Dual role of salt marsh retreat: Long‐term loss and short‐term resilience

Abstract

Two major causes of salt marsh loss are vertical drowning, when sediment accumulation on the platform cannot keep vertical pace with sea level rise, and horizontal retreat, associated with waveinduced marsh boundary erosion. Despite these processes having been extensively documented and modeled, it is unclear which loss modality dominates given a set of environmental parameters. A three-point dynamic model was developed to predict marsh loss as a function of sea level rise, allochthonous sediment supply, wind regime, tidal range, and marsh bank and mudflat erodability. Marsh horizontal and vertical evolutions were found to respond in opposing ways to wave-induced erosion processes. Marsh horizontal retreat was triggered by large mudflats, strong winds, high erodability of marsh bank and mudflat, whereas the opposite conditions acted to reduce the sediment supply to the marsh platform, promoting marsh loss to drowning. With low and moderate rates of sea level rise ( 5 mm/yr), retreat was found to be a more likely marsh loss modality than drowning. However, conditions associated with marsh retreat also increase the system resilience by transferring sediment on the marsh platform and preventing drowning. Our results suggest the use of a modular strategy for short-term marsh management: selectively protect extensive salt marsh regions by maintaining healthy vegetation on the platform, while allowing other areas to retreat, leveraging the natural resilience embedded in the lateral loss of marsh extent.

The effect of a small vegetation dieback event on salt marsh sediment transport

“…This marsh cannibalization process, which is found in some numerical and conceptual models, has been suggested to enhance overall marsh resiliency to sea-level rise (Mariotti and Carr, 2014;Currin et al, 2015;Hopkinson et al, 2018). This marsh cannibalization process, which is found in some numerical and conceptual models, has been suggested to enhance overall marsh resiliency to sea-level rise (Mariotti and Carr, 2014;Currin et al, 2015;Hopkinson et al, 2018).…”

Spatially integrative metrics reveal hidden vulnerability of microtidal salt marshes

“…As marshes lower in the tidal frame due to sea-level rise, there may be an increased propensity to trap more sediment and partially offset a sediment deficit4. From a whole-system perspective however, this depends on the reliability of an external sediment source, otherwise the likely source of trapped material is marsh edge erosion (that is, a cannibalization process30). …”

Revisiting salt marsh resilience to sea level rise: Are ponds responsible for permanent land loss?

“…Marsh loss can also occur by wave‐induced retreat of the marsh edge. Differently from the drowning, this loss can occur even if the vegetated platform keeps pace with RSLR [ Mariotti and Carr , ]. Marshes with large tidal ranges, even if more able to accrete vertically [ Kirwan et al , ], are not immune to this type of loss [ Leonardi and Fagherazzi , ].…”