Two simple conceptual approaches for the description of phosphorus accumulation and release from sediments are presented. The first model is a mass-balance over the well-mixed top-layer, and demonstrates the enhanced initial effect of sediment dilution on the long-term accumulation, which is magnified in the resulting internal loading, as a consequence of diffusive and advective transport, chemical equilibria, and mineralization. Two assumptions for the spatial distribution of mineralization are evaluated in two sets of analytical solutions for a number of boundary conditions. Results of model calculations are compared with some field data of Loosdrecht Lakes.