First year experiments of oxygenation research show decreased levels of hydrogen sulphide
20 April 2010, Marine, SYKE
The three-year joint Nordic project PROPPEN aims at demonstrating whether the state of coastal waters, suffering from oxygen depletion, can be improved by pumping oxygen-rich surface water to the bottom-near water layers. According to preliminary results, the amounts of hydrogen sulphide could thus be lowered. The project is implemented in two field experiment areas. The Finnish case area is located in the coastal Gulf of Finland, at Sandöfjärden off Raasepori. The second case area, Lännerstasundet, is located in the inner archipelago in front of Stockholm.
During the first year of the project, main effort was directed to testing the functioning of the pumps. The actual oxygenation pumpings were relatively short, and all results very preliminary.
In early August, the oxygenation experiment began at Sandöfjärden, using one oxygenation pump. Pumping efficiency was gradually increased, so that by the end of September all six pumps were in use. In Lännerstasundet, Sweden, the pumping experiment was delayed until December, as the deep waters of the water area had previously contained very large concentrations of hydrogen sulphide, and the risk of this poisonous substance reaching the surface layers was considered too great.
Increase in oxygenation efficiency reduced hydrogen sulphide concentrations
In both areas, the effect of pumping on water and seabed sediment status was monitored with continuous, automatic measurements as well as traditional sampling and laboratory analyses. The use of only one oxygenation pump at Sandöfjärden had no impact on the status of the water area beyond the waters in close proximity to the pump. When oxygenation efficiency was tripled, however, hydrogen sulphide concentrations in the deep waters diminished as a consequence. In late September - early October, when six pumps were used at full power, hydrogen sulphide concentrations diminished significantly. The total disappearance was, however, mainly due to natural oxygenation of deeper water layers.
At Lännerstasundet in Sweden, a short, two-week oxygenation pumping generated clear results: the high deep water hydrogen sulphide concentrations present before the experiment were not observed after the pumping.
In neither case area did pumping cause nutrients or hydrogen sulphide to move to the surface water layers. The deep waters of Sandöfjärden and the seabed surface nevertheless warmed up significantly during the experiment. Rising seabed temperatures increase oxygen consumption, whereas smaller temperature differences between the surface and the seabed weaken stratification.
Pumping experiments with longer duration planned for next summer
The experiments of the upcoming open water season will commence in May - June. The target is to find out, among other things, if pumping that is started early in the summer can prevent oxygen from running out, and, if this is possible, will the status of the seabed improve, and the sediment release of nutrients decrease.
The Finnish participants of the PROPPEN Project are the Finnish Environment Institute, Water Eco Ltd., the University of Helsinki, and Pöyry Environment Oy. Stockholm Vatten participates from Sweden, and VitusLab, Pöyry AS and the National Environmental Research Institute from Denmark. The project is coordinated by the Finnish Environment Institute, and its main financier is the Swedish Environmental Protection Agency.
Further information
- Leading Researcher Heikki Pitkänen, Finnish Environment Institute, Marine Research Centre, Tel. +358 40 582 3182
- Senior Research Scientist Jouni Lehtoranta, Finnish Environment Institute, Marine Research Centre, Tel. +358 400 148 532
- Vice Director Marko Reinikainen, Tvärminne Zoological Station of the University of Helsinki, Tel. +358 400 490 674
- Managing Director Erkki Saarijärvi, Water Eco, Tel. +358 44 279 8603
- Limnologist Christer Lännergren, Stockholm Water, Tel. +46 73 914 2454
create
print
send
share