Sources and transport of hydrocarbons in the Rhone delta sediments (Northwestern Mediterranean)

Summary

To assess sources and transport processes of hydrocarbons in the Rhone delta, superficial sediments were collected near the river mouth and at the limit of the continental shelf in February 85 and September 86. After spiking with perdeuterated standards and isolation of lipids, a normal-phase HPLC step permitted the separation of hydrocarbons in non-aromatics (NAH) and aromatics (PAH), and the fractionation of the latter into sub-groups as a function of the number of aromatic cycles. Analysis of fractions and quantitation of individual compounds were performed by GC and GC/MS. Hydrocarbon concentrations varied from 21.2 to 166.7 μg/g for the NAH, and from 1070 to 6363 ng/g for the PAH. Relevant seasonal variations were observed, reflecting quantitative and qualitative fluctuations of inputs. Petrogenic, pyrolytic and natural derived imprints, as well as their respective contributions were evidenced by distribution patterns, values of ratios of characteristic compounds and occurrence of specific components. Pyrolytic inputs were considerably higher in winter, reflecting intense inputs from combustion processes and/or run-off. On the contrary, fossil as well as natural inputs were significantly higher in summer.