Can sediment phosphorus concentration criteria be developed for shallow lakes? Challenges, advances, and an equilibrium-based framework

Abstract

Sediment phosphorus (P) release, or internal P loading, is a major source of water-column P in many shallow lakes. Although water-column P criteria are widely used in lake management, equivalent sediment P concentration criteria remain unavailable. This review examines the challenges associated with developing such criteria and synthesizes recent advances toward their establishment. Based on P adsorption–desorption equilibrium on iron/aluminium (Fe/Al) oxides, we develop an equilibrium-based framework linking sediment P status to water-column total phosphorus (TP). Within this framework, algae-available phosphorus (AAP), pH and an equivalent suspended sediment concentration (SSC_eqv), which integrates water depth and hydrodynamic effects, are identified as key controls of sediment–water P equilibrium. Model simulations indicate a highly linear relationship between sediment AAP and TP under equilibrium conditions. By incorporating SSC_eqv, this relationship can be generalized into a depth-dependent formulation, TP = R × AAP / z, where R is a lake-specific environmental regulation coefficient and z is mean lake depth. This formulation extends the Vollenweider framework from external P loading to sediment P concentration management. Comparison with observations from hundreds of lakes shows that the predicted TP–depth patterns across different AAP levels are broadly consistent with the observed large-scale TP–depth distribution, but this comparison does not constitute direct validation of the full TP = R × AAP / z relationship because the observational dataset lacks corresponding AAP measurements matched to the observed TP and water-depth data. Establishing matched AAP–TP–depth datasets to directly test this relationship will be important for its practical application.