Suchergebnisse

This book is a compilation of most of the seminars presented during a symposium held in Arnhem, the Netherlands. The introduction treats not only the Netherlands as wetland in a larger landscape but also the various wetland types within the country itself. The subsequent case studies concern representative wetland types. Both introduction and case studies give an historical, hydrological, physicochemical and biotic characterization of the wetland concerned as well as a description of management measures in the past and in the present; summarize the threats to the systems; and indicate prospects for the ecosystems, given the present environmental conditions and expectations for short and long term changes. In the introduction special attention is paid to the border-crossing biotic elements, such as birds. These sections are followed by a summary of the ecology of the Netherlands wetlands and indications for future ecological research. Finally, the environmental policy and its consequences for management on a national, regional and local scale are discussed

The Netherlands are a small, low-lying delta in W. Europe (42 000 km 2;50degrees-54degrees N; 3degrees-8degrees E), mainly consisting of alluvial deposits from the North Sea and from the large rivers Rhine and Meuse. The country was 'created by man'. The conversion of natural aquatic and terrestrial ecosystems into drained agricultural land was a major cultural operation over the past 1000 years. Roughly 55% of the country's surface area is still agricultural land. Some decades ago, The Netherlands' landscape was characterised by an armoured coastline and bridled estuaries, a drastically reduced area of saline and freshwater marshes, fully regulated rivers and streams, and numerous artificial lakes. The aquatic ecosystems beyond the influence of the large rivers, the Pleistocene raised bogs and moor lands, have almost been completely annihilated in the past. Acidification and eutrophication led to the deterioration of the remaining softwater lake vegetation. Last but not least, an artificial drainage system was constructed, leading to an unnatural water table all over the country, high in summer, low in winter. Only very recently, some 25 years ago, the tide has been turned and ecological rehabilitation and restoration of disturbed ecosystems are in full swing now, enhanced by the European Union policy to set aside agricultural land in the Netherlands in favour of the development of 'nature'. The state of the art of aquatic and semi-aquatic ecological restoration projects in the Netherlands is given. Starting from the conceptual basis of restoration ecology, the successes and failures of hundreds of restoration projects are given. Numerous successful projects are mentioned. In general, ecological restoration endeavours are greatly benefiting from progressive experience in the course of the years. Failures mainly occur by insufficient application of physical, chemical or ecological principles. The spontaneous colonisation by plants and animals, following habitat reconstruction, is preferred. But sometimes the ...