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Lake Varese is a very eutrophic environment that suffers from periodic anoxia and in fact the benthic fauna is composed of only five species. However, the abundance of these species is lower than expected, with an 80% decrease with respect to a previous study of 1963. Moreover, both chironomids and olgiochaetes display a marked preference for the shallowest areas of a lake.

Neither the seasonal evolution of the oxygen conditions, nor the organisms life cycles, could completely explain the observed data.

Therefore a possible influence of the sediment chemical composition has been investigated, revealing that the density of Chironomids is mainly controlled by the food availability, whereas the density of Chaoborus flavicans may be adversely affected by the uptake of Pb and Hg.

Additional information

Authors: EI, ;JRC-ISPRA (IT),
Bibliographic Reference: Article: The Status of Lake Varese in 1994
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