A simple model for predicting aluminum bound phosphorus formation and internal loading reduction in lakes after aluminum addition to lake sediment

• Empirical model can predict conversion of mobile sediment P to Al–P.
• Formation of Al–P is dependent on initial mobile sediment P content and Al added.
• Model output can be used to predict resulting internal P load after treatment.

The conversion of mobile phosphorus (P) to aluminum bound P (Al–P) after addition of Al to over 300 sub-samples from 35 sediment cores collected from 20 lakes in the upper Midwest, United States was investigated in this study. Consistent relationships between mobile P reduction and Al–P formation were detected across a broad range of mobile sediment P contents (0.04–2.8 g P m−2 cm−1 or 0.083–2.8 mg P g−1DW) and lake types. The conversion of mobile P to Al–P was dependent on the initial mobile sediment P content and the amount of Al added to the sediment. An empirical model was then developed to predict the formation of Al–P based on the amount of Al added relative to the initial mass of mobile P in the sediment. The results were compared to sediment collected from an Al treated lake and good agreement was found between the model and in-situ changes to sediment P fractions caused by Al treatment. The model developed in this study, unlike previous models with extreme, singular endpoints, allows for a continuum of estimates for mobile P conversion to Al–P, along with efficiency of P binding by Al, as Al dose varies. Model results can be used in conjunction with mobile sediment P based predictions for internal P loading to calculate an Al dose required to meet internal phosphorus loading goals for lake management and restoration without the need for expensive, time consuming Al additions to sediment.

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