Effects of oxygenation highly dependent on local conditions

Press release 2011-04-19 at 12:00

A pumping device
Photo: Water-Eco Ltd

The three-year joint Nordic project PROPPEN aims to demonstrate whether the state of coastal waters, suffering from oxygen depletion, can be improved by pumping oxygen-rich surface water to the water layers near the seabed. According to preliminary results, oxygen conditions can be improved, but the success of the procedure depends greatly on the bathymetric conditions and currents in the water area that is oxygenated.

Last summer, oxygenation pumpings were carried out in the two field experiment areas of the project, at Sandöfjärden in the coastal Gulf of Finland and at Lännerstasundet in the inner Stockholm archipelago. At Sandöfjärden, pumping started in June and ended at the beginning of October following water mixing. At Lännerstasundet in Sweden, a relatively short, three-week oxygenation pumping process was carried out in June.

Differences in the effects of oxygenation pumpings between the two areas

In both areas, the effect of pumping on water and seabed sediment status was monitored using continuous, automatic measurements as well as traditional sampling and laboratory analyses. At Sandöfjärden, the water layers near the seabed remained oxygenous until late summer, but the pumping capacity used failed to keep the area oxygenous throughout the summer season. As long as the waters remained oxygenous, the phosphorus level was low, but as soon as oxygen ran out, the phosphorus level increased rapidly almost to the level preceding oxygenation.

At Lännerstasundet, the pumping capacity used was higher in relation to the size of the area, and the water layers near the seabed could be oxygenated within a few weeks. The pumping strengthened local currents, enabling oxygenous waters to move towards the previously oxygen-depleted seabed. Phosphorus levels in the pumping area remained clearly lower than those in the adjacent control area due to the combined effect of oxygenation and dilution.

Local conditions seem to have a very considerable impact on the results of oxygenation pumping. In neither case area did pumping cause nutrients to move to the surface water layers. Pumping warmed up the water layers near the sea bed, which increases oxygen depletion.

Pumping efficiency to be increased at Sandöfjärden

The experiments of the upcoming open water season will commence in May–June. Pumping efficiency at Sandöfjärden will be increased by approximately 50% on previous years. The water to be pumped will also be taken from a deeper depth to reduce oxygen-depletion caused by rising seabed temperatures. At Lännerstasundet, pumping will be carried out in the same way as last summer. In particular, the effects of pumping on the flow and mixing of oxygenous water near the seabed will be monitored. The final report on the project will be published in spring 2012. In addition to the performance of oxygenation pumping and its effects on the ecosystem, the report will discuss the risks and cost-efficiency of the method.

The Finnish participants of the PROPPEN Project are the Finnish Environment Institute, Water-Eco Ltd., the University of Helsinki, and Pöyry Finland Oy. Stockholm Vatten participates from Sweden, and VitusLab, Pöyry AS and the National Environmental Research Institute (NERI) from Denmark. The project is coordinated by the Finnish Environment Institute, and its main financier is the Swedish Environmental Protection Agency.

Further information:

Mr. Heikki Pitkänen, Division Manager
Finnish Environment Institute SYKE, Marine Research Centre
Tel. +358 40 582 3182, firstname.surname@ymparisto.fi

Mr. Jouni Lehtoranta, Senior Research Scientist,
Finnish Environment Institute, Marine Research Centre
Tel. +358 400 148 532, firstname.surname@ymparisto.fi

Mr. Marko Reinikainen, Vice Director
Tvärminne Zoological Station at the University of Helsinki
Tel. +358 400 490 674

Mr. Erkki Saarijärvi, Managing Director
Water Eco, Tel. +358 44 279 8603

Mr. Christer Lännergren, Limnologist, Stockholm Water
Tel. +46 73 914 2454

Photo for the use of the media

PROPPEN pumping device (jpg, 2816 kb)

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