| Abstract
| - The influence of acid volatile sulfide (AVS) on thepartitioning of Cd, Ni, and Zn in porewater (PW) andsediment as reactive metals (SEM, simultaneously extractedmetals) was investigated in laboratory microcosms. Twospiking procedures were compared, and the effects of verticalgeochemical gradients and infaunal activity wereevaluated. Sediments were spiked with a Cd−Ni−Znmixture (0.06, 3, 7.5 μmol/g, respectively) containing fourlevels of AVS (0.5, 7.5, 15, 35 μmol/g). The results werecompared to sediments spiked with four levels of Cd−Ni−Zn mixtures at one AVS concentration (7.5 μmol/g). Avertical redox gradient was generated in each treatmentby an 18-d incubation with an oxidized water column. [AVS]in the surface sediments decreased by 65−95% due tooxidation during incubation; initial [AVS] was maintainedat 0.5−7.5 cm depth. PW metal concentrations were correlatedwith [SEM − AVS] among all data. But PW metalconcentrations were variable, causing the distributioncoefficient, Kdpw (the ratio of [SEM] to PW metalconcentrations) to vary by 2−3 orders of magnitude at agiven [SEM − AVS]. One reason for the variability was thatvertical profiles in PW metal concentrations appeared tobe influenced by diffusion as well as [SEM − AVS]. Thepresence of animals appeared to enhance the diffusionof at least Zn. The generalization that PW metal concentrationsare controlled by [SEM − AVS] is subject to someimportant qualifications if vertical gradients are complicated,metal concentrations vary, or equilibration times differ.
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