Tom Buijse: professor by special appointment with a mission for healthy freshwater ecosystems

Background

Tom Buijse has been working at Deltares since 2008. Originally trained as a biologist, he obtained a PhD in fisheries biology and, from that background, became involved in freshwater ecosystem restoration and the European Water Framework Directive. Through this work, he has been involved for more than twenty years in European projects that contribute to the implementation of the Directive and the restoration of inland waters. In these projects, he examines the conditions required to make ecological restoration possible.

Alongside his work at Deltares, he also became appointed as Special Professor at Wageningen University & Research in 2020. He carries out this role one day a week alongside his work at Deltares, and the position is jointly funded by Deltares and the Sportvisunie (formerly Sportvisserij Nederland).

In Wageningen, he focuses on freshwater fish ecology, a subject that is closely linked to his work at Deltares. Fish is one of the biological quality elements within the Water Framework Directive. To assess water quality, we look not only at chemical aspects but also at ecological aspects such as algae, aquatic plants, macroinvertebrates and fish.

When it comes to fish, this depends on their life stage, Tom explains: “Eggs need to be in places with sufficient oxygen available. Then the small larvae, which move to places where the current is less strong otherwise they will be carried away by the flow. They need a place where they can find food, but also where they can shelter. As they grow larger, their natural predators change. Initially, these are aquatic organisms living, but this shifts, for example, to birds. All these life stages place demands on the habitat and these needs to have sufficient variation. We call this habitat diversity.”

The proof of the pudding

At Deltares, Tom mainly focuses on the restoration of freshwater systems. Questions include: is there sufficient habitat diversity? Are habitats well connected? And which restoration measures are needed?

To investigate whether these measures actually are effective, field research is required. Such research is carried out by PhD candidates from Wageningen under Tom’s supervision. “The great advantage,” says Tom, “is that the university offers the space and opportunity to conduct in-depth research on a subject for four years. Within Deltares we often do not have that opportunity within projects. That is why the two worlds complement each other so well. Wageningen offers specialist expertise and in-depth research. Deltares contributes system knowledge, practical experience and interdisciplinary collaboration.”

“Deltares isn't an institute that specialises in fish. We mainly focus on creating the right abiotic conditions. Creating the conditions that allow ecological restoration to take place. But for that, we need collaboration with other parties that possess more ecological expertise. That expertise exists in Wageningen. Partly within the university and partly within Wageningen Marine Research, with whom I also work very closely in this context.”

Tom explains it using the English saying “the proof of the pudding is not in the making, but in the eating: “The ‘making’ is, for example, creating side channels, and the ‘eating’ is looking at whether fish use them and whether we see ecological recovery taking place there.”

The two worlds complement each other well. Wageningen offers specialist knowledge and in-depth research. Deltares brings system knowledge, practical experience and an interdisciplinary approach to the collaboration.

Tom Buijse

Haringvliet sluices

One example of this collaboration is the project surrounding the Haringvliet sluices. This dam with sluices has been constructed to protect the Netherlands from storms coming in from the sea and to discharge river water. As a result of these sluices, the Haringvliet changed from an estuary (a transitional area where rivers flow into the sea) into a freshwater reservoir. Unfortunately, they thereby form a barrier for migratory fish that want to travel from the sea into the Rhine and Meuse rivers.

In 2018, a new management strategy was launched as part of an experimental programme: “Learning by Implementing the Haringvliet Sluices Ajar”. Two key questions played a central role:

• How can we allow controlled inflow of salt water into the Haringvliet without creating problems for its freshwater supply function?
• Do migratory fish benefit from the adjusted management strategy?

For this research, Rijkswaterstaat initiated two expert groups. One investigates the effects of saltwater intrusion caused by opening the sluices and the extent to which this remains manageable without jeopardising freshwater supplies from the Haringvliet (Salinisation). The other investigates whether and how migratory fish benefit from the adjusted management (Nature).

Once or twice a year, both groups come together to share experiences and new insights, which form the basis for optimising management strategies for both issues. Tom participates in the Nature expert group on behalf of Deltares. His colleague Wouter Kranenburg participates in the Salinisation expert group.

In addition, Melanie Meijer zu Schlochtern is carrying out a PhD project in Wageningen in which migratory fish (Atlantic salmon, sea lamprey, North Sea houting and sea trout) are equipped with acoustic transmitters. By attaching these transmitters to fish and placing receivers on Rijkswaterstaat buoys in both the Haringvliet and the adjacent delta, researchers can track when and under which conditions fish enter the Haringvliet. This research investigates whether the adjusted management strategy does improve fish migration.

Migratory fish populations in the Donube

Another important example is the European project Danube Lifelines. This project focuses on the restoration of migratory fish populations within the Danube River Basin. One of the project’s objectives is to remove barriers to fish migration, improve connectivity within the water system and restore habitats.

Tom collaborates with Wageningen University & Research through this project. One of the researchers, Panos Panagiotopoulos, whom he previously supervised as a PhD candidate and who is involved in the project, now works partly at Deltares and partly at the university. This allows him to make use of both Wageningen’s ecological expertise and Deltares’ knowledge of habitat modelling and river management.

Benefits for both organisations

A collaboration between two knowledge institutes such as this offers opportunities, expertise and possibilities for both parties. Tom explains: “At Wageningen, I can do things that are more difficult to initiate within Deltares. PhD candidates are given four years to immerse themselves fully in a subject. This generates knowledge that we can later use in our projects and models. In addition, this group of PhD candidates forms a potential source of future colleagues.

Conversely, through my experience at Deltares, I can help PhD candidates place their research within a broader context. At Deltares, we work in an integrated and interdisciplinary way. This allows me to help connect research results to societal challenges and practical questions.

For Wageningen, Deltares mainly contributes system knowledge and modelling expertise. An example is research into the living conditions of juvenile sturgeon in the Rhine, where we used models to analyse the river stretch from Cologne to the North Sea.”

Supervising PhD candidates

One of the aspects of his work that Tom particularly enjoys is supervising PhD candidates. “Since 2020, I have supervised eleven PhD candidates. Three have already completed their doctorates and one is about to submit his thesis.”

His professorship was extended last year. According to Tom, this happened without any discussion, both at Deltares and at the university: “I see that as confirmation that the collaboration is working well.”

The relationship he builds with his PhD candidates over the years is something that gives him a great deal of satisfaction: “Supervising PhD candidates goes far beyond providing scientific guidance. You support someone over a period of four years. That also involves a coaching role. The rewards of scientific research often lie far in the future. A first scientific publication may only appear after two or even two and a half years.”

How does he approach this role? “I try to build an open and approachable relationship with the PhD candidates. I see myself mainly a supporter in a role to help them grow throughout the PhD process. So far, no one has dropped out. Some people take a little longer than others, but overall things progress well.”

Learning from each other

Although Tom may be the supervisor, he also learns a great deal from his PhD candidates: “PhD candidates have enriched my knowledge enormously. They work with new analytical techniques, AI applications and research methods that I do not practice daily. I also learn a great deal from new technologies, such as the use of acoustic telemetry to track fish. By being involved in this kind of research over many years, you learn far more than if you simply listen to a presentation about the results. We deliberately try not to define research too rigidly. There must be room for new insights and innovation.”

Applying knowledge in practice

“An important personal motivation is ensuring that research results are actually used. That was already the case during my own PhD research in fisheries biology and it remains true today. The projects I work on should contribute to better water management, nature management, and fisheries management. We want to know which restoration measures work well, and which measures still need improvement. This knowledge is important for the Water Framework Directive, but also for the European Nature Restoration Regulation.”

“That applies to the projects we carry out at Deltares, but also to the PhD research projects that I supervise. Their purpose is to support water management, nature management and fisheries management with new knowledge.”

According to Tom, a project is only truly successful when knowledge is put into practice. “That is why, within PhD projects, we deliberately collaborate with water managers such as Rijkswaterstaat and the regional water authorities. You can see that they value the new insights and genuinely use them. That is what makes our work worthwhile.”