Blackwater river explained

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.

Blackwater rivers are lower in nutrients than whitewater rivers and have ionic concentrations higher than rainwater.[1] [2] The unique conditions lead to flora and fauna that differ from both whitewater and clearwater rivers.[3] The classification of Amazonian rivers into black, clear, and whitewater was first proposed by Alfred Russel Wallace in 1853 based on water colour, but the types were more clearly defined by chemistry and physics by from the 1950s to the 1980s.[4] 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.[5]

Comparison between white and black waters

Table 1: Mean ionic composition, specific conductivity (μS/cm), and pH in Amazon waters.[6]
Solimões or
Amazon River
– whitewater
Rio Negro
– blackwater
Na (mg/L)2.3 ± 0.80.380 ± 0.124
K (mg/L)0.9 ± 0.20.327 ± 0.107
Mg (mg/L)1.1 ± 0.20.114 ± 0.035
Ca (mg/L)7.2 ± 1.60.212 ± 0.066
Cl (mg/L)3.1 ± 2.11.7 ± 0.7
Si (mg/L)4.0 ± 0.92.0 ± 0.5
Sr (μg/L)37.8 ± 8.83.6 ± 1.0
Ba (μg/L)22.7 ± 5.98.1 ± 2.1
Al (μg/L)44 ± 37112 ± 29
Fe (μg/L)109 ± 76178 ± 58
Mn (μg/L)5.9 ± 5.19.0 ± 2.4
Cu (μg/L)2.4 ± 0.61.8 ± 0.5
Zn (μg/L)3.2 ± 1.54.1 ± 1.8
Conductivity57 ± 89 ± 2
pH6.9 ± 0.45.1±0.6
Total P (μg/L)105 ± 5825 ± 17
Total C (mg/L)13.5 ± 3.110.5 ± 1.3
HCO3-C (mg/L)6.7 ± 0.81.7 ± 0.5
Black and white waters differ significantly in their ionic composition, as shown in Table 1. Black waters are more acidic, resulting in an aluminum concentration greater than that of the more neutral white waters. The major difference is the concentrations of sodium, magnesium, calcium, and potassium; these are very low in black waters. This has ecological implications. Some animals need more calcium than is available in blackwaters, so for example, snails, which need much calcium to build shells, are not abundant in blackwaters. The lack of dissolved ions in black waters results in a low conductivity, similar to that of rainwater.

Black and white waters differ in their planktonic fauna and flora. Tables 2 and 3 compare the number of planktonic animals caught in black and white water localities only a few meters apart. The black water was not as extreme an example as the Rio Negro system. However, it can be seen that the black water held greater numbers of rotifers but fewer crustaceans and mites. These crustaceans are important foods for larval fish. The zones where the two waters mix are attractive to ostracods and young fish. These mixing zones tend to have many animals. The abundance is shown in Table3, which compares animals in of water.[7]

Table 2: Planktonic organisms collected in black (Japura) and white (Solimões) waters.
Animal groups
present
Black
water
Mixed
water
White
water
Rotifera284230
Cladocera52943
Ostracoda399729
Calanoida115166
Cyclopoida224961
Chironomidae033
Acari (mites)002
Table 3: Number of planktonic organisms collected in 10L of black, white, and mixed waters.
Black waterMixed waterWhite water
Animal groups
present
Open
water
ForestOpen
water
ForestOpen
water
Forest
Volvocaceae42 38   
Rotifera87534   
Cladocera6 5 81
Ostracoda2113 7 
Calanoida23310   
Cyclopoida527191131
Mysidacea 1    
Diptera    1 
Acari (mites)  1 1 
Larval fish  1 1 

Comparison between clear and black waters

Blackwater rivers resemble clearwater rivers in having a low conductivity and relatively low levels of dissolved solids, but clearwater rivers have water that often only is somewhat acidic (typical pH ~6.5) and very clear with a greenish color.[8] The main Amazonian clearwater rivers have their source in the Brazilian Plateau (such as Tapajós, Tocantins, Xingu and some right tributaries of the Madeira), but some originate in the Guiana Shield (such as Nhamundá, Paru, and Araguari).[9]

Blackwater rivers of the world

Amazonia

a tributary of the Japurá River

a tributary of the Tapajós River

a tributary of the Mazaruni River

The largest blackwater river in the world; one of the largest Amazonian tributaries.

Orinoco basin

Southern United States

along with the Edisto and the Combahee Rivers in South Carolina makes up the ACE Basin National Wildlife Refuge.

a tributary of the Chowan River in Virginia

a major river in the western Florida panhandle

a tributary of the Pee Dee River in North and South Carolina

located in West Tennessee

66 mile-long river with its headwaters in Manatee County, Florida. The Myakka River discharges into Charlotte Harbor.

located in Northwest Tennessee

a river in northern Florida

a 245-mile river in eastern Georgia that passes to the south of the city of Savannah and enters the Atlantic Ocean at Ossabaw Sound.

a 119-mile-long (192 km) river in east-central Georgia. It is a tributary of the Altamaha River, which flows to the Atlantic Ocean.

a river in Northeastern North Carolina. Located between Camden and Pasquotank counties, the Pasquotank connects directly to the Albemarle Sound and is part of the Intracoastal Waterway via Elizabeth City.

located in central Florida, flows into Charlotte Harbor.

a small river in central Florida

a river in southern Delaware and southeastern Maryland on the Delmarva Peninsula. The river is a tributary to the Chesapeake Bay.

a river in northern Florida

a river in southeast Georgia that flows through the city of Waycross and empties into the Atlantic Ocean near Cumberland Island.

a small river in Washington and Tyrrell Counties in eastern North Carolina at Pettigrew State Park

a river in northern Florida

The largest river in Florida. Flows north through Jacksonville and into the Atlantic.

a large river in southern Georgia and northern Florida flowing into the Gulf of Mexico

arises in Northern Mississippi and runs through southwest Tennessee/Memphis into Mississippi River

Northern United States

a river in northern Minnesota that leaches from peat bogs and pine forests

Africa

Australia

Intermittent blackwater events

Other rivers in Australia may experience infrequent 'blackwater events' associated with flood waters connecting to forested floodplains and these events may be associated with hypoxic waters [low oxygen]. Examples include the Murray River, Edward River, Wakool River and Murrumbidgee River.[14]

Indonesia

See also

Notes and References

  1. 10.2307/2989823 . Janzen . D. H. . . Biotropica . 6 . 2 . July 1974 . 69–103 . 2989823.
  2. Sioli . Harald . 1975 . Tropical rivers as expressions of their terrestrial environments . Tropical Ecological Systems/Trends in Terrestrial and Aquatic Research . 275–288 . . New York City.
  3. Duncan . W. P. . Fernandes . M. N. . 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 . https://web.archive.org/web/20211113075416/https://www.researchgate.net/profile/Wallice-Duncan/publication/230692696_Physicochemical_characterization_of_the_white_black_and_clearwater_rivers_of_the_Amazon_Basin_and_its_implications_on_the_distribution_of_freshwater_stingrays_Chondrichthyes_Potamotrygonidae/links/0fcfd5032ba0ebcae3000000/Physicochemical-characterization-of-the-white-black-and-clearwater-rivers-of-the-Amazon-Basin-and-its-implications-on-the-distribution-of-freshwater-stingrays-Chondrichthyes-Potamotrygonidae.pdf . 13 November 2021.
  4. Book: Sioli . H. . 1984 . The Amazon: Limnology and landscape ecology of a mighty tropical river and its basin . Springer . 978-94-009-6544-7.
  5. 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 . 10.1590/S0101-81751982000200001 . free .
  6. Ribeiro . J. S. B. . A. J. . Darwich . Phytoplanktonic primary production of a fluvial island lake in the Central Amazon (Lago do Rei, Ilha do Careiro) . Amazoniana . Kiel . 12 . 3–4 . 365–383 . 1993.
  7. Web site: Comparison between white and black waters . 21 May 2006 . Amazonian Fishes and their Habitats . Pisces Conservation Ltd . https://web.archive.org/web/20110716122850/http://www.amazonian-fish.co.uk/indexc30.html . 16 July 2011 . dead .
  8. Book: Thomas A. . Giovannetti . Matthew M. . Vriends . Discus Fish . limited . Barron's . Hauppauge, NY . 1991 . 0-8120-4669-2 . 15.
  9. 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. 10.1007/s13157-011-0190-7 . 36001397 .
  10. Book: Brummett . R. . M. . Stiassny . I. . Harrison . Background . Allen . D. J. . E. G. E. . Brooks . W. R. T. . Darwall . The Status and Distribution of Freshwater Biodiversity in Central Africa . limited . 2011. 1–20 . Gland, IUCN . 978-2-8317-1326-7.
  11. Schliewen . U. K. . M. L. J. . Stiassny . 2006 . A new species of Nanochromis (Teleostei: Cichlidae) from Lake Mai Ndombe, central Congo Basin, Democratic Republic of Congo . Zootaxa . 1169 . 33–46 . 10.11646/zootaxa.1169.1.2 .
  12. Book: Thieme . M. L. . R. . Abell . N. . Burgess . B. . Lehner . E. . Dinerstein . D. . Olson . Freshwater Ecoregions of Africa and Madagascar: A Conservation Assessment . limited . 2005 . 60–62 . Island Press . 1-55963-365-4 .
  13. Web site: Noosa River Elanda Point to Campsite Fifteen Canoe Guidebook. www.upstreampaddle.com. 19 November 2014. 8 July 2020. https://web.archive.org/web/20200708025442/http://www.upstreampaddle.com/noosa.html. dead.
  14. Web site: Black water event in the Murray, Murrumbidgee and Lower Darling River catchments: March 2012 . www.dpi.nsw.gov.au . 8 August 2014 . dead . https://web.archive.org/web/20140808062137/http://www.dpi.nsw.gov.au/fisheries/habitat/threats/fish-kills/black-water-events-causing-fish-kills-in-the-murray%2C-murrumbidgee-and-lower-darling-river-catchments-march-2012 . 8 August 2014 .