Variations in storm-induced bed level dynamics across intertidal flats
Vet, P.L.M. de; Prooijen, B.C. van; Colosimo, I. ; Steiner, N. ; Ysebaert, T. ; Herman, P.M.J. ; Wang, Z.B. - \ 2020
Scientific Reports 10 (2020)1. - ISSN 2045-2322
Hydrodynamic forces on intertidal flats vary over a range of temporal and spatial scales. These spatiotemporal inhomogeneities have implications for intertidal flat morphodynamics and ecology. We determine whether storm events are capable of altering the long-term morphological evolution of intertidal flats, and unravel the contributions of tidal flow, wind-driven flow, waves, and water depth on inhomogeneities in bed level dynamics (bed level changes over ~days) across these areas. We complement decades of bed level measurements on eight intertidal flats in two estuaries in the Netherlands with an extensive 1-month field campaign on one of those flats. Across this intertidal flat, the hydrodynamics and morphodynamics of a storm event were captured, including the post-storm recovery. We show that individual events can persistently alter the morphological evolution of intertidal flats; magnitudes of some bed level changes are even comparable to years of continuous evolution. The morphological impacts of events are largely controlled by the relative timing of the forcing processes, and not solely by their magnitudes. Spatiotemporal variations in bed level dynamics of intertidal flats are driven by a combination of: (1) the inhomogeneous distributions of the hydrodynamic forcing processes (including the under-explored role of the wind); and (2) the linear proportionality between bed level dynamics and the local bed slope.
Sediment Disposals in Estuarine Channels Alter the Eco-Morphology of Intertidal Flats
Vet, P.L.M. de; Prooijen, B.C. van; Colosimo, I. ; Ysebaert, T. ; Herman, P.M.J. ; Wang, Z.B. - \ 2020
Journal of Geophysical Research: Earth Surface 125 (2020)2. - ISSN 2169-9003
ecology - estuaries - intertidal flats - morphology - sediment disposals - sediment management
Dredging of navigation channels in estuaries affects estuarine morphology and ecosystems. In the Western Scheldt, a two-channel estuary in the Netherlands, the navigation channel is deepened and the sediment is relocated to other parts of the estuary. We analyzed the response of an intertidal flat to sediment disposals in its adjacent channel. Decades of high-frequency monitoring data from the intertidal flat show a shift from erosion toward accretion and reveal a sequence of cascading eco-morphological consequences. We document significant morphological changes not only at the disposal sites, but also at the nearby intertidal flats. Disposals influence channel bank migration, driving changes in the evolution of the intertidal flat hydrodynamics, morphology, and grain sizes. The analyzed disposals related to an expansion of the channel bank, an increase in bed level of the intertidal flat, a decrease in flow velocities on this higher elevated flat, and locally a decrease in grain sizes. These changes in turn affect intertidal flat benthic communities (increased in quantity in this case) and the evolution of the adjacent salt marsh (retreated less or even expanded in this case). The shifts in evolution may occur years after dredged disposal begins, especially in zones of the flats farther away from the disposal locations. The consequences of sediment disposals that we identify stress the urgency of managing such interventions with integrated strategies on a system scale.
Limited seed retention during winter inhibits vegetation establishment in spring, affecting lateral marsh expansion capacity
Regteren, Marin ; Colosimo, Irene ; Vries, Pepijn ; Puijenbroek, Marinka Elisabeth Barbara ; Freij, Victor Sebastiaan ; Baptist, Martin Josephus ; Elschot, Kelly - \ 2019
Ecology and Evolution 9 (2019)23. - ISSN 2045-7758 - p. 13294 - 13308.
Coastal systems worldwide deliver vital ecosystem services, such as biodiversity, carbon sequestration, and coastal protection. Effectivity of these ecosystem services increases when vegetation is present. Understanding the mechanisms behind vegetation establishment in bio‐geomorphic systems is necessary to understand their ability to recover after erosive events and potential adaptations to climate change. In this study, we examined how seed availability affects vegetation establishment in the salt marsh–intertidal flat transition zone: the area with capacity for lateral marsh expansion. This requires vegetation establishment; therefore, seed availability is essential. In a 6‐month field experiment, we simulated a before and after winter seed dispersal at two locations, the salt‐marsh vegetation edge and the intertidal flat, and studied seed retention, the seed bank, and the seed viability of three pioneer marsh species: Salicornia procumbens, Aster tripolium, and Spartina anglica. During winter storm conditions, all supplied seeds eroded away with the sediment surface layer. After winter, supplied seeds from all three species were retained, mostly at the surface while 9% was bioturbated downwards. In the natural seed bank, A. tripolium and S. anglica were practically absent while S. procumbens occurred more frequently. The viability of S. procumbens seeds was highest at the surface, between 80% and 90%. The viability quickly decreased with depth, although viable S. procumbens seeds occurred up to 15 cm depth. Only when seeds were supplied after winter, many S. procumbens and some S. anglica individuals did establish successfully in the transition zone. Viable seed availability formed a vegetation establishment threshold, even with a local seed source. Our results suggest that, although boundary conditions such as elevation, inundation, and weather conditions were appropriate for vegetation establishment in spring, the soil surface in winter can be so dynamic that it limits lateral marsh expansion. These insights can be used for designing effective nature‐based coastal protection.
Beneficial use of dredged sediment to enhance salt marsh development by applying a ‘Mud Motor’: evaluation based on monitoring
Baptist, Martin ; Vroom, Julia ; Willemsem, Pim ; Puijenbroek, Marinka ; Maren, Bas van; Steijn, Pim van; Regteren, Marin van; Colosimo, Irene - \ 2019
Dordrecht : Ecoshape (Wageningen Marine Research report : C088/19) - 66
Beneficial use of dredged sediment to enhance salt marsh development by applying a ‘Mud Motor’
Baptist, Martin J. ; Gerkema, T. ; Prooijen, B.C. van; Maren, D.S. van; Regteren, M. van; Schulz, K. ; Colosimo, I. ; Vroom, J. ; Kessel, T. van; Grasmeijer, B. ; Willemsen, P. ; Elschot, K. ; Groot, A.V. de; Cleveringa, J. ; Eekelen, E.M.M. van; Schuurman, F. ; Lange, H.J. de; Puijenbroek, M.E.B. van - \ 2019
Ecological Engineering 127 (2019). - ISSN 0925-8574 - p. 312 - 323.
Building with Nature - Nature-based solutions - Cohesive sediment - Dredging - Salt marshes - intertidal flats
We test an innovative approach to beneficially re-use dredged sediment to enhance salt marsh development. A Mud Motor is a dredged sediment disposal in the form of a semi-continuous source of mud in a shallow tidal channel allowing natural processes to disperse the sediment to nearby mudflats and salt marshes. We describe the various steps in the design of a Mud Motor pilot: numerical simulations with a sediment transport model to explore suitable disposal locations, a tracer experiment to measure the transport fate of disposed mud, assessment of the legal requirements, and detailing the planning and technical feasibility. An extensive monitoring and research programme was designed to measure sediment transport rates and the response of intertidal mudflats and salt marshes to an increased sediment load. Measurements include the sediment transport in the tidal channel and on the shallow mudflats, the vertical accretion of intertidal mudflats and salt marsh, and the salt marsh vegetation cover and composition. In the Mud Motor pilot a total of 470,516 m 3
of fine grained sediment (D50 of ∼10 μm) was disposed over two winter seasons, with an average of 22 sediment disposals per week of operation. Ship-based measurements revealed a periodic vertical salinity stratification that is inverted compared to a classical estuary and that is working against the asymmetric flood-dominated transport direction. Field measurements on the intertidal mudflats showed that the functioning of the Mud Motor, i.e. the successful increased mud transport toward the salt marsh, is significantly dependent on wind and wave forcing. Accretion measurements showed relatively large changes in surface elevation due to deposition and erosion of layers of
watery mud with a thickness of up to 10 cm on a time scale of days. The measurements indicate notably higher sediment dynamics during periods of Mud Motor disposal. The salt marsh demonstrated significant vertical accretion though this has not yet led to horizontal expansion because there was more hydrodynamic stress than foreseen. In carrying out the pilot we learned that the feasibility of a Mud Motor depends on an assessment of additional travel time for the dredger, the effectiveness on salt marsh growth, reduced dredging volumes in a port, and many other practical issues. Our improved understanding on the transport processes in the channel and on the mudflats and salt marsh yields design lessons and guiding principles for future applications of sediment
management in salt marsh development that include a Mud Motor approach