Adsorption Characteristics of Organic Phosphorus on Marine Sediments and Key Influencing Factors

The authors investigated the effects of organic matter (OM) content and composition, as well as medium temperature, salinity and pH, on the sorption of organic phosphorus (OP) using methylphosphonic acid (MPn) and 5′-adenosine monophosphate (AMP) as the model compounds. An 3% increase in the proportion of light fraction organic matter (LFOM) in the HCl treated sediment samples increased the sorption capacity (Q_m) for AMP and MPn by 35% and 32%, respectively, indicating that the LFOM made a significant contribution to OP sorption. The input of algal-derived organic matter (AOM) during algal blooms increased the proportion of LFOM in sediments, enhancing the sorption of OP. However, the released dissolved organic carbon (DOC) inhibited the further enhancement of sorption ability. Fraction analysis after OP sorption revealed that the increase of OM content favored the accumulation bioavailable phosphorus after sorption. The influence of environmental factors on OP sorption was investigated using MPn as an example. Compared to artificial seawater (ASW), the sediment exhibited stronger sorption ability for OP in diluted ASW, with higher sorption observed in 1/2 ASW than in 1/4 ASW. Under pH=7~8 conditions, the electrostatic repulsion on the sediment surface partially inhibited the sorption of MPn. Thermodynamic parameters (ΔG^θ < 0, ΔH^θ>0, ΔS^θ>0) indicated that MPn sorption was a spontaneous and endothermic process.