Collaborative meeting of the CaSuLO project brings together scientists, local officials and the community
The Caldas da Rainha Municipal Library welcomed around thirty local stakeholders on July 23rd for the third collaborative meeting of the project CaSuLO - Between Exploitation and Conservation of Resources: Pathways to Sustainability in the Óbidos Lagoon. Local officials, researchers, shellfish harvesters, fishers, environmental associations and technicians from various entities sat at the same table to discuss the future of the Óbidos Lagoon, in a meeting that covered four main topics: sedimentation, seagrass meadows, water quality and lagoon governance.
Asked about sedimentation trends in the Óbidos Lagoon and possible solutions to control them, geologist Rui Taborda (Instituto Dom Luiz | FCUL) responded with another question: what is actually wanted for this ecosystem? To keep the lagoon fixed as it is today, or let it evolve naturally? The audience had no doubts, reaffirming that the essential thing is to keep the lagoon connected to the sea, preserving the economic and social benefits that this connection guarantees. Vítor Marques, mayor of Caldas da Rainha, went straight to the main challenge facing those managing the territory on the ground: reconciling tourism, fishing and sports with a lagoon that naturally tends toward sedimentation.
From the discussion came a concrete proposal: the continuous use of small dredgers, complementing large scale dredging works with cooperative funding between local entities and community funds. However, Helena Alves, from the Portuguese Environment Agency, noted that community funds do not usually cover regular maintenance, only one-off interventions, and suggested that lagoon management should be conceived as a true "mega-project," jointly led by the municipalities of Óbidos and Caldas da Rainha, capable of accommodating both small and large interventions.
Regarding the accelerated growth of seagrass meadows observed in the lagoon in recent years, biologist Ricardo Melo (MARE | ARNET | FCUL) explained that these habitats respond to environmental changes within a few months, much faster than might be expected. The most likely explanation is linked to nutrient abundance, sediment type and hydrodynamics, not to changes in salinity. The fact that nutrient-rich water stays longer in the lagoon due to sedimentation favors the growth of seagrasses.
It was precisely regarding nutrients that the discussion turned to water quality and shellfish contamination. "How can the water be considered good quality if shellfish harvesting is still banned?" asked a shellfish harvester in the room. Chemical engineer Carlos Vale (CIIMAR) and representatives from the Portuguese Environment Agency (APA) explained that the network classifying bathing water as "Excellent" measures the water column, not the sediment, and it is precisely in the sediment that the problem lies.
The bacterium Escherichia coli and other fecal contamination indicators settle in the sediment and can survive for days or weeks. Since shellfish live buried, they remain exposed to this contamination even when the surrounding water is clean. This is why water quality, sediment quality, and microbiological contamination of shellfish are three distinct parameters, assessed by different monitoring systems, which explains how an "Excellent" classification and a harvesting ban can coexist without contradiction.
The discussion closed on the topic of governance. Geographer João Ferrão (Institute of Social Sciences, University of Lisbon) posed the key question: "What use is a strategic plan if it never gets implemented?" He argued for a systemic view of the problems, integrated intervention and, above all, the ability to anticipate funding opportunities, pointing to available instruments that should be taken advantage of. As an example that it's possible to turn diagnosis into action, he cited the creation process of the Leça River Corridor, the first inter-municipal association formed in Portugal with the sole purpose of restoring a river, today responsible for the country's first Specific Water Management Plan.
The next participatory meeting of the project will take place on September 24th, marking the start of the process to define actions and concrete solutions for the Óbidos Lagoon Strategic Plan.
The CaSuLO project, which aims to build collaborative governance instruments for the Óbidos Lagoon, is funded by the Municipality of Caldas da Rainha, with support from the MAR 2030 Programme, and is carried out in partnership with the Municipality of Óbidos, MARE, through its units at the Faculty of Sciences of the University of Lisbon and the Escola Superior de Turismo e Tecnologia do Mar of the Polytechnic Institute of Leiria, the PATO Association, and APMALO, the Association of Fishers and Shellfish Harvesters of the Óbidos Lagoon.
Text by: Vera Sequeira and Maria João Correia
Photographs: see individual captions