Salt marshes, also known as tidal marshes, are coastal areas rich in sediment that are periodically flooded by the sea and where plants have started to grow. Sediments are deposited onto the surface of the marsh by the sea, which gradually raises the bed level. Salt marshes are found on barrier islands, estuaries and sheltered coasts along the North Sea. De Groot studied the salt marshes on the island of Schiermonnikoog. Salt marshes are not only important for biodiversity -- many rare species of plants and birds can be found there -- but also play an important role in coastal defence.
Radioactive salt marshes
The biologist used a novel method for studying the salt marshes: she analysed the gamma radiation naturally present in the sand and the clay of the salt marsh. Most sediments contain small amounts of radioactive elements that emit low levels of gamma radiation. This enabled her to determine the composition of the soil in the salt marshes. She combined the new radiometric method with measurements using a soil corer. She discovered that heavy storms deposit sand on the salt marshes about once every decade, which is far more frequent than was thought until now. The contribution of this sand to the total increase in soil elevation of the salt marsh appears to be small however, meaning that 'normal' sedimentation is by far the most important factor for the growth of the salt marshes.
De Groot's method offers many possibilities for further research. In addition, she shows that commonly used small-scale measurements are insufficient for making reliable predictions about the development of the salt marshes, with respect to rising sea levels for example. This is evident from the complicated sedimentation patterns she discovered in the salt marshes. Her discoveries can be used to improve the set-up of sedimentation measurements.
Dynamic coastal zone management
The possibilities for 'dynamic coastal zone management' are of increasing interest in the Netherlands. Therefore, in certain areas the coast is being left to develop naturally. But this can only be done safely if we understand how our coastline develops. De Groot's research makes a major contribution to such insights.
Alma de Groot's research is part of the NWO programme Land-Ocean Interactions in the Coastal Zone (LOICZ). This programme will be concluded by a symposium on 24 November 2009.