Impact of mangrove age on sediment retention and wave dissipation and its links to ecosystem services in the Red River Delta, Vietnam

Mangroves provide critical ecosystem services that support livelihoods and communities at the coastal margin. They are key natural flood defences to tropical cyclone driven storm surges, they store sediment that is vital for maintaining delta surface elevations in the face of rising sea levels, and transfer key nutrients to agricultural land. Over the past few decades, stressors on mangroves have increased with associated declines in global areal extent, and growing concern about their condition, including for forests that have been restored or afforested. Most remaining mangrove forests comprises a mix of ages and quality. Limited research exists exploring how differing age, structure and health of mangroves impacts sediment retention and aids the dissipation of wave and storm energy, and links these physical processes to the delivery of ecosystem services.

In this study, we demonstrate how mangrove age and health differentially impacts rates of sedimentation, attenuates water level and tidal propagation and aids storm energy dissipation along a section of mangrove forest in Thai Binh province on the Red River Delta in Vietnam. Data were collected over a four month period and highlight spatially variable responses to tides and the increasing influence of the nearby Thai Binh River. We show that sedimentation rates vary from 0.8 m/yr to 0.14 m/yr with increasing distance inland, whilst peak tidal range varies from 1.5 m to 0.5 m with mangrove age. We demonstrate that these spatial patterns correlate not only to distance inland, but also mangrove age, and the provision of ecosystem services as recorded by household surveys from local communities. This highlights the need for global mangrove databases to account for mangrove quality and health data in order to capture definitively the ecological, hydrodynamic and sedimentological impacts of mangrove forests on coastal and deltaic regions.