RESTORATION ECOLOGY OF RIVERINE WETLANDS .2. AN EXAMPLE IN A FORMER CHANNEL OF THE RHONE RIVER

Riverine wetlands, which provide numerous valuable functions, are disa ppearing in floodplains of a channelized European river. A restoration project has been proposed by scientists to restore a former braided c hannel of the Rhone River by the removal of fine organic sediments in order to enhance groundwater supply. A precise and intensive prerestor ation monitoring program during one year (including comparison with a reference channel) has taken into account several variables and ecolog ical performance indicators measured at various spatial and temporal s cales. Three restoration techniques were then suggested, taking into a ccount two characteristics of ecosystem functions for increasing resto ration success and self-sustainability: (1) the riparian forest as wel l as the shores must be preserved or disturbed as little as possible; and (2) the upstream alluvial plug must be preserved to prevent direct supply of nutrient-rich water from the Rhone River. Among the three r estoration options proposed, it was not possible to carry out the less ecologically disturbing one as it was considered too expensive, time consuming, and difficult to realize. A precise and intensive postresto ration monitoring program, conducted over two years, demonstrated rest oration success but also unpredicted problems, such as a locally thick layer of fine organic sediment. As long as a self-sustainable state i s not achieved, this monitoring should be continued. Afterwards, a les s precise and less intensive long-term monitoring should enable the de tection of future events that may influence ecosystem changes.