Tracking the trajectory of mangrove dynamics in the Zambezi Delta, East Africa's largest river Delta

The Zambezi Delta hosts one of Africa's largest mangrove ecosystems, providing vital ecosystem services including carbon storage, coastal protection, and biodiversity support. However, the long-term spatiotemporal evolution of these mangroves and their responses to changing environmental drivers remain insufficiently understood. By integrating 35 years of Landsat imagery from 1989 to 2024 with fluvial sediment and hydrodynamic datasets, this study systematically investigates mangrove dynamics and their underlying mechanisms. The total mangrove area expanded at 307.08 ha yr^-1 from 1989 to 2001, before declining at -107.47 ha yr^-1 from 2001 to 2024. Spatially, the landward zone gained 2010 ha through encroachment into high-tide areas and tidal channels, whereas the mangrove seaward edge retreating at an average rate of -1.54 m yr^-1. Although fluvial sediment discharge increased, mangrove responses were highly non-linear and spatially heterogeneous, indicating that localized sediment redistribution was strongly modulated by hydrodynamic processes. Southeasterly waves promoted seaward edge retreat and sediment resuspension, while seasonal northeastward currents likely transported part of the resuspended sediment into tidal channels, where mangrove colonization and sediment trapping promoted channel narrowing. This expansion may have reduced upstream tidal connectivity, contributing to the replacement of upper-channel mangroves by terrestrial vegetation. Our findings reveal a coupled hydrodynamic and bio-geomorphic mechanism governing mangrove redistribution in the Zambezi Delta, with important implications for managing mixed-energy deltaic mangrove systems.