Polycyclic aromatic hydrocarbons at subcritical levels as novel indicators of microbial adaptation in a pre-industrial river delta.

Marine sediment is considered a vast sink for organic pollutants including polycyclic aromatic hydrocarbons (PAHs). However, little is known about the relationship between subcritical PAH allocation and benthic microbial patterns. Thus, we carried out a field investigation at the abandoned Yellow River Delta (AYRD) to deepen the understanding of PAHs' horizontal distribution and ecological roles on the continental shelf. The PAH level in the AYRD is relatively low and distance-independent, indicating it resulted from long-term, chronic, anthropogenic input. The combined application of diagnostic molecular ratios reported inconsistent PAH sources, which might be due to the low PAH concentrations and the complexity of contributing sources. Positive Matrix Factorization provided a more robust source classification and identified three main PAH sources-coal combustion and vehicle emissions, petrogenic process, and fossil fuels. The benthic microbiome did not show a significant response to PAHs in terms of microbial assemblage or alpha-diversity. However, Operational Taxonomic Units in some specific phyla, like Thaumarchaeota, Proteobacteria, Acidobacteria, and Chytridiomycota, correlated with the PAH source indicators, supporting the notion that PAH source indicators can act as a novel environmental indicator for microbial adaption. What's more, Microbial Ecological Networks show more connection at sites identified as biomass combustion by both Fluoranthene/(Fluoranthene + Pyrene) and Indeno(1,2,3-cd)pyrene/(Indeno(1,2,3-cd)pyrene + Benzo(ghi)perylene) compared to the ones identified as biomass combustion by Fluoranthene/(Fluoranthene + Pyrene) and petroleum combustion by Indeno(1,2,3-cd)pyrene/(Indeno(1,2,3-cd)pyrene + Benzo(ghi)perylene). Herein, we demonstrate that the PAHs' source indicator can serve as a novel indicator of the interactions between microorganisms, and thus, should be applied to the sustainable management effort in the offshore area.