Sea-levels have been rising at a faster rate than expected. Because of the maladaptive outcomes of engineering-based hard coastal protection infrastructure, policy makers are looking for alternative adaptation approaches to buffer against coastal flooding—commonly known as nature-based coastal adaptation (NbCA). However, how to implement NbCA under an institutional structure demonstrating ‘inertia’ to alternative adaptation approaches is a question that seeks scientific attention. Building on a case study derived from a highly climate-vulnerable Canadian province, this study shows how the entrepreneurial use of scientific information and institutional opportunities helped institutional actors overcome the inertia. Drawing on secondary document analysis and primary qualitative data, this study offers five key lessons to institutional actors aiming at implementing NbCA: (i) develop knowledge networks to help avoid uncertainty; (ii) identify and utilize opportunities within existing institutions; (iii) distribute roles and responsibilities among actors based on their capacity to mobilize required resources; (iv) provide entrepreneurial actors with decision-making autonomy for developing agreed-upon rules and norms; and (v) facilitate repeated interactions among institutional actors to develop a collaborative network among them. This study, therefore, helps us to understand how to implement a relatively new adaptation option by building trust-based networks among diverse and relevant institutional actors.

Introduction: Tidal wetland restoration in the Bay of Fundy involves restoring tidal hydrology to sites with tidal restrictions. Most have focused on salt marsh sites close to the mouth of estuaries, but there are also many tidally restricted wetlands closer to the freshwater end of tidal rivers. Recovery of salt marsh vegetation has been rapid in past projects, but little is known about sediment and vegetation dynamics post restoration in tidal brackish or freshwater environments.Methods: We implemented tidal wetland restoration projects on two tidal rivers near the inland limit of saltwater. Hydrological restoration involved breaching (St. Croix) or realigning agricultural dykes (Belcher Street). We monitored hydrology, sediment accretion and vegetation at replicated plots on restoration sites and nearby reference tidal marshes; and conducted habitat mapping and elevation surveys using drones.Results: After re-establishing tidal flow, sediment accretion was very rapid, leading to a deep layer of new sediments. Plant colonization at both sites resulted in a high diversity of halophytes in the first 2 years post restoration, but the St. Croix site transitioned to freshwater wetland species dominating by the fifth year post- restoration. The Belcher St. site has a mix of freshwater and brackish wetland species after the fourth-year post-restoration.Discussion: High suspended sediment concentrations at both sites suggest that each site was positioned closed to the estuarine turbidity maximum within its river. Tidal wetland restoration at the head of estuaries may benefit from the large ecological disturbance associated with rapid sediment accretion, providing a productive substrate with little competition from prior vegetation. However ultimate vegetation patterns may take longer to develop as elevation gains alter tidal flooding frequency. Low salinities suggest that the physical disturbance of sediment burying prior vegetation is the main mechanism creating a clean slate for plant recolonization, rather than mortality of terrestrial vegetation due to salt water. The majority of elevation change was due to allochthonous sediment deposition, with belowground processes playing a minor role. The wetlands restored showed substantial net elevation gains in the first years following tidal hydrological restoration, but long-term monitoring is required to track their overall resilience in the face of sea level rise.

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.