Case Study: Marconi salt marsh, The Ems Estuary, The Netherlands
The Marconi Buitendijks project was commissioned to address the deteriorating ecological condition of the Ems estuary in the Netherlands. A seawall along the coast of Delfjizl was relocated and reinforced and two salt marshes were constructed by raising the seabed to the mean high tide with dredged sand. One salt marsh is open to the public, while the other is a pioneer salt marsh open only to researchers. This pioneer salt marsh of 15 ha is a pilot and is being used for experiments to understand the development of salt marshes. Researchers are testing the effect of enriching the salt marsh with mud and the effect of planting versus natural colonisation of vegetation. The pilot marsh consists of six 1 ha compartments each with different percentages of mud, sand, and fine sediments, some of which are seeded and some that are allowed to vegetate naturally. Heavy machinery was used to mix mud in the top 1 m of the sandy bed (note that this caused the machines to sink). From November 2018 to September 2020, the salt marsh was inundated approximately 70 times. In May 2019, the research team manually sowed long-spiked glasswort Salicornia procumbens. Before sowing, the glasswort was dried, cut into pieces and soaked in fresh water for four days to allow the seeds to germinate. Glasswort plants appeared one and a half years after seeding (in July).
What has been learned from the project so far?
● The effect of seeding was temporary: seeded areas had a higher cover of glasswort plant than non-seeded areas but only in the first year. ● A higher percentage of mud (25 – 48%) in the top layer of sediment led to more total vegetation cover, while vegetation cover was significantly lower with less mud (7 – 9%). ● Higher mud content led to higher species richness. ● No vegetation was found in plots with high rates of erosion (>2.5 mm per month). ● Vegetation only developed with areas enclosed by brushwood groynes. ● Overall, the researchers conclude that mixing the top layer of the sandy bed with mud to 25% boosts vegetation cover and species richness and is practically feasible.
Sources: Baptiste et al . (2021); de Vries et al . (2021); Video: Research on the pioneer salt marsh Marconi Delfzijl (youtube.com/watch?v=V8zCrhG-jtY)
5. Other sources of information
Literature review of best practices for salt marsh creation: de Groot A.V. & van Duin W.E. (2013) Best Practices for Creating New Salt Marshes in an Estuarine Setting: A Literature Study . Report no. IMARES C145/12. EcoShape – Building with Nature: The Netherlands. Available at: https://edepot.wur.nl/248715
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