Spatiotemporal variability of hydrocarbons in surface sediments from an intensively human-impacted Xiaoqing River-Laizhou Bay system in the eastern China: Occurrence, compositional profile and source apportionment

Abstract

Hydrocarbons in coastal sediments record organic matter sources, and thus are widely used to elucidate both natural and anthropogenic inputs and for the estimation of pollution levels. Surface sediments were taken from Xiaoqing River and Laizhou Bay of eastern China in spring and summer of 2014, and were analyzed to determine the characteristics of aliphatic and aromatic hydrocarbons. Various hydrocarbons were identified, including n-alkanes, monomethylated alkanes (MMAs), isoprenoid alkanes, linear alkylbenzenes (LABs), hopanes, steranes and polycyclic aromatic hydrocarbons (PAHs). They were used to track both biogenic (terrestrial plant and microbial inputs) and anthropogenic inputs (petroleum and fossil fuel or biomass burning) in this ecosystem. The major part of hydrocarbons identified came from anthropogenic inputs including petroleum residues and synthetic detergents related hydrocarbons (16.2-90.3%), followed by higher plant (4.5-80.5%) and microbial inputs (0.8-57.5%). Interestingly, significant differences in hydrocarbon concentrations and distributions were observed between spring and summer. In particular, significant higher percentages of microbially derived hydrocarbons, but lower percentages of anthropogenic and vascular plant derived hydrocarbons were observed in summer than spring. Further principal component analyses suggested that the overall distribution of aliphatic hydrocarbons was mainly controlled by seasonality instead of spatiality. In contrast, the distribution of PAHs showed insignificant spatial and seasonal differences. Physical processes such as atmospheric transportation and further deposition, may be factors influencing the distribution of PAHs in the study area with widely biomass and fossil fuel burning. The decoupled distributions of aliphatic and aromatic hydrocarbons warrant further study for a comprehensive understanding of long term sedimentary hydrocarbon sources and input dynamics with increasing human activities.

Major finding: Seasonal difference in aliphatic hydrocarbon composition was observed in surface sediments of Laizhou Bay, which is mainly caused by stronger phytoplankton and microbial inputs in summer under the overall high pollution background.

Keywords: Laizhou Bay; River-estuary system; Sedimentary hydrocarbons; Source apportionment; Spatiotemporal variability.