the Rio Parana and then to become the Rio Plate in Argentina (see Por 1995 for further details). The river water that supplies it is primarily "clearwater" (sensu Sioli 1984), with little suspended material under pristine conditions. A unique feature of the Pantanal is that it experiences substantial changes in the area that is under water between wet and dry seasons each year, with as little as 10 percent of the area inundated during the dry season and as much as 70 percent during the four-to-six-month wet season. During the dry season, shallow, isolated water bodies develop aquatic communities that are characterized by high turbidity because of the density of bacteria and algae as well as black coloration in the water from humic materials released during decomposition. Nevertheless, these temporary aquatic ecosystems have no endemic or even rare species. This is because of the likelihood of extinction during occasional very dry periods followed by the certainty of the extensive mixing among aquatic and wetland ecosystems that follows flooding in the wet season.
The seasonal wet-dry cycle provides a wide range of ecosystem services of great ecological and economic value. There were a large number of indigenous people who cultivated wild water rice, hunted deer, and constructed artificial islands within the swamps on which to live (Moss 1998). Water supply, food production, and waste processing all still contribute important economic values to the region, and benthic communities play an important role. The Pantanal is characterized by a density of large vertebrates and unique food webs (Heckman 1998). In addition to providing habitat to endangered terrestrial and semi-aquatic species such as the spotted jaguar (Panthera onca), giant anteater (Myrmecophaga tridactyla), and giant river otter (Pteronura braziliensis), this vast region supports more than 40 species of wading birds and more than 400 species of fish. These species have high "existence values" for many people, and they maintain the complex pelagic and benthic food webs that are the basis of many ecosystem services. Recreational uses are also of major economic importance. Hunters, fishermen, and conservationists travel from all over the world to view and to exploit this exceptional biodiversity.
During the dry season, much of the unflooded matrix within the Pantanal wetland becomes a savanna used for grazing large herds of cattle that are supported by nutrient cycling in the sediments. The savanna is divided into a series of cattle ranches (based on several million zebu cattle and local breeds) that have been burned regularly by ranch ers for the last 150 years. Deforestation by burning to create more grazing land has led to soil erosion and high rates of sedimentation (see Covich et al., Chapter 3 and Ine-son et al., Chapter 9). In more recent years, nonnative grasses have been introduced to improve forage, and pesticides and fertilizer use has increased in an effort to support the growth of rice and soybeans. These increased chemical inputs have negative effects— such as bioaccumulation and eutrophication—as occur elsewhere in the world (Moss 1998). Gold mining predates ranching by about 100 years, and open-pit gold mines are still being established. Purification of gold ore utilizes mercury, which is then evaporated, and there is some evidence of mercury pollution affecting birds (as in the Everglades). Subregions within the basin (such as Nhecolandia, Brazil, the second largest of 11 subregions) are being studied with remote sensing to increase available data on land-use values. Meanwhile, threats from the watershed have also increased, and the rivers feeding the Pantanal now introduce chemical contaminants, nutrients, and sediment from increasing urban developments, agricultural operations, and mines. Seidl and Moraes (2000) estimate the annual total value of ecosystem goods and services to the Nhecolandia subregion is more than US$15.5 billion.
The conflict is clear in the Pantanal between the maintenance of natural provisioning, supporting, and enriching services and the increase of the delivery of artificial services through agriculture and exploitation of natural resources. It is quite remarkable that such a diverse and unusual animal assemblage exists, given that it is dependent on a food chain with a very important benthic base that itself is by no means unique in its diversity or nature. How long the Pantanal ecosystems can continue to provide the wealth of ecosystem services under the increasing effects of the various stressors is unknown.
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