Morphodynamics of deltaic wetlands and implications for coastal ecosystems - A case study of Save River Delta, Mozambique

Deltaic wetlands experience changes over time, with substantial impacts on the coastal ecosystems. These changes, whether they are natural or human-induced, are caused by multiple factors through complex links and interdependences, and constitute challenges for coastal management aiming to set up practical adaptation measures. In this study, we investigate a case study of Save River Delta to interpret the typical morphodynamic pattern on the deltaic plain over an interdecadal timescale and the implications of geomorphological changes for the coastal ecosystems, with emphasis on mangroves. Our results reveal the pattern of the geomorphological changes on the deltaic wetland in river and back-barrier sectors. In both sectors, erosion and accretion are mutually adjusting processes, and they result in geomorphological settings characterized by a distinctive interaction with the ecosystem; on the one hand, mangrove trees colonize new favorable settings; on the other hand, the existing mangrove trees undergo degradation related to the morphodynamic processes. Notwithstanding current episodic events that affect the deltaic wetlands (e.g. cyclones and floods), the changes observed in the study area are part of interdecadal timescale morphodynamics. These changes were consistent for the 50-year time period analyzed. If, on the one hand, some of the episodic and high magnitude weather events such as floods undermine the status of the deltaic ecosystem, on the other hand these events contribute to develop the same ecosystem over a longer timescale. Within interdecadal timescales, biogeomorphological changes in deltaic wetlands are a critical reference frame for understanding future scenarios of environmental changes caused by climate change.