In order to elucidate the instantaneous toxicity that might occur during oxidation of reduced sediment and elemental sulphur (S8) is formed, toxicity tests were conducted in the laboratory where three ubiquitous Baltic Animal species were exposed in an aquarium for 24 hours. Oxygen-rich surface water was pumped down to an anoxic bottom with reduced sediment. A dozen individuals from each group of these animals were collected from the test location Kanholmsfjärden in September 2010. After exposure to the oxidation of the sediment the animal recovery was followed up during a period of 7 days after which they were returned to the Baltic. Both mobility and activity was studied. When the exposure was stopped the oxygen saturation in bottom waters had increased to between 50 and 70%.
One of the concerns raised against large-scale oxygenation is that this would lead to increased contaminant concentrations in water and biota, e.g. because redox-sensitive metals would go into solution at oxidized conditions. There are a number of studies that show that this is not the case in areas where oxygen depletion is abated (mostly naturally). There are therefore no observations to suggest that improved oxygen conditions would lead to problems linked to the release of environmentally harmful substances. Also in our project this problematic was addressed. Figure 3.9 shows measured levels in Kanholmsfjärden before and after the deep water oxygenation. Concentrations after oxygenation were approximately a factor of 3 lower.
With the contribution of the LIFE financial instrument of the European Community