1 Department of Biology, Faculty of Science, SDU2 Faculty of Science, SDU3 CLEAR, Department of Biology, Faculty of Science, SDU4 Department of Biology, Faculty of Science, SDU
Many shallow eutrophic lakes cannot meet the EU WFD-criteria in 2015 without restoration. The sediment P-pools must be reduced. Chemical treatment like aluminium-addition is an obvious technique in reaching the WFD-criteria. But there is no information available on the effect of chemical treatments on aluminium mobility, sediment stability or light climate. A laboratory flume experiment including three shallow Danish lakes was conducted. We measured the effects of aluminium, Phoslock (a commercial product), bentonite, and a combination of bentonite/aluminium. Each treatment caused a varying consolidation of the sediment. The largest consolidation occurred using Phoslock- and bentonite-addition followed by bentonite/aluminium-addition, whereas aluminium alone had no effect. Sediment stability thresholds were measured before and after addition. Especially Phoslock, but also bentonite and bentonite/aluminium increased sediment erosion threshold, with respectively 200%, 43% and 57%. Aluminium, bentonite/aluminium, and Phoslock improved the light conditions in the water phase, with respectively 60%, 57% and 50%, whereas bentonite created higher turbidity. Conclusively aluminium improved the light conditions but was very mobile and had no positive effect on sediment stability and compaction, whereas the combination bentonite/aluminium improved all parameters.