Internal loading of phosphorus in a sedimentation pond of a treatment wetland: Effect of a phytoplankton crash

►We study mechanisms controlling summer internal loading of P in a sedimentation pond. ►The sediment behaved as a sink of P in March, but switched to a source of P in June. ►Microbial degradation of diatom biomass led to a reduction in the D.O concentration. ►This led to subsequent redox-dependent release of phosphorus from the sediment. ►SRP was also released through decomposition of algal matter within the water column.