The objectives of this paper are to review the role of rivers as a pathway of chemical elements from the land to the ocean and to assess the significance of river input of pollutants to oceanic chemistry.The major importance of river suspended matter (R.S.M.) on the transport of chemical elements to the ocean is underlined. The relationship between river water/river suspended sediment partition coefficient and the electronegativity function QYO has been reassessed. A comparison between theoretical erosion and actual fluxes of material carried by rivers shows that for most chemical elements these two figures are similar. Additional fluxes are observed in rivers for some elements like Sb, Zn and Pb. This discrepancy is discussed in terms of steady state and non-steady state erosional processes.During estuarine mixing the discharge of riverine elements to the ocean is drastically modified. More than 90% of the R.S.M. settles with its associated colloidal material produced when river water mixes with sea water. Consequently, due to the strong association of chemical elements with R.S.M., only a small percentage of the continental material will reach the sea. However, the comparison of R.S.M. with deep-sea clay composition emphasizes the prime influence of river input on oceanic sediment composition 265 C. S. Wong et al. (eds.), Trace Metals in Sea Water
Colloidal organic C and trace metals from the waters of a highly productive coastal environment (the Venice Lagoon, Italy) have been separated by a cross-flow ultrafiltration device. On average, 18% of organic C, 34% of Cd, 46% of Cu, 87% of Fe, 18% of Ni, 58% of Pb, and 54% of Mn which previously would have been considered in the dissolved phase are actually associated with colloidal material. Thus, past studies overestimate the dissolved trace-metal concentration in the nearshore environment.Compared to total concentration, the proportion of the colloidal fraction represents on average 15% of organic C, 18% of Cd, 28% of Cu, 11% of Fe, 11% of Ni, 29% of Pb, and 12% of Mn. This fraction acts differently from the truly dissolved and macroparticulate phases. The behavior of organic C and trace elements during mixing between freshwater and seawater is more complicated than expected when a colloidal fraction is involved. The flocculation of colloids, encountered normally during estuarine mixing, is not very significant on the time scale of mixing in the lagoon. Conversely, the interaction between colloidal and truly dissolved phases seems important. The partitioning of trace metals between different fractions of organic C appears variable, Fe and Mn are preferentially tied to macroparticulate organic matter, and Cu and Cd are preferentially tied to colloidal organic matter in seawater. Truly dissolved organic C appears to be important for Ni. Pb is mainly associated with macroparticulate organic matter at most stations except in the highly productive region where Pb prefers colloidal organic C.
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