Dynamic sulfur-iron cycle promoted phosphorus mobilization in sediments driven by the algae decomposition

Area of Science:

• Environmental Science
• Geochemistry
• Microbiology

Background:

• Eutrophic freshwater lakes are susceptible to algae blooms.
• The impact of algae decomposition on sediment biogeochemistry, particularly sulfur and iron cycling and phosphate release, is not well understood.

Purpose of the Study:

• To investigate the dynamic changes in sulfur, iron, and phosphorus species in water and sediment during algae decomposition.
• To assess the variation in sulfate-reducing bacteria (SRB) abundance in sediments.
• To elucidate the mechanisms of iron oxide reduction and Fe-P release mediated by the sulfur cycle.

Main Methods:

• Microcosm experiments were conducted to simulate algae decomposition in lake sediments.
• Analysis of sulfur (sulfate, sulfide, elemental sulfur), iron (Fe(II)), and phosphorus (Fe-P) species in water and sediment.
• Quantification of sulfate-reducing bacteria (SRB) abundance.

Main Results:

• Algae decomposition significantly stimulated sulfate reduction, leading to decreased sulfate and increased sulfide and SRB abundance.
• Accumulation of acid volatile sulfide (AVS), pyrite sulfur (Pyrite-S), and elemental sulfur (S⁰) in sediments.
• Significant reduction (35.4%) in iron oxides-bound phosphate (Fe-P) was observed, linked to iron oxide reduction mediated by sulfide.

Conclusions:

• Algae decomposition drives a coupled sulfur-iron biogeochemical cycle in eutrophic freshwater lake sediments.
• Sulfide produced during sulfate reduction facilitates the reduction of iron oxides, promoting the release of sediment-bound phosphate.
• These findings highlight the importance of understanding sulfur-iron interactions for managing eutrophic freshwater ecosystems.