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The concentrations of Cd, Cu, and Zn were evaluated bimonthly in the soil solution of five acidic loamy‐sand soil plots during an 18‐mo period, before and after application of 25 Mg ha−1 cattle‐manure slurry on top of the plots. pH, Cd, Zn, Cu, and Fe concentrations, electrical conductivity (EC), and dissolved organic carbon (DOC) were monitored in the soil‐solution samples extracted from soil down to 80‐cm depth. Dissolved metal concentrations ranged from 9 × 10−7 to 9 × 10−5 mmol m−3 for Cd, from 0.14 to 33 mmol m−3 for Zn, from 0.005 to 5 mmol m−3 for Cu, and from 0.54 to 4.6 × 10−3 mmol m−3 for Fe. Maximum soil solution concentrations of Cd (9 × 10−5 mmol m−3) and Zn (33 mmol m−3) were found between 0‐ and 40‐cm depth 6 wk after cattle‐manure slurry application; Cu and Fe concentrations were not elevated. Except for the peak concentrations of Cd and Zn following the cattle‐manure slurry application, no statistically significant temporal trends in heavy metal concentrations were observed. Multiple linear regression analysis showed a positive correlation between the metal concentrations with DOC and a negative correlation with pH. High EC levels in topsoil layers, resulting from manuring were also found to increase metal concentrations. In the topsoil the Cd and Zn concentrations were affected by soil solution pH, and in the subsoil by DOC variations. The Cu concentration was affected by DOC variations in all soil layers. Supercentrifugation of selected subsoil samples from one sampling date removed 80% of the Cd, Zn, and Cu from the solution along with DOC and Fe. Cation‐exchange column experiments as well as anodic stripping voltammetry measurements (speciation) of selected soil solution samples, showed that 30 to 70% of the dissolved Cu and all Cd was bound in relatively fast dissociating metal complexes. The observed variations in soil solution heavy metal concentration and speciation show that a distribution coefficient that describes the partition of metals over soil solution and solid phase is not a constant but depends on the physicochemical situation.

ABSTRACT. Colonies of Pharocjstis sp. (Ilaptophyceae] isolated from the North Sea accumulated manganese during ~ncubati.on of 15 d in a culture med~um w~t h near-natural (0 45 ~rmol l ' 1:ln) conccntratlon When maximum cell density was reached, u p to 75'1L of the manganese originally prcsrnt in the medium was found in the colonies; the amount of manganese in the single cells remained at a constant level of about 7 '%B.

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Soil solution samples collected during a 14‐mo period from manured, loamy‐sand soil profiles in the Netherlands showed variations in dissolved Zn, Cd, and Cu concentrations of up to two orders of magnitude. To try to account for variations in the dissolved metals, a thermodynamic model was developed for the chemical‐equilibrium computer program CHARON. In addition to solution complexation and solid‐phase precipitation of inorganic components, the model accounted for metal complexation with dissolved organic carbon (DOC) ligands and with a solid organic matter (OM) exchanger phase. Both dissolved and solid organic materials were assumed to behave like fulvic acid having a complexing capacity for Zn2+, Cd2+, Cu2+, Ca2+, Mg2+, and Al3+ of 2 tool kg−1 of C. To obtain a single (pH‐dependent) stability constant for each metal‐organic ligand complex, stoichiometries of 1:1:n metal/organic‐ligand/OH− complexes were determined from published linear relationships between pH and average equilibrium quotients normalized for complexing capacity of a polyfunctional complexer. Exchange in the exchanger phase included monovalent cations and anions to maintain phase electroneutrality. Model predictions of dissolved Zn, Cd, and Cu were calculated from relevant soil properties and macrochemical concentrations in each of 44 soil‐solution samples collected from three manured field plots. Model‐predicted Zn and Cd concentrations deviated from measured concentrations on the average 1.4‐ and 2‐fold for measured concentration ranges of 120‐ and 34‐fold (respectively). Copper was typically underpredicted by the model. Model‐predicted speciation between the two principal dissolved metal species, free‐ionic and DOC ligand‐complexed, varied depending on soil solution macrochemistry. Soil solution chemical conditions ranged from pH 4.5 to 6.7, 30 to 260 g DOC m−3, and electrical conductivities (EC) of 15 to 510 mS m−1.