Different distribution of polycyclic aromatic hydrocarbons (PAHs) between Sphagnum and Ledum peat from an ombrotrophic bog in Northeast China

Abstract

The aims of this study are to investigate historical PAH deposition through the analysis of PAHs in bulk peat cores and reveal the different distribution of PAHs in Sphagnum and Ledum peat from peat cores. Peat cores from Jingjiang peatland are collected, and Sphagnum peat samples are manually separated from bulk peat. The remaining bulk peat samples are defined as “Ledum peat.” 137Cs is used to date the peat cores. PAH contents as well as physicochemical property of Sphagnum and Ledum peat are determined. The PAH deposition rates measured in the bulk peat cores range from 3.5 to 12.8 ng cm−2 year−1, which are different in both absolute values and trends from those of nearby sediment cores. Concentrations of PAHs in Sphagnum and Ledum at the surface are similar, indicating the accumulation ability by adsorption and uptake between two species of plants are similar. However, at depths of 5–30 cm, concentrations of PAHs in Sphagnum peat are higher than those in Ledum peat, which can be attributed to their different PAH accumulation abilities or to different PAH degradation rates. An increase in PAHs/TOC ratios with depth in Sphagnum peat indicates that PAHs are resistant to degradation in Sphagnum peat. While a significant positive correlation between C/N and PAHs in Ledum peat suggests that PAHs may be degraded during peat decomposition in Ledum peat. This study finds a difference in PAH concentrations between Sphagnum and Ledum peat. The results suggest that peat quality rather than microbials results in a difference in both PAH accumulation and degradation in peat cores.