How do major ions and fulvic acid affect dissolved inorganic phosphorus adsorption onto suspended particulate matter in estuarine environment?

The adsorption and desorption of Dissolved Inorganic Phosphorus (DIP) onto Suspended Particulate Matter (SPM) are of key importance for the biogeochemistry in estuarine system. These processes are susceptible to changes in environmental factors, especially the inherent changes in levels of major ions, fulvic acids and salinity. As anthropogenic organic contamination in estuaries increases, aniline was chosen to investigate the influence of anthropogenic organic matter on DIP adsorption The influence of these factors on adsorption and desorption of phosphate onto SPM in estuarine aquatic system was examined using batch experiments in single and combined systems. The study showed that the adsorption of DIP onto SPM in estuaries was mainly controlled by salinity, especially the concentration of calcium (Ca2+), magnesium (Mg2+), sulfate (SO42−) and bicarbonate (HCO3−). Increased concentrations of major cations (Ca2+ and Mg2+) enhance DIP adsorption, while increased concentrations of major anions (SO42− and HCO3−) reduce adsorption. The amount of DIP adsorbed to SPM was mainly governed by the concentration of Ca2+, while the effect of differences in salinity was mainly dictated by the concentration of major anions. The facilitating effect of fulvic acid on DIP adsorption was generally negatively affected by increased salinity, as the fulvic acid increasingly reduced the enhancing effect of Ca2+ on DIP adsorption by forming stable complexes. Fulvic acids had no significant influence on the effect of Mg2+ and HCO3− on DIP adsorption to SPM. Aniline slightly inhibited DIP adsorption by competing with DIP for active sites on SPM. Aniline had no significant influence on the effect of cations on DIP adsorption to SPM, while slightly increasing inhibitory influence on anions.