H. Bard1*, T.J. Grandjean2 , T.J. Bouma1,2,T.D.Price1
1 Utrecht University, The Netherlands; 2 NIOZ - Royal Netherlands Institute for Sea Research, The Netherlands
* Corresponding author: h.e.bard@uu.nl
Introduction
Intertidal estuarine environments, including tidal flats and saltmarshes are dynamic systems with wide ranging benefits from flood resilience to habitat biodiversity. Saltmarshes and tidal flats are eroding globally with an estimated saltmarsh loss of 0.28% per year between 2000 to 2019 [1]. This is expected to continue with rising sea levels, increased storm intensity, and human interventions that are reducing sediment supply. The protection of saltmarshes and tidal flats from erosion is therefore key to enable continued benefit realisation.
Despite many long term erosive trends, in the short term, the same saltmarsh may retreat and expand and the same tidal flat may erode and accrete indicating they are naturally rebuilding systems. This poses an opportunity to manage these natural processes to minimise the erosion whilst maximising the expansion.
Objective and Methods
We aim to provide conceptual models to explain the processes that drive tidal flats and saltmarsh biomorphodynamics globally. For tidal flats we focus on the vertical changes in sediment, whereas at the saltmarsh edge we focus on the horizontal movement. These conceptual models are based on global literature, including management and recommendation manuals. This aims to provide an understanding of the similarities and differences in the processes occurring and the management strategies to optimise resilience.
Results
Conceptual models have been designed for the processes occurring on tidal flats and saltmarshes globally.
In the short term (days), tidal flats experience fluctuations in the bed shear stress due to the hydrodynamics, which can trigger either erosion or accretion. Over the long term, the tendency towards erosion or accretion depends on the sediment supply into the system as more energy is required to keep more sediment in suspension. Once a tidal flat enters a long term state of erosion or accretion, the shape reinforces this process, creating a self-sustaining morphological cycle.
Saltmarshes experience an expansion-retreat cycle, influenced by the sediment dynamics at the tidal flat- saltmarsh interface. The retreat stage is triggered when a height difference forms, leading to marsh cliff formation. However, short term retreat does not always indicate long term trends, as accretion on the tidal flat or a toppled marsh platform may reduce the height difference, fostering seed settlement.
Since saltmarshes and tidal flats are highly interrelated, management approaches must consider the system as a whole. During the meeting I will discuss how these processes can be used to improve management of intertidal estuary environments.
References
[1] Campbell, A.D., Fatoyinbo, L., Goldberg, L. et al. Global hotspots of salt marsh change and carbon emissions. Nature 612, 701–706 (2022). https://doi.org/10.1038/s41586-022-05355-z
