From local-to global-scale control factors of wave attenuation in mangrove environments and the role of indirect mangrove wave attenuation

Abstract

Wave dissipation by drag forces is considered the dominant wave transformation process in fringe mangroves even though other process may be present. Furthermore, mangrove loss generates vertical erosion and changes in the nearshore profile that can affect wave breaking, whereas changes in vegetation density owing to species composition or disturbances may affect drag dissipation. The aim of this study is to identify local and global geographical control factors of wave attenuation in mangrove environments and to assess the effect of nearshore profile modifications by mangrove loss on wave breaking dissipation. Bottom wave attenuation from breaking and shoaling, the total wave energy attenuation rate, and wave reflection were estimated using modeling, pressure sensors, and reflection coefficients, respectively, at sites with contrasting wave power, bathymetric slope changes, vegetation density, and logging disturbance. Wave breaking changes by mangrove loss were estimated using wave evolution modeling under three successive slope increments by 0.7% in two background mangrove nearshore profiles. The wave energy attenuation rate at the study sites was affected by incident wave height (28–76%), epiphytic oyster presence, vegetation density, tidal inundation (41–55%), and wave reflection from cliffs. The last two variables explained the wave attenuation rate variability at a cliffed study site (61–70%), whereas the last three variables explained the wave attenuation rate variability on a global scale (92%). Wave attenuation rates by vegetation and bottom friction were underestimated (2–59% from global scale data) when wave shoaling was not considered. The wave energy increased or moved further inland in unvegetated scenarios in comparison with vegetated shores. In addition to drag forces, mangroves can promote wave attenuation by inducing friction, wave breaking, and wave reflection from prop-roots epiphytic organisms, shallow nearshore profiles, and cliffed edges, respectively.