The precise evaluation of the conservation status of salt marshes, the understanding of the mechanisms behind loss and degradation and the anticipation of future threats are fundamental to assist management solutions able to reverse the declining trend observed in these environments. Previous methods combining remote sensing and hydrodynamic modelling have been revealed to be effective in assessing degradation in restricted marshes, but unable to characterise dynamics of marshes at the estuarine scale. This study proposes an alternative methodology to identify priority areas for conservation by combining LANDSAT satellite remote sensing and numerical modelling. Using the Ria de Aveiro as case-study, the main objectives of this work are to: (1) identify vegetation loss and degradation in estuarine marshes; (2) determine the mechanisms behind marsh deterioration; (3) anticipate future threats posed by climate-induced mean sea level rise and; (4) provide management solutions aiming to protect and recover degraded salt marshes. LANDSAT imagery reveals that the most deteriorated salt marshes are located on the central and upper lagoon regions, and the numerical results support that marsh loss and degradation result from the increased tidal action triggered by the deepening of the lagoon channels. The increase in tidal currents promoted the erosion of marsh shoreline, whereas the changes in the inundation patterns over the intertidal areas triggered interior drowning. Climate-induced mean sea level rise will likely exacerbate marsh deterioration, increasing the urgency to implement a management plan aiming to protect marshes from erosion and promote sedimentation in submerged marshes, to ensure their sustainability.
K E Y W O R D Smarsh drowning, marsh shoreline erosion, Ria de Aveiro, salt marsh management, tidal dynamics
| INTRODUCTIONSalt marshes are considered among the most valuable and productive ecosystems in the world, providing a broad range of services, such as nutrient regeneration, primary production, habitat for marine species and coastal defence (Boorman, 1999). Despite their multiple values, salt marsh area and condition are declining globally, due to growing threats posed by both socioeconomic ('human') and biogeophysical ('natural') actions, exacerbated by climate changes impacts (Mariotti & Carr, 2014). In recognition to their value and to reverse this tendency, management and conservation policies for these habitats have been developed and implemented all over the world; however, these proved to be insufficient in many systems, which continue to degrade (Hansen & Reiss, 2015). Mariotti (2016) summarised three major