Salt marshes are valuable ecosystems that provide numerous services and act as natural coastal defences by buffering storm waves and stabilising sediments. However, it is not clear whether they will be able to retain their resilience with accelerating rate in sea-level rise, possible increases in storm intensity and increasing land reclamation. 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. Here we present the results of a series of studies that used an integration of modelling and paleoenvironmental analysis and a sediment budget approach to investigate the resilience of estuaries and salt marshes to projected rise in sea-level, possible increases in storm activity and existing anthropogenic disturbance. The studies were conducted using the Ribble Estuary-NorthWest England-as a test case, the hydrodynamic model Delft3D to simulate the estuary morpho-dynamics under selected scenarios, and optically stimulated luminescence (OSL), geochemistry and particle size distribution 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 aid the resilience of the system by promoting flood dominance and triggering a net import of sediment and 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.References Leonardi, N., Ganju, N.K. and Fagherazzi, S. (2016). A linear relationship between wave power and erosion determines salt-marsh resilience to violent storms and hurricanes. Proceedings of the National Academy of  Sciences 113(1), 64-68. Ganju, N.K., Kirwan, M.L., Dickhudt, P.J., Guntenspergen, G.R., Cahoon, D.R. and Kroeger, K.D. (2015). Sediment transport-based metrics of wetland stability. Geophysical Research Letters, 42(19), 7992-8000.

Salt marshes are ecosystems with significant economic and environmental value. With accelerating rate in sea-level rise, it is not clear whether salt marshes will be able to retain their resilience. Field and numerical investigations have shown that storms play a significant role in marsh accretion and that they might be crucial to salt marsh survival to sea-level rise. Here we present the results from two studies (Pannozzo et al., 2021a,b; Pannozzo et al., 2022) that used numerical and field investigations to quantify the impact of storm surges on the sediment budget of salt marshes within different sea-level scenarios and to investigate how sediment transport pathways determine marsh response to storm sediment input. The Ribble Estuary, North-West England, was used as a test case. The hydrodynamic model Delft3D was used to simulate the estuary morpho-dynamics under selected storm surge and sea-level scenarios. In addition, sediment samples collected with a monthly frequency from different areas of the marsh were analysed with sediments collected from possible sources to integrate field observations with the numerical investigation of sediment transport pathways during stormy and non-stormy conditions. Results showed that, although sea-level rise threatens the estuary and marsh stability by promoting ebb dominance and triggering a net export of sediment, storm surges promote flood dominance and trigger a net import of sediment, increasing the resilience of the estuary and salt marsh to sea-level rise, with the highest surges having the potential to offset sea-level effects on sediment transport and sediment budget of the system. However, although storm sediment input resulted to be significant for the accretion of the marsh platform and particularly for the marsh interior, data showed that storms mainly remobilise sediments already present in the intertidal system and only to a minor extent transport new sediment from external sources.ReferencesPannozzo N. et al., 2021. Salt marsh resilience to sea-level rise and increased storm intensity. Geomorphology, 389 (4): 107825.Pannozzo N. et al., 2021. Dataset of results from numerical simulations of increased storm intensity in an estuarine salt marsh system. Data in Brief, 38 (6): 107336.Pannozzo N. et al., 2022. Sediment transport pathways determine the sensitivity of salt marshes to storm sediment input. In preparation.

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. ReferencesLeonardi, 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.