Aquatic plants are typically used to reduce the sediment phosphorus (P) release from eutrophic urban lakes. However, aquatic plants do not necessarily function well to control P release from urban lakes with high internal sediment P loading. To identify an effective method, aquatic plants (Vallisneria spiralis) and lanthanum-modified clay (LMC) were combined or used individually to remediate sediment P of various concentrations (low, moderate, high, and extremely high levels). Our results showed that the combination can efficiently control the P concentration in water columns and pore water, and inhibited sediment P release regardless of internal P level. At low and moderate internal P levels, Vallisneria spiralis alone exerts a similar control effect on pore water P and P flux compared with the combination method. However, there was 51% less reduction of P flux in Vallisneria spiralis treatment compared with combination treatment at high or extremely high level. Aquatic plants can only efficiently reduce sediment mobile P proportion (6%–7%) at low and moderate level. By contrast, LMC efficiently reduced the sediment mobile P proportion (13%–21%) and concurrently increased inert P fractions (HCl–P) at all investigated sediment P levels. The combination of chemical and ecological methods integrated all the advantages and can overcome the impact of high sediment internal P loading. This novel remediation method offers high application prospects in eutrophic urban lakes affected by severe internal P pollution.
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