engleski

Speciation of Zero-Valent Sulfur in Natural Aquatic Systems: Implications for Biogeochemical Sulfur Cycle

In natural aquatic systems zero-valent sulfur (ZVS) can exist in various forms: dissolved cyclooctasulfur (S8) [1], soluble polysulfides (Sn2- and protonated forms, in the presence of S(II)) [2], colloidal elemental sulfur of abiotic and biological origins and crystalline rhombic cyclooctasulfur (α-S8). We report here ZVS speciation and particle size distribution in various systems: water columns of Baltic Sea, meromictic Fayetteville Green Lake (FGL) and permanently stratified 6 Rogoznica Lake in Croatia and Wadden Sea tidal flat pools. We compared our result to the sulfur speciation in Cariaco Basin reported by Li et al. [3]. In stratified water columns of lakes, which are included in this study (FGL, Rogoznica Lake), chemocline is rich in phototrophic purple sulfur bacteria, which store sulfur intracellularly. Most of sulfur is in the colloidal non-crystalline form [4] . Though individual polysulfides were not detectable in these water columns, sulfur isotopes composition of elemental sulfur at the chemocline of FGL suggests the presence of intracellular polysulfides. In FGL near bottom the presence of low concentration of polysulfides was shown by analysis of total ZVS content after filtration through 0.2 µm filter. Dissolution of sulfur particles formed in the chemocline during sinking through sulfide-rich waters of Baltic Sea (Gotland Deep) and Cariaco Basin produces polysulfides. Though concentrations of individual polysulfide species are too low to be detected directly, increase of fraction of sulfur passing through 0.2 µm filter supports this hypothesis. Sinking of elemental sulfur particles was shown to be important for distribution of other sulfur species (e.g. thiosulfate) in Baltic Sea water column [5]. Study of sulfur speciation in the Wadden Sea tidal flat pools, where concentration of ZVS is relatively high (tenth of micromoles per liter), showed that the system is dominated by colloidal sulfur. Polysulfides concentrations are lower than predicted by thermodynamic considerations [2]. Colloidal sulfur particle size increases with time leading to the production of crystalline sulfur, when particle size reaches >5 µm.

zero-valent sulfur; biogeochemical sulfur cycle

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