THE RIVERS RHINE AND MEUSE IN THE NETHERLANDS - PRESENT STATE AND SIGNS OF ECOLOGICAL RECOVERY

The ecosystems of the rivers Rhine and Meuse have suffered drastic env ironmental changes, for example because of the regulation of the strea m bed and the construction of weirs and dams. Furthermore, discharges of industrial and municipal waste water have caused the water quality of these rivers to deteriorate; this problem became acute in the sixti es and seventies. Recently some chemical parameters of water quality h ave improved in the Rhine, and as a consequence some aquatic communiti es are showing signs of recovery after decades of severe degradation. This paper describes the present state of the aquatic communities in t he Dutch part of the rivers Rhine and Meuse, using published observati ons on plankton, macrophytes, invertebrates, and fish. The sparse info rmation on the food chain in these rivers is summarized. The main chan nels of the Rhine and Meuse are characterized by a dense plankton that develops rapidly in the nutrient-rich river waters. The stream beds, now dominated by wave-exposed sand and gravel, have a sparse fauna and flora. The river banks, mostly consolidated by blocks of stone, offer a substratum for numerous benthic organisms, particularly now that th e water quality has improved. The floodplain waters and old river chan nels harbour a flora and fauna rich in species. The degree of water ex change with the river is crucial for the ecological development of the river and its backwaters. Today the freshwater tidal reaches of the r ivers occupy a very restricted area, and only remnants of the previous ly abundant vegetation of rushes are found. Losses in the numbers of a nimal and plant species, notably those specific to rivers, are evident , but over the last 15 years several species have returned. Allochthon ous species (exotics), including crustaceans and molluscs, have also s ettled in the Rhine and Meuse. Fish species characteristic of these ri vers, such as river lamprey, sea trout, barbel, and flounder, have rec ently been observed in appreciable numbers. The Rhine Action Programme provides a framework for the large-scale rehabilitation of the Rhine. Experiments on re-stocking the Rhine with Atlantic salmon,and on the ecological rehabilitation of floodplains are being carried out on the assumption that there will be a further reduction of the pollution loa d. A similar programme is required for the Meuse.