PRELIMINARY ASSESSMENT OF THE DISTRIBUTIONS OF SOME TRACE-ELEMENTS (AS, CD, CU, FE, NI, PB AND ZN) IN A PRISTINE AQUATIC ENVIRONMENT - THE LENA RIVER ESTUARY (RUSSIA)

Dissolved and particulate trace elements have been determined in the L ena River and its mixing zone in the Laptev Sea during September 1989. Average dissolved concentrations (in nM) in river water were: As = 2. 0, Cd = 0.05, Cu = 9.7, Ni = 5.2, Pb = 0.08, Zn = 5.3 and Fe = 410. Th ese concentrations are comparable to and often lower than those observ ed in large unpolluted world rivers. In the mixing zone, the suspended matter composition in the surface plume varies from 90% detrital to 5 0% detrital (estimated) and the distribution of particulate trace meta ls reflects the relative proportions of these particles. Particulate C u and Ni are preferentially associated to organic matter and clay mine rals, respectively, whereas no distinct trend is seen for Pb and Zn. T he distribution of dissolved concentrations shows little consistent ev idence of elemental transfers between the dissolved and particulate ph ases (Cd, Ni, Pb, Zn), with the exception of the usual Fe removal, and a possible As uptake by phytoplankton. Some Cu uptake probably also o ccurs, but its effect does not alter significantly the apparent conser vative behaviour of Cu. On the whole, terrigenous trace element supply does not appear to be significantly altered by transfer processes in the summer period, but this conclusion only relies on a limited number of preliminary measurements.