Mangroves as a major source of soil carbon storage in adjacent seagrass meadows

Study Number

97

Author

Guangcheng Chen, Muhammad Husni Azkab, Gail L. Chmura, Shunyang Chen, Pramudji Sastrosuwondo, Zhiyuan Ma, I.Wayan Eka Dharmawan, Xijie Yin & Bin Chen

Abstract

Mangrove forests have the potential to export carbon to adjacent ecosystems but whether mangrove derived organic carbon (OC) would enhance the soil OC storage in seagrass meadows adjacent to mangroves is unclear. In this study we examine the potential for the contribution of mangrove OC to seagrass soils on the coast of North Sulawesi, Indonesia. We found that seagrass meadows adjacent to mangroves had significantly higher soil OC concentrations, soil OC with lower δ13C, and lower bulk density than those at the non-mangrove adjacent meadows. Soil OC storage to 30cm depth ranged from 3.21 to 6.82kgC m−2, and was also significantly higher at the mangrove adjacent meadows than those non-adjacent meadows. δ13C analyses revealed that mangrove OC contributed 34 to 83% to soil OC at the mangrove adjacent meadows. The δ13C value of seagrass plants was also different between the seagrasses adjacent to mangroves and those which were not, with lower values measured at the seagrasses adjacent to mangroves. Moreover, we found significant spatial variation in both soil OC concentration and storage, with values decreasing toward sea, and the contribution of mangrove derived carbon also reduced with distance from the forest.

Main Results and Conclusions

• OC concentrations at two mangrove adjacent sites were significantly higher than those at non-mangrove adjacent sites
  • “At each set of the three seagrass sample stations located at varying distances from mangrove or land edge the OC concentrations of the two most offshore were not significantly different from each other, but were significantly lower than stations closest to the mangrove or land edge.” (2)
• Seagrass meadows in North Sulawesi are rich in organic carbon storage.
  • “The soil OC concentrations in our study are higher than those reported elsewhere in Southeast Asia further confirming that seagrass meadows in North Sulawesi are rich in soil OC and are sites of substantial carbon storage.” (5)
• The role seagrass plays in carbon storage is geographically variable.
  • “…in our study seagrass tissue contributed a minimal proportion of the soil OC in the meadows adjacent to mangrove forests. Even in the two non-mangrove adjacent meadows, seagrass was rarely the dominant OC source in the underlying seagrass soils.” (6)
• Large organic carbon concentrations are more likely to be associated with mangroves than seagrass beds. Larger organic carbon concentrations in seagrass are directly linked to interactions between seagrass and mangroves.
  • “…in our study seagrass tissue contributed a minimal proportion of the soil OC in the meadows adjacent to mangrove forests. Even in the two non-mangrove adjacent meadows, seagrass was rarely the dominant OC source in the underlying seagrass soils.” (6)
  • “The exported OC in the form of mangrove detritus could be efficiently trapped in the dense seagrass meadows adjacent to mangroves and result in a higher soil OC concentration at the interface between mangrove and seagrass.” (6)
• Seagrass meadows located near mangroves or land edge tend to be richer in organic carbon than offshore meadows. (7)