Spatiotemporal distribution and source variations of hydrocarbons in surface sediments from the Pearl River Estuary, Southern China

Abstract

Variations in hydrocarbon composition and concentration are essential for the assessment of its source and environmental health in estuarine environments. This study aims to reveal the spatial and temporal distribution of multiple hydrocarbons in surface sediments of the Pearl River Estuary, and to further determine various sources of these hydrocarbons. Surface sediments were taken monthly from four sites along a spatial transect from the Pearl River Estuary in a whole year by using a gravitational bottom sampler. A series of bulk parameters including the grain size, total organic carbon content, and total nitrogen content were measured. Hydrocarbons in sediments were extracted and analyzed by the gas chromatography-mass spectrometry. The abundances of higher plants and phytoplankton-derived n-alkanes, petrogenically derived pristane, phytane, hopanes, and steranes with geological configuration, and anthropogenically derived hydrocarbons, including linear alkylbenzenes and polycyclic aromatic hydrocarbons all showed decreasing trends towards the coastal ocean. In contrast, the diatom-derived C25 highly branched isoprenoids increased towards saline sites. Monthly fluctuations of aliphatic and aromatic hydrocarbons at the estuarine mouth were smaller than the upstream freshwater sites, where high monthly variation (up to fivefold) was observed for most of the hydrocarbons detected. This study showed substantial monthly and spatial variations of hydrocarbons in the surface sediments of the Pearl River Estuary. Distribution and composition of sedimentary hydrocarbons indicate mainly anthropogenic inputs (e.g., petroleum residues and synthetic detergents) and terrestrially higher plants, followed by aquatic inputs.