Importance of floodplain waters for the conservation of chironomid (Diptera) biodiversity in a 6^thorder section of the Garonne river (France)

Abstract

The chironomid populations of a 6 th order section (400 m) of the middle Garonne river were studied monthly from September 1996 to October 1997.For the first time the main channel of the river was investigated including two floodplain waters : a side arm and an oxbow. Two sampling techniques were used for drift and benthic collections. A total of 21 766 specimens (pupae and pupal exuviae) were sorted and 137 species were identified. Among these, 12 species are new for the fauna of France : their ecology and biogeography are given. The chironomid population of the backwaters is especially diverse and distinctive since the waterbody is disconnected from the main channel.The studied section appears to be transitional corresponding with the epipotamal-metapotamal zones. The embankment of the watercourse since 1958, which has isolated floodplain waters and increased the current velocity in the main channel, mainly explains the dual typologie status observed. The main channel is colonised by rheophilous Orthocladiinae whereas the backwaters shelter a mixed population of limnophilous Chironominae and potamobiont Orthocladiinae.This study demonstrates the urgency for preserving floodplain waters because of their species richness, their uniqueness and their faunal interaction with the main channel. The strong faunal contribution of floodplain waters highlights the topicality and the value in investigating the less disturbed potamal zones of large rivers to increase our knowledge on biodiversity, ecology and biogeography of chironomid populations.Importance des annexes fluviales pour le maintien de la biodiversité des Chironomidés (Diptera) sur une section d'ordre 6 de la Garonne (France) Mots-clés : Diptera, Chironomidae, Garonne, zone potamique, annexes fluviales, biodiversité. . Cette étude montre la nécessité de préserver de telles zones annexes en raison de leur richesse, de leur spécificité et de leur interaction faunistique avec le chenal principal. La forte contribution faunistique des annexes fluviales souligne l'intérêt et l'actualité de prospecter les zones potamiques les moins perturbées des grandes rivières pour une meilleure connaissance de la biodiversité, de l'écologie et de la biogéographie des populations chironomidiennes.

Bidirectional exchanges of benthic invertebrates in a large river–floodplain system (Paraná River, Argentina)

“…In addition, we found an increase in the diversity, abundance, and richness from the main river to the lake, and this result was in accordance with other studies of large rivers, showing an increase in complexity from the main channel to the floodplain waterbodies (Tockner et al, 1998;Garcia and Laville, 2001;Amoros and Bornette, 2002;Arscott et al, 2005;Ezcurra de Drago et al, 2007;Reese and Batzer, 2007;Gallardo et al, 2008;Behrend et al, 2009). Lower species diversity, richness, and density near the bank of the main channel may be explained by low organic matter content and granulometry of the sediments, and by high current velocity that excludes lentic organisms as these are not adapted to maintain their position to prevent accidental loss under high current velocity (Bogatov et al, 1995;Dudgeon, 1995;Takeda et al, 2001;Ezcurra de Drago et al, 2004, 2007.…”

Chironomids (Diptera) in river floodplains: their status and potential use for palaeoenvironmental reconstruction purposes

“…It was impossible to find any modern chironomid assemblages here in order to determine the habitat preferences of the chironomids (chironomid hydrological statuses) on a qualitative gradient across the floodplain. We therefore based our deductions on the hypothesis that the ecology of the chironomids sampled in the Saint-Omer basin is similar to that of the chironomids studied in cross-sections of the Garonne (Garcia & Laville 2001) and Lower Rhône (Franquet 1996) river floodplains. A more general reference work on the ecology of chironomids (Wiederholm 1983) was also used.…”

“…In order to test the use of chironomid analysis in river floodplains, a sedimentary core from the Saint-Omer marsh (downstream floodplain of the Aa river, Northern France) was collected. In the first part of this study, based on the data available so far on the status of chironomid Diptera in river floodplains (Franquet 1996, Garcia & Laville 2001, it was proposed to draw a picture of the palaeoenvironment and hence of the past hydrodynamic conditions pertaining in the Aa river (Junk et al 1989, Ward & Stanford 1995. The structure of habitats and chironomid assemblages depends on the level of connection between the main channel and the various parts of the floodplain, and hence on the intensity, frequency and duration of the floods.…”

The lotic Chironomidae (Diptera) of Corsica (France)

“…In comparison the list of 147 species-level taxa collected for a short time and in only 24 rivers implies a greater biodiversity in the island.The Corsican list of 158 species (Table 1 & 5) represents 23.6 % of the 670 chironomid species recognized in the French inventory : 646 compiled by Laville & Serra-Tosio (1996) plus 12 more recently listed in the River Loire (Garcia & Laville 2000) and 12 in the River Garonne (Garcia & Laville 2001). This Corsican list represents 50 % of the 317 chironomids species recently reported from Morocco by Kettani et al (2001).…”