Eelgrass and seaweed in large-scale efforts for the Danish coastal waters

In a little while, DTU Aqua will take the first solid step into a large-scale national effort to improve the marine environment in the Danish coastal waters, when this autumn the researchers deliver their first part of the package to the Ministry of the Environment: A comprehensive body of knowledge of conditions for marine agents such as eelgrass and seaweed as well as methods for calculating the properties of eel grass and seaweed as a climate change agent.

This first delivery is part of a new major research project that the Ministry of the Environment has launched with funds from the political agreement on the green transformation of Danish agriculture. Here, the politicians set aside 34 million. DKK for development initiatives for marine instruments.

In the ministry's research project, the aim is to find evidence of whether eelgrass and seaweed can remove nitrogen from the sea.

"Previous studies have indicated that eelgrass and possibly also the cultivation of seaweed can contribute to improving the environmental quality and biodiversity in coastal waters. We look forward to testing and substantiating our hypotheses and documenting to what extent and also in which coastal waters the means of action can contribute to improve the state of the environment," says head of DTU Aqua's involvement in the project, Professor Karen Timmermann.

The research in the project must be carried out in collaboration between the Danish institutions SDU, AU, DHI, KU and DTU, each of which has a lead on different parts of the project.

DTU Aqua's task is specifically to grow seaweed on a large scale in the Limfjord and map areas with opportunities to re-establish eelgrass and cultivate seaweed in the Danish coastal waters and assess the possible effects on the marine environment.

The nitrogen target

The newly established eel grass and seaweed will benefit the wildlife, i.e. biodiversity, in the sea and in that sense contribute to the nature restoration part of the project. At the same time, the researchers must then examine the ability of marine plants to remove nitrogen and phosphorus in the sea and look at effects on biodiversity.

"If we find evidence that eelgrass and seaweed can be used to capture and store CO2, then eelgrass and seaweed can possibly also be used as climate change agents," says Karen Timmermann.

One of the most important things to succeed with the project and improve the environmental condition of the coasts is to achieve the goal of reducing the discharge of nutrients into coastal waters.

In the broad political agricultural agreement from last autumn, the parties agreed to reduce nitrogen emissions by 10,800 tonnes of nitrogen in 2027.

The Ministry of the Environment summarizes the background for making efforts to reduce nitrogen like this: "When nitrogen is spread as fertilizer on the fields, part of what is not taken up by the crops can be washed out and end up in the water environment. Here, nitrogen also acts as fertilizer – just for the algae. Too much algae in the water can result in oxygen depletion, which can kill plant and animal life on the seabed.”

"This is a really important project to get started on, because even if the target for reducing nitrogen is achieved, it will take time before Danish coastal waters achieve a good ecological condition - natural restoration does not happen overnight," says Karen Timmermann.

Bad light

'Good ecological condition' is the official term for a healthy marine environment - and it is precisely not a term we can use for Danish coastal waters these days.

Algae growth is too high, eelgrass and macroalgae, i.e. seaweed, cannot grow at a sufficiently large water depth due to lack of light, and the species composition of benthic animals is too low. Therefore, according to Karen Timmermann, the environmental quality in the Danish coastal waters does not meet the water framework directive's requirements for good ecological condition.

It is therefore not in all places that the light conditions are good enough to plant eelgrass and grow seaweed. So the researchers must also examine interactions between environment, survival success and growth rates.

Status 23/24 and possible expansion of the eelgrass/kelp project

The results of the research project must be included when the ministry in 2023 and 2024 takes stock of how the effort to reduce nitrogen is going. Here the politicians must assess how a possible remaining efforts must be organized and whether efforts with eelgrass and seaweed can be extended to more places in the country.

Photo by Mikael Van Deurs