Elevation, drainage, and spatially heterogeneous vulnerability of tidal marshes to sea level rise

Abstract

AbstractMarsh plants regulate marsh surface elevation through organic matter accumulation and sediment capturing, thus feedback loops and relationships between vegetation and marsh elevation form the basis of numerical models that estimate and predict marsh vulnerability to Sea Level Rise (SLR). However, with interior portions of shallow-sloping microtidal marshes suffering much more extensive inundation relative to edge marshes, it is necessary to identify factors in addition to elevation that create spatial heterogeneity in flood vulnerability. Here we studied the influence of drainage on vulnerability of the marsh interior and the marsh edge. Specifically, we compared the deviation ofin situobserved hydrological metrics for surface (hydroperiod, daily inundation duration) and subsurface (soil saturation index, or SSI) soil levels of interior and edge marsh from expected values estimated using elevation and tidal regime alone. We further analyzed the bias that hydrological deviation introduced to marsh vulnerability estimation using growth response curves of typical marsh macrophytes to hydroperiod. We found that the water table fluctuation was attenuated from marsh edge to interior, which resulted in a higher sensitivity of interior marsh to elevation deficiency. At the brim of marsh collapse in the marsh interior, hydroperiod and SSI increased dramatically; they were 20-50% higher than at the same elevation at the marsh edge, which greatly reduces the window of opportunity for interior marsh plant communities to adapt to SLR. Our findings demonstrate the importance of drainage in explaining spatial patterns in vulnerability across the marsh platform, which should be considered in future empirical studies and numerical simulations to develop practical tools for coastal management.