Influences of phosphorus concentration and porewater advection on phosphorus dynamics in carbonate sands around the Weizhou Island, northern South China Sea

A series of flow-through reactor experiments were undertaken to assess the potential effect of porewater advection and dissolved inorganic phosphorus (DIP) concentration on benthic DIP dynamics in permeable sediments collected from the Weizhou Island, northern South China Sea. The flux of DIP ranged from −0.13 to 0.05 mmol m−2 h−1, and the reversal from DIP efflux to influx occurred when the DIP concentration reached a threshold. DIP release from the sediment into the seawater peaked at intermediate advection rate, which perhaps provide optimum conditions for DIP release related to CaCO3 dissolution. Phosphorus limitation in seawater could be relieved by DIP release from the sediment, and CaCO3-bound P in carbonate sands may play a major role in benthic DIP release and decrease in the molar nitrogen/phosphorus ratio in seawater around the Weizhou Island. •Seriously phosphorus limitation occurred in the aquatic environment around the Weizhou Island.•The release of DIP from the sediments can decrease the DIN/DIP ratio in seawater.•There was a reversal from DIP efflux to DIP influx at the threshold DIP concentration of 0.40 ± 0.06 μmol l−1.•DIP release from the sediment into the seawater peaked at the intermediate advection rate of 96 l m−2 h−1.