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what this project was about

The project "Sustainable method to reduce the leakage of phosphorus from fish farms" was carried out during February 2023 - March 2024. The project partners were Stockholm University (Department of Ecology, Environment and Botany – DEEP), Levande Hav Ab, Ålands Fiskodlarförening r.f. and Invenire Ab.

​This project tested the use of activated limestone to bind phosphorus in nutrient-rich sediment samples from the Baltic Sea in a lab environment. Activated limestone was found to be effective in stopping phosphate release from these sediments, thereby potentially reducing eutrophication.

The project was financed by the Nordic Council of Ministers, the Nordic Working Group for Oceans and Coastal Areas (NHK)


what we did in the project

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​In the project, the researchers at Stockholm University took water and sediment samples next to Åland fish farming sites and conducted laboratory tests to study the effectiveness of different doses of activated limestone to bind phosphorus in these samples. They then treated the nutrient-rich fish farm sediment with activated limestone in a lab experiment and showed how activated limestone can stop phosphate release from these nutrient-rich sediments, thereby potentially reducing eutrophication.

You can read more about the research and the results in the project report.

what is activated limestone?

Activated limestone is a newly developed product that is produced from marl, which is a by-product of the mining of lime, and contains over 90% calcium carbonate (CaCO₃). Activated limestone can bind phosphorus in seas and lakes, and its phosphorus uptake is more than 500 times higher than that of the original marl. Activated limestone is dispersed as particles at the water surface, after which it sinks to the bottom to bind phosphate in the sediment. This process reduces the availability of phosphorus in the water, which in turn reduces the growth of algae and other plants. Adding activated limestone to a lake or inland sea to bind phosphorus is not harmful to the ecosystem, and plants and animals can continue to live in these areas. Activated limestone is relatively cost-effective compared to other advanced techniques and engineering solutions to reduce eutrophication. Activated limestone can be spread using spreaders, helicopters or drones, making it a relatively quick process.

Read more about activated limestone in our whitepaper, downloadable here.

results seminar

The results seminar for the project took place on 15th March 2024 at Lagtinget's auditorium

on Åland & online.


Recording of the seminar and the presentations can be accessed below. 

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