High surface elevation gains and prediction of mangrove responses to sea-level rise based on dynamic surface elevation changes at Dongzhaigang Bay, China

Abstract

Mangrove forest responses to sea-level rise (SLR) are likely misestimated in many studies because current assessment methods often assume a constant rate of surface elevation change along the intertidal profile. Most studies also neglect the ecogeomorphic feedback process known to accelerate soil building with SLR. Here, an empirical, dynamic model that accounts for the above processes is constructed for the intertidal zone of a mangrove bay in Hainan, China. The model allows us to explore the response of a tide-dominated mangrove forest to different rates of SLR. Rod surface elevation table-marker horizon (RSET-MH) data (2015–2018) indicate rather high rates of surface accretion (13.3–57.9 mm yr−1) and surface elevation changes (7.9–35.5 mm yr−1). Surface accretion and surface elevation change decreased exponentially with increasing ground elevation. Our model showed that SLR (at rates of 4 and 16 mm yr−1) would not lead to the loss of mangrove cover but that it could alter mangrove species zonation along the intertidal profile by 2100 due to a rich sediment supply and ecogeomorphic feedback. Importantly, rapid SLR and landward barriers can pose a considerable threat to the high-intertidal community by causing increased inundation of the high-intertidal zone, subsequent shifts in species zones, and the loss of mangrove biological and structural diversity along the intertidal profile. Overall, this study predicts probabilities of habitat suitability for mangrove species under SLR and expands our current understanding of the impacts of SLR on tide-dominated mangrove forests in sediment-rich systems. Incorporation of extensive, long-term RSET data into this kind of dynamic model could contribute to the better prediction of mangrove responses to SLR at large scales in the future.