Laboratory study of phosphorus retention and release by eutrophic lake sediments: Modeling and implications for P release assessments

The need for minimizing water eutrophication makes controlling phosphorus (P) release and/or loss from sediments/soil an urgent matter. This research seeks to develop methods to predict P release in sediments. We first studied the P adsorption in 10 sediments from a sub lake of Taihu Lake, China for 80 days. After adsorption, the sediments were extracted with 0.01 M CaCl2 and 0.5 M pH 8.5 NaHCO3 solutions. We found strong linear relationships between the equilibrium concentration and CaCl2-P (R2 = 0.91) and between P adsorbed and NaHCO3-P (R2 = 0.90). This result suggests that: (I) CaCl2-P can be used as a proxy for the P concentration between the sediment interface and overlying water when it is difficult to measure P; (II) NaHCO3-P is able to evaluate the newly adsorbed P in the sediments which may reflect the enriched process. The results indicate that we could link CaCl2-P and NaHCO3-P further using common isotherm models. This hypothesis was tested for our sediment data and soil data from published literature. Models derived from Langmuir and Temkin isotherms could successfully fit the data. In more general applications, our models are also capable of describing the relationship of NH4Cl-P and TP. They are routine indexes to assess the status of sediment P. The fact that the models predict P loss in soils or P release from sediment well makes them potentially useful in areas of wide P risk assessment.