Unravelling interactions between salt marsh evolution and sedimentary processes in the Wadden Sea (southeastern North Sea)

Abstract

Salt marshes in the Wadden Sea constitute about 20% of all salt marshes along European coasts. They are of immense importance for coastal protection reasons and as habitat for coastal plant, bird, and invertebrate species. The Wadden Sea is a coastal sedimentary ecosystem in the southeastern North Sea. Besides salt marshes, it is composed of tidal flats, high sands, and sandy shoals, dissected by (sub)tidal channels and located behind barrier islands. Accelerated global sea-level rise (SLR) and changes in storm climate have been identified as possible threats for the persistence of the Wadden Sea ecosystem including its salt marshes. Moreover, it is known that the amount and composition of the sediment available for salt marshes are the most important parameters influencing their ability to adapt to current and future SLR. Assessing these parameters requires a thorough understanding of the sedimentary system of the salt marshes and the adjacent tidal basins. In the present review, we investigate and unravel the interactions of sedimentary processes in the Wadden Sea with the processes taking place on the salt marshes. We identify the most crucial processes and interactions influencing the morphological development of salt marshes in the Wadden Sea. A conceptual model is proposed, intended as a framework for improved understanding of salt marsh development and for incorporation into new salt marsh models. The proposed model may also be applicable to regions other than the Wadden Sea.

Role of wind in erosion‐accretion cycles on an estuarine mudflat

“…In recent decades, especially since the construction of the Three Gorges Dam, the Yangtze's sediment discharge has decreased by nearly 80% [e.g., Yang et al ., ], which has resulted in long‐term erosion in the mudflats and has greatly decreased the progradation of salt marshes in the delta front [ Yang et al ., ]. In the context of an increase in intensity of storms [ Woodruff et al ., ; Möller et al ., ; Schuerch et al ., ] and a reduction of riverine sediment loads, it can be expected that coastal ecosystems will be further affected by sedimentary processes.…”

“…Previous studies showed that intertidal sediment dynamics can significantly affect coastal ecosystems [e.g., Zhu et al ., ; Gao et al ., ; Schuerch et al ., ]. For example, short‐term sediment dynamics on tidal flats can initiate adjacent lateral marsh erosion, and marsh erosion rates depend on sediment type, hydrodynamics, and difference in elevation between the tidal flat and adjacent marsh [ Bouma et al ., ].…”

Short-term mudflat dynamics drive long-term cyclic salt marsh dynamics

“…Getting this process‐based understanding of tipping points governing salt‐marsh dynamics is highly important both for i) being able to translate ecological concepts (van de Koppel et al ; Mariotti and Fagherazzi ; Tambroni and Seminara ) towards management measures aimed at preserving marshes and for ii) enhancing current insights in the importance of ecosystem connectivity at the landscape‐scale (in our case the tidal flat and salt marsh) for the long‐term dynamics of such ecosystems (cf. Gillis et al ; Schuerch et al ; van de Koppel et al ). It is noted that although we identify the short‐term tidal mudflat sediment dynamics as key‐process for understanding the long‐term cyclic salt‐marsh dynamics, this does not imply that long‐term changes in external forcing are unimportant.…”

“…Also in designing restoration projects, process‐based understanding on thresholds enables engineers to create the proper hydrodynamic conditions and thereby, more importantly, the proper sediment conditions to facilitate ecosystem dynamics. Attention for this aspect, however, should not obliterate the necessity to also include any long‐term accretion or erosional trends when making restoration designs (Schuerch et al ). Modelling of the short‐term sediment dynamics on a mudflat is complicated, with limited formulations available, which are still poorly validated against observations (Shi et al , and references therein; but also see Hu et al for a novel modelling approach).…”

Contrasting biogeomorphic processes affecting salt‐marsh development of the Mokbaai, Texel, The Netherlands

“…Scyphers et al, 2011;Temmerman et al, 2013). Additionally, the production of pseudofaeces by shellfish may enhance sedimentation on the intertidal flats and salt marsh (Borsje et al, 2011;Schuerch et al, 2014). However, the bank may block the transport of sediment towards the marsh.…”