The Pantanal: A large South American wetland and its position in limnological theory

The Pantanal of MatoGrosso and Mato Grosso do Sul is situated in a large intracontinental depression that is drained by the Paraguay River. Pliocene-Pleistocene sandy sediments fi ll the depression but are eroded in the surrounding uplands by the Paraguay River and its large tributaries, which form a large inland delta. Paleoclimatic changes between wetter and dryer periods led to the formation of sediment cones, which in part rise above the actual mean fl ood level. The annual pronounced rainy and dry seasons have resulted in the formation of a wetland that follows the behaviour described by the flood pulse concept. According to hydrological parameters, the Pantanal is a floodplain that is subject to a monomodal, predictable flood pulse of low amplitude and a smooth shape. However, the local flood pattern is highly variable because of the different discharge patterns of the Paraguay River and its large tributaries and the impact of local rainfall, which varies between regions and years. In addition to the flood stress, the extended dry season causes intense drought and fire stress, with impacts on the Pantanal’s plants and animals. The region’s paleoclimatic instability favoured the immigration from the surrounding biomes of species with a large ecological amplitude and hindered the development of endemic species. The low nutrient status of most upland areas is reflected in the soils and waters of the Pantanal, which are of low fertility. However, internal nutrient-retention mechanisms driven by the change between aquatic and terrestrial phases, and the associated flora, support a rich wildlife and form the basis for low- density cattle- ranching. Threats to the system are the products of changes in the flood pulse due to reservoir construction at the tributaries in the uplands and by dike and road construction locally inside the Pantanal. Construction of the highly controversial hidrovia, which would drain parts of the Pantanal and modify the flood pattern in large areas, would likewise have a catastrophic impact on the region. The increasing load of suspended material by strong erosion in agrarian areas located in the uplands fills the channels inside the Pantanal such that during high-water periods the rivers are forced above their beds and thus flood the surroundings for long periods of time, as is the case for the Taquari River. Untreated wastewater and solid waste from the region’s fast-growing cities pollute several areas of the Pantanal. The intensifi cation of cattle- breeding destroys habitats and reduces species diversity. Although local, national, and international efforts to protect the Pantanal have recently been undertaken, they need to be strengthened in order to reduce the negative impacts of ongoing development projects and to reinforce plans for the sustainable use of the region