Interactions of riverine suspended particulate matter with phosphorus inactivation agents across sediment-water interface and the implications for eutrophic lake restoration

Phosphorus (P) inactivation agents (PIAs) have been widely used in lakes for eutrophic management. However, the interactions of riverine suspended particulate matter (SPM) with PIAs have not been elucidated to the point of complete confidence in the success of PIA application to eutrophic lakes. In this study, a long-term field incubation experiment was carried out to investigate the effects of riverine SPM on sediment internal P management. Fluorescence excitation emission matrix coupled with parallel factor (EEM–PARAFAC) was used to characterize dissolved organic matter (DOM) derived from SPM/sediment, and to study its complexation with La (III) and Ca (II) contained in two PIAs. The analysis identified one protein-and two humic-like components in these samples, which show variable quenching effects by La (III) and Ca (II). The continuous settling of SPM can bury PIAs deeper into the sediment layers and while increasing the mobile P content in surface sediments. This consequently made an increase of P fluxes and surface sediment reactivity, which was witnessed by the increased labile P concentration measured by diffusive gradient in film (DGT). However, the binding capacity of PIAs towards sediment mobile P was kept in a buried layer during the six months’ field experiment. This study indicates that the influence mechanism of riverine SPM on PIAs was through a decrease of the reactive sorption sites of PIAs by complexing with DOM and continuously increasing the mobile P content in surface sediment thereby largely surpassing their maximum P sorption capacity. Repeated dosing at scheduled times would be better for turbid eutrophic lake remediation with high input of riverine SPM in long-term management.