Evaluation study for phosphorus mobilisation-release behaviour on different marine sediments: Focus on phosphate sorption characteristics

Phosphorus is well known as an important nutrient element associated with eutrophication in the marine ecosystem, and its sorption on sediments plays a key role in its immobilisation in the bio-geochemical cycle. In this paper, the sorption behaviour of phosphorus onto sediments collected from 23 different sites in estuary, coastal sea and aquaculture areas of China was studied. The main aim is to determine the phosphorus sorption characteristics of these sediments thereby assessing their phosphorus buffering capacities. Both kinetic and equilibrium isotherms of the sorption and desorption of phosphorus were assessed. The resultant sorption and desorption kinetic curves fit well to a two-compartment first-order equation. The equilibration time was considered as 48 h. The isotherms agreed well with the Freundlich and Langmuir equations. The hysteresis coefficient values showed an obvious sorption-desorption hysteresis. Decreasing salinity was favourable for the sorption ability in the range from 30 to 3. The mean values of the phosphorus sorption-desorption equilibrium concentration and the maximum phosphorus sorption capacity were 0.098 mg L and 0.086 mg g for sediments in the Changjiang Estuary and East China Sea shelf, and 0.138 mg L and 0.067 mg g for the sediments in the aquaculture area. The fractions of clay, calcite and organic matter influenced the sorption and retention abilities and the effects were different for sediments obtained from different origins.