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, increasing land reclamation and changes in sediment supply. 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 two studies (Pannozzo et al., 2021a,b; Pannozzo et al., 2021c) 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, existing anthropogenic disturbance and natural sediment supply. The studies were conducted using the Ribble Estuary - North-West 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. Pannozzo et al. (2021a,b) 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. Pannozzo et al. (2021c) showed that the addition of embankments can further promote ebb dominance in the system and intensify sediment export, further threatening marsh stability. This latest effect, however, becomes negligible with high natural sediment supply to the system.@en

There are still numerous uncertainties over the influence of anthropogenic interventions on salt marsh dynamics. This study uses the Ribble Estuary as a test case and an integrated approach of numerical modeling and paleoenvironmental analysis to investigate the contribution of embankment construction to long-term marsh accretion. Accretion rates derived using optically stimulated luminescence dating (OSL) were combined with a multi-proxy paleoenvironmental investigation on sediment cores extracted from the salt marsh, the mobile seafloor of the central Irish Sea and the river catchment area. These analyses provided a first evolutionary perspective on the Ribble Estuary preceding any management interventions. The paleoenvironmental analyses were then compared to simulations conducted using the hydrodynamic model Delft3D to investigate the effects of embankment construction on estuarine hydrodynamics and morphodynamics of the salt marsh over the period constrained by the OSL. The numerical simulations showed that embankments were responsible for an overall intensification of the ebb currents in the system which promoted sediment export. The paleoenvironmental analyses showed that the marsh has been accreting at a rate of 4.61 to 0.86 cm yr−1 over the last ca. 190 years and that the high sedimentation rate was caused by a naturally high rate of sediment supply. The model-data integration showed that the effects of the embankment construction on sediment transport did not compromise the long-term resilience of the salt marsh because of the high rates of sediment supply and the river dredging which enhanced the flood dominance of the tide near the tidal flat.@en