Dynamic interactions between coastal storms and salt marshes: A review

Abstract

This manuscript reviews the progresses made in the understanding of the dynamic interactions between coastal storms and salt marshes, including the dissipation of extreme water levels and wind waves across marsh surfaces, the geomorphic impact of storms on salt marshes, the preservation of hurricanes signals and deposits into the sedimentary records, and the importance of storms for the long term survival of salt marshes to sea level rise. A review of weaknesses, and strengths of coastal defences incorporating the use of salt marshes including natural, and hybrid infrastructures in comparison to standard built solutions is then presented. Salt marshes are effective in dissipating wave energy, and storm surges, especially when the marsh is highly elevated, and continuous. This buffering action reduces for storms lasting more than one day. Storm surge attenuation rates range from 1.7 to 25 cm/km depending on marsh and storms characteristics. In terms of vegetation properties, the more flexible stems tend to flatten during powerful storms, and to dissipate less energy but they are also more resilient to structural damage, and their flattening helps to protect the marsh surface from erosion, while stiff plants tend to break, and could increase the turbulence level and the scour. From a morphological point of view, salt marshes are generally able to withstand violent storms without collapsing, and violent storms are responsible for only a small portion of the long term marsh erosion. Our considerations highlight the necessity to focus on the indirect long term impact that large storms exerts on the whole marsh complex rather than on sole after-storm periods. The morphological consequences of storms, even if not dramatic, might in fact influence the response of the system to normal weather conditions during following inter-storm periods. For instance, storms can cause tidal flats deepening which in turn promotes wave energy propagation, and exerts a long term detrimental effect for marsh boundaries even during calm weather. On the other hand, when a violent storm causes substantial erosion but sediments are redistributed across nearby areas, the long term impact might not be as severe as if sediments were permanently lost from the system, and the salt marsh could easily recover to the initial state.

Seagrass Impact on Sediment Exchange Between Tidal Flats and Salt Marsh, and The Sediment Budget of Shallow Bays

“…Specifically, as the seagrass is removed the mean shear stress increases for both unvegetated (Figure 3a) and vegetated areas (Figure 3b), even if differences in previously vegetated areas are more evident (Figure 3b). A uniformly distributed input sediment concentration represents potential riverine inputs during flood conditions, or large resuspension events during storms; such situations are the major contributors of inorganic sediments to salt marsh systems (e.g., Fagherazzi & Priestas, 2010;Falcini et al, 2012;Leonardi et al, 2016Leonardi et al, , 2017. This effect also depends on plant density and tends to decrease for less dense meadows ( Figure S4).…”

“…To quantitatively evaluate the impact of seagrasses on the sediment budget, a series of simulations were conducted to relate changes in the extent of meadows with the amount of sediments stored within the bay after 30 days, given the same input concentration and sediment distribution. A uniformly distributed input sediment concentration represents potential riverine inputs during flood conditions, or large resuspension events during storms; such situations are the major contributors of inorganic sediments to salt marsh systems (e.g., Fagherazzi & Priestas, 2010;Falcini et al, 2012;Leonardi et al, 2016Leonardi et al, , 2017. The total sediment mass can be stored within the estuary in one of the…”

Changes in the wind‐wave field and related salt‐marsh lateral erosion: inferences from the evolution of the Venice Lagoon in the last four centuries

“…Since the impinging of the wind wave strongly contributes to salt-marsh horizontal erosion (e.g. Schwimmer, 2001;Marani et al, 2011;Mariotti and Fagherazzi, 2013a;Leonardi et al, 2016aLeonardi et al, , 2018, understanding the relationship between erosion rate and impacting wave-power density is critical also for the maintenance and management of marsh ecosystems.…”

El Niño Increases High‐Tide Flooding in Tidal Wetlands Along the U.S. Pacific Coast

“…Tidal wetlands along the Pacific coast of North America are composed primarily of flood‐tolerant emergent vegetation that usually occupies low‐slope platforms adjacent to upland habitats or human infrastructure (Kennish, ). These wetlands provide important coastal ecosystem services such as habitat for wildlife and fish (Takekawa et al, ), protection against storm surges (Leonardi et al, ), water‐quality regulation (Jordan et al, ), and climate change mitigation by efficiently sequestering carbon (Macreadie et al, ). Long‐term tidal wetland sustainability is influenced by both terrestrial and oceanic processes.…”