NATURE AND DISTRIBUTION OF PHENOLIC-COMPOUNDS IN WATER AND SEDIMENTS FROM MEDITERRANEAN DELTAIC AND LAGUNAL ENVIRONMENTS

The nature and distribution of phenolic compounds were studied in suspended particles, sediment trap material and deposits in deltaic, marine and lagunal environments of the northwestern Mediterranean sea (Gulf of Lions). In deltaic environments (Rhone delta), the river flow controlled amounts of terrestrial run-off offshore as characterized by the abundance of phenolic compounds. A clear distinction appeared between surface water layers and deep layers. In the former, organic matter was less degraded and richer in phenolic acids than in the latter, where an abundant lithogenic phase was associated with degraded organic material rich in phenolic aldehydes, partly due to anthropogenic pollution. During the spate period, some compounds, such as phenolic aldehydes, were good indicators of hydrodynamic conditions, as they were carried down from the river bed to the prodelta. There, associated with the organo-mineral complex, they sank down to reach the benthic nepheloid layer and flowed out offshore. Considering the chemical nature of phenolics, suspended material contained more labile phenolic compounds such as syringyl phenols. In contrast, vanillyl phenols, which are rather refractory components, were more concentrated in sediments. In the Lacaze-Duthiers Canyon (south of the Gulf of Lions), trapped material from the euphotic zone was relatively rich in phenols of marine origin. Similarities in phenolic composition appeared between trapped organic material in bottom layers of the Tet prodelta and of the side of the Canyon, reflecting a transfer of particles by advective currents from the shelf to the deep sea. In deposits containing relatively abundant phenols, humic acids were richer in phenols than fulvic acids. In lagunal environments, phenol contents in suspended material and deposits were relatively high, resulting from the abundant vegetal cover. Highest dissolved phenol contents occurred in water at the end of summer and early autumn on the edges of the Canet lagoon where abundant debris of decaying plants accumulated. Their nature depended essentially on the extent of phanerogam populations (Ruppia maritima, Phragmites australis), which are their major sources. In this area, fine deposits contained humic fractions richer in phenols than coarse sediments were.