Sediment addition to address tidal marsh elevation deficits caused by farm impoundments: a Delaware Bay, New Jersey, <scp>United States</scp> case study

Abstract Introduction Dredge material use is emerging as an important technique for restoring marshes threatened by historic mismanagement and sea‐level rise, yet optimal methods to maximize ecological benefit remain under development. The Delaware Estuary is in urgent need of restoration, as historic agricultural conversion caused substantial and persistent elevation loss. Objectives We conducted a pilot project in a previously restored marsh where elevation deficits continued to inhibit revegetation. Using material from maintenance dredging of tidal channels, we elevated a 0.4 ha site contained with coir logs to create conditions conducive to plant recolonization and long‐term recovery. Methods Dredging occurred from Fall 2018 through March 2019, with sediment pumped into containment to raise elevations to a target of 0.5–0.7 m NAVD88 (just below MHW). Elevation and vegetation were monitored before, immediately after, and across five growing seasons following construction. Results Target elevations were achieved, producing a mean post‐construction elevation of 0.54 m (0.53–0.56, 95% CI), a 0.42 m increase from pre‐project conditions. Vegetation cover rose from 55 to 86% by the second season and reached 100% by year 5, despite 0.1 m of settling. Areas 50–100 m outside the containment also gained elevation and vegetation, indicating localized sediment dispersal. Previously vegetated zones that received material did not settle and instead showed increasing elevation across all five seasons. Conclusions This project demonstrates that integrating hydrological restoration with sediment addition can restore optimal elevations for Spartina alterniflora and accelerate vegetation recovery in degraded mid‐Atlantic marshes.