Combining participatory and GIS-based multi-criteria decision analysis for salt marsh restoration and rebuilding planning in the Venice lagoon

The Venice Lagoon has experienced a long-term decline of salt marsh habitats due to sediment deficit, morphological deepening, increased hydrodynamic exposure, and human-induced alterations to lagoon processes. Identifying suitable locations for restoration is therefore a key challenge for lagoon management. This study applies a participatory GIS-based Multi-Criteria Decision Analysis (S-PMCA) to support the spatial prioritization of salt marsh restoration and rebuilding within the framework of the WaterLANDS and REST-COAST projects. The analysis combined stakeholder knowledge with spatially explicit environmental information. An initial set of criteria was reviewed through a pre-workshop survey involving 21 stakeholders and subsequently refined during a workshop attended by 43 participants. The final analysis incorporated six spatial criteria: distance from canals, wind fetch, proximity to existing salt marshes, historical salt marsh loss, seagrass protection, and water quality. Criteria were transformed into standardized suitability layers and weighted according to stakeholder preferences. Distance from canals received the highest average importance weight (21.4/100), whereas water quality received the lowest (13.8/100). Suitability maps were generated using an Ordered Weighted Averaging (OWA) approach and combined with a bathymetry-based proxy of restoration costs to perform a spatial cost-effectiveness assessment. Priority restoration areas were identified along lagoon margins and near the Malamocco-Marghera Canal, where wave attenuation potential, ecological connectivity, historical marsh presence, and favourable implementation conditions converge. By combining stakeholder preferences with morphodynamic conditions, ecological factors, and implementation costs, this study supports the identification of restoration areas that are both feasible and strategically relevant in the Venice Lagoon.