Sorption Properties of the Bottom Sediment of a Lake Restored by Phosphorus Inactivation Method 15 Years after the Termination of Lake Restoration Procedures

Artificial mixing and phosphorus inactivation methods using aluminum compounds are among the most popular lake restoration methods. Dugie Lake (Olsztyskie Lakeland, Poland) was restored using these two methods. Primarily, P precipitation and inactivation methods significantly increased the sorption properties of Dugie Lake bottom sediment. Fifteen years after the termination of the restoration procedure, the alum-modified "active" sediment layer still has higher P adsorption abilities, which can limit P internal loading. Relatively low amounts of phosphates in the near-bottom water of Dugie Lake, even in anoxia, as well as the fact that the assessed maximum sediment P sorption capacity is still higher than NH4Cl-P (labile P) and BD-P (Fe-bound P) sum ("native exchangeable P"), confirm that hypothesis. Among the tested P adsorption models for the sediment, the double Langmuir model showed the best fit to the experimental data (the highest R-2 values). This may indicate that phosphorus adsorption by the tested sediments most likely occurs through phosphate binding at two types of active sorption sites. P adsorption by the studied lake sediment during experiments was significantly connected to aluminum content in sediment. The research into the adsorption properties of sediment can be used as a tool for the evaluation of lake restoration effects.