Sediment deposition affects mangrove forests in the Mekong delta, Vietnam

Enhanced deposition is common near river mouths where large amounts of sediment is available. Our study focuses on the effects of sediment deposition on a mangrove forest in the Mekong river delta, Vietnam. At this site, the mangrove forest fringe is characterized by Sonneratia spp. and both mud and sand are present. High deposition rates bury mangrove roots and pneumatophores, causing forest dieback. Field measurements indicate that dead trees in a ghost forest have roots buried in about 1.20 m of sediments, while surviving trees have a typical root depth of 0.6 m. Saplings revegetating the dieback area have a root depth around 0.2 m. Root depth is further related to forest basal area and number of pneumatophores per square meter. Sediment burial covers the pneumatophores smothering the mangroves roots and decreasing the health of the forest. Remote sensing images indicate that the dieback occurred in 2014, with a sharp drop in Normalized Difference Vegetation Index (NDVI). The forest partly recovered in the following 5 years reaching the NDVI value of 2013. Our study is adding a new understanding of the coupling between mangrove forest evolution and sediment transport in tropical deltas.

Automated summary

Enhanced deposition near river mouths affects mangrove forests in the Mekong river delta, leading to forest dieback. The burial of sediment covers pneumatophores, decreasing the health of the mangroves. However, the study also shows that the forest partly recovers after a period of dieback.