Carbon and nitrogen cycling in the Zhubi coral reef lagoon of the South China Sea as revealed by 210Po and 210Pb

► 210Po/210Pb disequilibria were used to trace export of POC and PON in a coral lagoon. ► Recycling of POC and PON were quantified by a mass balance budget in a coral lagoon. ► 210Po excess could be used to qualify the degradation of particulate organic matter. ► Degradation rate constant of POM was much more in the lagoon than in the open sea.