Poorten naar de zee: open, dicht en op een kier
Voorzichtige revalidatie voor onze estuaria?
Erika Van den Bergh & Dick de Jong
estuaria, ecosysteemfuncties, degradatie, herstelstrategie
Waar getij- en rivierdynamiek elkaar ontmoeten wordt het estuariene landschap geboetseerd. In Nederland en Vlaanderen boetseert de mens sinds mensenheugenis mee, we weten zelfs niet hoe dit landschap eruit zou zien zonder onze tussenkomst. In de tweede helft van de vorige eeuw groeide het besef dat ons boetseren schade toebrengt aan de morfologie en ecologie én aan de gebruiksfuncties van estuaria. Daarom wordt de afgelopen decennia, met wisselend succes, gewerkt aan herstel.
Estuaries, gateways to the sea: open, closed and ajar
Erika Van den Bergh & Dick de Jong
Estuaries, ecosystem functions, degradation, restoration strategies.
Estuarine landscapes are shaped by the interactions of tidal currents and river flows. Gradients in salt, inundation regime, hydrodynamics, turbidity, organic matter and sediment composition create a mosaic of gulleys, bare mudf lats and sand bars, vegetated tidal marshes and connecting tidal creeks. The complexity and completeness of the habitat network relies on the available uninterrupted space for habitat differentiation. The habitat configuration and connectivity with the hinterland determine the estuarine functionality, especially for estuarine species that rely on different habitats in different life stages. Estuaries are cited among the most productive ecosystems. They process the exogenic input of nutrients and organic matter from the sea and the river into food for all kinds of species that live permanently or temporally in the estuary. Traditionally, estuaries are attractive settlement places and typical port development areas. For centuries, estuarine management aimed at economic optimization only, leading to the near destruction of the ecosystem services and biodiversity. In the Netherlands estuaries were closed from the sea by dams or storm surge barriers for safety reasons. After some decades water quality problems arose in the artif icial lakes, threatening ecosystems and human use. It also became apparent that the estuaries had lost their function for migrating fish due to the closures and for migrating birds due to extensive habitat loss. At first some species specific rehabilitation measures were taken locally, but the need to include local people and governments led to the installation of institutions in the different areas which are an alliance of different government levels, entrepreneurs and shareholders to address the water problems and look for climate proof, ecologically resilient and economically vital areas, the South-west Delta, the Scheldt estuary and the Ems. In the Flemish Scheldt the Sigma Plan aims at both safety for floods and ecological restoration. These institutions take estuarine restoration strategies and decisions to a higher level of integration and sustainability. They aim to recover ecosystem goods and services and measures are taken to reinstate the underlying estuarine processes. For the Ems-Dollard area the Netherlands and Germany have also jointly drawn up an Integrated Management Plan, which contains among others Natura 2000 plan development tackling issues such as the interaction between water flow and sediment, sand and sludge, and options for intervention to reduce turbidity in the estuary. Modeling results and expert judgment underpinning the projected outcome and cost/benefits for different scenarios facilitate the societal debates about choices to be made. Economic arguments however mostly prevail disproportionally in the final decision processes. The article mentions examples of it.
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