For determination of mangrove soil C, we collected soil cores (4 cm in diameter and 100 cm deep; three per site) with a soil auger and PVC tubes. It was difficult to draw soil cores out using large tubes.We tested three sizes of PVC tubes (3, 4, and 6 cm) and found 4 cm was the best one. We separated each 10-cm layer for the top 70 cm (seven layers), while the 70 -100 cm depth was sampled as one layer because of its relatively constant C concentration (Zhang et al., 2011).