The Human Footprint in Wetlands
Economic development in the Amazon Basin in the last several decades has resulted in the creation of many human-made wetlands, and these will continue to increase rapidly as large-scale infrastructure projects, such as new highways and dams, are constructed. The extent to which wetlands, especially floodplains, might have been modified by indigenous peoples prior to European colonization is still unclear. Studies of what are now wetland savanna areas, such as the Llanos de Moxos in Bolivia and Marajó Island in Brazil, revealed that indigenous peoples greatly modified these areas with some combination of fire, raised agriculture fields, canals and other bulwarks. The Ramsar Convention on Wetlands considers the following human-made wetlands: aquaculture; ponds; irrigated land; seasonally flooded agricultural land; water storage areas; excavations; wastewater treatment areas; canals and drainage channels; and ditches.
Aquaculture has expanded rapidly in the Amazon Basin since the early 1990s and several native fish species, such as tambaqui and matrinxã, now appear regularly in local markets, especially in Brazil. Most aquaculture is taking place in drier areas, such as in the savanna areas of Roraima, but also in Rondônia and near Manaus. It is also expanding in lowland areas of the Andean countries. Small streams are often dammed and divided into ponds, or ponds are excavated in upland areas. As fish from river and floodplain fisheries becomes rarer, it can be expected that aquacultural wetlands will continue to increase. It should also be mentioned that trout farming is widespread in the Andes and many small streams are dammed or have concrete ponds along their sides.
Small ponds are common throughout the Amazon where there is agriculture and livestock ranching, especially near highways and roads. However, there is little information on ponds and they are not generally recognized in imagery analyses. Livestock ponds are also common in the drier areas of the Andes.
Experimental and advanced irrigation projects are well underway in both the drier parts of the Amazon Basin, such as in Roraima and Eastern Bolivia, and in the humid areas near the Andes in Peru, Ecuador and Colombia. In the wetter areas, rice is the main crop irrigated, whereas soybeans and other non-rice crops are being experimented with in drier areas. Considering possible climatic drying and anticipated expansion of rice farming, it can be expected that irrigated land will greatly increase in the Amazon Basin in the next few decades.
Seasonally flooded agricultural land is inundated by overflow from adjacent rivers or streams or just by rainwater. In the Andes, it can also include intensively managed or grazed wet meadow or pasture. Many of the seasonally flooded savanna areas in the Amazon are now largely managed for livestock ranching, such as on Marajó Island and some areas of the Amazon River floodplain where cattle and water buffalo are grazed, even during the floods. Many of these areas have introduced grasses, most of African origin. Rice fields near the Andes are flooded by local rainfall though some also use diverted stream water as well.
Water storage areas are mostly dam reservoirs. All large dams in the Amazon Basin are thus far used mostly for generation of hydroelectricity, though there are numerous small dams in the drier regions of the Cerrado and savannas that are used locally for irrigation. In dry areas of the Andes, small dams are also being constructed to support the rapidly expanding agricultural sector. The first relatively large dam in the Amazon Region was constructed in 1972 on the Araguari River in the state of Amapá near the Atlantic coast. The reservoirs of Tucuruí Dam (1986) on the Tocantins River and the Balbina Dam (1989) on the Uatumã River near Manaus are approximately 2,400 km2 each, and are among the largest dam reservoirs in the world. The other Amazonian dam reservoirs are less than 600 km2. The Santo Antonio and Jirau dams on the Madeira River, which began functioning in 2011, were the first “run-of-the-river” dams in the Amazon Basin and both have reservoirs smaller than 350 km2. Other than the large dams mentioned above, there are now thousands of small dams used for water storage and these will probably continue to increase almost exponentially, especially considering expected drier conditions in some parts of the Amazon basin.
Mining excavations are most extensive in the Amazon Basin where there is or has been gold mining, much if not most of it illegal. Especially noteworthy are the gold mining areas in the foothill region of the Madre de Dios Basin in Peru, some of which now look like moonscapes with numerous pits often filled with water, especially during the rainy season. Other types of mining, such as for bauxite and iron, create fewer pits with water. Near urban areas, there are often pits where clay has been mined for making bricks and these often become filled with water during the rainy season. The impact of mining on Amazonian wetlands in general has yet to be analyzed.
Wastewater treatment areas include sewage farms, settling ponds and oxidation basins. Domestic and industrial wastewater management has been poorly reported on for the Amazon and most cities and towns discharge untreated waste to some extent directly into rivers or streams. Some of these become so polluted that they might be considered uncontrolled waste treatment areas. Various types of mining ponds are common in heavily mined areas of the Amazon, such as in the far-western headwaters of the Mantaro sub-basin of Peru, which is in the Ucayali Basin and within 150 km of the Pacific. The bauxite processing complex on Barcarena Island near Belém (Pará, Brazil) requires settling ponds, but these appear to be well controlled.
Canals are constructed for transportation, irrigation or drainage. There are only a few canals of notable size in the Amazon Bbasin. The most notable is the Canal da Tartaruga on Marajó Island constructed in the 1950s for transportation to the interior of the island and also to help facilitate drainage of the savannas where livestock are grazed. Proposed inland waterway systems for the Amazon, generally called hidrovias, would include river channel straightening and deepening and connecting canal excavation. Hidrovias also include locks, especially where dams have been constructed, and Tucuruí Dam on the Tocantins River already has two locks to facilitate barge transportation for soybeans and minerals.