Legacy Vegetation and Drainage Features Influence Sediment Dynamics and Tidal Wetland Recovery After Managed Dyke Realignment

Managed dyke realignment (MR) is a nature-based technique that shifts dyke systems farther inland, allowing for restoration of tidal flow and tidal wetland vegetation. While restoration of tidal flow can result in rapid sediment accretion and vegetation recovery, dykelands on the east coast of Canada are often agricultural, with legacy vegetation and ditches present upon initiation of MR. We combined measurements of sediment flux and accretion, digital surface and drainage network models, and vegetation mapping to understand the effects of legacy features on geomorphological evolution and restoration trajectory at a Bay of Fundy MR site. Removal of legacy vegetation and channels in a borrow pit allowed comparison with unaltered areas. Magnitudes of volumetric change from erosion at the channel mouth were similar to gains on the borrow pit, suggesting that channel mouth erosion could represent a significant sediment subsidy for restoring the marsh platform. Pre-existing pasture vegetation is likely to have slowed wetland vegetation establishment, suggesting that mowing prior to MR may speed recovery. Repeated high resolution vertically precise aerial surveys allowed understanding of the effects of elevation and proximity to the drainage network on spatial and temporal variability in marsh surface elevation increase and vegetation recovery.