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Blackwater river

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A swamp-fed stream in northern Florida, showing tannin-stained undisturbed blackwater

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 Harald Sioli [de] from the 1950s to the 1980s.[3][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 ± 0.8 0.380 ± 0.124
K (mg/L) 0.9 ± 0.2 0.327 ± 0.107
Mg (mg/L) 1.1 ± 0.2 0.114 ± 0.035
Ca (mg/L) 7.2 ± 1.6 0.212 ± 0.066
Cl (mg/L) 3.1 ± 2.1 1.7 ± 0.7
Si (mg/L) 4.0 ± 0.9 2.0 ± 0.5
Sr (μg/L) 37.8 ± 8.8 3.6 ± 1.0
Ba (μg/L) 22.7 ± 5.9 8.1 ± 2.1
Al (μg/L) 44 ± 37 112 ± 29
Fe (μg/L) 109 ± 76 178 ± 58
Mn (μg/L) 5.9 ± 5.1 9.0 ± 2.4
Cu (μg/L) 2.4 ± 0.6 1.8 ± 0.5
Zn (μg/L) 3.2 ± 1.5 4.1 ± 1.8
Conductivity 57 ± 8 9 ± 2
pH 6.9 ± 0.4 5.1±0.6
Total P (μg/L) 105 ± 58 25 ± 17
Total C (mg/L) 13.5 ± 3.1 10.5 ± 1.3
HCO3-C (mg/L) 6.7 ± 0.8 1.7 ± 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.[citation needed]

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 Table 3, which compares animals in 10 litres (2.2 imp gal; 2.6 US gal) of water.[7]

Table 2: Planktonic organisms collected in black (Japura) and white (Solimões) waters.[6]
Animal groups
Rotifera 284 23 0
Cladocera 5 29 43
Ostracoda 39 97 29
Calanoida 11 51 66
Cyclopoida 22 49 61
Chironomidae 0 3 3
Acari (mites) 0 0 2
Table 3: Number of planktonic organisms collected in 10 L of black, white, and mixed waters.[6]
Black water Mixed water White water
Animal groups
Forest Open
Forest Open
Volvocaceae 42   38      
Rotifera 87 5 34      
Cladocera 6   5   8 1
Ostracoda 2 11 3   7  
Calanoida 23 3 10      
Cyclopoida 5 27 19 1 13 1
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)[3] 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




Orinoco basin


Southern United States

The Lumber River as seen from the boat launch at Princess Ann near Orrum, North Carolina

Northern United States

Chocolate-colored Tahquamenon Falls





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]



Images of blackwater rivers


See also



  1. ^ Janzen, D. H. (July 1974). "Tropical Blackwater Rivers, Animals, and Mast Fruiting by the Dipterocarpaceae". Biotropica. 6 (2): 69–103. doi:10.2307/2989823. JSTOR 2989823.
  2. ^ Sioli, Harald (1975). "Tropical rivers as expressions of their terrestrial environments". Tropical Ecological Systems/Trends in Terrestrial and Aquatic Research. New York City: Springer-Verlag: 275–288.
  3. ^ a b c 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)" (PDF). PanamJAS. 5 (3): 454–464. Archived from the original on 13 November 2021.
  4. ^ Sioli, H., ed. (1984). The Amazon: Limnology and landscape ecology of a mighty tropical river and its basin. Springer. ISBN 978-94-009-6544-7.
  5. ^ Goulding, M.; Carvalho, M. L. (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.
  6. ^ a b c Ribeiro, J. S. B.; Darwich, A. J. (1993). "Phytoplanktonic primary production of a fluvial island lake in the Central Amazon (Lago do Rei, Ilha do Careiro)". Amazoniana. 12 (3–4). Kiel: 365–383.
  7. ^ "Comparison between white and black waters". Amazonian Fishes and their Habitats. Pisces Conservation Ltd. Archived from the original on 16 July 2011. Retrieved 21 May 2006.
  8. ^ Giovannetti, Thomas A.; Vriends, Matthew M. (1991). Discus Fish. Hauppauge, NY: Barron's. p. 15. ISBN 0-8120-4669-2.
  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. doi:10.1007/s13157-011-0190-7. S2CID 36001397.
  10. ^ Brummett, R.; Stiassny, M.; Harrison, I. (2011). "Background". In Allen, D. J.; Brooks, E. G. E.; Darwall, W. R. T. (eds.). The Status and Distribution of Freshwater Biodiversity in Central Africa. Gland, IUCN. pp. 1–20. ISBN 978-2-8317-1326-7.
  11. ^ Schliewen, U. K.; Stiassny, M. L. J. (2006). "A new species of Nanochromis (Teleostei: Cichlidae) from Lake Mai Ndombe, central Congo Basin, Democratic Republic of Congo". Zootaxa. 1169: 33–46. doi:10.11646/zootaxa.1169.1.2.
  12. ^ Thieme, M. L.; Abell, R.; Burgess, N.; Lehner, B.; Dinerstein, E.; Olson, D. (2005). Freshwater Ecoregions of Africa and Madagascar: A Conservation Assessment. Island Press. pp. 60–62. ISBN 1-55963-365-4.
  13. ^ "Noosa River Elanda Point to Campsite Fifteen Canoe Guidebook". www.upstreampaddle.com. Archived from the original on 8 July 2020. Retrieved 19 November 2014.
  14. ^ "Black water event in the Murray, Murrumbidgee and Lower Darling River catchments: March 2012". www.dpi.nsw.gov.au. Archived from the original on 8 August 2014. Retrieved 8 August 2014.