MOLECULAR CHARACTERIZATION OF THE ORGANIC FRACTION OF SUSPENDED MATTER IN THE SURFACE WATERS AND BOTTOM NEPHELOID LAYER OF THE RHONE DELTA USING ANALYTICAL PYROLYSIS

Curie Point-pyrolysis-gas chromatography (CuPy-GC) and Curie Point-pyr olysis-gas chromatography-mass spectrometry (CuPy-GC-MS) were applied to characterize the macromolecular content of the suspended particles in the surface waters and benthic nepheloid layer of the Rhone delta. The chromatogram of the pyrolysate of the Rhone River particles reveal ed a low pyrolysis yield from the riverine material in which polysacch arides and lipid-derived substances prevailed. The absence of levogluc osan and other pyrolysis products related to cellulose suggested that no intact polysaccharides were present. Lignin-derived products were v irtually absent. In the salinity gradient, a wide variety of products, including saturated and monounsaturated acids, phytadienes, n-alkylni triles and pyrolysis products from proteins were determined, indicatin g a major contribution from freshly produced autochthonous material. A suite of dipeptides of bacterial origin was also identified. Lignin-d erived products from terrigenous sources were minor. Further offshore qualitative differences, with respect to the previous samples were app arent. Polysaccharides were less pronounced, possibly due to the dilut ion of the suspended load of the waters, and/or the microbial consumpt ion of these readily degradable compounds. In contrast, the relative a bundances of autochthonously derived compounds increased as a result o f nutrient inputs from the Rhone River which fertilize coastal waters. The occurrence of 1,1,3,3,5,5, hexamethylcyclotrioxane as well as sty rene provided indications of anthropogenic inputs to the site. The mac romolecular constituents of suspended solids in the benthic nepheloid layer strikingly resembled those of the riverine material. Polysacchar ides together with phytadienes and C-14, C-16 and C18 acids accounted for the major pyrolysis products. The persistence of this fingerprint in the benthic layer was observed from the mouth to stations ZD1 and Z A7. Beyond this point, due to the influence of the Liguro-Provencal cu rrent flowing westwards, the composition of the pyrolysates changed to wards a marine signature. Flocculation of suspended matter in which po lysaccharides would make particles stick together or salt flocculation were proposed as an alternative scenarios to explain the formation of the nepheloid layer.