Interstitial fauna in newly-created floodplain canals of a large regulatedriver

Artificial drainage canals are often dug in large river floodplains to prev ent winter inundation when groundwater level increases. Nothing is known ab out the biodiversity of the interstitial fauna of these artificial aquatic systems. The water chemistry and interstitial fauna of four drainage canals along the River Rhone (dug 11-15 years ago) were sampled in July during 3 years (1995-1997). A total of 53 taxa were found, with both epigean and hyp ogean organisms, and some rare phreatobites previously considered as absent from this sector of the Rhone. The faunal assemblage is characterized by l imited temporal Variations between the 3 successive years. Differences in i nterstitial fauna composition between the four drainage canals were mostly linked to oxygen availability and to heterogeneity in water origin (true gr ound water or surface water infiltration through embankment). Low oxygen co ntent results in poorly diversified assemblages, which are always dominated by the same small set of species. Tn contrast, heterogeneity in water orig in resulted in elevated faunal diversity. Copyright (C) 2000 John Wiley & S ons, Ltd.