Figure 3.7 shows oxygen concentrations in the bottom waters (100 meters depth) in Kanholmsfjärden near the WEBAP II pilot during the project. It is noted that relatively soon after the pump been put into continuously operation an oxygenation of bottom waters occurs. However, measurements in adjacent bays with similar bathymetry showed increased oxygen levels in the same period. Therefore, it was concluded that the improved oxygen levels may mainly be explained by the natural inflow of oxygen-rich water, but it cannot be excluded that the pumping also had a positive impact.
Figure. Oxygen concentration (mg/l) June 2010-May 2013in the bottom water in Kanholmsfjärden adjacent to the WEBAP II pilot.
Figure 3.8 shows total phosphorus concentration in the bottom waters (100 meters depth) and surface water (5 m) in Kanholmsfjärden near the WEBAP II pilot during the project period. It is noted that relatively soon after the bottom water gets oxygenated phosphorus concentration decreased from 250 mg/l to about 70 g/l. However, no significant change in phosphorus concentration in the surface water was observed. This contradicts fears that oxygenation disturb existing stratifications and thus initially lead to increased levels of phosphorus in surface waters as a result of phosphorus-rich bottom water would move to the surface. The ultimate aim of oxygenation is that phosphorus concentrations shall decrease also in surface waters, which would lead to a reduced primary production in the photic zone.
With the contribution of the LIFE financial instrument of the European Community