Abstract: Treatment of lake sediments with salts is a promising approach for preventing phosphorus release from sediments. Five 35-d treatments of undisturbed sediment cores in the East Lake, Wuhan, China were applied under anoxic conditions: nothing added (control), Al₂(SO₄)₃ added, FeCl₃ added, CaCl₂ added, and NaNO₃ added. To identify changes in the P binding sites in the sediment caused by the treatments, different P binding forms were extracted from the sediment before and after the treatments. We found that the mean P release rates for anoxic treatments with Al₂(SO₄)₃, FeCl₃, CaCl₂ and NaNO₃ were −0.6, 0.03, 0.6 and 2.6 mg/(m²·d), respectively, while the P release rate with no additives was 7.3 mg/(m²·d). In suboxic conditions, the concentration of total phosphorus (TP_average 657 mg/kg) in sediment was much lower than that of untreated sediment (TP_average 688 mg/kg) and treatments with salts (TP(Al₂(SO₄)₃) 793 mg/kg, TP(FeCl₃) 781 mg/kg, TP(NaNO₃) 802 mg/kg, TP(CaCl₂) 747 mg/kg). We also found that adding CaCl₂ prevented P release because of apatite formation and because P_Ca (Ca bound P) increased at the sediment surface. Addition of Fe³⁺ and NO₃⁻ to the sediment increased the amounts of P_{Fe, Mn} (Redox-sensitive P, mostly Fe and Mn compounds), since iron oxide has the ability to combine P. Addition of Al₂(SO₄)₃ increased the fraction of P_{Al, Fe} (P bound to metal oxides (Al, Fe)) and decreased the P and Fe in the water above the anoxic sediment, showing the greater ability of Al in binding P. The results showed that Al₂(SO₄)₃, FeCl₃, CaCl₂ and NaNO₃ all had an effect in controlling phosphorus release. The effect was related to the forms of phosphorus existing in the sediment before treatment and the forms resulting after adding the four reagents. The combination of Al³⁺ or Fe³⁺ with NO₃⁻ promises to be a reasonable chemical treatment for increasing the P retention capacity of sediments in eutrophic lakes. If chemical treatment is combined with bioremediation, the aim of environmental repair may be achieved.

Key words: Sediment, Internal phosphorus, Aluminum, Iron, Calcium, Nitrate, P fraction

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