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

Abstract

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.

Coupling between tidal mudflats and salt marshes affects marsh morphology

“…In previous studies, the erosion of tidal mudflats due to wave activity has widely been attributed to strong wind and storm events, with calm weather periods being responsible for intertidal sediment accretion, creating an equilibrium profile, adjusted to the prevailing wind and tide conditions (Janssen-Stelder, 2000;Le Hir et al, 2000). The data reported here, however, show little sign of elevation increases of the tidal mudflat during calm weather periods, and bed level changes are not significantly related to wave activity, a finding that is confirmed by recent data on mudflat elevation changes in various marsh system across the North Sea (Willemsen et al, 2018). The dominant signal is one of surface lowering, suggesting that the mudflat is out of equilibrium with prevailing energy conditions.…”

Multiple Environmental Variables Affect Germination and Mortality of an Annual Salt Marsh Pioneer: Salicornia procumbens

“…They were anchored firmly in the soil with a metal rod of 1.2 m. The data were retrieved from the logger once during the experiment (while the instrument remained in the sediment for continuity in the measurements) and at the end of the experiment. The SED data were converted into bed-level change information following Willemsen et al (2018). SED time series were subdivided into the same intervals as those in which the vegetation was assessed.…”

“…The transition zone is the vital area for salt marsh expansion but it is also where bed level is very dynamic (Widdows et al 2008;Willemsen et al 2018). There is an intricate interplay between the sedimentation and erosion at the salt marshintertidal flat transition zone.…”

Beneficial use of dredged sediment to enhance salt marsh development by applying a ‘Mud Motor’: evaluation based on monitoring

“…The SEDs were checked approximately every eight weeks to ensure data collection, clean the sensors and retrieve the data. Collected raw data from the Surface Elevation Dynamics (SED) sensors were converted using well-documented software (Willemsen et al 2018).…”