Kelp mariculture enhances the burial ability of polycyclic aromatic hydrocarbons: Evidence from Ailian Bay, China

Kelp mariculture plays an important role in carbon sequestration. Burial by coastal sediments is an important way to reduce the risk of organic contaminants. However, the influences of kelp mariculture-induced carbon dynamics on the organic contaminant burial remain largely unknown. Here, we demonstrated that long-term kelp (Saccharina japonica) mariculture has enhanced the burial ability (burial flux/emission density) of the sixteen priority polycyclic aromatic hydrocarbons (PAHs) in coastal sediments, as evidenced by the study from a mariculture base in Ailian Bay, China. We reconstructed the historical production of kelp mariculture in Ailian Bay by the kelp environment DNA (eDNA) in the sediment core. The quantity of kelp eDNA increased from 0.02 ± 0.01 to 0.06 ± 0.01 ng g⁻¹ in the period from 1989 to 2020 (p < 0.05), indicating that kelp mariculture had expanded during this period. The total organic carbon (TOC) in the sediment core of Ailian Bay varied from 16.1 to 24.0 mg g⁻¹. The average burial ability of the individual PAHs varied from 0.01 ± 0.02 to 0.10 ± 0.10 in Ailian Bay. The expansion of kelp mariculture enhanced the content of TOC and the recalcitrant humic acid-like carbon components, which promoted the burial ability of the PAHs (except for naphthalene, fluorene, anthracene, and dibenzo[a,h]anthracene) in the period from 1989 to 2020. Kelp mariculture activities influenced more on the burial ability of the lower molecular weight PAHs than that of the higher molecular weight PAHs.