Scientists bring oxygen back to dead fjord

More and more of the world’s waters are seriously lacking oxygen.

Could we use pumps to bring oxygen and thus higher life back into these waters? A Danish/Swedish research team says yes. They installed pumps in a Swedish fjord that showed a strong oxygen deficit and now they report that all the right oxygen-loving organisms have come back to the fjord.

Lack of oxygen is a major problem in many of the world’s waters. Both big oceans and small fjords are affected, and climate models predict an increase of this phenomenon in the future. To bring oxygen and thus higher life back to these waters is a huge task. But maybe it is possible – at least judging by a pilot project in a Swedish fjord.

“Our Swedish colleagues got the idea to use a pump to mix oxygen-rich surface water into the deeper parts of the water column in the fjord which was lacking oxygen”, says postdoc Michael Forth and Associate Professor Alexander Treusch from the Nordic Center for Earth Evolution, Institute of Biology at the University of Southern Denmark.

Could also help the Baltic Sea

The Swedish part of the team, Professor Anders Stigebrandt and Dr. Bengt Liljebladh from the Department of Earth Sciences, Oceanography, and Professor Per Hall from the Department of Chemistry and Molecular Biology, Marine Chemistry at the University of Gothenburg, were interested if pumps could support and enhance natural venting events, that bring oxygen-rich water into deeper parts of the water column. Ultimately such an approach could be used to increase water quality in the oxygen-lacking Baltic Sea, they believe.

To test these ideas, a large-scale experiment was conducted in a Swedish fjord called Byfjord, which is located near the town of Uddevalla. Similarly to the Baltic, the four kilometer long and 1.5 km wide fjord has a shallow entrance with a deeper basin that, in the case of the fjord, is 51 m deep. The water in the fjord’s deep basin doesn’t get mixed as oxygen-rich water coming in from the Kattegat Ocean and the river Bävenå exchanges only the surface water. Therefore the bottom waters suffer from a long-term lack of oxygen.

The pump was used during multiple periods between 2010 and 2013 to bring oxygen-rich water from the fjord’s surface down to about 35 meters depth. The surface water then was naturally and instantly replaced with new water from the Kattegat Ocean, creating inflows of oxygen-rich water into the fjord.

Two months of pumping

Did the experiment work? After two months of pumping, higher oxygen concentrations became detectable in the bottom waters.

Forth says “Already while the pumps were working we could see how some oxygen requiring bacteria returned into the deeper water of the fjord and some that don’t like oxygen disappeared.”

Read more: Scientists bring oxygen back to dead fjord

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