Eutrophication-induced regime shifts reduced sediment burial ability for polycyclic aromatic hydrocarbons: Evidence from Lake Taihu in China

Regime shifts from a vegetated state with clear water to a turbid state with high contents of phytoplankton and suspended particles have been found in numerous waters worldwide. The fate and risks of hydrophobic organic contaminants (HOCs) in such waters may be altered, and the effects on burial ability of HOCs remain unknown. Influences of regime shifts on sediment burial ability for 16 polycyclic aromatic hydrocarbons (PAHs) (defined as burial/emission ratio) were investigated based on the evidence from the third largest freshwater lake (Lake Taihu) in China. The results of δ13C, δ15N, atomic ratio of Corg/N, and the content of total organic carbon testing and historical data suggested that the regime shifted abruptly from macrophytes to phytoplankton dominance in Lake Taihu in the late 1980s. The annual burial ability for the PAHs decreased gradually over time by 63.2%–98.9% in the period from 1980 to 2016. Meanwhile, the decrease rates of PAH burial ability varied from −1.65% y−1 to −2.98% y−1, depending on the hydrophobicity of the compound. The PAH burial ability varied with the dominant primary producers associated with the trophic level index of the water column. Regime shifts had a stronger influence on the burial ability of PAHs with higher hydrophobicity. This study helps to understand the fate and potential risks of HOCs in waters due to eutrophication-induced regime shifts. [Display omitted] •Regime shifted from macrophytes to phytoplankton dominance in late 1980s.•Regime shifts reduced the sediment burial ability for 16 PAHs in Lake Taihu.•Burial ability for PAHs varied with trophic level index of the water column.•Effects of regime shifts on burial ability increased with PAH hydrophobicity.