Influence of polycyclic aromatic hydrocarbons on nitrate reduction capability in mangrove sediments

In the present study, we investigated the influence of phenanthrene (PHE), a three-ring polycyclic aromatic hydrocarbon (PAH) compound, on nitrate (NO₃⁻) reduction processes in mangrove sediments using microcosms. After 10 days, nitrate/nitrite reductase activity and abundance of narG and nirS significantly decreased in the bulk sediment at both 10/50 mg PHE kg^{− 1} contamination groups. In the rhizosphere, abundance of narG, nirS and nirK markedly declined at PHE treated sediments, while the drop in reductase activity at 10 mg kg^{− 1} PHE treatment was insignificant. After 50 days, apart from 10 mg Phe kg^{− 1} treated bulk sediment, abundance of denitrifiers and reductase activity in all PHE spiked sediment samples significantly dropped. Therefore, the influence of PAHs on NO₃⁻ reduction capability in mangrove sediments is dependent on spiked concentration, temporal scale of exposure and interaction with roots. Generally, PAHs play an inhibitor role, slowing NO₃⁻ turnover rates, which warrant attention from coastal managers.