GARCIA (X.F.) & LAVILLE (H.) 2001 - Importance of floodplain waters for the conservation of chironomid (Diptera) biodiversity in a 6th order section of the Garonne river (France). Annls. Limnol., 37(1) : 35-47.


The chironomid populations of a 6th order section of the Garonne River was studied intensively from September 1996 to October 1997.

For the first time, two floodplain waters were prospected : a side arm and an oxbow. Two sampling techniques were used for drift and benthic collections. 137 species were identified including 12 species new for the fauna of France. Their ecology and biogeography are given. The chironomid population of the backwaters is especially diversified and particular since the water bodie is disconnected from the main channel.

The studied section of the Garonne River appears to be a transitional section corresponding to an epipotamal/metapotamal. The embankment of the bed since 1958, which have isolated the floodplain waters and increase the current velocity of the flood in the main channel, mainly explain the dual typologic status observed. Then, the main channel is colonised by rheophilous Orthocladiinae whereas the backwaters shelter a mixed population with limnophilous Chironominae and potamobiont Orthocladiinae.

The study point out the urgency to preserve the floodplain waters due to their species richness, their uniqueness and their faunistical interaction with the main channel. The strong faunistical contribution of the floodplain waters highlights the actuality and the interest to prospect the potamals of the large rivers in order to increase the knowledge on the biodiversity, the ecology and the biogeography of the Chironomids.