Black water river
Black water rivers , along with white water rivers and clear water rivers, are among the three dominant river types in the tropics . Black water rivers have a brownish color, which is caused by the large amount of dissolved humic acids and fulvic acids and which is similar to the color of coffee. They appear dark because they hardly contain any nutrients, suspended matter or sediment particles that could reflect the incident sunlight.
The origin of tropical black water rivers is typically found in moors or humus rainforest soils. Due to the dissolved humic substances, the water is very acidic , also low in electrolytes and therefore has a relatively low conductivity. The degradation of humic substances is slow, but leads to oxygen consumption in the deeper layers . The rivers are extremely poor in nutrients, and primary production remains low due to the limitation of light . The fish fauna is poor, but many invertebrates - with the exception of molluscs - are richly represented.
Blackwater rivers hardly contain any natural sediments . The particles caused by erosion such as sand and silt are missing, as there is no particle entry through mountains and their geological degradation processes. They themselves therefore only have a reduced erosive effect on their surroundings. That is why there are often many rapids in blackwater rivers , which are more slowly eroded by water without sediment load.
Examples of black water rivers are the Congo in Africa and the Rio Negro , Rio Cururu and Río Caroní in South America. Occasionally the term is given a wider definition and extra-tropical rivers are also referred to as blackwater rivers.
In the Amazon, the floodplain forests on black water rivers are called Igapó forests .
literature
- Wilfried Schönborn: Textbook of Limnology . E. Schweizerbart'sche Verlagbuchhandlung, Stuttgart 2003, ISBN 3-510-65204-5