Quantifying Bed Level Change at the Transition of Tidal Flat and Salt Marsh: Can We Understand the Lateral Location of the Marsh Edge?

P. W. J. M. Willemsen, B. W. Borsje, S. J. M. H. Hulscher, D. van der Wal, Z. Zhu, B. Oteman, B. Evans, I. Möller, T. J. Bouma

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Bed level dynamics at the interface of the salt marsh and tidal flat have been highlighted as a key factor connecting the long-term biogeomorphological development of the marsh to large-scale physical forcing. Hence, we aim to obtain insight into the factors confining the location of the marsh edge (i.e., boundary between tidal flat and salt marsh). A unique data set was collected, containing measurements of daily bed level changes (i.e., integrative result of physical forcing and sediment properties) at six intertidal transects in the North Sea area. Moreover, various biophysical parameters were measured, such as sediment characteristics, waves, inundation time, and chlorophyll-a levels. The data show that both bed level change and waves decreased from the lower intertidal flat toward the marsh edge and further diminished inside the marsh. However, no direct general relation was found between waves and bed level change. Bed level change inside the marsh was always small, regardless of wave energy. By combining the data sets, we demonstrate that the location of the lower marsh edge is restricted by two interacting factors: inundation time and bed level change. For vegetation establishment to withstand longer inundation stress, which slows down plant growth, more stable bed levels are required so that plants are not heavily disturbed. Conversely, to withstand more dynamic bed levels that disturbs plant growth, lower inundation stress is needed, so that plants grow fast enough to recover from the stress. The results suggest that bed level change is important in determining the position of the marsh edge.

Original languageEnglish
Pages (from-to)2509-2524
Number of pages16
JournalJournal of geophysical research: Earth surface
Issue number10
Early online dateOct 2018
Publication statusPublished - 1 Oct 2018


  • field observations
  • marsh edge location
  • nature-based flood defense
  • salt marsh dynamics
  • tidal flat
  • bed level dynamics


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