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5/21/2018 9:00 AM

Highly eutrophic Lake Kymijärvi to be restored using a new method

A decision has been made to begin restoring Lake Kymijärvi in Lahti using a new method. The groundbreaking project is funded by the Finnish Ministry of the Environment, and it is conducted by the researchers of the Ecosystems and Environment Research Programme of the University of Helsinki.
Lake Kymijärvi fish

​The project team will employ and study a globally novel restoration method to remove nutrients accumulated in the lake's sediments and use them as soil conditioners. Lake Kymijärvi, which has the worst ecological status of all lakes in the Lahti region, has been chosen as the pilot site.

The restoration method involves pumping of hypolimnetic water from the profundal zone of the lake and filtering it to remove impurities. A pump and filter station will be built in the Rekolanpohja area of Lake Kymijärvi in May/June for this purpose.

Nutrient-rich water from the profundal zone will be pumped through filters, and the filtered water will be discharged back to the lake via an artificial wetland in Kivipuro. The wetland was originally constructed for treating urban run-off from the Karisto area.

"What gives this method its novelty value is the fact that it allows for the filtered hypolimnetic water to be returned to the same lake and for the recovered phosphorus to be reused. Previous restoration projects of this kind have involved discharging hypolimnetic water from one lake into the next, thus passing the nutrients on along the lake chain. The phosphorus levels in lake sediments must be lowered in order to get permanent results", explains Water Protection Manager Ismo Malin.

University of Helsinki to study the impacts of the project

The project is funded by the Finnish Ministry of the Environment, and it is part of the Ecosystems and Environment Research Programme of the University of Helsinki. In addition to researchers from the University of Helsinki, the project team includes representatives of the City of Lahti and Nordkalk, which will supply the nutrient filtering system to be used in the restoration operation.

The project team will study the efficiency of the filtering system and monitor water and sediment quality in both the artificial wetland and the lake. The pump station will be operational throughout the summer at least in 2018 and 2019. The future of the project will be decided on the basis of the results.

Lahti – a pioneer in water body restoration

A wide range of water body restoration projects have been carried out in the Lahti area since the 1970s. The City of Lahti is a pioneer in experimenting with a number of restoration methods, such as biomanipulation, phosphorus precipitation and large-scale oxidation. The restoration of Lake Vesijärvi in Lahti is a globally renowned success story.

City of Lahti, Environmental Services

Water Protection Manager Ismo Malin
tel. +358 50 525 9579, ismo.malin@lahti.fi

University of Helsinki

Project Manager, Professor Jukka Horppila
tel. +358 29 415 8473, jukka.horppila@helsinki.fi