Abstract
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.