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Trace metal distribution coefficients in the Weser Estuary (Germany)

1992; Elsevier BV; Volume: 12; Issue: 11 Linguagem: Inglês

10.1016/0278-4343(92)90064-q

1873-6955

A. Turner, G.E. Millward, Bastian Schuchardt, Michael Schirmer, A. Prange,

Groundwater and Isotope Geochemistry

Trace metals in the dissolved phase, and in operationally defined available and total particulate associations, have been determined along an axial transect of the Weser Estuary, together with measurements of salinity, temperature, pH, dissolved oxygen, suspended particulate matter (SPM), chlorophyll a, free and attached bacteria, particulate carbon and particle specific surface area. Throughout the estuary the dissolved metals exhibited non-conservative behaviour due to sorption reactions with particle surfaces and sediment-water exchange processes. This reactivity was enhanced at the fresh water-brackish water interface where changes in the master variables were most pronounced. The influence of sorptive processes on total particulate metal distributions was not evident and major compositional variability was ascribed to physical mixing of different particle populations. The relative proportions of trace metals in the dissolved and solid phases were interpreted in terms of conditional distribution coefficients, KDs, whose magnitude depends critically on which fraction of particulate metal is selected (i.e. available or total). The KDs for Fe and Mn increased with increased SPM concentration, whereas those for Cu, Ni, Zn and possibly Pb decreased with SPM; such observations are related to whether particle-water exchange processes at any locality in the system are far from or at (quasi-) equilibrium, and to differences in the sorptive characteristics of suspended particle populations. These results have implications for the behaviour of trace metals in the Weser Estuary and are also discussed in the context of the value of the KD concept for quantitative modelling of dissolved trace metal distribution in estuaries.