whitewater river (river type)

File:Amazonriverbasin basemap.png. Rivers that originate in the Andes (far west and southwest in basin) are typically whitewater.]]

The best-known whitewater rivers are Amazonian and have their source in the Andes. The main whitewater rivers are Solimões–Amazon, Caquetá–Japurá, Putumayo, Marañón, Ucayali, Javary, Juruá, Acre, Purus, Madre de Dios, and Madeira. Although the Branco River traditionally is considered whitewater,{{cite journal | author1=Venticinque|author2=Forsberg|author3=Barthem|author4=Petry|author5=Hess|author6=Mercado|author7=Cañas|author8=Montoya|author9=Durigan|author10=Goulding | year=2016 | title=An explicit GIS-based river basin framework for aquatic ecosystem conservation in the Amazon | journal=Earth Syst. Sci. Data | volume=8 |issue=2| pages=651–661 | doi=10.5194/essd-8-651-2016 |bibcode=2016ESSD....8..651V|doi-access=free}}{{cite book| editor1=Val, A.L.|editor2=V.M.F. de Almeida-Val|editor3=D.J. Randall | year=2013 | title=Fish Physiology: The Physiology of Tropical Fishes | page=27 | isbn=978-0-12350-445-6 }} 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.{{cite journal | author1=de Souza kodra, A.|author2=M.N. Fernandes|author3=W.L. Paxiúba Duncan | year=2014 | title=Effect of clearwater on osmoregulation of cururu ray, Potamotrygon sp. (Chondrichthes; Potamotrogonidae), an endemic species from blackwater river | journal=Scientia Amazonia | volume=3 | issue=1 | pages=15–24 }}

Outside the Amazon, a small number of South American rivers are considered whitewater, most notably certain tributaries of the Orinoco such as the Guaviare, Meta and Apure Rivers, and of the Paraná—Paraguay such as the Bermejo and Salado Rivers, which have their source in the Andes.{{cite web | author1=Petry, P. | author2=J. Hales | year=2002 | title=Orinoco Llanos | url=http://www.feow.org/ecoregions/details/orinoco_llanos | publisher=Freshwater Ecoregions of the World | access-date=2017-03-15 | archive-date=2017-01-16 | archive-url=https://web.archive.org/web/20170116162819/http://www.feow.org/ecoregions/details/Orinoco_Llanos | url-status=dead }}{{cite journal | author=Zalocar de Domitrovic, Y. | year=2002 | title=Structure and variation of the Paraguay River phytoplankton in two periods of its hydrological cycle | journal=Hydrobiologia | volume=472 | issue=1 | pages=177–196 | doi=10.1023/A:1016304803431 | s2cid=189775082 | hdl=11336/54485 | hdl-access=free }}{{cite journal | author1=Scarabotti, P.A.|author2=J.A. López|author3=M. Pouilly | year=2011 | title=Flood pulse and the dynamics of fish assemblage structure from neotropical floodplain lakes | journal=Ecology of Freshwater Fish | volume=20 |issue=4| pages=605–618 | doi=10.1111/j.1600-0633.2011.00510.x }}

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 Niger main stem and its floodplain, Orashi,{{cite book | author1=Thieme, M.L. | author2=R. Abell | author3=N. Burgess | author4=B. Lehner | author5=E. Dinerstein | author6=D. Olson | title=Freshwater Ecoregions of Africa and Madagascar: A Conservation Assessment | year= 2005 | pages=60–62 | publisher=Island Press | isbn=1-55963-365-4 }} the Nile (notably the Blue Nile), the middle and lower Zambezi, and the Cross, Mungo, Sanaga, and Wouri rivers.{{cite book | author1=Brummett, R.|author2=M. Stiassny|author3=I. Harrison | chapter=Background | editor1=Allen, D.J.|editor2=E.G.E. Brooks|editor3=W.R.T. Darwall | title=The Status and Distribution of Freshwater Biodiversity in Central Africa | year= 2011| pages= 1–20 | publisher=Gland, IUCN | isbn=978-2-8317-1326-7}} In Asia, examples are the Mekong mainstream (especially in the rainy season),{{cite journal | author1=Baird, I.G.|author2=B. Phylavanh|author3=B. Vongsenesouk|author4=K. Xaiyamanivong | year=2001 | title=The ecology and conservation of the smallscale croaker Bosemania microlepis (Bleeker 1858-59) in the mainstream Mekong River, Southern Laos | journal=Nat. Hist. Bull. Siam Soc. | volume=49 | pages=161–176 }} and several upland streams in large river basins in the southern and southeastern part of the continent. In Europe, sections of the Danube have whitewater characteristics.{{cite book | author1=Markert, B.|author2=S. Fränzle|author3=S. Wünschmann | title=Chemical Evolution: The Biological System of the Element | year= 2015| pages= 111–112| publisher=Springer International Publishing | isbn=978-3-319-14354-5}}

File:Porto Velho 3 09072007.jpg showing the typical pale muddy colour of a whitewater river as it flows past Porto Velho, Brazil]]

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 metals and carbonate), and high electric conductivity. The water is turbid, with a low visibility that is usually between {{convert|20|and(-)|60|cm|ft|abbr=on|1}}. In the main stem of the Amazon River, about 82% of the total suspended solids and 90–95% of the suspended load of sediments originate from the Andes.{{cite journal | author1=McClain, M.E.|author2=R.J. Naiman | year=2008 | title=Andean Influences on the Biogeochemistry and Ecology of the Amazon River | journal=BioScience | volume=58 | issue=4 | pages=325–338 | doi=10.1641/B580408 | doi-access= }} 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%.{{cite web | url=http://amazonwaters.org/waters/flows-and-floods/ | title=Waters | date=28 May 2014 | publisher=Amazon Waters | access-date=30 December 2016 }} 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.{{cite web | url=http://amazonwaters.org/waters/river-types/whitewater-rivers/ | title=Whitewater Rivers | publisher=Amazon Waters | access-date=26 December 2016 }}

In some parts of the Amazon where the rivers are not naturally whitewater, "pseudo-whitewater" exists because of soil erosion from human activities.

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File:Schwarzer Pacu Colossoma macropomum Tierpark Hellabrunn-1.jpg, an important species in Amazonian fisheries, relies on whitewater to breed]]

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.{{cite journal| author1=Saint-Paul, U.|author2=J. Zuanon|author3=M.A. Villacorta Correa|author4=M. García|author5=N.N. Fabré|author6=U. Berger|author7=W.J. Junk | year=2000 | title=Fish communities in Central Amazonian white and blackwater floodplains | journal=Environmental Biology of Fishes | volume=57 |issue=3| pages=235–250 | doi=10.1023/A:1007699130333 |s2cid=25361090}}{{cite book | author=Kullander, S.O.|author-link=Sven O. Kullander|year=1986 | title=Cichlid fishes of the Amazon River drainage of Peru | publisher=Swedish Museum of Natural History | isbn=91-86510-04-5 }}{{cite journal | author1=Henderson, P.A.|author2=W.G.R. Crampton | year=1997 | title=A comparison of fish diversity and abundance between nutrient-rich and nutrient-poor lakes in the Upper Amazon | journal=Journal of Tropical Ecology | volume=13 |issue=2 | pages=175–198 | doi=10.1017/s0266467400010403|s2cid=84919041 }} 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 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 cyprinids, catfish, and elephantfish, whereas blackwater rivers usually have more characiforms and cichlids.

The high nutrient levels in whitewater rivers allow high levels of periphyton (in contrast to the nutrient-poor blackwater rivers), but the water turbidity restricts light, thereby limiting photosynthetic processes, which are necessary to algae and submerged macrophytes, to the uppermost part of the water column. The periphyton roughly equals the production level in temperate eutrophic lakes.{{cite journal| author=Putz, R.| year=1997 | title=Periphyton communities in Amazonian black- and whitewater habitats: Community structure, biomass and productivity | journal=Aquatic Sciences | volume=59 | issue=1 | pages=74–93 | doi=10.1007/BF02522552| s2cid=26021866 }} Bacterial 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.{{cite journal | author1=Benner, R.|author2=S. Opsahl|author3=G. Chin-Leo | year=1995 | title=Bacterial carbon metabolism in the Amazon River system | journal=Limnol. Oceanogr. | volume=40 | issue=7 | pages=1262–1270 | doi=10.4319/lo.1995.40.7.1262|bibcode=1995LimOc..40.1262B| doi-access=free }}

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, várzea covers roughly {{convert|200000|km2|mi2|abbr=on}}, equalling 4% of the entire area (twice the area covered by igapó).{{cite journal| author1=Fernandez Piedade, M.T.|author2=W. Junk|author3=S.A. D'Angelo|author4=F. Wittmann|author5=J. Schöngart|author6=K.M. do Nascimento Barbosa|author7=A. Lopes | year=2010 | title=Aquatic herbaceous plants of the Amazon floodplains: state of the art and research needed | journal=Acta Limnol. Bras. | volume=22 | issue=2 |pages=165–178| doi=10.4322/actalb.02202006 |doi-access=free}} 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.{{cite book | editor1=van der Sleen, P.|editor2=J.S. Albert | year=2017 | title=Field Guide to the Fishes of the Amazon, Orinoco, and Guianas | publisher=Princeton University Press | page=20 | isbn=978-0691170749 }} These floating meadows are home to the richest Amazonian community of aquatic invertebrates{{cite book | editor=Junk, W.J. | year=1997 | title=The Central Amazon Floodplain: Ecology of a Pulsing System | publisher=Springer Science & Business Media | isbn=978-3-662-03416-3 }} and important to fish,{{cite web | url=http://amazonwaters.org/fisheries/geography/floodplain-or-varzea/ | title=Floodplain or Várzea | date=28 May 2014 | publisher=Amazon Waters | access-date=30 December 2016 }} 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 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 catfish species (especially pimelodids such as Brachyplatystoma) perform long migrations up whitewater rivers to spawn.{{cite book|title=The catfish connection: ecology, migration, and conservation of Amazon predator | author1=Barthem, R.B.|author2=M. Goulding | year=1997 | publisher=Columbia University Press | isbn= 978-0231108324}} Most of the large cities in the Amazon region, such as Iquitos, Manaus, Santarém and Belém, 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.{{cite journal | author1=Gomez-Salazar, C.|author2=F. Trujillo|author3=H. Whitehead | year=2011 | title=Ecological factors influencing group sizes of river dolphins (Inia geoffrensis and Sotalia fluviatilis) | journal=Marine Mammal Science | volume=28 | issue=2 | pages=E124–E142 | doi=10.1111/j.1748-7692.2011.00496.x |url=http://babel.banrepcultural.org/cdm/ref/collection/p17054coll23/id/588}}

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Category:Aquatic ecology

Category:Rivers