Sediment characteristics of a restored saltmarsh and mudflat in a managed realignment scheme in Southeast England

Kadiri, Margaret Osikhofe; Spencer, Kate L.; Heppell, Catherine M.; Fletcher, Paul W.

doi:10.1007/s10750-011-0755-8

Cited by 20 publications

(12 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Natural freshwater tidal marshes are built up of sediment that was deposited by the tidal water over hundreds of years. Together with the mineral sediment, organic matter is deposited and gets buried within the soil (Kadiri et al, 2011). During the low water phase, the groundwater table in the marsh declines, inducing soil aeration (Xin et al, 2010).…”

Section: Changed Soil Properties As a Results Of Agricultural Land Usementioning

confidence: 99%

Groundwater dynamics in a restored tidal marsh are limited by historical soil compaction

Putte

Temmerman

Verreydt

et al. 2020

Estuarine, Coastal and Shelf Science

View full text Add to dashboard Cite

In places where tidal marshes were formerly embanked for agricultural land use, these marshes are nowadays increasingly restored with the aim to regain important ecosystem services. However, there is growing evidence that restored tidal marshes and their services develop slowly and differ from natural tidal marshes in many aspects. Here we focus on groundwater dynamics, because these affect several key ecosystem functions and services, such as nutrient cycling and vegetation development. We hypothesize that groundwater dynamics in restored tidal marshes are reduced as compared to natural marshes because of the difference in soil structure. In the macro-tidal Schelde estuary (Belgium), in both a natural and a restored (since 2006) freshwater tidal marsh, we measured depth profiles of soil properties (grain size distribution, LOI (loss on ignition), moisture content and bulk density) and temporal dynamics of groundwater levels along a transect with increasing distance from a tidal creek. X-ray micro CT-scanning was used to quantify soil macroporosity. The restored marsh has a twolayered soil stratigraphy with a topsoil of freshly accreted sediment (ranging in depth between 10 and 60 cm, deposited since 2006) and a subsoil of compact relict agricultural soil. We found that both the soil in the natural marsh and the topsoil of the restored marsh consist of loosely packed sediment rich in macropores and organic matter, whereas the relict agricultural soil in the restored marsh is densely packed and has few macropores. Our results show that groundwater level fluctuations in the restored marsh are restricted to the top layer of newly deposited sediment (i.e. on average 0.08 m depth). Groundwater level fluctuations in the natural marsh occur over a larger depth of the soil profile (i.e. on average 0.28 m depth). As a consequence, the reduced groundwater dynamics in restored tidal marshes are expected to alter the subsurface fluxes of water and nutrients, the sourcesink function and the development of marsh vegetation.

show abstract

Section: Changed Soil Properties As a Results Of Agricultural Land Usementioning

confidence: 99%

Groundwater dynamics in a restored tidal marsh are limited by historical soil compaction

Putte

Temmerman

Verreydt

et al. 2020

Estuarine, Coastal and Shelf Science

View full text Add to dashboard Cite

show abstract

“…The bulk densities of the relict agricultural CRT soil are lower than known from other managed realignment (MR) studies; often values above 1.0 g cm -3 were measured elsewhere. These different bulk densities cannot be explained by organic matter contents, which are similar in the CRT (table 2) and MR sites, but may be explained by their higher sand contents (>10%) and consequently lower porosity (Burden et al 2013;Clapp 2009;French 2006;Kadiri et al 2011;Tempest et al 2015). Moisture content of the new sediments in the CRT area decreases with depth, and subsequently declines greatly in the relict agricultural soil.…”

Section: Shallow Subsidencementioning

confidence: 91%

Tidal Marsh Restoration Design Affects Feedbacks Between Inundation and Elevation Change

Oosterlee¹,

Cox²,

Vandenbruwaene³

et al. 2017

Estuaries and Coasts

View full text Add to dashboard Cite

Tidal marsh restoration or creation on formerly embanked land is increasingly executed along estuaries and coasts in Europe and the USA, either by restoring complete or reduced tidal exchange. Ecosystem functioning and services are largely affected by the hydro-geomorphologic development of these areas. For natural marshes, the latter is known to be steered by feedbacks between tidal inundation and sediment accretion, allowing marshes to reach and maintain an equilibrium elevation relative to mean sea level, and steering ecological succession towards a climax state. However, for marsh restoration sites, these feedbacks may be disturbed depending on the restoration design. This was investigated by comparing the inundation-elevation change feedbacks in a natural versus restoration site with reduced tidal exchange in the Scheldt estuary (Belgium). This study analyses long term (15 years) datasets on elevation change and tidal inundation properties to disentangle the different mechanisms behind this elevation-inundation feedback. Moreover, subsequent changes in sediment properties that may affect this feedback were explored. We found in the restoration area with reduced tidal exchange a different elevation-inundation feedback than on natural marshes, i.e. a positive feedback on initially high sites (i.e. sediment accretion leads to increasing inundation, hence causing accelerating sediment accretion rates) and a gradual silting up of the whole area. Furthermore, there is evidence for the presence of a relict consolidated sediment layer. Consequently, shallow subsidence is less likely to occur. Although short term ecological development of the tidal marsh was not impeded, long term habitat development may be different by the disturbed hydro-geomorphological interactions. Potential consequences for ecosystem functioning and services are discussed. Ecosystem trajectories may be controlled or changed by adaptive management, and suggestions for improved management are made.

show abstract

“…Many projects involve new marsh development on low elevated, initially bare flats in front of the embankment, where sediment accretion might be relatively fast (Vandenbruwaene et al, 2011;Oosterlee et al, 2018), resulting in less consolidated sediments, low bulk densities, poor drainage and hence lower shear strengths (Watts et al, 2003;Van Putte et al, 2020). Experience from existing tidal marsh (re)creation projects suggests that it might take several years before marshes develop with sediments that have enough strength to withstand high shear stresses (Fearnley, 2008;Kadiri et al, 2011;Tempest et al, 2015;Sha et al, 2018) as can be expected on the marsh platform in front of a dike breach. In this respect, further research is needed on the rates of development of marsh sediment strength, as marshes develop from young pioneer marshes to older established marshes.…”

Section: Suggestions For Further Researchmentioning

confidence: 99%

Stability of a Tidal Marsh Under Very High Flow Velocities and Implications for Nature-Based Flood Defense

et al. 2022

View full text Add to dashboard Cite

Nature-based strategies, such as wave attenuation by tidal marshes, are increasingly proposed as a complement to mitigate the risks of failure of engineered flood defense structures such as levees. However, recent analysis of historic coastal storms revealed smaller dike breach dimensions if there were natural, high tidal marshes in front of the dikes. Since tidal marshes naturally only experience weak flow velocities (~0-0.3 ms-1 during normal spring tides), we lack direct observations on the stability of tidal marsh sediments and vegetation under extreme flow velocities (order of several ms-1) as may occur when a dike behind a marsh breaches. As a first approximation, the stability of a tidal marsh sediment bed and winter-state vegetation under high flow velocities were tested in a flume. Marsh monoliths were excavated from Phragmites australis marshes in front of a dike along the Scheldt estuary (Dutch-Belgian border area) and installed in a 10 m long flume test section. Both sediment bed and vegetation responses were quantified over 6 experimental runs under high flow velocities up to 1.75 ms-1 and water depth up to 0.35 m for 2 hours. These tests showed that even after a cumulative 12 hours exposure to high flow velocities, erosion was limited to as little as a few millimeters. Manual removal of the aboveground vegetation did not enhance the erosion either. Present findings may be related to the strongly consolidated, clay- and silt-rich sediment and P. australis root system in this experiment. During the flow exposure, the P. australis stems were strongly bent by the water flow, but the majority of all shoots recovered rapidly when the flow had stopped. Although present results may not be blindly extrapolated to all other marsh types, they do provide a strong first indication that marshes can remain stable under high flow conditions, and confirm the potential of well-developed tidal marshes as a valuable extra natural barrier reducing flood discharges towards the hinterland, following a dike breach. These outcomes promote the consideration to implement tidal marshes as part of the overall flood defense and to rethink dike strengthening in the future.

show abstract

Sediment characteristics of a restored saltmarsh and mudflat in a managed realignment scheme in Southeast England

Cited by 20 publications

References 33 publications

Groundwater dynamics in a restored tidal marsh are limited by historical soil compaction

Groundwater dynamics in a restored tidal marsh are limited by historical soil compaction

Tidal Marsh Restoration Design Affects Feedbacks Between Inundation and Elevation Change

Stability of a Tidal Marsh Under Very High Flow Velocities and Implications for Nature-Based Flood Defense

Contact Info

Product

Resources

About