Speciation of potentially mobile Si in Yangtze Estuary surface sediments: estimates using a modified sequential...

Area of Science:

• Geochemistry
• Environmental Science
• Marine Biology

Background:

• Estuarine ecosystems with large subaqueous deltas are crucial for biogeochemical cycling.
• Understanding silicon (Si) speciation is vital for estuarine Si budgets and processes.
• The Yangtze Estuary (YE) is a key estuarine system with significant deltaic features.

Purpose of the Study:

• To investigate the speciation of Si in the surface sediments of the Yangtze Estuary.
• To determine the relationships between different Si species and sediment bulk parameters.
• To assess the mobility and significance of various Si pools in deltaic sediments.

Main Methods:

• Modified sequential extraction method to determine five potentially mobile Si pools: weak acid leachable Si (W-Si), Si bound to organic matter (H-Si), Si coprecipitated with amorphous Fe/Al oxides (O-Si), Si coprecipitated with crystalline Fe/Al oxides (Ouv-Si), and biogenic silica (B-Si).
• Analysis of total potentially mobile Si (T-Si) concentrations.
• Correlation analysis between Si fractions and sediment grain size compositions.

Main Results:

• Total potentially mobile Si (T-Si) ranged from 1689.31 to 5487.10 μg/g, with highest values in deltaic mud deposits.
• Si fractions, except for O-Si, showed strong correlations with grain size compositions.
• O-Si exhibited a lack of correlation with grain size in deltaic mud deposits due to organic matter loss and Fe oxide recycling.
• O-Si demonstrated greater mobility compared to Ouv-Si.

Conclusions:

• The speciation of Si in YE surface sediments reveals distinct mobile pools.
• O-Si is a significant and highly mobile Si fraction in deltaic sediments.
• Quantifying the O-Si pool is essential for accurately assessing Si mobility and biogeochemical cycling in estuarine environments.