Salinity Effects on Iron Speciation in Boreal River Waters.

Area of Science:

• Environmental Chemistry
• Geochemistry
• Aquatic Chemistry

Background:

• Boreal river mouths exhibit high and increasing iron (Fe) concentrations.
• This iron (Fe) shows notable stability against salinity-induced aggregation in estuaries.

Purpose of the Study:

• To investigate how iron (Fe) speciation influences its stability across salinity gradients.
• To understand the role of organic matter (OM) in stabilizing iron (Fe) in aquatic systems.

Main Methods:

• Mixing experiments using river water and artificial seawater to test Fe phase stability.
• Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy to determine Fe speciation.
• Analysis of Fe speciation in river waters and salinity-induced aggregates.

Main Results:

• The relative abundance of organically complexed Fe and colloidal Fe (oxy)hydroxides varied significantly among rivers.
• Fe (oxy)hydroxides were selectively removed via aggregation with increasing salinity.
• Organically complexed Fe demonstrated greater stability, though Fe-OM complexes were also found in aggregates.

Conclusions:

• Iron (Fe) speciation, particularly organically complexed Fe, is crucial for its stability in estuarine environments.
• While Fe (oxy)hydroxides aggregate with salinity, Fe-OM complexes contribute to overall Fe stability.
• Colloid size and organic matter (OM) composition are additional factors influencing iron (Fe) behavior.