IMPLICATIONS OF A MULTILAYERED NEPHELOID SYSTEM FOR HYDROCARBON DISTRIBUTIONS AND TRANSPORT IN A MICROTIDAL MEDITERRANEAN ESTUARY

The origin and fate of non-aromatic hydrocarbons (NAH) and polycyclic aromatic hydrocarbons (PAH) were studied at the land-sea boundary in t he mirotidal estuary of the Rhone River. The sampling strategy was bas ed on the collection of particles in the multi-layered nepheloid syste m which develops off the river mouth and extends towards teh continent al shelf. After separation by normal phase HPLC, hydrocarbons were ana lyzed by gas chromatography and gas chromatography/mass spectrometry. The distributions of NAH and PAH among the various nepheloid layers ar e discussed in terms of abundances, compositional patterns and related diagnostic criteria. Advection within the benthic nepheloid layer (BN L) appeared to constitute an important transport pathway for hydrocarb ons, and particularly for PAH. This layer showed a preferential enrich ment in fossil fuel related PAH, and to a lesser extent in n-alkanes, whereas pyrolytic inputs were essentially transported within the surfa ce layer. The qualitative decoupling of hydrocarbons between the two l ayers strongly supported the hypothesis that processes such as floccul ation, aggregation and interactions between different phases are the d ominant mechanisms leading to the formation of the BNL. A comparison b etween the hydrocarbon distribution in the BNL and in the underlying s urface sediments confirmed the distinct character of the BNL and sugge sted that resuspension does not significantly contribute to the BNL ma terial.