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<p>Lake sediments are key reservoirs for sulfur (S), iron (Fe), and their associated compounds, playing a central role in the coupled Fe–S biogeochemical cycle. However, the dynamics of this cycle vary greatly among lakes with different pollution histories and redox conditions. To clarify how Fe–S cycling responds to varying geochemical environments, this study investigates the vertical distribution and speciation of multiple sulfur and iron forms, acid-volatile sulfide (AVS), elemental sulfur, Fe(III), and Fe(II), in sediments from three lakes in Guizhou, China—Maoshitou, Aha, and Hongfeng—which are characterized by distinct pollution and redox histories. We combined sequential extraction with sediment geochemical analysis to quantify the reactivity of Fe(III) and explore its role in the coupled Fe–S processes. The results show that the three lakes exhibit contrasting redox environments, leading to markedly different vertical profiles of S and Fe species. In particular, Maoshitou Lake displays unusually high concentrations of dissolved elemental sulfur, reflecting unique redox transitions in its sediments. Elevated AVS concentrations in deeper, more reducing sediments reflect active sulfate reduction and the subsequent formation of iron sulfide minerals. In these environments, solid-phase Fe(III), mainly as iron (oxyhydr)oxides, is reduced to Fe(II), which then reacts with sulfide to form FeS minerals. These results highlight that differences in lake pollution history and oxidative conditions strongly influence Fe–S coupling and the transformation pathways of reactive Fe(III) and reduced S species. The enhanced Fe(III) reactivity observed in Maoshitou Lake underscores its pivotal role in regulating Fe–S biogeochemical cycling under varying redox regimes.</p>

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Vertical distribution of redox-active sulfur and iron species in Karst Lake sediments and their implications for coupled iron–sulfur cycling

  • 期刊论文

  • 发表日期：

    2026年3月12日

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  • Hao Wang,
  • Jian Zhu,
  • Liao Peng,
  • Ruyi Zheng

摘要

Lake sediments are key reservoirs for sulfur (S), iron (Fe), and their associated compounds, playing a central role in the coupled Fe–S biogeochemical cycle. However, the dynamics of this cycle vary greatly among lakes with different pollution histories and redox conditions. To clarify how Fe–S cycling responds to varying geochemical environments, this study investigates the vertical distribution and speciation of multiple sulfur and iron forms, acid-volatile sulfide (AVS), elemental sulfur, Fe(III), and Fe(II), in sediments from three lakes in Guizhou, China—Maoshitou, Aha, and Hongfeng—which are characterized by distinct pollution and redox histories. We combined sequential extraction with sediment geochemical analysis to quantify the reactivity of Fe(III) and explore its role in the coupled Fe–S processes. The results show that the three lakes exhibit contrasting redox environments, leading to markedly different vertical profiles of S and Fe species. In particular, Maoshitou Lake displays unusually high concentrations of dissolved elemental sulfur, reflecting unique redox transitions in its sediments. Elevated AVS concentrations in deeper, more reducing sediments reflect active sulfate reduction and the subsequent formation of iron sulfide minerals. In these environments, solid-phase Fe(III), mainly as iron (oxyhydr)oxides, is reduced to Fe(II), which then reacts with sulfide to form FeS minerals. These results highlight that differences in lake pollution history and oxidative conditions strongly influence Fe–S coupling and the transformation pathways of reactive Fe(III) and reduced S species. The enhanced Fe(III) reactivity observed in Maoshitou Lake underscores its pivotal role in regulating Fe–S biogeochemical cycling under varying redox regimes.