Internal phosphorus load in a Mexican reservoir through sediment speciation analysis

Area of Science:

• Environmental Chemistry
• Limnology
• Geochemistry

Background:

• Eutrophic lakes like Valle de Bravo reservoir face challenges with internal phosphorus (P) loading.
• Understanding P fractions in sediment is crucial for managing lake water quality.

Purpose of the Study:

• To determine the contribution of different phosphorus fractions in sediment to the internal P load (IPL) of Valle de Bravo reservoir.
• To analyze the relationship between environmental parameters (redox potential, pH) and P release.

Main Methods:

• Sequential extraction of sediment P into five fractions (MilliQ, BD, NaOH, HCl, K2S2O8).
• Monitoring of bottom water redox potential (Eh), pH, and total phosphorus (TP).
• Analysis of P fraction distribution in sediment profiles.

Main Results:

• Phosphorus fractions bound to iron (Fe) and aluminum (Al) oxides dominated, comprising ~50% of total P.
• These dominant P fractions were concentrated in the top 5 cm of sediment.
• Decreasing Eh and increasing pH in bottom waters correlated with increased P concentration.

Conclusions:

• Fe/Mn and Al/Fe oxide-bound P fractions are the primary contributors to potentially available P release in the reservoir.
• These fractions represent a significant internal P load (IPL) of 23.5 ± 1.4 t/year.
• Sediment P fractionation is a valuable tool for assessing IPL in eutrophic lakes.