A swamp-fed stream in northernFlorida, showingtannin-stained undisturbed blackwater
Ablackwater river is a type ofriver with a slow-moving channel flowing through forestedswamps orwetlands. Most major blackwater rivers are in theAmazon Basin and theSouthern United States. The term is used influvial studies,geology,geography,ecology, andbiology. Not all dark rivers are blackwater in that technical sense. Some rivers in temperate regions, which drain or flow through areas of dark blackloam, are simply black due to the color of the soil; these rivers areblack mud rivers. There are also black mudestuaries.
Blackwater rivers are lower in nutrients thanwhitewater rivers and haveionic concentrations higher than rainwater.[1][2] The unique conditions lead to flora and fauna that differ from both whitewater andclearwater rivers.[3] The classification of Amazonian rivers into black, clear, and whitewater was first proposed byAlfred Russel Wallace in 1853 based on water colour, but the types were more clearly defined by chemistry and physics byHarald 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]
Black andwhite waters differ significantly in their ionic composition, as shown inTable 1. Black waters are moreacidic, resulting in analuminum concentration greater than that of the more neutral white waters. The major difference is the concentrations ofsodium,magnesium,calcium, andpotassium; 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 lowconductivity, similar to that of rainwater.[citation needed]
Black and white waters differ in theirplanktonic fauna and flora.Tables 2 and3 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 theRio Negro system. However, it can be seen that the black water held greater numbers ofrotifers but fewercrustaceans andmites. These crustaceans are important foods forlarval fish. The zones where the two waters mix are attractive toostracods and young fish. These mixing zones tend to have many animals. The abundance is shown in Table3, 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]
Blackwater rivers resembleclearwater rivers in having a low conductivity and relatively low levels ofdissolved 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 theBrazilian Plateau (such asTapajós,Tocantins,Xingu and some right tributaries of theMadeira), but some originate in theGuiana Shield (such asNhamundá,Paru, andAraguari).[9]
Blackwater River, West Virginia: Located in theBlackwater Canyon in Tucker County. Blackwater Falls, a five-story waterfall, is located along this river with rapids ranging from ClassIII-V+.
St. Mary's River (Florida–Georgia): a 130-mile river located in southeast Georgia and is bordered by the Satilla River Basin to the north and the Suwannee River Basin to the west.
Pieman River, Tasmania: a river on the West Coast which leaches from rainforests and heathlands
Davey River, Tasmania: a relatively small river in the southwest corner of the island which runs through extensive heathlands, peat bogs andbutton grass plains
Noosa River,Queensland: a small section of the Noosa River running between Lake Cootharaba and Lake Cooroibah[13]
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 theMurray River,Edward River,Wakool River andMurrumbidgee River.[14]
Manaus, the largest city on theAmazon River, from aNASA satellite image, surrounded by the muddy Amazon river and the blackwaterRio Negro
A cypress slough wherebaygall blackwater (left) mixes with the more typical muddy waters (right) of the region.Big Thicket National Preserve, Jack Gore Baygall Unit, Hardin Co. Texas; 3 April 2020
Caño Ceima Cachivera, Mitú, Vaupés: one of the most visited waterfalls and indigenous communities InMitú, Colombia
^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.
^abcRibeiro, 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.
^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.
