Sedimentary organic carbon dynamics in a native and an exotic mangrove plantation based on dual carbon isotopic analyses

Background/Question/Methods

Many studies have increased our knowledge about the dynamics of C in mangrove forests. We still lack, however, a complete understanding of the dynamics of sedimentary organic carbon (SOC) in the mangrove forests. Sedimentary organic carbon (SOC) was quantified in two mangrove plantations and a nearby barren site based on measurements of C and C isotopes in sediment cores.we (1) quantified SOC accumulation in both plantations and in a reference barren flat located between the plantations; (2) separated SOC decomposition stages in both plantations based on vertical variations of ƒÔ¹³C values; and (3) estimated the contributions of new C to the total SOC in both plantations.

Results/Conclusions

Relative to the barren site, the native Kandelia candel plantation and the exotic Sonneratia apetala plantation greatly affected values for SOC content, ƒÔ¹³C, and ¹⁴C age from 0 to about 60 cm but not at greater depths. SOC densities to a 60-cm depth were 155 and 174 Mg ha^-1 in the native and exotic plantation, respectively. Change of SOC ƒÔ¹³C with depth was similar in both plantations, and the new contributions to the total SOC in the upper 16 cm were also similar (45–47%). At 16–60 cm, however, the new C contributions were only 9% in the native plantation but as high as 31% in the exotic plantation, i.e., the exotic S. apetala stored more mangrove-derived new C in its anaerobic sub-surface than the native K. candel. From the perspective of SOC storage, S. apetala rather than K. candel is recommended for restoring the degraded coastal area in Southern China.