In the Eastern Scheldt (The Netherlands), a continuous net erosion of the intertidal flats takes place. Salt marshes are declining and experience erosion, whereas pioneer saltmarsh has almost disappeared. This is a consequence of the morphological disequilibrium caused by the construction of the storm surge barrier and compartmentalization dams in the 1980s. In this pilot Ecoshape investigates a new method to re-establish Spartina anglica (cord grass) in an attempt to protect higher intertidal areas against erosion and to promote the development of pioneer saltmarsh. When certain conditions are met (e.g. sufficient sediment input), the plants may grow in time into healthy salt marshes and add to the biodiversity and ecological functioning of the area.
Salt marshes can protect coastal zones from currents and waves by stabilizing sediments and reducing wave action. They grow in the highest zone of beaches and mud flats. The structures associated with the plants also induce deposition of sediment and organic material from the water column. This material is consolidated between the plants and is a source of food for fauna associated to these habitats. Under certain circumstances, salt marshes are able to maintain the coastline relative to sea level rise by accreting sediment at a level comparable to or even higher than sea level rise, providing a further reduction in vulnerability to hazards and climate change. Besides this dynamic interaction with the physical environment, salt marshes provide economic benefits and contribute to a healthier ecosystem functioning.
The project objective is to create/restore pioneer salt marsh with cord grass (Spartina anglica) in the high intertidal zone in the Eastern Scheldt, thus contributing to coastal protection, biodiversity and ecosystem functioning. The restoration of Spartina marsh is one of the objectives for the Eastern Scheldt in the light of the European Water Framework Directive. Spartina marsh is also a protected habitat within Natura2000.
Salt marshes are characterized by a succession in age and elevation from the sea towards the land (e.g. Van Wijnen and Bakker, 2001). Spartina is one of the pioneer species of salt marshes. Single-plant establishment in the pioneer zone requires characteristics such as rapid anchoring through rapid root emergence and development. The associated sediment binding and dewatering increases the shear strength of the soil around the seedling (Friess et al., 2012, and references therein), which protects the juvenile plant from dislodgement by wave- and current-induced drag forces.
To facilitate the establishment of Spartina in the high intertidal, plants are grown on coconut mats in which the roots can anchor. These mats can be placed on the high mudflat and will protect the Spartina plants against dislodgement during the initial period of rooting. Under the right conditions, the plants can form tussocks and later a continuous meadow. The coconut fibre of which the mats are made will degrade over time and the salt marsh remains. By taking this approach instead of building dams to protect marshes from cliff erosion, existing salt marshes are protected from wave action and erosion without being restricted in their future extension towards the sea.
The current pilot project provides the Building with Nature program with:
- Critical thresholds for the survival of transplanted cord grass.
- Scientifically supported design rules and norms.
- Insight into the effectiveness of this technique.
Within the Building with Nature program, the concept of using ecosystem engineers for coastal protection and flood mitigation is being studied. Several pilot experiments are ongoing, among which the use of shellfish reefs and mangroves. Yet, shellfish need a relatively high inundation time and can therefore only be used in the lower intertidal. Vegetation like mangroves and willow forests occur high in the intertidal. Mangroves only occur in tropical ecosystems. In temperate regions coastal vegetation is mainly saltmarsh. Saltmarshes grow in the high intertidal zone of sheltered beaches and mudflats.
The use of ecosystem engineers or vegetation instead of the more traditionally used hard infrastructure for coastal protection, has the additional value of providing a number of other ecosystem services that may be utilized. Examples are food and raw material production, nutrient cycling, biologically mediated habitat, gas and climate regulation and disturbance prevention (Beaumont, Austen et al., 2007). Saltmarshes constitute ecologically valuable habitats and have a function in stabilizing the seabed and reducing wave action on the shoreline (e.g. Mangi, Davis et al. 2011, Shepard et al. 2011). The plants increase deposition rates by trapping sediment and organic matter. In the last century, saltmarshes development was actively stimulated in the Netherlands, for coastal protection and shore stabilization and to accelerate reclamation (e.g. through the artificial introduction of Spartina anglica).
In recent decades, salt marshes have declined considerably in the Netherlands, especially in the South-western Delta, as a consequence of land reclamation and hydro morphological changes. In the South-western Delta mainly mature marshes are left, whereas new pioneer marsh is found only locally. Physical constraints most likely hamper plant establishment (e.g. Friess et al. 2012). This project will take the first steps towards utilizing cord grass (Spartina anglica) as an ecosystem engineer in the Dutch Eastern Scheldt. Cord grass is a pioneer salt marsh plant that grows at the mudflat/marsh transition zone. By planting cord grass in front of existing mature salt marshes or dikes it will add to coastal protection. If the plants catch on and form a healthy meadow, they may lead to extension of the existing marsh over time. This project focuses on designing and testing a new method, based on growing Spartina plants grown in coconut fibre mats before putting them in place, in order to protect them from dislodgement. This gives the plants a better chance to settle, survive and thrive. It may help to protect the coast and preserve ecologically valuable tidal wetlands.