Journal Article

Sediment Exchange Across Coastal Barrier Landscapes Alters Ecosystem Extents

Reeves, I. R. B., Moore, L. J., Fagherazzi, S., Valentine, K., Kirwan, M. L.

2023

Overview

Barrier coastlines and their associated ecosystems are rapidly changing. Barrier islands/spits, marshes, bays, and coastal forests are all thought to be intricately coupled, yet an understanding of how morphologic change in one part of the system affects the system altogether remains limited. Here we explore how sediment exchange controls the migration of different ecosystem boundaries and ecosystem extent over time using a new coupled model framework that connects components of the entire barrier landscape, from the ocean shoreface to mainland forest. In our experiments, landward barrier migration is the primary cause of back‐barrier marsh loss, while periods of barrier stability can allow for recovery of back‐barrier marsh extent. Although sea‐level rise exerts a dominant control on the extent of most ecosystems, we unexpectedly find that, for undeveloped barriers, bay extent is largely insensitive to sea‐level rise because increased landward barrier migration (bay narrowing) offsets increased marsh edge erosion (bay widening). Plain Language Summary Barrier coastlines consist of barrier islands or spits, salt marshes, bays, and mainland forest. To understand how the migration and change in size of one ecosystem influences the others, we develop a new computer model that simulates the exchange of sediment between all ecosystems. Using this model, we find that salt marshes adjacent to barriers are rapidly lost when the barrier migrates and its sediment is washed onto the marsh, but can potentially expand and recover when the barrier is not migrating. Additionally, we find that changing the rate of sea‐level rise in the model does not significantly change the size of the bay because the effects of sea‐level rise on barrier migration and marsh edge erosion offset each other. Our simulations suggest that these interactions among different ecosystems result in complex evolution of coastal barrier systems and can be a leading cause of change. Key Points Cross‐landscape interactions are explored in new model framework connecting entire barrier system from shoreface to mainland forest Simulations suggest barrier migration leads to rapid back‐barrier marsh loss, while barrier stability enables back‐barrier marsh recovery Bay extent is insensitive to sea‐level rise rates because of offsetting responses from barrier migration and marsh‐edge erosion processes

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: barrier / Barrier islands / Bays / coastal / Coastal evolution / Coasts / ecosystem / Ecosystems / Exchanging / Forests / Landscape / marsh / Marshes / Modelling / Salt marshes / Saltmarshes / Sea level rise / Sediment / Sediments / Soil erosion / Spits