Salt marshes are ecosystems with significant economic and environmental value. They provide numerous ecosystem services and act as natural coastal defences by buffering storm waves and stabilising sediments (Leonardi et al., 2016). However, with accelerating rate in sea-level rise, possible increases in storm intensity and increasing land reclamation, it is not clear whether salt marshes will be able to retain their resilience. The current paradigm is that a positive sediment budget supports the survival and accretion of salt marshes while a negative sediment budget causes marsh degradation (Ganju et al. 2015). Here we present the results of a series of studies that used a sediment budget approach and an integration of modelling and paleoenvironmental analysis to investigate the resilience of estuaries and salt marshes to rise in sea-level, change in storm activity and anthropogenic interventions. The Ribble Estuary, North-West England, was used as a test case, as it is one of the largest salt marsh systems in Europe, it was subject to several anthropogenic interventions (e. g. embankment construction) and it was anthropogenically restored through managed realignment to provide coastal protection against flooding (Pontee et al., 2014). The various processes were investigated using the hydrodynamic model Delft3D to simulate the estuary morpho-dynamics under selected scenarios, and optically stimulated luminescence (OSL), geochemistry and particle size analysis to reconstruct the past evolution and adaptation of the estuary morphology. Results showed that sea-level rise threatens estuary and marsh stability by promoting ebb dominance and triggering a net export of sediment. Conversely, storm surges promote flood dominance and trigger a net import of sediment, therefore aiding the resilience of the system. Storms with the highest intensities also have the potential to counteract the negative impact of sea-level rise by masking its effects on the sediment budget. The addition of embankments, on the other hand, can further promote ebb dominance in the system and intensify sediment export, further threatening marsh stability.

Leonardi, N. et al. (2016). PNAS, 113(1), 64-68.

Ganju, N.K. et al. (2015). Geoph. Res. Lett., 42(19), 7992-8000.

Pontee, N.I. et al. (2009). Eng. Sust., 162(4), 223-228.