Clearwater river (river type)

Last updated
Like many clearwater rivers, the Xingu has sections with rapids that are home to many threatened rheophilic fish found nowhere else in the world Rio Xingu, Vitoria do Xingu - Para.jpg
Like many clearwater rivers, the Xingu has sections with rapids that are home to many threatened rheophilic fish found nowhere else in the world

A clearwater river is classified based on its chemistry, sediments and water colour. Clearwater rivers have a low conductivity, relatively low levels of dissolved solids, typically have a neutral to slightly acidic pH and are very clear with a greenish colour. [2] [3] [4] Clearwater rivers often have fast-flowing sections. [3]

Contents

The main clearwater rivers are South American and have their source in the Brazilian Plateau or the Guiana Shield. [4] [5] [6] Outside South America the classification is not commonly used, but rivers with clearwater characteristics are found elsewhere. [7]

Amazonian rivers fall into three main categories: clearwater, blackwater and whitewater. This classification system was first proposed by Alfred Russel Wallace in 1853 based on water colour, but the types were more clearly defined according to chemistry and physics by Harald Sioli  [ de ] from the 1950s to the 1980s. [2] [8] [9] Although many Amazonian rivers fall clearly into one of these categories, others show a mix of characteristics and may vary depending on season and flood levels. [9] [10]

Location

Map of the Amazon basin. Tributaries of the Amazon River in the eastern part of the basin are typically clearwater Amazonriverbasin basemap.png
Map of the Amazon basin. Tributaries of the Amazon River in the eastern part of the basin are typically clearwater

The main clearwater rivers are South American and have their source in the Brazilian Plateau or the Guiana Shield. Examples of clearwater rivers originating in the Brazilian Plateau include Tapajós, Xingu, Tocantins, several large right-bank tributaries of the Madeira (notably Guaporé, Ji-Paraná and Aripuanã) and Paraguay (although heavily influenced by its whitewater tributaries). [4] [5] [6] [11] The Tapajós and Xingu alone account for 6% and 5%, respectively, of the water in the Amazon basin. [12] Examples of clearwater rivers originating in the Guiana Shield include the upper Orinoco (above the inflow of the blackwater Atabapo and whitewater Inírida–Guaviare), Ventuari, Nhamundá, Trombetas, Paru, Araguari and Suriname. [4] [5] [6] [13]

Outside South America the classification is not commonly used, but rivers with clearwater characteristics are found elsewhere, such as the upper Zambezi River, certain upland streams in major river basins of South and Southeast Asia, and many streams of northern Australia. [7]

Chemistry and sediments

The confluence of the Madeira River and Aripuana River (dark). Despite its colour on this photo, Aripuana is clearwater, while the Madeira is whitewater Confluence of the Madeira River and Aripuana River.jpg
The confluence of the Madeira River and Aripuanã River (dark). Despite its colour on this photo, Aripuanã is clearwater, while the Madeira is whitewater

In South America, clearwater rivers typically have their source and flow through regions with sandy soils and crystalline rocks. These are generally ancient, of Precambrian origin, and therefore heavily weathered, allowing relatively few sediments to be dissolved in the water. [2] [4] This results in the low conductivity, relatively low levels of dissolved solids and clear colour typical of clearwater rivers. [2]

Sand and kaolinite are the typical sediments transported by clearwater rivers, similar to blackwater, but unlike whitewater that also transports high levels of illite and montmorillonite, resulting in a significantly higher fertility of places influenced by the latter river type. [8] Nevertheless, although clearwater rivers can have extremely low nutrient levels similar to blackwater, some such as the Tapajós, Xingu and Tocantins have nutrient levels that are intermediate between black and whitewater. [8] The exact chemistry of clearwater rivers varies, [8] but it is often very similar to rainwater, low in major nutrients with sodium as the relatively dominating chemical. [14]

The water is typically neutral to slightly acidic, [4] [14] but the pH can range between 4.5 [8] and 8. [2] In the Amazon basin, clearwater rivers flowing through regions with sediments of Tertiary age are typically highly acidic, while those flowing through sediments of Carboniferous age are closer to neutral or slightly basic. [8]

As suggested by the name, clearwater rivers are highly transparent with a typical visibility of 1.5–4 m (5–13 ft). [15] There can be large variations, even within a single river, depending on season or heavy rains. [8]

Average physico-chemical characteristics [9]
Juruá River (typical whitewater) Tapajós River (typical clearwater) Tefé River (typical blackwater)
pH 7.276.565.03
Electric conductivity (μS/cm)191.1414.337.36
Total suspended solids (mg/L)51.4210.567.90
Ca (mg/L)32.550.520.71
Mg (mg/L)4.420.260.22
Na (mg/L)10.191.500.40
K (mg/L)1.980.931.41
Total P (mg/L)0.0800.0100.033
CO
3 (mg/L)		106.148.806.86
NO
3 (mg/L)		0.0310.0400.014
NH
4 (mg/L)		0.0620.190.13
Total N (mg/L)0.390.350.24
SO
4 (mg/L)		2.560.304.20
Colour (mg/Pt/L)41.614.0254.90
Si (mg/L)5.785.250.33
Cl (mg/L)4.750.530.85

Ecology

The zebra pleco is one of the many species, including several other catfish, that are restricted to clearwater rivers and threatened by dams Hypancistrus zebra4305.jpg
The zebra pleco is one of the many species, including several other catfish, that are restricted to clearwater rivers and threatened by dams

The difference in chemistry and visibility between the various black, white and clearwater rivers result in distinct differences in flora and fauna. [2] Although there is considerable overlap in the fauna found in the different river types, there are also many species found only in one of them. [18] [19] [20] Many blackwater and clearwater species are restricted to relatively small parts of the Amazon, as different blackwater and clearwater systems are separated (and therefore isolated) by large whitewater sections. [2] [19] These "barriers" are considered a main force in allopatric speciation in the Amazon basin. [2]

Potamotrygon leopoldi is part of a species complex of blackish river rays with contrasting pale spots from Brazilian clearwater rivers White-blotched River Stingray Potamotrygon leopoldi 2284px.jpg
Potamotrygon leopoldi is part of a species complex of blackish river rays with contrasting pale spots from Brazilian clearwater rivers

Many species of fish, which often are threatened (especially by dams), are only known from clearwater rivers. [1] [2] Large sections with rapids are home to specialized, rheophilic fish, [1] [17] as well as aquatic plants such as Podostemaceae. [8] [22] There are major differences in the amount of macrophytes and this is mainly related to light: heavily shaded clearwater rivers have few, while those flowing through more open regions often contain many. [8] Clearwater rivers have relatively low productivity compared to whitewater rivers, resulting in a comparably low insect abundance. [4]

Related Research Articles

<span class="mw-page-title-main">Branco River</span> River in Brazil

The Branco River is the principal affluent of the Rio Negro from the north.

<span class="mw-page-title-main">Xingu River</span> Tributary river of the Amazon River in South America

The Xingu River is a 1,640 km (1,019 mi) river in north Brazil. It is a southeast tributary of the Amazon River and one of the largest clearwater rivers in the Amazon basin, accounting for about 5% of its water.

<span class="mw-page-title-main">Rio Negro (Amazon)</span> Tributary of the Amazon River

The Rio Negro, or Guainía as it is known in its upper part, is the largest left tributary of the Amazon River, the largest blackwater river in the world, and one of the world's ten largest rivers by average discharge.

<span class="mw-page-title-main">Amazon basin</span> Major drainage basin in South America drained via the Amazon River into the Atlantic Ocean

The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about 6,300,000 km2 (2,400,000 sq mi), or about 35.5 percent of the South American continent. It is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, and Venezuela, as well as the territory of French Guiana.

<span class="mw-page-title-main">Tapajós</span> River in Brazil

The Tapajós is a river in Brazil. It runs through the Amazon Rainforest and is a major tributary of the Amazon River. When combined with the Juruena River, the Tapajós is approximately 2,080 km (1,290 mi) long. It is one of the largest clearwater rivers, accounting for about 6% of the water in the Amazon basin.

<span class="mw-page-title-main">Blackwater river</span> Slow-moving, dark-colored river flowing through forested swamps or wetlands

A blackwater river is a type of river with a slow-moving channel flowing through forested swamps or wetlands. Most major blackwater rivers are in the Amazon Basin and the Southern United States. The term is used in fluvial studies, geology, geography, ecology, and biology. Not all dark rivers are blackwater in that technical sense. Some rivers in temperate regions, which drain or flow through areas of dark black loam, are simply black due to the color of the soil; these rivers are black mud rivers. There are also black mud estuaries.

<span class="mw-page-title-main">Potamotrygonidae</span> Family of cartilaginous fishes

River stingrays or freshwater stingrays are Neotropical freshwater fishes of the family Potamotrygonidae in the order Myliobatiformes, one of the four orders of batoids, cartilaginous fishes related to sharks. They are found in rivers in tropical and subtropical South America. A single marine genus, Styracura, of the tropical West Atlantic and East Pacific are also part of Potamotrygonidae. They are generally brownish, greyish or black, often with a mottled, speckled or spotted pattern, have disc widths ranging from 31 to 200 centimetres (1.0–6.6 ft) and venomous tail stingers. River stingrays feed on a wide range of smaller animals and the females give birth to live young. There are more than 35 species in five genera.

<span class="mw-page-title-main">Tambaqui</span> Species of fishes

The tambaqui is a large species of freshwater fish in the family Serrasalmidae. It is native to tropical South America, but kept in aquaculture and introduced elsewhere. It is also known by the names black pacu, black-finned pacu, giant pacu, cachama, gamitana, and sometimes as pacu.

Ossubtus is a genus of fish in the family Serrasalmidae. It contains a single species, Ossubtus xinguense, the parrot pacu or eaglebeak pacu, The species is endemic to rapids in the Xingu River basin in the Brazilian Amazon. This vulnerable species is primarily a herbivore.

<span class="mw-page-title-main">Xingu River ray</span> Species of cartilaginous fish

The Xingu River ray, white-blotched river stingray, or polka-dot stingray is a species of freshwater fish in the family Potamotrygonidae. It is endemic to the Xingu River basin in Brazil and as such prefers clear waters with rocky bottoms. It is sometimes kept in aquaria, like its more common relative the Motoro.

<span class="mw-page-title-main">Igapó</span> Blackwater-flooded Amazon forests

Igapó is a word used in Brazil for blackwater-flooded forests in the Amazon biome. These forests and similar swamp forests are seasonally inundated with freshwater. They typically occur along the lower reaches of rivers and around freshwater lakes. Freshwater swamp forests are found in a range of climate zones, from boreal through temperate and subtropical to tropical. In the Amazon Basin of Brazil, a seasonally whitewater-flooded forest is known as a várzea, which is similar to igapó in many regards; the key difference between the two habitats is in the type of water that floods the forest.

<i>Sternarchorhynchus</i> Genus of fishes

Sternarchorhynchus is a genus of ghost knifefishes with a long, decurved snout that are found in river basins in tropical South America.

A várzea forest is a seasonal floodplain forest inundated by whitewater rivers that occurs in the Amazon biome. Until the late 1970s, the definition was less clear and várzea was often used for all periodically flooded Amazonian forests.

<span class="mw-page-title-main">Amazon biome</span> Ecological region of South America

The Amazon biome contains the Amazon rainforest, an area of tropical rainforest, and other ecoregions that cover most of the Amazon basin and some adjacent areas to the north and east. The biome contains blackwater and whitewater flooded forest, lowland and montane terra firma forest, bamboo and palm forest, savanna, sandy heath and alpine tundra. Some areas of the biome are threatened by deforestation for timber and to make way for pasture or soybean plantations.

<span class="mw-page-title-main">Whitewater river (river type)</span> Category for certain types of rivers

A whitewater river is classified based on its chemistry, sediments and water colour. Whitewater rivers have high levels of suspended sediments, giving the water a pH that is near-neutral, a high electric conductivity and a pale muddy, café au lait-like colour. Whitewater rivers are of great ecological importance and are important to local fisheries. The major seasonal Amazonian floodplains known as várzea receive their water from them.

<span class="mw-page-title-main">Negro–Branco moist forests</span> Tropical broadleaf forest covering portions of Venezuela, Colombia, and Brazil

The Negro–Branco moist forests (NT0143) is an ecoregion of tropical moist broadleaf forest to the east of the Andes in southern Venezuela, eastern Colombia and northern Brazil, in the Amazon biome. It lies on the watershed between the Orinoco and Rio Negro basins. It includes both blackwater and whitewater rivers, creating different types of seasonally flooded forest. The vegetation is more typical of the Guiana region than the Amazon.

<span class="mw-page-title-main">Madeira–Tapajós moist forests</span>

The Madeira-Tapajós moist forests (NT0135) is an ecoregion in the Amazon basin. It is part of the Amazon biome. The ecoregion extends southwest from the Amazon River between its large Madeira and Tapajós tributaries, and crosses the border into Bolivia. In the south it transitions into the cerrado biome of Mato Grosso. In the state of Rondônia it contains some of the most degraded land of the Amazon basin.

<span class="mw-page-title-main">Tapajós–Xingu moist forests</span>

The Tapajós–Xingu moist forests (NT0168) is an ecoregion in the eastern Amazon basin. It is part of the Amazon biome. The ecoregion extends southwest from the Amazon River between its large Tapajós and Xingu tributaries.

<span class="mw-page-title-main">Xingu–Tocantins–Araguaia moist forests</span>

The Xingu–Tocantins–Araguaia moist forests (NT0180) is an ecoregion in the eastern Amazon basin. It is part of the Amazon biome. The ecoregion is one of the most severely degraded of the Amazon region, suffering from large-scale deforestation and selective extraction of timber, particularly along the Trans-Amazonian Highway and in the higher and more populated southern portions.

<i>Bryconops transitoria</i> Species of fish

Bryconops transitoria is a small freshwater fish that lives in the rivers of South America. It is a poorly-studied member of the genus Bryconops with few records and vague distribution accounts, though it is believed to be endemic to the Rio Tapajós. It was originally thought to be a subspecies of congener Bryconops melanurus, but is now accepted as its own species.

References

  1. 1 2 3 Andrade, M.C.; L.M. Sousa; R.P. Ota; M. Jégu; T. Giarrizzo (2016). "Redescription and Geographical Distribution of the Endangered Fish Ossubtus xinguense Jégu 1992 (Characiformes, Serrasalmidae) with Comments on Conservation of the Rheophilic Fauna of the Xingu River". PLOS ONE. 11 (9): e0161398. Bibcode:2016PLoSO..1161398A. doi: 10.1371/journal.pone.0161398 . PMC   5035070 . PMID   27662358.
  2. 1 2 3 4 5 6 7 8 9 Duncan, W.P.; M.N. Fernandes (2010). "Physicochemical characterization of the white, black, and clearwater rivers of the Amazon Basin and its implications on the distribution of freshwater stingrays (Chondrichthyes, Potamotrygonidae)". PanamJAS. 5 (3): 454–464.
  3. 1 2 Giovanetti, T.A.; Vriends, M.M. (1991). Discus Fish . Barron's Educational Serie. p.  15. ISBN   0-8120-4669-2.
  4. 1 2 3 4 5 6 7 van der Sleen, P.; J.S. Albert, eds. (2017). Field Guide to the Fishes of the Amazon, Orinoco, and Guianas. Princeton University Press. pp. 13–18. ISBN   978-0-691-17074-9.
  5. 1 2 3 Junk, W.J.; Piedade, M.T.F.; Schöngart, J.; Cohn-Haft, M.; Adeney, J.M.; Wittmann, F.A. (2011). "Classification of Major Naturally-Occurring Amazonian Lowland Wetlands". Wetlands. 31 (4): 623–640. doi:10.1007/s13157-011-0190-7. S2CID   36001397.
  6. 1 2 3 Venticinque; Forsberg; Barthem; Petry; Hess; Mercado; Cañas; Montoya; Durigan; Goulding (2016). "An explicit GIS-based river basin framework for aquatic ecosystem conservation in the Amazon". Earth Syst. Sci. Data. 8 (2): 651–661. Bibcode:2016ESSD....8..651V. doi: 10.5194/essd-8-651-2016 .
  7. 1 2 Winemiller, K.O.; A.A. Agostinho; É.P. Caramaschi (2008). "Fish Ecology in Tropical Streams". In Dudgeon, D. (ed.). Tropical Stream Ecology . Academic Press. pp.  112–113. ISBN   978-0-12-088449-0.
  8. 1 2 3 4 5 6 7 8 9 Sioli, H., ed. (1984). The Amazon: Limnology and landscape ecology of a mighty tropical river and its basin. pp. 160–161, 219, 276–280, 445, 493–494. ISBN   978-94-009-6544-7.
  9. 1 2 3 Ríos-Villamizar, E.A.; M.T.F. Piedade; J.G. da Costa; J.M. Adeney; J. Junk (2013). "Chemistry of different Amazonian water types for river classification: A preliminary review".
  10. ↑ Goulding, M.; M.L. Carvalho (1982). "Life history and management of the tambaqui (Colossoma macropomum, Characidae): an important Amazonian food fish". Revista Brasileira de Zoologia. 1 (2): 107–133. doi: 10.1590/S0101-81751982000200001 .
  11. ↑ Blettler, M.C.M; M.L. Amsler; I.E. de Drago; L.A. Espinola; E. Eberle; A. Paira; J.L. Best; D.R. Parsons; E.E. Drago (2007). "The impact of significant input of fine sediment on benthic fauna at tributary junctions: A case study of the Bermejo-Paraguay River confluence, Argentina" (PDF). Ecohydrology. 8 (2): 340–352. doi:10.1002/eco.1511. hdl:11336/31047. S2CID   55234507.
  12. ↑ "Waters". Amazon Waters. Retrieved 10 October 2017.
  13. ↑ Mol, J.H.; B. de Mérona; P.E. Ouboter; S. Sahdew (2007). "The fish fauna of Brokopondo Reservoir, Suriname, during 40 years of impoundment". Neotrop. Ichthyol. 5 (3): 351–368. doi: 10.1590/S1679-62252007000300015 .
  14. 1 2 "Clearwater Rivers". Amazon Waters. Retrieved 1 October 2017.
  15. ↑ Goulding, M. (1981). Man and Fisheries on an Amazon Frontier. p. 10. ISBN   978-90-481-8520-7.
  16. ↑ "Habitat". zebrapleco.com. Retrieved 10 October 2017.
  17. 1 2 Hyland, T.; M.H.S. Perez. "Race against time". Exel Magazine. Retrieved 10 October 2017.
  18. ↑ Saint-Paul, U.; J. Zuanon; M.A. Villacorta Correa; M. García; N.N. Fabré; U. Berger; W.J. Junk (2000). "Fish communities in Central Amazonian white and blackwater floodplains". Environmental Biology of Fishes. 57 (3): 235–250. doi:10.1023/A:1007699130333. S2CID   25361090.
  19. 1 2 Kullander, S.O. (1986). Cichlid fishes of the Amazon River drainage of Peru. Swedish Museum of Natural History. ISBN   91-86510-04-5.
  20. ↑ Henderson, P.A.; W.G.R. Crampton (1997). "A comparison of fish diversity and abundance between nutrient-rich and nutrient-poor lakes in the Upper Amazon". Journal of Tropical Ecology. 13 (2): 175–198. doi:10.1017/s0266467400010403. S2CID   84919041.
  21. ↑ de Carvalho, M.R. (2016). "Description of two extraordinary new species of freshwater stingrays of the genus Potamotrygon endemic to the rio Tapajós basin, Brazil (Chondrichthyes: Potamotrygonidae), with notes on other Tapajós stingrays". Zootaxa. 4167 (1): 1–63. doi: 10.11646/zootaxa.4167.1.1 . PMID   27701358.
  22. ↑ Collinson, A.S. (1988). Introduction to World Vegetation (2 ed.). p.  222. ISBN   0-04-581031-1.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.