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Strategy, planning & design
Salinity gradients

At the place where a river runs into the sea, there are natural gradients in salinity. Places with such gradients are very valuable from the perspective of ecology and natural beauty. In Holland, after the realisation of the Zuider Zee and the Delta works, distinct dividing lines between the freshwater and saline environments came into existence. On top of that, the influence of tidal processes diminished. The total extent of brackish environments decreased substantially in this way. It is exactly these brackish environments that create special habitats for many terrestrial and aquatic organisms. The importance of salinity gradients is now recognized internationally and wherever it is possible, conservation policies are aimed at the restoration of these special habitats. Bureau Waardenburg has already been involved in many projects in this field of study.

Aquatic projects

Areas with a saline gradient form important elements in the aquatic ecosystems of an estuary. For many species of fish they constitute a breeding ground. Some species use the river as a migration route, as do 15 species of fish in Holland and many crustaceans.For these species the gradual change from a saline to a freshwater environment is important for their acclimatisation. Many of these species have become rare in Holland. Bureau Waardenburg has participated in several plans for the restoration of brackish environments.

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Projecten
	Pilot studies restoration transition between fresh and salt water

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Terrestrial projects

Saline gradients are reflected by the transition of saline to brackish and freshwater vegetation.The most common habitat on this gradient is formed by all kinds of salt marshes. A special feature of large rivers like the ones in Holland are freshwater tidal zones. These are characterized by marshes, reedlands, and flooded woodlands consisting mainly of willow species. After restoration of the original saline gradient these vegetation types will re-establish themselves in the tidal zones. Bureau Waardenburg is very active in research and planning in this field.

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Projecten
	Wetland development in the Delta region, The Netherlands
	Delta Synergy

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Projects on birds

Saline gradients contain a large biomass of invertebrates that are preyed upon by marine and aquatic birds. Many ducks and plovers use the tidal zone to forage when the water is at a low level. The decrease of areas with a salinity gradient and tidal processes has had a detrimental effect on the occurrence of bird populations in these areas. Restoration of the natural processes in the tidal zones is a development that will benefit many bird species. Bureau Waardenburg is actively involved in several projects in this field.

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