Mangroves: testing a natural water filtration system in Vietnam

In Vietnam’s Mekong Delta, efforts towards establishing  a nature-based filtration system to make aquaculture more sustainable and efficient are progressing. Two Dutch companies and one Vietnamese company have joined forces to use mangroves to address issues around groundwater extraction, water contamination and coastal protection in relation to shrimp farming.

The need for change in shrimp farming practices

Rogier Becker is an emerging market advisor at Larive International, a Netherlands-based company. He is a member of an initiative with Nienke Oostenbrink from Ocean Health, an initiative of the Dutch international marine contractor Van Oord and Minh Anh Tran Ng, representing RYNAN Smart Aquaculture, a Vietnamese company that recognizes the need for innovation in traditional shrimp farming in the Mekong Delta. Together, the three organisations have developed a model to transform conventional practices passed down from generation to generation.

From left to right: Rogier Becker, Nienke Oostenbrink and Minh Anh Tran Ng.

Coastal protection and mangrove destruction

Becker begins by explaining the need for change. “The coastal regions of Vietnam, particularly the Mekong Delta, are characterised by vast rice fields further inland and extensive aquaculture, primarily shrimp farming, nearer  the coast where the water is brackish. A natural belt of mangroves along the shoreline has played a vital role in preventing coastal erosion by trapping sediment and safeguarding the land.”

Water travels through various mangrove plots when flowing from aquaculture facilities to the river. These mangroves absorb nutrients from shrimp farming, using them for their own growth, creating a natural purification system. Over the years, many shrimp farmers have cleared parts of the mangrove belt to expand their operations. This deforestation has led to increased coastal erosion, shrinking the once-protective mangrove belt to a fraction of its former size.

Water pollution

“Another significant problem is water pollution”, Becker continues. “Upstream farmers use pesticides and other chemicals on their crops, which contaminates the Mekong River as runoff flows downstream. As the water continues its journey, it picks up additional pollutants from each subsequent farm, exacerbating the contamination. This is cumulative, creating a domino effect,” he explains, “leaving the farmers furthest downstream with severely degraded water quality, posing a serious challenge to the quality of the shrimp and the overall ecosystem.”

The TOMGOXY model

Becker, together with the other consortium partners, have been at the forefront of innovative technology.  Now known as the TOMGOXY model, this digital system for operating shrimp farms in a sustainable manner has resulted in more efficient use of resources and less negative impacts on the environment. This approach is supported by replanting mangroves and integrating them into farming systems.

Becker explains, “We’re exploring a combined approach of aquaculture and mangrove restoration, involving local farmers. While mangrove replanting is welcome, many restoration projects fail due to poor location selection and monoculture planting. Our process involves transplanting seedlings from nurseries to carefully chosen sites where suitable conditions for mangroves are generated, with the goal of creating a diverse ecosystem.” By carefully selecting and nurturing mangrove seedlings in nurseries before planting them pitfalls are avoided, ensuring a better chance of survival

Testing and preliminary results

Becker adds, “We’re in a testing phase, exploring opportunities and preparing to report on the results at the beginning of next year. Tests to assess mangrove growth and water purification will start soon. While the business model exists due to shrimp profitability, we’re still determining the optimal ratio of mangrove blocks to shrimp ponds for economic efficiency. Previous tests have confirmed mangroves’ purifying capabilities, but we’re now focusing on creating a circular system for water reuse. The difference between these methods lies mainly in the density of shrimp in the ponds and the amount of oxygen they need.”

Mangrove integration in other regions

In some Vietnamese regions, like Cà Mau, intensive shrimp farming is naturally integrated into mangrove forests. Shrimp are grown in nets within the mangroves, benefiting from the natural environment. However, the model under development now involves a more controlled method where shrimp are raised in tanks. The wastewater from these tanks, which contains nutrients like nitrate, is not immediately released into rivers. Instead, it is first filtered through plots of mangroves, which use the nutrients for their growth, helping to purify the water before it is released back into the environment.

Van Oord’s role: designing and testing

Nienke Oostenbrink, from Van Oord’s Ocean Health initiative, oversees the restoration initiative in Vietnam. “We collaborate closely with RYNAN, to strengthen their ‘TOMGOXY solution’, by adding the mangrove component to it. During testing at the demonstration site in Vietnam, we aim to gather valuable insights into the filtering capacity of mangroves in different set ups.”

While RYNAN implements the broader concept, Van Oord’s expertise lies in designing and testing how mangroves can naturally filter wastewater. According to Oostenbrink, the TOMGOXY concept allows for hyper intensive farming, producing high outputs per square meter. This reduces the need for land and makes space available for restoration of mangrove areas.

Studying mangrove filtration capacity

“We study the capacity of mangroves to absorb nutrients by pumping wastewater from the shrimp ponds into three different mangrove plots. The three plots have unique experimental conditions, allowing us to identify the most favourable conditions for nutrient uptake and mangrove growth. In order to obtain this information, the nutrients in the water and soil and health of the mangroves are closely measured. After the experimental phase, we have acquired the necessary knowledge of the filtration capacity of mangroves in combination with shrimp farming using TOMGOXY.”

The project is complex and will require about nine months of testing before definitive conclusions can be drawn. Even then, the scalability of this solution depends heavily on local conditions. Oostenbrink acknowledges that mangroves require specific environmental conditions to thrive, such as tide-induced flooding of and salinity levels. The design of the mangrove area and site conditions need to be tailored to the selected location.

Scalability and future goals

Ultimately, the success of this project depends on demonstrating that the mangrove filtration system is both effective and economically viable. “If so,” Oostenbrink states, “we will upscale from the current demonstration project to a larger pilot project, where a site needs to be selected and prepared for large scale filtration of aquaculture effluent by mangroves.” This will entail ongoing collaboration with local partners, insights from continued experimental testing and the development of a sustainable financial model. Partners for Water helped finance the initial feasibility study and Oostenbrink highlights how crucial this support was in getting the project off the ground.

RYNAN’s optimism

Minh Anh (RYNAN) embarked on this ambitious project in early 2024. She explains that the collaboration with Van Oord represents a significant development in the net-zero shrimp farming paradigm, lays out a strong foundation for maximising the effect of mangroves in reducing  the amount of gas emissions released from shrimp farming activity and also “seeks to overcome the limitations of relying solely on NGO and government funding for such initiatives.”

While RYNAN has been working on shrimp farms issues, the mangrove integration aspect is relatively new for them. Based on Van Oord’s specifications, RYNAN is preparing to collect data using advanced digital tools, including drones and a network of IoT devices that automate operations and assist in real-time measurement. The testing will involve monthly data collection to assess the effectiveness of the mangrove-shrimp farming system in terms of:

• Treating waste water from shrimp farming activities;
• Reduce the gas emissions amount from shrimp farming;
• Potential scale up to apply to wider range of shrimp farming/mangrove rehabilitation.

Challenges and concerns

In order to ensure the accuracy of the measurements, Van Oord also helped in surveying and conducting comparison experiments with natural mangrove sites. The project promises to not only resolve the environmental issues of the area, but also the social and economic problems faced by local farmers and agricultural funding.

While the team is optimistic about the project’s potential, they have identified some concerns. Minh Anh notes, “The project duration might be extended if turbulent weather conditions occur”. She also questioned the next step of scaling up the project amongst the local shrimp farming community, which farmers are not technically prepared for.

Conclusion

In summary, the model represents a significant departure from traditional shrimp farming methods, paving the way for a more responsible and productive shrimp farming industry.

Partners for Water in Vietnam

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