Water-level fluctuations regulate the availability and diffusion kinetics process of phosphorus at lake...

Area of Science:

• Environmental Chemistry
• Geochemistry
• Aquatic Science

Background:

• Phosphorus (P) cycling is crucial for aquatic ecosystem health.
• Sediment-water interactions play a key role in nutrient dynamics.
• Understanding labile P fractions and their release mechanisms is vital.

Purpose of the Study:

• To quantify labile phosphorus (P), iron (Fe2+), and sulfide (S2-) fluxes in sediments using in-situ diffusive gradients in thin films (DGT).
• To investigate the impact of water-level fluctuations on P speciation and release.
• To model dynamic diffusion parameters and assess P resupply potential.

Main Methods:

• Sequential extraction techniques to determine P fractions.
• In-situ diffusive gradients in thin films (DGT) for measuring labile P, Fe2+, and S2- fluxes.
• DGT-induced fluxes in sediments (DIFS) model for dynamic diffusion parameter fitting.

Main Results:

• Fe-bound P (Fe-P) was the dominant P pool, contributing significantly to P resupply.
• Upward fluxes of labile P, Fe2+, and S2- decreased in microcosms, indicating immobilization under oxic conditions.
• Water-level fluctuations significantly regulated adsorption-desorption of P bound to Fe-containing minerals.
• Higher labile analyte concentrations were observed in shallow lake regions with greater water-level variations.
• A positive correlation between S2- and Fe2+ suggested S2- oxidation triggers Fe reduction and P release.

Conclusions:

• Frequent water-level fluctuations enhance the formation of Fe(II) phases in sediments.
• These fluctuations facilitate P desorption coupled with Fe release into the aqueous phase, especially under high water levels.
• The study highlights the critical role of water-level dynamics in regulating P bioavailability in lake systems.