Computer Science
Scientific paper
Jul 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53.1511t&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 7, pp.1511-1522
Computer Science
5
Scientific paper
Zinc concentrations were measured in oxic sediments and in the associated interstitial and overlying waters (vertical profiles) at 40 littoral stations of various lakes; the stations were chosen to represent a large range of lake pH (pH 4-8.4) and of zinc concentrations in the sediments and the overlying waters. Large concentration gradients of dissolved zinc (leading presumably to large downward fluxes) were found at the sediment-water interface of acid lakes (pH < 6). Concentrations of dissolved zinc [Zn]in the overlying waters were found to be highly undersaturated with respect to Zn(OH)2 (s) and ZnC03 (s), and in general with respect to ZnSiO3 (s), ruling out solubility equilibrium with pure solid phases as a mechanism of control of zinc concentrations in the overlying waters. The partitioning of zinc between the overlying water and the surficial sediments was described by sorption processes, using either the distribution coefficient model or a simplified version of the surface complexation model. In relation with this latter model, binding intensity values, k a , for the sorption of zinc to natural iron oxyhydroxides have been estimated using the field data, I.E., the partitioning of Zn in oxic lake sediments and their dissolved concentrations in the associated overlying waters. The following empirical relationship between ka and lake pH has been found: log k a = 1.21 pH - 2.83 (r2 = 0.89). The pH dependence of KA is in agreement with recent theory on the adsorption of trace metals at oxyhydroxide surfaces; however, the binding intensity values derived from field measurements differ markedly in some cases from those of the equilibrium constants obtained for zinc in laboratory experiments. As several observations suggest that Fe-bound zinc is mobile, the distribution of labile zinc between the water column and the sedimentary iron oxyhydroxides has been calculated as a function of pH for typical shallow lakes with the log KA-pH empirical relationship. This model predicts that most of the mobile Zn should be present in the water column at pH < 5 and in the surficial sediments above pH 7. The pH interval 5.5-6.5 (into which fall a large number of poorly buffered lakes receiving acidic deposition) defines a region where changing pH in the water column should have the most pronounced effect on the partitioning of Zn between the water column and the sediment.
Carignan Richard
Dubreuil B.
Rapin F.
Tessier Alexandre
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