engleski

Geochemistry of inorganic iodine in the Rogoznica Lake

Iodine is the most abundant redox-sensitive and biophilic minor element in seawater. In contrast to open-ocean and stream aquatic systems, in small and semi-closed marine sub-environments the intensity of interactions between iodine system, biota and sediment is altered. Rogoznica Lake is a small, eutrophicated saline lake. Due to high productivity, restricted water exchange and specific mixing regime, sulphides bearing anoxic conditions are common in deeper layers and iodine speciation is additionally affected by redox reactions with reducible sulphur species and allochthonous organic matter. The concentrations of both inorganic and organic iodine species in the lake water were always higher than in the surrounding seawater, and seasonal pattern has been confirmed. In this study iodine speciation was investigated in water column and sediment pore water of the Rogoznica Lake in order to explain high concentrations of iodide in the water column bellow the chemocline during stratification periods (up to 2.3 &micro ; mol L− 1). Sediment cores were sampled at different depths with aim to catch different redox conditions (oxic-anoxic) in the overlying water. Pore water sub-samples contained only reduced chemical form of iodine due to anoxic conditions within sediment. Based on concentration gradients in the pore water and at the sediment-water interface, the fluxes of dissolved iodide were calculated. In addition to iodate reduction which takes place at the interface of oxic water layer-anoxic sediment and plays important role in speciation of iodine, diffusion of iodide from sediment is among most important factors that control concentration level of iodine in the entire water column.

iodine speciation; anoxia; porewater; seawater lake; sediment; Rogoznica Lake

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