How effective are tidal marshes as nature‐based shoreline protection throughout seasons?

Abstract

Nature-based mitigation is increasingly proposed as a strategy to cope with global change and related risks for coastal flooding and erosion. Tidal marshes are known to provide shoreline protection as their aboveground biomass attenuates waves and their belowground biomass contributes to reducing erosion rates. The aim of this study was to quantify how effectively wave attenuation rates and erosion reduction rates are sustained throughout seasons in pioneer tidal marshes in the Elbe estuary (Germany). Changes in hydrodynamics and sediment dynamics were measured during 17 months along three sea-to-land transects of 50 m length. Simultaneously, changes in biomass of the monospecific pioneer vegetation (Bolboschoenus maritimus) were measured monthly. This study shows that wave and flow attenuation rates positively correlate with seasonal variations in aboveground biomass, that is: in summer, aboveground biomass and associated wave and flow attenuation rates are highest; while aboveground biomass is washed away during the first storms in autumn or winter, resulting in low wave and flow attenuation rates. Contrastingly, maximum incoming wave heights and flow velocities occur during winter, indicating that wave and flow attenuation is most needed then. However, hibernating root biomass assures low erosion rates in winter, especially at sandy sites. Although wave attenuation by pioneer marshes is highly variable throughout seasons and pioneer marshes alone are not so effective, they might facilitate the survival of higher marshes. Therefore, it is important to conserve or restore a gradual sea-to-land gradient from tidal flats, over pioneer marsh to high marsh to provide nature-based shoreline protection.

The Sensitivity of a Dike-Marsh System to Sea-Level Rise—A Model-Based Exploration

“…The 750 m width of the marsh is still sufficient to cope with recession. While direct dampening by stems was not included in this study, this agrees with many observations that most waves break at the edge of the marsh and further dampen decays landward [10,45,46]. According to Möller et al [10], a width of 40 m is sufficient to already reduce 15% of an incoming wave's height.…”

“…The attenuation of waves by a marsh is one of the benefits for flood protection. Many studies have found significant wave height reductions within the first 10s of metres of marsh [10,16,[43][44][45]. Waves are dampened further with distance travelled across the marsh.…”

“…Studies tend to highlight the large reductions achieved with wave heights below 1 m and biomass under peak summer conditions. Field studies have found a strong seasonality in wave attenuation corresponding to seasonal changes in vegetation density [16,45,46]. Vuik [23,47] showed that the capacity of marshes to attenuate waves is hampered by the breaking of stems under high wave loads.…”

Tall Wheatgrass (Thinopyrum ponticum): Flood Resilience, Growth Response to Sea Water Immersion, and Its Capacity for Erosion and Flooding Control of Coastal Areas

“…The most significant issues in coastal dune management are related to the mitigation of negative impacts during and consequences after unusual storms and floods with different origins [8]. The holistic approach of integrated coastal zone management recommends nature-based mitigation strategies based on the replacement of artificial coastal protection and stabilization structures with dunes stabilized with plants [12,14]. Natural dune vegetation reduces wind velocity, and with its extensive system of horizontal and vertical rhizomes, holds a large amounts of trapped sand that absorbs wave energy [9,[15][16][17].…”

“…As a result, the coastal areas lose their buffering function permanently or till the recovery of plant communities of dominant sand stabilizers, mostly within one vegetation season (Figure 1b). dunes stabilized with plants [12,14]. Natural dune vegetation reduces wind velocity, and with its extensive system of horizontal and vertical rhizomes, holds a large amounts of trapped sand that absorbs wave energy [9,[15][16][17].…”