Cross-case review identifies five building blocks for scaling European freshwater restoration

A cross-case review of 18 European freshwater restoration demonstration cases has identified five interdependent building blocks for scaling Nature-based Solutions: comprehensive status review, narratives of the future, an evidence-informed approach, resource management and stakeholder engagement. The review synthesises experiences from the EU Horizon 2020 MERLIN project rather than reporting results from a single controlled experiment, and its authors caution that the framework offers practice-relevant insights without claiming empirical generalisability.

MERLIN brought together 47 partner institutions to support restoration in rivers and catchments, peatlands, wetlands and floodplains. The demonstration cases extended from northern Finland to southern Portugal, from the British Isles to the Northern District of Israel, and included wetland rewetting, barrier removal, floodplain reconnection, river engineering and educational or stakeholder initiatives. Each site used a transdisciplinary “living lab” approach involving practitioners, researchers and local stakeholders.

The project embedded its actions within existing long-term restoration processes rather than treating demonstration interventions as isolated activities. During the 4.5-year project period, the cases sought to reinforce and accelerate pre-existing initiatives while connecting them with local strategies, governance systems and visions for socio-ecological change. The review describes the building blocks as interdependent functions that should be addressed in parallel and revisited iteratively, with stakeholder engagement underlying all stages rather than functioning as a final step.

The first two building blocks concern diagnosis and planning. A comprehensive status review requires assessment of ecological conditions alongside stakeholder interests, institutional constraints and potential entry points for action. MERLIN teams used stakeholder mapping, harmonised SWOT analyses based on the IUCN Global Standard for Nature-based Solutions, and Theory of Change workshops. At a wider scale, the project also combined ecological status, species distributions, ecosystem-service delivery, human pressures and enabling factors at the resolution of River Restoration Units to map potential restoration priorities across Europe.

Narratives of the future link local objectives to broader policy ambitions. Representatives in each demonstration case collaboratively developed Theory of Change pathways describing how specific measures were expected to contribute to longer-term outcomes for biodiversity, climate resilience and societal well-being. These qualitative pathways were complemented by scenario modelling. In the Rhine floodplains, an integrated ecosystem-service analysis compared three restoration strategies. The narrow benefit–cost ratio, including agricultural yields, flood protection and navigation, was 1.00, 0.10 and 0.03 for the three scenarios, respectively. When carbon sequestration, nutrient retention, recreation, amenity, bequest and existence benefits were also included, the broad ratios were 0.25, 0.87 and 1.27. The most ambitious “Room for Living Rivers+” scenario included 74 km of dyke relocation, 118 km of side channels and conversion of all floodplain land use from agriculture.

The third building block requires evidence to inform adaptive action. MERLIN developed a monitoring framework with 13 criteria covering environmental, social and economic domains, including biodiversity net gain, climate regulation, job creation, inclusive governance and the circular economy. Essential Restoration Variables included species richness, water-storage capacity, greenhouse-gas emissions, stakeholder representation and financial leverage. Across the 18 cases, reported activities included reconnecting 287 km of rivers and rewetting 1,528 ha of floodplain or peatland habitat. Some cases also reported increased recreational access, local employment and stakeholder engagement, although data were more limited for some sectoral criteria.

Monitoring also identified trade-offs rather than uniformly positive outcomes. In some wetland cases, rewetting initially increased pollutant mobilisation, while agricultural land conversion conflicted with food-production goals. The review therefore describes an evidence-informed approach that combines systematic monitoring and impact evaluation with expert judgement and contextual understanding. This reflects the difficulty of demonstrating linear causality within project time frames and the potentially different effects of the same intervention under different biophysical, governance and stakeholder conditions.

Resource management addresses the stable and diversified resourcing required for landscape-scale restoration. The review cites an estimated annual funding gap of €8–25 billion for meeting EU policy targets. Public instruments such as LIFE, Common Agricultural Policy eco-schemes and national green-infrastructure programmes remain important, but many support three- to five-year project cycles and involve administrative complexity. MERLIN teams reported limited experience with private finance, uncertainty about ecological alignment and difficulty articulating viable business models. A four-pillar financial framework addresses project planning and engagement, cost-benefit assessment, funding and revenue diversification, and alignment with long-term goals. Cases supported by planning mandates, policy integration or dedicated public staffing reported greater leverage in securing resources and scaling action, although the review does not establish a general causal effect.

Stakeholder engagement is presented as a structural condition for durable restoration. A justice analysis covering representation, procedure and distribution found that public actors dominated many processes, while community groups, smallholders and marginalised actors were comparatively less involved and power asymmetries persisted. MERLIN developed sectoral strategies with agriculture, hydropower, insurance, navigation, peat extraction and water supply, identifying evidence gathering, dialogue, capacity-building, enabling policy and investment as common actions. Several teams reported that engagement consumed at least a third of their working hours. The review concludes that the five-part framework is a translation tool for practitioners, policy-makers and funders, not a uniform template: its usefulness depends on adapting the blocks to local ecological, institutional and social conditions and sustaining action beyond project cycles.

Subject of Research: Cross-case review of place-based strategies for scaling freshwater ecosystem restoration through Nature-based Solutions.

Article Title: Building blocks for upscaling freshwater ecosystem restoration: Place-based strategies for a transdisciplinary challenge

Article References: Birk, S., Anzaldua, G., Baattrup-Pedersen, A., Bérczi-Siket, A., Blackstock, K., Buijse, T., Carmen, E., Carvalho, L., Garcia, X., Gerner, N., Grondard, N., Hernandez Herrero, E., Ibrahim, A., Kok, S., Lenz, M.-I., Nyírő, F., Okruszko, T., Penning, E., Pott, L., … Hering, D. (2026). Building blocks for upscaling freshwater ecosystem restoration: Place-based strategies for a transdisciplinary challenge. Nature Conservation, 62, 261-287. https://doi.org/10.3897/natureconservation.62.148938

Image Credits: AI Generated

DOI: 10.3897/natureconservation.62.148938

Keywords: freshwater restoration, Nature-based Solutions, MERLIN project, ecosystem restoration, stakeholder engagement, adaptive management, environmental monitoring, restoration finance, European Union, Building, blocks, upscaling