Particles estuarine

While Fe- and Mn-oxides certainly are important in the binding and transport of the trace metals in the estuarine system, organic matter appears to play a dominant role in the coagulation step. For instance, adjustment of the solution pH to values where humics normally precipitate (pH = l to 3) causes all the components (Fe and Mn, organics, and trace metals) to coagulate into filterable particles. By contrast, adjustment of the pH upward, which would normally favor precipitation of Fe- and Mn-oxides, has no effect. In view of this it is not... 

The water column distribution of particulate " Th in partially mixed estuaries aids in assessing the transport of particles throughout the system, as a consequence of tidal mixing or the estuarine circulation. Feng et al. (1999a) took advantage of the fact that the... 

Figure 2. Simplified box model depicting the dominant input and removal functions for a particle reactive radionuclide such as in a well-mixed estuarine system.

River inputs. The riverine endmember is most often highly variable. Fluctuations of the chemical signature of river water discharging into an estuary are clearly critical to determine the effects of estuarine mixing. The characteristics of U- and Th-series nuclides in rivers are reviewed most recently by Chabaux et al. (2003). Important factors include the major element composition, the characteristics and concentrations of particular constituents that can complex or adsorb U- and Th-series nuclides, such as organic ligands, particles or colloids. River flow rates clearly will also have an effect on the rates and patterns of mixing in the estuary (Ponter et al. 1990 Shiller and Boyle 1991). 

Removal to sediments. Removal of surface-reactive trace elements from the oceans readily occurs by adsorption onto settling particles, and this process is most pronounced in the typically high-energy, particle-rich estuarine environment. Particles are supplied by rivers, augmented by additions of organic material generated within the estuary. Also, floes are created in estuaries from such components as humic acids and Fe. The interaction between dissolved and colloidal species is enhanced by the continuous resuspension of sediments in... 

Importance of particles and colloids for controlling estuarine uranium... 

Two important geochemical characteristics make Ra isotopes potentially useful as an estuarine tracer 1) having highly particle reactive Th isotopes residing largely in sediments as its direct radiogenic parents, which ties Ra directly to bottom sediments, and 2) exhibiting vastly different environmental behavior in fresh water and saltwater systems. 

Cochran JK (1984) The fates of U and Th decay series nuclides in the estuarine environment. In The Estuary as a Filter. Kennedy VS (ed) Academic Press, London, p 179-220 Cochran JK (1992) The oceanic chemistry of the uranium - and thorium - series nuclides. In Uranium-series Disequilibrium Applications to Earth, Marine and Environmental Sciences. Ivanovich M, Harmon RS (eds) Clarendon Press, Oxford, p 334-395 Cochran JK, Masque P (2003) Short-lived U/Th-series radionuclides in the ocean tracers for scavenging rates, export fluxes and particle dynamics. Rev Mineral Geochem 52 461-492 Cochran JK, Carey AE, Sholkovitz ER, Surprenant LD (1986) The geochemistry of uranium and thorium in coastal marine-sediments and sediment pore waters. Geochim Cosmochim Acta 50 663-680 Corbett DR, Chanton J, Burnett W, Dillon K, Rutkowski C. (1999) Patterns of groundwater discharge into Florida Bay. Linrnol Oceanogr 44 1045-1055... 

A series of experiments was also conducted by Bowman et al. [34] to ascertain the effects of differing environmental factors on the sediment-water interactions of natural estrogens (estradiol and estrone) under estuarine conditions. Sorption onto sediment particles was in this case relatively slow, with sorption equilibrium being reached in about 10 and 170 h for estrone and estradiol, respectively. On the other hand, true partition coefficients calculated on colloids were found to be around two orders of magnitude greater that those on sediment particles. Hence, it was concluded that under estuarine conditions, and in comparison to other more hydrophobic compounds, both estrone and estradiol... 

The important forces involved in the adsorption of metals on to particles are attractive electrostatic or van der Waals forces. These concepts explain many of the properties of colloids with respect to the adsorption of contaminants or ion-exchange factors and the aggregation of the colloids into larger particles. These larger particulates may then descend the water column to the sediment. This occurs most notably in estuarine environments, as increases in salinity lead to estuarine silting. Binding of electrolytes to hydrophobic colloids is often used to facilitate their coagulation and precipitation. 

In a laboratory study by Schlekat et al. [15], it was demonstrated that coating silica particles with an exopolymer prepared from an estuarine bacterium enhanced the sorption of cadmium on to the particles. The composition of the exopolymer was glucose, galactose and glucuronic acid in the ratio 5 2 1. These investigations also compared the effects of salinity, pH and different concentrations of cadmium. Increasing salinity resulted in less cadmium associated with the particles, presumably due to competition with the chloride ion. The pH had a dramatic effect, resulting in only ca. 10% absorbed at pH 5 to more than 95% at pH 9. 

Svetlicic, V., V. Zutic, and J. Tomaic (1990), "Estuarine Transformation of Organic Matter Single Coalescence Events of Estuarine Surface Active Particles", Marine Chemistry 32, 253-267. 

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