Dynamics of Marsh‐Derived Sediments in Lagoon‐Type Estuaries

Carmine Donatelli,Xiaohe Zhang,Tarandeep Singh Kalra,Sergio Fagherazzi,Nicoletta Leonardi

doi:10.1029/2020jf005751

Abstract

AbstractSalt marshes are valuable ecosystems that must trap sediments and accrete in order to counteract the deleterious effect of sea level rise. Previous studies have shown that the capacity of marshes to build up vertically depends on both autogenous and exogenous processes including ecogeomorphic feedbacks and sediment supply from in‐land and coastal ocean. There have been numerous efforts to quantify the role played by the sediments coming from marsh edge erosion on the resistance of salt marshes to sea level rise. However, the majority of existing studies investigating the interplay between lateral and vertical dynamics use simplified modeling approaches, and they do not consider that marsh retreat can affect the regional‐scale hydrodynamics and sediment retention in back‐barrier basins. In this study, we evaluated the fate of the sediments originating from marsh lateral loss by using high‐resolution numerical model simulations of Jamaica Bay, a small lagoonal estuary located in New York City. Our findings show that up to 42% of the sediment released during marsh edge erosion deposits on the shallow areas of the basin and over the vegetated marsh platforms, contributing positively to the sediment budget of the remaining salt marshes. Furthermore, we demonstrate that with the present‐day sediment supply from the ocean, the system cannot keep pace with sea level rise even accounting for the sediment liberated in the bay through marsh degradation. Our study highlights the relevance of multiple sediment sources for the maintenance of the marsh complex.

Highlights

Salt marshes provide critical ecosystem services to coastal communities (Costanza et al, 1997)
Our findings show that up to 42% of the sediment released during marsh edge erosion deposits on the shallow areas of the basin and over the vegetated marsh platforms, contributing positively to the sediment budget of the remaining salt marshes
We have demonstrated that salt marsh resistance to sea level rise can benefit from marsh degradation as the latter can contribute to the local sediment budget, albeit in this specific test case marsh lateral erosion results in loss of habitat, as salt marshes cannot migrate landward given the high level of urbanization of the watershed

Summary

Introduction

Salt marshes provide critical ecosystem services to coastal communities (Costanza et al, 1997). Lateral marsh dynamics are strongly related to the rate of sea level rise and to the extension of nearby tidal flats (Fagherazzi et al, 2013; Mariotti & Fagherazzi, 2013a). Projections of coastal wetland response to sea level rise suggest a 20% to 50% reduction of the present‐day marsh area by 2100 (Craft et al, 2009; McFadden et al, 2007). These predictions raise concerns about the adaptive capacity of salt marshes to environmental change. A better understanding of the mechanisms governing salt marsh evolution is crucial to predict the future impact of sea level rise in coastal areas (Orson et al, 1985; Reed, 1995; Stevenson et al, 1985)

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