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The inland water fishes of Africa

 | 
Didier Paugy
, 
Christian Levêque
, 
Olga Otero

Fish communities in shallow lakes

Christian Levêque

Résumé

While there is an intuitive understanding of what “shallow lake” means, it is more difficult to provide a precise definition of the term. For our purposes, we could include in this category lakes with a depth not exceeding 10 m and with no permanent stratification of the water column (Lévêque & Quensière, 1988). Shallow lakes are thus lakes in which the coastal area and bankside vegetation play an important role in the function of the system, in contrast to deep lakes where the pelagic zone is particularly well-developed.
Shallow lakes generally occupy depressions in areas with moderate reliefs. Despite their diversity, they all share certain characteristics:
• There is significant development of grassy zones that can occupy large surfaces.
• Macrophytes develop on the shoals and produce a large amount of organic matter;
• Fluctuations in the water balance (summation of water inputs and outputs) manifest as large fluctuations in water level and surface, owing to the basin’s lack of relief.
• The water balance depends greatly on the local climate as well as the climate of the basin feeding the tributaries, and on the shape of the lake basin;
• The absence of permanent thermal stratification favours the rapid recycling of nutritive elements as well as the development of benthic fauna that helps increase the productivity of these physical systems.

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Extrait du texte

Elements for a physicochemical typology of shallow lakes

Different types of shallow lakes can be distinguished based on their hydrological function and physiochemical characteristics.

First, while many lakes are open, with one or more superficial outflows that allow the emptying of excessive water inputs, other types of lakes, called endorheic lakes, are closed basins with no outflows. These endorheic lakes are areas for the spread and evaporation of water, responding to fluctuations in water inputs by more marked variations in surface. Lake Chad, fed by the Chari, and Lake Ngami, fed by the Okavango, are examples of endorheic lakes in Africa.

We can also distinguish several major types of shallow lakes based on the characteristics of the water balance:

  • pluvial, dominated by the precipitation-evaporation cycle. Lake Victoria, which receives 83% of its inputs from rainfall and loses the equivalent through evaporation, is a good example. This type is characteristic of many water bodies in...

Auteur

Research director at IRD. He has published numerous works on the systematics, distribution, and ecology of West African fresh water fishes, and expanded the collections of the MNHN in Paris.

© IRD Éditions, 2017

Conditions d’utilisation : http://www.openedition.org/6540

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