Manaus Encontro das aguas 10 2006 103 8x6

A whitewater river is classified based on its chemistry,

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

s and water colour. Whitewater rivers have high levels of suspended sediments, giving the water a pH that is near-neutral, a high

electric conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...

and a pale muddy, coffee and cream-like colour. Whitewater rivers are of great

ecological Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...

importance and are important to local fisheries. The major seasonal Amazonian floodplains known as '' várzea'' receive their water from them. The best-known whitewater rivers are Amazonian and have their source in the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

, but there are also whitewater rivers elsewhere in South America and in other continents. Amazonian rivers fall into three main categories: whitewater, blackwater and clearwater. This classification system was first proposed by

Alfred Russel Wallace Alfred Russel Wallace (8 January 1823 – 7 November 1913) was a British natural history, naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution thro ...

in 1853 based on water colour, but the types were more clearly defined according to chemistry and physics by from the 1950s to the 1980s. 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.

Location

In South America

The best-known whitewater rivers are Amazonian and have their source in the

. The main whitewater rivers are Solimões–

Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technolog ...

, Caquetá–Japurá, Putumayo, Marañón,

Ucayali The Ucayali River ( es, Río Ucayali, ) is the main headstream of the Amazon River. It rises about north of Lake Titicaca, in the Arequipa region of Peru and becomes the Amazon at the confluence of the Marañón close to Nauta city. The city o ...

, Javary, Juruá,

Acre The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong (66 by 660 feet), which is exactly equal to 10 square chains, of a square mile, 4,840 square ...

, Purus, Madre de Dios, and

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. Although the

Branco River The Branco River ( pt, Rio Branco; Engl: ''White River'') is the principal affluent of the Rio Negro from the north. Basin The river drains the Guayanan Highlands moist forests ecoregion. It is enriched by many streams from the Tepui highlands ...

traditionally is considered whitewater, it has a number of characteristics (some of them varying with season) that do not fit clearly into the classification and some refer to it as clearwater. Outside the Amazon, a small number of South American rivers are considered whitewater, most notably certain tributaries of the

Orinoco The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers , with 76.3 percent of it in Venezuela and the remainder in Colombia. It is the fourth largest river in the wor ...

such as the Guaviare,

Meta Meta (from the Greek μετά, '' meta'', meaning "after" or "beyond") is a prefix meaning "more comprehensive" or "transcending". In modern nomenclature, ''meta''- can also serve as a prefix meaning self-referential, as a field of study or end ...

and

Apure River The Apure River is a river of southwestern Venezuela, formed by the confluence of the Sarare and Uribante near Guasdualito, in Venezuela, at , and flowing across the Llanos into the Orinoco. It provides significant transportation in the area. Orig ...

s, and of the Paraná—

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to t ...

such as the Bermejo and Salado Rivers, which have their source in the Andes.

In other continents

Outside South America, this system of classification is not widely used, but there are several rivers with mainly whitewater characteristics. In Africa, these include the

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Nile The Nile, , Bohairic , lg, Kiira , Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest riv ...

(notably the

Blue Nile The Blue Nile (; ) is a river originating at Lake Tana in Ethiopia. It travels for approximately through Ethiopia and Sudan. Along with the White Nile, it is one of the two major tributaries of the Nile and supplies about 85.6% of the water to ...

), the middle and lower

Zambezi The Zambezi River (also spelled Zambeze and Zambesi) is the fourth-longest river in Africa, the longest east-flowing river in Africa and the largest flowing into the Indian Ocean from Africa. Its drainage basin covers , slightly less than ha ...

, and the

Cross A cross is a geometrical figure consisting of two intersecting lines or bars, usually perpendicular to each other. The lines usually run vertically and horizontally. A cross of oblique lines, in the shape of the Latin letter X, is termed a s ...

, Mungo, Sanaga, and Wouri rivers. In Asia, examples are the

Mekong The Mekong or Mekong River is a trans-boundary river in East Asia and Southeast Asia. It is the world's twelfth longest river and the third longest in Asia. Its estimated length is , and it drains an area of , discharging of water annual ...

mainstream (especially in the rainy season), and several upland streams in large river basins in the

southern Southern may refer to: Businesses * China Southern Airlines, airline based in Guangzhou, China * Southern Airways, defunct US airline * Southern Air, air cargo transportation company based in Norwalk, Connecticut, US * Southern Airways Express, M ...

and

southeastern The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each sep ...

part of the continent. In Europe, sections of the

Danube The Danube ( ; ) is a river that was once a long-standing frontier of the Roman Empire and today connects 10 European countries, running through their territories or being a border. Originating in Germany, the Danube flows southeast for , pa ...

have whitewater characteristics.

Chemistry and sediments

In South America, most whitewater rivers originate in the Andes where they collect high levels of nutrient-rich sediments, notably illite and montmorillonite. They have a near-neutral pH (typically 6.5–7), high levels of dissolved solids (especially

alkali earth metal The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar properties: they are all ...

s and

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

), and high

. The water is

turbid Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids c ...

, with a low visibility that is usually between . In the main stem of the Amazon River, about 82% of the total suspended solids and 90–95% of the

suspended load The suspended load of a flow of fluid, such as a river, is the portion of its sediment uplifted by the fluid's flow in the process of sediment transportation. It is kept suspended by the fluid's turbulence. The suspended load generally consists ...

of sediments originate from the Andes. Along their course, whitewater rivers often become diluted due to the inflow of black- and clearwater tributaries. For example, the Rio Negro, the largest blackwater tributary, accounts for 14% of the total Amazon basin water and Tapajós, the largest clearwater tributary, accounts for 6%. Consequently, although the Amazon River is whitewater throughout its course, the electric conductivity is 120–200 μS/cm in the Andes, but by the time it reaches Santarém (after the inflow of Rio Negro, Tapajós, and some smaller black- and clearwater tributaries), it has fallen to 40-70 μS/cm. At high elevations in the Andes near the headwater, the pH of whitewater rivers can be above 8. In some parts of the Amazon where the rivers are not naturally whitewater, "pseudo-whitewater" exists because of

soil erosion Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, a ...

from human activities.

Ecology

Schwarzer Pacu Colossoma macropomum Tierpark Hellabrunn-1

The difference in chemistry and visibility between the various black, white and clearwater rivers result in distinct differences in flora and fauna. 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. 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. These "barriers" are considered a main force in

allopatric speciation Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

in the Amazon basin. As in South America, distinct differences between species in black- and whitewater can be seen in Asia and Africa. For example, the fish fauna in African whitewater rivers tend to be dominated by

cyprinid Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest ...

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...

, and elephantfish, whereas blackwater rivers usually have more characiforms and

cichlid Cichlids are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, the Labroidei, along with the wrasses ( Labridae), in the order Perciformes, but molecular studies have contradicted th ...

s. The high nutrient levels in whitewater rivers allow high levels of

periphyton Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs (German "surface growth" or "overgrowth") refers to the col ...

(in contrast to the nutrient-poor blackwater rivers), but the water turbidity restricts light, thereby limiting

photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

processes, which are necessary to

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

and submerged macrophytes, to the uppermost part of the water column. The periphyton roughly equals the production level in temperate

eutrophic Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplan ...

lakes.

Bacterial Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...

abundance and production rates are roughly equal in whitewater and blackwater rivers, but both vary with water level and productions are higher during the high-water season. The major seasonal Amazonian floodplains known as '' várzea'' receive their water from whitewater rivers and are home to many animals and plants. In the

Brazilian Amazon Brazilian commonly refers to: * Something of, from or relating to Brazil * Brazilian Portuguese, the dialect of the Portuguese language used mostly in Brazil * Brazilians, the people (citizens) of Brazil, or of Brazilian descent Brazilian may als ...

, ''várzea'' covers roughly , equalling 4% of the entire area (twice the area covered by '' igapó''). In addition to forests and woodlands with trees and other plants that are seasonally covered by water, about one-third of this floodplain's area is covered by large floating meadows. These floating meadows are home to the richest Amazonian community of aquatic invertebrates and important to fish, especially species that visit during the flood season for feeding or breeding (a lower number of fish species live in the habitat year-round). The floodplains are also very important for fisheries. For example, in the Brazilian Amazon, 61% of the yields from

subsistence A subsistence economy is an economy directed to basic subsistence (the provision of food, clothing, shelter) rather than to the market. Henceforth, "subsistence" is understood as supporting oneself at a minimum level. Often, the subsistence econo ...

and local market fisheries is from districts with ''várzea''. Several of the most important species in Amazonian fisheries rely on whitewater for breeding: The tambaqui (''Colossoma macropomum''), black prochilodus (''Prochilodus nigricans'') and '' Semaprochilodus'' spp. move into whitewater rivers to spawn, and many large

species (especially pimelodids such as ''

Brachyplatystoma ''Brachyplatystoma'' is a genus of catfish from the family Pimelodidae. As the occasionally used common name goliath catfishes indicates, this genus includes some of the largest species of catfish, including the piraíba, ''B. filamentosum'', wh ...

'') perform long migrations up whitewater rivers to spawn. Most of the large cities in the Amazon region, such as

Iquitos Iquitos (; ) is the capital city of Peru's Maynas Province and Loreto Region. It is the largest metropolis in the Peruvian Amazon, east of the Andes, as well as the ninth-most populous city of Peru. Iquitos is the largest city in the world t ...

Manaus Manaus () is the capital and largest city of the Brazilian state of Amazonas. It is the seventh-largest city in Brazil, with an estimated 2020 population of 2,219,580 distributed over a land area of about . Located at the east center of the s ...

, Santarém and

Belém Belém (; Portuguese for Bethlehem; initially called Nossa Senhora de Belém do Grão-Pará, in English Our Lady of Bethlehem of Great Pará) often called Belém of Pará, is a Brazilian city, capital and largest city of the state of Pará in ...

, are located on clear- or blackwater rivers (which have fewer insects), but at the junction of whitewater rivers (which have better fishing). Due to the high level of prey fish, the largest group-size of '' Inia'' river dolphins are in sections of the Amazon and Orinoco basins that are directly influenced by whitewater.

References

{{Wetlands Aquatic ecology Rivers