A blackwater river is a river with a deep, slow-moving channel that flows through forested swamps and wetlands. As vegetation decays in the water, tannins are leached out, resulting in transparent, acidic water that is darkly stained, resembling tea or coffee. Most major blackwater rivers are in the Amazon River system and the Southern United States.
Blackwater rivers are much lower in nutrients than whitewater rivers and have ionic concentrations only slightly higher than rainwater.[1][2] The unique water conditions lead to a composition of flora and fauna that differs significantly from that found in whitewater sources. Areas where blackwater rivers and whitewater rivers combine are particularly attractive to a diverse group of organisms.
Contents |
Comparison between white and black waters
| 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 |
Black and white waters differ significantly in their ionic composition, as shown in Table 1. 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 major difference is 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 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 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. These mixing zones tend to have high numbers of animals. 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.[4]
| 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 |
| 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
Indonesia
Amazonia
- Apaporis River: A tributary of the Yapura River.
- Arapiuns River: A tributary of the Tapajós River.
- Coari River
- Mirití-Paraná River
- Rio Negro: The largest blackwater river in the world; one of the largest Amazonian tributaries.
- Piorini River
- Tahuayo River
- Tefé River
- Uatamã River
- Urubu River
- Vaupés
Orinoco basin
- 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 Guaviare River which flows into the Orinoco
- Ventuari: from eastern Venezuela southwest into the Orinoco
- Vichada: from Colombia east into the Orinoco
- Tomo: from Colombia east into the Orinoco
- Tuparro: from Colombia east into the Orinoco
Southern United States
- Ashepoo River: Along with the Edisto and the Combahee Rivers in South Carolina makes up the ACE Basin National Wildlife Refuge.
- Big Cypress, Black Cypress, and Little Cypress and the small rivers in the watershed of Caddo Lake in Texas and Louisiana.
- Blackwater River: a tributary of the Chowan River in Virginia.
- Blackwater River: a major river in the western Florida panhandle.
- Black River: a tributary of the Pee Dee River in North and South Carolina.
- Cape Fear River, North Carolina: flows into the Atlantic Ocean.
- Cashie River, North Carolina: flows into Albemarle Sound.
- Caloosahatchee River, Florida: flows west from Lake Okeechobee to the Gulf of Mexico.
- Chowan River, North Carolina: flows into Albemarle Sound.
- Edisto River, South Carolina: flows into the Atlantic Ocean; the longest undammed, unleveed blackwater river in North America.
- Econlockhatchee River, a tributary of the St. Johns River in Central Florida.
- Great Coharie Creek, North Carolina: flows into the Black River.
- Little Pee Dee River, South Carolina: flows into the Pee Dee River.
- Lumber/Drowning Creek: located in North and South Carolina. Part of Lumber River State Park
- Ogeechee River: 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.
- Pithlachascotee River: A small river in central Florida.
- Satilla River: A river in southeast Georgia that flows through the city of Waycross and empties into the Atlantic Ocean near Cumberland Island.
- Scuppernong River: A small river in Washington and Tyrrell Counties in eastern North Carolina at Pettigrew State Park.
- St. Johns River: The largest river in Florida. Flows north through Jacksonville and into the Atlantic.
- Suwannee River: A large river in southern Georgia and northern Florida flowing into the Gulf of Mexico.
- Upper Little River, North Carolina: flows into the Cape Fear River.
- Blackwater River, West Virginia: Located in the Blackwater Canyon in Tucker County. Blackwater Falls a five-story waterfall is located along this river with rapids ranging from Class III-V+
- Waccamaw River, North and South Carolina: flows into the Atlantic Ocean.
- White Oak River, North Carolina: flows into the Atlantic Ocean.
Northern United States
- Black River, New York: A river starting in the western Adirondacks that flows into Lake Ontario.
- Tahquamenon River, Michigan: A river in the Upper Peninsula that flows into Lake Superior.
- Tuckahoe River, New Jersey: A short river in southern New Jersey that flows into Great Egg Harbor.
Australia
- Gordon River,Tasmania: A river rising in the centre of the island and flowing westward, emptying into Macquarie Harbour on the West Coast.
Images of blackwater rivers
 Amazon River tributary classified as blackwater |
 Manaus, the largest city on the Amazon River, as seen from a NASA satellite image, surrounded by the muddy Amazon River and the blackwater Rio Negro. |
 Looking down at the confluence of the blackwater Morava River (flowing from right to upper left) into the whitewater Danube (in upper left corner of photo). |
See also
References
- ^ Janzen, D H (July 1974). "Tropical Blackwater Rivers, Animals, and Mast Fruiting by the Dipterocarpaceae". Biotropica 6 (2): pp. 69–103.
- ^ 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): pp. 275–288.
- ^ a b c J S B, Ribeiro; A J Darwich (1993). "Phytoplanktonic primary production of a fluvial island lake in the Central Amazon (Lago do Rei, Ilha do Careiro)". Amazoniana (Kiel) 12 (3-4): pp. 365–383.
- ^ "Comparison between white and black waters". Amazonian Fishes and their Habitats. Pisces Conservation Ltd. http://www.amazonian-fish.co.uk/indexc30.html. Retrieved 2006-05-21.
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