Oxygenation at a depth of 120 meters can save the Baltic Sea

April 18, 2011, University of Gothenburg

Oxygenation brings dead sea bottoms to life. This creates the necessary conditions for the establishment of new ecosystems that enable nature itself to deal with eutrophication. By conducting pilot studies in two fjords in Sweden, researchers at the University of Gothenburg have demonstrated that pumping oxygen-rich surface water down to sea bottoms is effective. A large wind-driven pump is now to be tested in open water in the Baltic.

"Today everyone is focused on reducing nutrient inputs to the sea in order to reduce eutrophication in the Baltic, but by helping nature itself to deal with the that is discharged we can create a turbo effect in the battle against eutrophication," says Anders Stigebrandt, Professor Emeritus at the Department of Earth Sciences, University of Gothenburg.

The idea of oxygenating dead sea bottoms comes from nature itself. The method of oxygenating the deep water in the Baltic can be compared to creating wetlands on land. Both methods are based on creating the conditions required for ecosystem services by establishing new that can effectively bind the nutrients.

"If oxygen-free bottoms in the Baltic are oxygenated, it can be anticipated that every square kilometre of bottom surface will be able to bind 3 tonnes of phosphorus in a short time, which is a purely geochemical effect. If the bottoms are then kept oxygenated for a prolonged period, fauna becomes established on and in the bottoms. This leads to the bottom sediments being oxygenated down to a depth of several centimetres, and the new ecosystem probably contributes to the possibility of further phosphorus being bound to the sediment."

The research project Baltic Deepwater Oxygenation, directed by Stigebrandt, is testing the hypothesis that prolonged oxygenation of the Baltic deep water results in long-term and increasing binding of phosphorus in bottom sediment. An important question to be answered is how the oxygenated deep-water areas can bind phosphorus in the longer term. The answers are being sought through pilot studies in Byfjorden on the west coast and Kanholmsfjärden on the east coast, as well as in laboratory experiments. The project includes examining how the oxygenated bottoms are colonised and how this affects phosphorus uptake.

Stigebrandt is now planning a trial involving large-scale wind-driven pumping in the open water of the Baltic, in cooperation with Inocean AB, which is designing the pump on the basis of established technology from the off-shore industry. The pump is contained in a 60 metres high and 100 metres deep tubular buoy which is anchored in an open location, in a deep basin yet to be decided off the east coast of Sweden. As a result of the buoy being given a small cross-sectional area at the water surface, the pump becomes non-sensitive to wave motions.

"The pump is to have capacity to pump 30 cubic metres of water per second, which is 15 times more than the pump in the Byfjord experiment. If this works, using a five times larger pump in a buoy around 120 metres deep should not pose major problems. This is the size we anticipate pumps needing to have in a future large-scale system for oxygenation of the Baltic ," says Stigebrandt.

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not rated yet Apr 19, 2011
Good job trying to reclaim and renew what humans ruined.
not rated yet Apr 20, 2011
Winter ice will be a problem. I assume the machine is a standard wind turbine, which do not do well in areas where ice can form on the blades. Of course surface sea ice would also be a concerne so I guess you would only install these pumps in the parts of the Baltic that don't freeze and don't get much pack ice drifting into them? From wiki: "It is known that since 1720, the Baltic Sea has frozen over entirely only 20 times". The Baltic is a rough place to work.

The oxyegenation of the Baltic is driven by inflow episodes from the North Sea. The Baltic is brackish water and the difference in salinity causes periodic episodes of water flow between the salt sea and the fresh water in the Baltic. The average period of the exchange is not constant, though it has slowed since the 80's. Since the recent change has been relatively short-lived it is probably premature to blame it on humans. It may be a temporary natural variation like a drought. 30 years isn't a very long record of observati
not rated yet Apr 20, 2011
Of course you also have to beware of unintended concequences. The Baltic has a large salinity gradient. That gradient is what drives the periodic exchange of water between the North Sea and the Baltic. That in turn is what normally oxygenates the Baltic deep water. If you start pumping fresh water from the surface down to mix with the salty water below, you could further damage the natural mechanism that drive the periodic natural mixing. I doubt that wind driven pumps could even come close to compensating for the scale of the natural cycle. As we have seen so many times before (forest fire control?) when we mess with nature we need to be really thoughtfull and humble.

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