|Lake Grevelingen: a case study of ecosystem changes in a closed estuary|
Nienhuis, P.H. (1978). Lake Grevelingen: a case study of ecosystem changes in a closed estuary. Hydrobiol. Bull. 12(3-4): 246-259
In: Hydrobiological Bulletin. Netherlands Hydrobiological Society: Amsterdam. ISSN 0165-1404, more
1. Grevelingen estuary, formerly in open connection with the rivers Rhine and Meuse and with the North Sea, was closed by a dam in May 1971, excluding influences both from the rivers and from the sea (tides dropped out); brackish Lake Grevelingen originated.2. A number of changes took place in the environment, on species level, on community level and on ecosystem level.3. Changes on species level. The life cycles of certain species were blocked, because their food disappeared, the particle size spectrum of the food changed, or their migration routes were blocked. It was found that (1) species richness decreased; (2) shifts in numbers per species took place; (3) species with broad ecological tolerance remained; (4) brackish water species appeared.4. Changes on community level. Structural aspects: (a) habitats disappeared; (b) pattern diversity decreased; (c) habitat-bound species disappeared. Functional aspects (trophic relations): (a) the energy subsidy from the North Sea was blocked; (b) the amount of organic matter decreased; (c) the production of some primary consumer groups decreased (d) tertiary and some secondary consumers disappeared; (e) the food chains shortened.5. Changes on ecosystem level. The overall ecosystem simplified, both in structure and in functioning. The impact of the shallow macrophyte dominated subsystem increased.