Insights on the coastal ecosystem dynamics for their application on coastal protection in the face of climate change.
This is me collecting soil samples in a salt marsh from Schiermonnikoog, an island in the Dutch Wadden Sea, to understand the erosion mechanisms of saltmarshes (Photo and scheme by Beatriz Marin).
Motivation and practical challenge
From the coastal areas near my home in Barcelona to the Dutch coast that I now study, I acknowledge that hard engineering measures such as dikes are needed for flood protection. However, their implementation may negatively affect the foreshore areas near the coast. The changes to the coastal dynamics deteriorate many natural ecosystems, such as the salt marshes, which are salt-tolerant plants growing in areas that are flooded by the high tides. These plants are important for coastal protection by reducing waves, but also provide other important ecosystem services like water quality improvement and carbon sequestration. As an environmental biologist, I am therefore motivated to protect our ecosystems by offering alternatives to hard engineering with ecosystem-based coastal defences. For example, by preserving along the Wadden Sea natural ecosystems like the salt marshes but also the mudflats, about 100 km of dikes may, in theory, convert their safety status from insufficient to safe. Nevertheless, the uncertainties about the actual effects also hamper the practical implementation of these ecosystem-based measures.
Therefore, in this project, I investigate how the foreshore ecosystems near the coast work, and what is the effect of their management on gaining both flood protection and ecological value.
Four main components of the research to understand foreshore ecosystems near the Dutch coast (Photos and schemes by Beatriz Marin).
I address the above challenge through four research components, each with the following unique aspects to understand:
- The soil erosion mechanisms of all mudflats and salt marshes studied. On flow and wave flumes, I test the erosion of soil samples from bare mudflats, grazed and not grazed vegetated salt marshes.
- The utilisation of artificial reefs for coastal protection. The mussel beds may help the salt marshes expansion, therefore increasing the protection of the dikes. In 2017, together with colleagues at the institute, we recreated this process into an artificial reef experiment and I am studying both the wave attenuation effects and the mudflat change of elevation.
- The role of salt marshes on wave attenuation and reduction of wave run up on the dikes. We are monitoring these variables at locations in the north and south Dutch coast.
- Influential factors for the salt marshes development in the Wadden Sea. By analysing aerial images on different colour compositions, I explore factors such as the soil elevation change and the effects of different management styles over time.
Relevant for whom and where?
Researchers, nature managers, organisations, and authorities involved in the design of ecosystem-based coastal defence.
Locations studied near the north and south Dutch coast and the artificial experiment in the north Island of Griend.
Progress and practical application
The research is still ongoing. Yet, progress results show, for example, that saltmarshes with fine-grained sediment are more cohesive together with the roots of the plants than bare mudflats, thus providing a more stable soil to the dikes in case of failure. Moreover, the grazing of small and large herbivores such as hares, geese and cattle may reduce saltmarsh lateral erodibility. However, intensive cattle grazing may lower soil elevation, which could negatively impact the resilience to sea level rise in the face of climate change. Last, we found that salt marshes attenuate waves and reduce wave run up on the dikes, but their effects vary across the monitored locations.
Status for day-to-day practice
Based on these preliminary results, we recommend the management of foreshores for coastal protection by preserving existent salt marshes. This can be, for example, through the maintenance of brushwood groynes built from the dike out into the sea to control erosion. We also recommend preserving small herbivores such as hares and geese in the low salt marshes as they may limit erosion without reducing the soil elevation.
We will continue analysing results from the experiments and storms monitoring during 2020-2021. We are further looking for relationships between large scale factors and the variables that we measure in the different locations. These relationships in the Wadden Sea may be also useful for designing a more ecosystem-based coastal protection at other locations.
Last modified: 01/09/2020
Beatriz Marin Diaz
NIOZ Royal Netherlands Institute for Sea Research
- Marin‐Diaz, B., Bouma, T. J., & Infantes, E. (2019). Role of eelgrass on bed‐load transport and sediment resuspension under oscillatory flow. Limnology and Oceanography. https://doi.org/10.1002/lno.11312.