A mathematical model for phosphorus interactions and transport at the sediment-water interface in a large shallow lake

Sediment phosphorus (P) biogeochemical processes impact water quality. Restoration measures and global warming lead to the same outcome, namely that reactive P moves from the sediments to the bottom waters. In this study, a vertical-compressed sediment P transport model was developed and coupled with a three dimensional (3-D) hydrodynamic-ecological model (EcoLake). The proposed model was used to evaluate the effects of two different strategies (external loads reduction and global warming) on sediment P release flux and P concentrations in the water column of Lake Chaohu, the fifth largest shallow lake in China. The results found that the coupled model accurately reflected P transport in the water column, sediment, and dissolved reactive P (SRP) diffusion at the sediment and water interface. The degradable rate of rapidly degradable organic P (vp1) and adsorbed rate (kad) are the most sensitive parameters influencing sediment P release flux. The internal SRP loads caused by diffusion accounted for roughly 5% of the total external P loads, with higher values in heavily polluted lake basins (western and eastern) and during warmer seasons (summer and autumn). Sediment P release may have caused the current lake water SRP concentrations to increase by 31.1, 12.0, and 21.2%, in western, central, and eastern basins, respectively, due to the large difference of sediment SRP concentration between three basins. The SRP concentration in water responded to changing loads and water temperature strategies more in the western basin than in the other two basins. The sediment P release flux showed spatially contrary responses between two strategies. These findings have important implications with respect to the effects of sediment P release on water quality, and will assist water quality managers in developing appropriate P control measures.