Abstract:
Salt-marshes are highly valuable ecosystems due to their role in supporting the aquatic and bird life. Furthermore, many
anthropogenic activities such as agriculture, salt production or aquaculture targets these areas. They also act as
protective barriers to shores, given their ability to dissipate most of the wave and current energy in high tide. Sea level
rise can place these intertidal zones at risk, reinforcing the need to understand their morphosedimentary and dynamic
response to the variations on the forcing factors, thus allowing for a better management of these environments. Large
expansions of salt-marshes and tidal flats are among the morphodynamic contents of the Tagus estuary. This study
focuses on the recent past evolution of Tagus marsh areas in order to understand their geomorphological response to
higher sea level scenarios. Cores were taken in four contrasting high salt-marsh expansions in estuarine margins
(Trancão – TR, Mouchão da Póvoa – MP, Pancas – PA and Corroios - CO). Marsh surfaces were surveyed using
DGPS-RTK and tidal regime characterized at each location. The cores reached at least 1.20m in depth and were subsampled
every cm for 210Pb and 137Cs radioisotope determination, allowing the derivation of sedimentation rates. In all
locations, accretion rates clearly exceed the post-1920 mean rate of sea level rise (+0.21cm/year, Cascais gauge). Their
linear extrapolation into the future, until reaching the upper threshold of marsh surface aggradation (MSHT), suggests
that Tagus marginal marshes will not drown under the projected sea level elevation scenarios for the end of the 21th
century.