Search for: All records

Abstract Complex coastal ecosystems require management that addresses interacting stressors affecting ecosystem size and persistence. In natural systems, lateral erosion of salt‐marsh edges and mudflats is thought to enhance vertical resilience to sea‐level rise (SLR) by augmenting sediment delivery to the marsh platform. Using the Coastal Landscape Transect model, we test how two common restoration practices, shoreline stabilizations and thin‐layer placements, affect vertical and lateral resilience of marshes under accelerating SLR. We find that shoreline stabilization provides optimum restoration at low rates of SLR, but in later years, as SLR accelerates and losses from drowning supersede those associated with edge erosion, thin‐layer placement imparts a higher degree of marsh resilience. Furthermore, stabilizing the marsh edge eventually facilitates threshold responses to SLR with sudden and extensive narrowing of the marsh due to interior drowning. However, contrary to expectations, results suggest that vertical‐lateral couplings fail to meaningfully counteract drowning with a 1 m yr⁻¹increase in edge erosion delaying initiation of interior drowning by <3 years. Finally, we propose “volumetric elevation capital” as a metric that allows for the assessment of marsh health across multiple dimensions, thereby avoiding drawbacks otherwise associated with threshold responses to management interventions. 

Abstract Landward migration of coastal ecosystems in response to sea-level rise is altering coastal carbon dynamics. Although such landscapes rapidly accumulate soil carbon, barrier-island migration jeopardizes long-term storage through burial and exposure of organic-rich backbarrier deposits along the lower beach and shoreface. Here, we quantify the carbon flux associated with the seaside erosion of backbarrier lagoon and peat deposits along the Virginia Atlantic Coast. Barrier transgression leads to the release of approximately 26.1 Gg of organic carbon annually. Recent (1994–2017 C.E.) erosion rates exceed annual soil carbon accumulation rates (1984–2020) in adjacent backbarrier ecosystems by approximately 30%. Additionally, shoreface erosion of thick lagoon sediments accounts for >80% of total carbon losses, despite containing lower carbon densities than overlying salt marsh peat. Together, these results emphasize the impermanence of carbon stored in coastal environments and suggest that existing landscape-scale carbon budgets may overstate the magnitude of the coastal carbon sink.