Blackwater River
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- This article is unconnected to the various rivers named Blackwater: see Blackwater River (note capitalization)
A blackwater river is one with a deep, slow-moving channel that flows through forested swamps and wetlands. The term blackwater describes the appearance of the water of such rivers, which is a dark coffee color. This color results from the leaching of tannins from the decaying leaves of adjoining vegetation.
Comparison between white and black waters
Black and white waters differ significantly in their ionic composition, as shown in Table 1 below. Black waters have ionic concentrations not much greater than that of rainwater. They are, however, much more acidic and this results in black waters having an aluminium concentration greater than that of the more neutral white waters. The most striking differences are in the concentrations of sodium, magnesium, calcium and potassium; these are very low in black waters. This has considerable ecological implications. Some animal groups, such as snails, need a lot of calcium with which to build their shells and so are not abundant in black waters. The lack of dissolved ions in black waters results in a low conductivity, similar to that of rainwater.Black and white waters also differ in their planktonic fauna and flora. Tables 2 and 3 below compare the number of planktonic animals caught in black and white water localities only a few meters apart. In fact, the black water was not even as extreme an example as can be found in the Rio Negro system. However, it can be seen that the black water held far 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 particularly attractive to ostracods and young fish. Anywhere in the world where you see these mixing zones there tend to be high numbers of animals and this is certainly the case in the Amazon. The high abundance of animals is shown clearly in Table 3 which compares the numbers of animals present in 10 litres of water in each habitat sampled.Comparison between white and black waters. (no date). Retrieved May 21, 2006 from http://www.amazonian-fish.co.uk/indexc30.html
| Table 1: Mean ionic composition, specific conductivity (μS/cm), and pH in Amazon waters. Data from Ribeiro and Darwich (1993).#redirect [[Template:Fact]] | ||
| Solimoes 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 |
| Table 2: Different planktonic organisms collected in black (Japura) and white (Solimoes) waters. Data from Ribeiro and Darwich (1993).#redirect [[Template:Fact]] | |||
| Animal groups present | Black water | Mixed water | White water |
| 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 10L of black, white and mixed waters. Data from Ribeiro and Darwich (1993).#redirect [[Template:Fact]] | ||||||
| Black water | Mixed water | White water | ||||
| Animal groups present | Open water | Forest | Open water | Forest | Open water | Forest |
| 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 | ||||
Blackwater rivers of the world:
Amazonia
- Apaporis River: A tributary of the Yapura River.
- Arapiuns River: A tributary of the Tapajós River.
- Coari River
- Mirití-Paraná River
- Negro River: By far the largest blackwater river in the world; one of the largest Amazonian tributaries.
- Piorini River
- Tahuayo River
- Tefé River
- Uatamã River
- Urubu River
- Vaupés
- Atabapo: from the Guiana Highlands of Venezuela west into the Orinoco
- Caroní River: from the Guiana Highlands of Venezuela west into the Orinoco
- Inírida: from Colombia northeast into the Orinoco, flows first into the Guaviare River and this flows into the Orinoco
- Ventuari: from eastern Venezuela (the Guiana Highlands) southwest into the Orinoco
- Vichada: from Colombia east into the Orinoco
American South
- Black River: a tributary of the Pee Dee River in North and South Carolina in the United States.
- Cape Fear River: A large river in North Carolina in the United States flowing into the Atlantic Ocean.
- Cashie River: A river in North Carolina in the United States flowing into Albemarle Sound.
- Caloosahatchee River: A river in Florida flowing west from Lake Okeechobee to the Gulf of Mexico.
- Chowan River: A river in North Carolina in the United States flowing into Albemarle Sound.
- Edisto River: A river in South Carolina in the United States flowing into the Atlantic Ocean.
- Great Coharie Creek: A river in North Carolina in the United States flowing into the Black River.
- Little Pee Dee River: A river in South Carolina in the United States flowing into the Pee Dee River.
- Lumber/Drowning Creek: A river in North and South Carolina in the United States.
- Suwannee River: A large river in southern Georgia and northern Florida in the United States flowing into the Gulf of Mexico.
- Upper Little River: A river in North Carolina in the United States flowing into the Cape Fear River.
- Waccamaw River: A river in North and South Carolina in the United States flowing into the Atlantic Ocean.
- White Oak River: A river in North Carolina in the United States flowing into the Atlantic Ocean.
North America
- Tahquamenon River: A river in the Upper Peninsula of Michigan flowing into Lake Superior.
See also
- Blackwater River, a list of rivers by this name.
References
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