The role of vegetation on sediment transport in a macrotidal fringe mangrove forest

Abstract

Mangroves are globally distributed ecosystems that provide numerous ecosystem services. They act as natural barriers along coastlines, mitigating the impact of waves and tidal forces. In doing so, they play a crucial role in controlling erosion and providing various resources for local human populations. The eastern sector of the Amazon coastal zone boasts the world's longest continuous mangrove belt, covering approximately 8000 km². The regional dynamics are intense due to persistent Northeastern trade winds, associated wave climate, and a macrotidal regime, all of which shape the fringing mangroves responsible for coastal protection, sediment stabilization, and biodiversity. This study, therefore, assesses the extent of tidal current attenuation by fringe mangroves and its consequent influence on sediment transport and deposition. Current meters, pressure sensors/data loggers, and turbidity meters were deployed at three points along a transversal transect. The composition and structure of the mangrove forest along the transect were also investigated, using saltmarsh beds (Spartina alterniflora) as the proximal Station P1 and the mangrove forests (Laguncularia racemosa, Avicennia germinans, and Rhizophora mangle) as the intermediate and distal Stations P2 and P3, respectively. Our findings indicate a direct correlation between vegetation density and flow attenuation. An integrated analysis reveals an ebb-dominant flow pattern, where transport from the mangrove forest to the tidal channel predominates, contributing to observed mangrove progradation. Understanding sediment dynamics and balance in mangrove forests is key to managing coastal ecosystems in a scenario of sea-level rise. Our findings reinforce how critical sediment supply is for fringing mangrove areas.