COLONIZATION AND SUCCESSION OF MACROINVERTEBRATES IN RECENTLY FRESHENED LAKE VOLKERAK-ZOOM (THE NETHERLANDS)

Macroinvertebrates were studied during the first five years after closure and freshening of the lake system Volkerak-Zoom, two lakes interconnected by a channel. Before embankment, in 1987, these lakes were part of the tidal Eastern Scheldt estuary in the south-western part of The Netherlands. Four months after embankment, the first freshwater species were found. In general, the colonization process followed the same pattern as was reported for newly created reservoirs. In Lake Volkerak-Zoom differences in colonization time were observed between distinguished depth zones. Within the chironomid assemblages, dominance of Chironomus muratensis was followed by a dominance of Procladius, Glyptotendipes and Cladotanytarsus. The succession was related to changes in phytoplankton concentrations. Although in 1991 changes in macrofauna composition were less pronounced as compared to previous years, succession was still going on.