Tidal Flats: Geomorphology and Dynamics

An estimate 1.2 million km of the world׳s coast is occupied by wetlands; of that, about 300,000 km corresponds to tidal flats. From the perspective of ecosystem dynamics, we define tidal flats as ecosystems of unconsolidated sediments with relatively low relief, mainly influenced by tidal processes without vascular vegetation. Except for those wetlands that originated from the marine flooding of continental lands, all wetlands, such as marshes or mangroves, started as tidal flats. Therefore, understanding the genesis, dynamics, and evolution of this basic geomorphologic feature is essential for comprehending the properties and processes that are observed in the vast majority of coastal wetlands.The formation and evolution of tidal flats depend on a set of variables (geological, sedimentologic, hydrodynamic, and biological) that acting with different intensities in relation to the local conditions, giving the particular characteristics of each flat. Once established, the degree of inundation/exposure defines a zonation which is parallel to the tidal channel. Phyto and zoobenthos then play important roles in the processes of stabilization and destabilization. Either influences the sediment transport by currents and waves.Only recently, tidal flats and the depressions that are present on their surface have been recognised as significant for Blue Carbon sequestration. Studies made in the last decade demonstrated that tidal flats retain blue carbon at the same level as marshes and mangroves. This extra property, together with its important impact on buffering mean sea level increase, makes tidal flats a very important ecosystem that must be preserved.