Phosphorus sorption kinetics and sorption capacity in agricultural drainage ditch sediments in reclaimed land, Kasaoka Bay, Japan

Equilibrium analysis is essential to evaluate sorption capacity and to determine whether sediment acts as a source or sink of phosphorus (P). This study was carried out to determine whether or not the sediment in drainage ditches acts as a source or sink of P, evaluate phosphorus sorption kinetics, and determine the potential P sorption by using the Langmuir isotherm sorption model. Surface sediment (0–10 cm) and the overlying water were collected from three drainage ditches for the experiments. Results showed that the drainage ditch that was the most contaminated with P had the highest sediment zero-equilibrium phosphorus concentration (EPC 0 ). Because sediment EPC 0 of the three ditches was higher than water P concentration, they acted as a sink of P across the sediment interface. The kinetic sorption of sediments consisted of two stages that were quick and slow, regardless of the sampling sites. The amounts of P sorbed to sediments at equilibrium ( Q e ) ranged from 50.8 to 77.5 mg kg −1 . Phosphorus sorption capacity ( Q max ) of sediments ranged from 447.0–493.8 mg kg −1 with the constant related to binding energy ( K ) (0.140–0.171 L mg −1 ). The results from this study indicate the importance of ditch sediment in controlling P dynamics in discharge from agricultural farms.