The Oosterschelde estuary, a case-study of a changing ecosystem: an introduction

Abstract

During the period 1980-1990 long-term physical, chemical and ecological studies were carried out, to study the changes induced by the building of a storm-surge barrier in the mouth of the Oosterschelde estuary and two large auxiliary compartment dams in the rear ends of the estuary . The storm-surge barrier was constructed in the mouth of Oosterschelde estuary (SW Netherlands) during the period 1979-1986 . The barrier allows the tides to enter the estuary freely, and, on the other hand, the barrier guarantees safety for the human population and their properties when a stormflood threatens the area .Oosterschelde estuary is isolated from the river input, the rear ends of the ecosystem were separated from the estuary by sea-walls and the strongly decreased tidal exchange with the North Sea induced sheltered circumstances . The Oosterschelde changed from a turbid estuary into a tidal bay, and yet primary production responses appear to be robust and resilient, and the biological communities showed only quantitative shifts from the dominance of specific species assemblages to other assemblages . In many cases predicted changes in the structure of the biological communities could not be verified owing to the large natural variability mainly caused by physical factors (e .g . temperature) . The Delta Project -Storm flood protection in the OosterscheldeThe Netherlands Delta Project covers the socalled Delta area, created by the rivers Rhine, Meuse and Scheldt . Like most delta-estuarine environments, this area represents, in its natural state, complicated ecosystems consisting of a complex hydrodynamic regime, with fast-flowing water masses in tidal channels, changing estuarine configurations, inhomogeneous tidal and subtidal sediments, and salt-marsh areas subject to periodic flooding . The history of the SW Netherlands is marked by a continuous struggle between man and the sea . Since the year 1000 man reclaimed salt-marsh areas and transformed those into agricultural land . But irregularly occurring stormfloods broke the man-built seawalls and recaptured parts of the gained land. On February 1, 1953, a northwesterly storm induced tides to 3 m above normal levels, breached approximately 180 km of coastal-defense dikes and flooded 160000 hectares of polderland . 1835 people lost their lives in this large storm flood, more than 46000 farms and buildings were destroyed or damaged, and approximately 200000 farm animals were lost .The Delta Project, formalized in 1957 by an act

Evaluation of a tidal flat sediment nourishment as estuarine management measure

“…The historical morphological evolution of the Eastern Scheldt estuary is described in detail by Eelkema (2013). Nowadays, the Eastern Scheldt has an average freshwater load of 25 m 3 /s and is mesotrophic with an average salinity of 30 (Nienhuis and Smaal, 1994). Sections 3.1 and 3.2 provide more information on the hydrodynamic conditions in the Eastern Scheldt.…”

“…1), several measures to mitigate the loss of tidal flats due to ongoing erosion are currently being proposed and experimented with. The Eastern Scheldt is a good example of a coastal system that underwent large physical and ecological changes due to a system-wide human interference (Nienhuis and Smaal, 1994;Cozzoli et al, 2014). As a response to the severe storm surge in 1953, the Dutch Government initiated the Delta works.…”

Toxic effects of increased sediment nutrient and organic matter loading on the seagrass Zostera noltii

“…Mean surface water temperature fluctuates between 0-22°C annually. Freshwater input into the former estuary has become highly limited after the implementation of major water works in the past, and salinity is generally around 30 (Nienhuis and Smaal, 1994).…”

The Decline and Restoration of a Coastal Lagoon (Lake Veere) in the Dutch Delta

“…Initially Lake Veere as all other inlets in the area was planned to become a freshwater lake. With the decision in 1976 to build a storm surge barrier (designed to remain open except by extreme weather conditions) instead of a dyke in the mouth of the Eastern Scheldt (Nienhuis and Smaal 1994), Lake Veere was kept brackish. The water level in the lake was however artificially remained at an unnatural level of −0.70 m NAP (Amsterdam Ordnance Datum) in winter and around NAP between April to September (Coosen et al 1990).…”