On October 14, 2024, the third meeting with stakeholders of the Venice Lagoon took place, organized by the Interregional Office for Public Works for Veneto, Trentino Alto Adige, and Friuli Venezia Giulia, CORILA, and CMCC as part of the H2020 REST-COAST project, in collaboration with the WaterLANDS project. REST-COAST focuses on restoring coastal ecosystems through Nature-Based Solutions (NbS), while WaterLANDS, with its emphasis on maintaining European wetlands, provides an ideal synergistic contribution to addressing the environmental challenges of the lagoon. The meeting aimed to define shared criteria for guiding the future priorities of the Venice Lagoon, integrating ecological, socio-economic, and landscape aspects.

During the workshop, environmental experts, institutional representatives, and local stakeholders collaborated to define a common vision for the lagoon, based on a morphological-dynamic balance capable of ensuring biodiversity, ecosystem services, socio-ecological resilience, and economic sustainability. The analysis of ongoing experiences, including interventions on saltmarshes in the central lagoon and environmental monitoring, provides essential knowledge for planning future actions. These include maintaining the lagoon’s forms and functions, counteracting marine intrusion, and optimizing sediment reuse.

Participants engaged a Participatory Multi-Criteria Analysis (PMCA) to identify priority areas for restoring saltmarshes in the lagoon. This analysis combines suitability assessments with spatial cost-effectiveness analysis, which was carried out collaboratively by the two European research projects, WaterLANDS and REST-COAST. The synergy between the projects and stakeholders allowed the integration of knowledge and expertise to address the complexity of managing the lagoon’s saltmarshes.

WaterLANDS contributed with a participatory and multi-criteria approach, while REST-COAST provided technical expertise on restoration and its network of stakeholders. This synergy enabled a comprehensive analysis of the issue, albeit at a preliminary level, forming one of WaterLANDS’ contributions that will have a lasting impact beyond the project’s duration and will serve as a foundation for future, more detailed activities, aimed at restoration interventions planned by REST-COAST.

Prior to the meeting, a questionnaire was sent out to gather input and suggestions from participants on the selected spatial criteria, resulting in a validated list of six criteria (Figure 1, where each box plot shows the distribution of values for each criterion, highlighting variability, mean values (X), and extremes).

Figure 1. Box plot of the six elicited spatial criteria, showing the outliers (dots), the median (line inside the box), the mean (X), and the interquartile ranges (IQR, represented by the box edges). The whiskers extend to 1.5 times the IQR from the first and third quartiles. Each criterion represents a key factor considered in the spatial analysis, including proximity to main channels, wind fetch, areas previously occupied by saltmarshes, presence of seagrasses, proximity to other saltmarshes, and the ecological status of water.

During the workshop, participants assigned weights to the selected criteria, expressing their opinions by constructing a “weight vector.” The “optimal distance from canals” was identified as the criterion with the highest weight. Subsequently, small heterogeneous groups of stakeholders discussed the best value function to assign to this criterion, associating a numerical score with each alternative. This approach allowed not only the representation of preferences for the selected criterion but also comparisons between different criteria, highlighting the complexity and uncertainties in synthesising diverse situations (e.g., the speed or size of ships navigating the canals) and pursuing multiple objectives, such as reducing erosion risks, protecting biodiversity, and minimising costs.

The final maps (Figure 2), developed after the workshop, are based on the results obtained through the PMCA and by integrating all six criteria (previously presented in Figure 1). Figure 2a identifies the areas with varying levels of suitability for saltmarsh restoration (from 0 to 1 as priority increases). These data were then integrated with preliminary cost estimates for saltmarsh restoration based on a proxy of the costs using the bathymetry to generate clusters of areas with similar cost-effectiveness ratios (Figure 2b). To facilitate the use of our results for orienting future restoration investments, we carried out a spatial cluster analysis of the maps produced so far and generated a preliminary zoning of suitability, which allows to identify the areas of greater interest for wetland restoration. The results reported in Figure 2b highlight distinct spatial clusters with varying cost-effectiveness for saltmarsh restoration investments. Cluster 1, covering 11,760 hectares, is the lowest-performing area, characterized by high costs and proximity to canals. Cluster 2, spanning 5,439 hectares, shows potential conflicts with existing seagrasses but benefits from limited fetch risk and good water quality. Cluster 3, with an area of 10,916 hectares, demonstrates intermediate performance due to favourable MCA values but higher costs. Finally, Cluster 4, encompassing 7,261 hectares, achieves the highest cost- effectiveness, combining excellent MCA performance with lower costs, making it the most suitable zone for future restoration investments. This map can thus be considered as a preliminary attempt of zoning areas with different levels of priority (dark green representing high priority areas).

Figure 2. Maps developed with the elicited weights from the stakeholders showing: a) Suitability index for saltmarsh restoration, derived from the elicited weights obtained during the workshop. Areas in red represent higher suitability for restoration, while dark blue areas indicate lower suitability. The analysis integrates multiple spatial criteria to prioritize locations for effective restoration efforts. b) Cost-effectiveness clusters.

The subsequent session that morning focused on defining pathways for climate change adaptation. During the workshop, stakeholders contributed to defining a future vision for the Venice Lagoon and strategies to achieve it. This exercise forms the basis for evaluating large-scale transformations, moving beyond pilot sites, and developing climate adaptation pathways aimed at analysing the impact of restoration on risk reduction across the entire lagoon.

Adaptation pathways are an essential part of adaptation plans. They are based on identifying objectives, constraints, and uncertainties relevant to decision-making to outline a series of plausible futures. This session focused on developing climate adaptation pathways for the Venice Lagoon with active stakeholder involvement. Through participatory discussion, strategies were explored to integrate saltmarsh restoration with long-term measures for climate risk mitigation. This exercise highlighted the need for a systemic approach, considering not only pilot sites but the entire lagoon ecosystem.

Stakeholders emphasized the importance of key objectives, including:

• maintaining the lagoon’s morphological forms and functions and adapting the system to climate change;
• enhancing ecosystem services and biodiversity;
• promoting economic development compatible with landscape protection and the sustainable use of the environment and territory.

Proposed interventions during the workshop included a combination of nature-based solutions, such as saltmarsh restoration and sediment reuse optimization, as well as governance initiatives and environmental education and awareness programs. The outcomes will serve as an important foundation for developing scenarios through modelling to evaluate the large-scale impact of restoration on the lagoon’s resilience in a climate change context.

Figure 3. Ranking of the strategic objectives derived from the desired future, the ranking reflects priority but acknowledges that objectives may intersect and influence each other due to their shared vision established in the desired future.

This third stakeholder workshop marked a crucial step toward defining shared strategies for the future of the Venice Lagoon, integrating diverse experiences, expertise, and perspectives, and promoting a common declaration of intent to ensure an inclusive and transparent decision-making process.

Based on the day’s discussions, the vision for the future of the lagoon is:

“A resilient socio-ecological system, which offers ecosystem services and supports biodiversity, safety and health, continuously adapting to climate change, ensuring sustainability, protection of the landscape and its usability”