Effect of Groundwater Irrigation on Soil PAHs Pollution Abatement and Soil Microbial Characteristics: A Case Study in Northeast China

To evaluate the effect of groundwater irrigation on the polycyclic aromatic hydrocarbons (PAHs) pollution abatement and soil microbial characteristics, a case study was performed in the Shenfu irrigation area of Shenyang, Northeast China, where the irrigation with petroleum wastewater had lasted for more than fifty years, and then groundwater irrigation instead of wastewater irrigation was applied due to the gradually serious PAHs pollution in soil. Soil chemical properties, including PAHs and nutrients contents, and soil microbial characteristics, including microbial biomass carbon, substrate-induced respiration, microbial quotient (qM), metabolic quotient (qCO2), dehydrogenase (DH), polyphenol oxidase (PO), urease (UR) and cellulase (CE) in surface and subsurface were determined. Total organic C, total N, total P, and available K were significantly different between the sites studied. The PAHs concentrations ranged from 610.9 to 6 362.8 μg kg−1 in the surface layers (0-20 cm) and from 404.6 to 4 318.5 μg kg−1 in the subsurface layers (20-40 cm). From the principal component analysis, the first principal component was primarily weighed by total PAHs, total organic C, total N, total P and available K, and it was the main factor that influencing the soil microbial characteristics. Among the tested microbial characteristics, DH, PO, UR, CE, qM and qCO2 were more sensitive to the PAHs stress than the others, thus they could serve as useful ecological assessment indicators for soil PAHs pollution.