Long-term Surface Elevation Change in Salt Marshes: a Prediction of Marsh Response to Future Sea-Level Rise

Abstract

Accretion rates and surface elevation changes were measured in three natural salt marshes in the Wadden Sea. Derived from these measurements, a simple predictive model was made which describes changes in surface elevation during more than 100 years of salt-marsh development at several sea-level rise scenarios. The model was tested with data on long-term surface elevation changes at several successional stages in the salt marsh of Schiermonnikoog (The Netherlands), where sites differ in age from a few years to more than 100 years.The model predicts in all scenarios a fast increase in surface elevation during the first 100 years of marsh development. Results showed a very high similarity between the prediction of the model and field-data. A scenario without sea-level rise revealed a stabilization of surface elevation and inundation frequency after approximately 100 years. In a scenario with a rise in mean sea-level, however, marsh surface elevation continues to increase after 100 years, although at a slower pace. Previous studies expected marsh surface elevation on coastal barrier marshes to keep pace with sea-level rise, if sea-level rise was lower than 5mmyr−1. We found that inundation frequency starts to increase after 100 years of marsh development, even if sea-level rise is lower than 5mmyr−1. Shrinkage of the clay layer during summer probably caused an elevation deficit in older marshes. This means that in the long run (more than 500 years) marshes will probably degenerate on these islands, especially at a low elevation. New marshes may develop at sites with a higher elevation, if these sites are available.