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Mosquito larvae in backwaters along the Waal

Numbers of dancing midges in artificial backwaters that have been created along the Waal have rapidly attained a level comparable with the level found in more natural rivers.

Trends


In 1996 and 1999 three new backwaters were dug along the Waal, near Gameren, to increase the water storage capacity (and thus reduce the risk of flooding) and to recreate habitats that had disappeared. Dansing midges (more precisely: their bottom-dwelling larvae) are among the species that have been monitored to assess the impact on nature conservation. They are a useful indicator, as they react strongly and quickly to changes in habitat.

Within a few years the backwaters were harbouring appreciably more species of dancing midges than the main river. This is because they have more variation in water depth, flow and bed than the main channel. In addition, there are more hiding places in and alongside them and their fringing vegetation provides the adult mosquitoes with shelter for their mating dances.

The number of species in the backwaters is now similar to what it was in the Rijn around 1900, and resembles that of the Tisza, a more natural river in Eastern Europe.

Technical note


Mosquito larvae have a hard head casing, which makes it possible to determine the species that used to occur in the Rijn in 1900 by analysing cores of sediment from the river bed. The Tisza is a tributary of the Danube that has features in common with the Rijn, but has retained a more natural character.

References


  • Klink, A. en B. bij de Vaate (1994). De Tisza, een ecologische referentie voor makro-evertebraten in nevengeulen langs de Rijn? Hydrobiologisch Adviesburo Klink Rapp. Med. 50.
  • Klink, A. (1989). The Lower Rhine. Palaeoecological analysis. In: Historical change of large alluvial rivers: Western Europe. G.E. Petts (ed.). John Wiley & Sons Ltd. 183-201.
  • Jans, L. et al. (1998). Monitoringsprogramma voor nevengeulen in de Gamerensche, de Stiftse en de Afferdensche en Deestsche Waarden: morfologie, hydraulica, ecologie, bodemchemie en ecotoxicologie. Projectplan. RIZA Werkdocument 98.071. Lelystad.
  • Jans L. et al. (2002). Monitoring Nevengeulen, integrale jaarrapportage 2000/2001. RIZA werkdocument 2002.083. Lelystad.
This page was last changed on 06 May 2004  (version 01).