THE SIGNIFICANT ROLE OF COLLOIDS IN THE TRANSPORT AND TRANSFORMATION OF ORGANIC-CARBON AND ASSOCIATED TRACE-METALS (CD, CU AND NI) IN THE RHONE DELTA (FRANCE)

The distribution of organic C and trace elements (Cd, Cu, and Ni) betw een truly dissolved and colloidal phases was determined in May 1992, i n order to better understand their behavior during estuarine mixing in the Rhone delta (France). Colloidal material (10(4) Daltons-0.4 mu m) was separated with an ultra-clean cross-flow filtration system. A con siderable part of the organic C and trace metals studied, used to be c onsidered to occur in the so-called ''dissolved'' pool, is associated with colloidal material. The significant correlation between colloidal organic C and colloidal Cu suggests an important involvement of collo idal organic material in the transport of this element. The correlatio n between Ni, Cd and organic matter mainly occurs in the truly dissolv ed fraction, suggesting that the truly dissolved organic C is importan t for these two elements. Truly dissolved and colloidal organic C and trace-metal fluxes transported from the River Rhone to the northwester n Mediterranean Sea were estimated.