33
© Springer Nature Singapore Pte Ltd. 2019
T. Kuwae, M. Hori (eds.), Blue Carbon in Shallow Coastal Ecosystems,
https://doi.org/10.1007/978-981-13-1295-3_2
Chapter 2
Carbon Sequestration in Sediment
as an Ecosystem Function of Seagrass
Meadows
Toshihiro Miyajima and Masami Hamaguchi
Abstract Seagrass meadows have the potential to sequester large amounts of
organic carbon (OC) in underlying sediments as detrital OC. This ecosystem
function of seagrass meadows depends not only on the high primary productivity of
seagrasses and associated algae, but also on the physical and hydrological properties
of seagrass meadows that accumulate fine-grained mineral sediment and
allochthonous organic matter and stabilize the sediment. The burial efficiency of
OC in marine sediment is constrained principally by (i) structural recalcitrance of
accumulated organic matter, (ii) enhancement of OC preservation through organic–
mineral interactions, and (iii) the length of the oxygen exposure time in the reactive
layer of sediment. We discuss how these mechanisms contribute to and constrain
OC sequestration in seagrass sediments. From the sediment source–sink perspective,
long-term carbon sequestration capacity can be viewed as an emergent property of
coastal vegetated ecosystems such as seagrass meadows. Sequestration of OC also
depends on the nature of the OC supplied, which is largely determined by the origin
of the OC. The major sources of OC to seagrass meadow sediments are reviewed
and classified in terms of their mode of transport and degradability in the early
diagenetic process. The available methods of evaluating various OC sources,
including recently developed environmental DNA techniques, are also critically
reviewed. Finally, available data are compiled on the concentration and burial rate
of OC in seagrass meadow sediments and a tentative global estimate of the longterm (~1000 years) OC sequestration rate in seagrass meadows as 1.6–9.4 Tg C
year
−1
is provided. This is lower than previous estimates of the global OC burial rate
in seagrass meadows.
T. Miyajima (*)
Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan
e-mail: miyajima@aori.u-tokyo.ac.jp
M. Hamaguchi
National Research Institute of Fisheries and Environment of Inland Sea, Japan Fisheries
Research and Education Agency, Hatsukaichi, Hiroshima, Japan
© Springer Nature Singapore Pte Ltd. 2019
T. Kuwae, M. Hori (eds.), Blue Carbon in Shallow Coastal Ecosystems,
https://doi.org/10.1007/978-981-13-1295-3_2
Chapter 2
Carbon Sequestration in Sediment
as an Ecosystem Function of Seagrass
Meadows
Toshihiro Miyajima and Masami Hamaguchi
Abstract Seagrass meadows have the potential to sequester large amounts of
organic carbon (OC) in underlying sediments as detrital OC. This ecosystem
function of seagrass meadows depends not only on the high primary productivity of
seagrasses and associated algae, but also on the physical and hydrological properties
of seagrass meadows that accumulate fine-grained mineral sediment and
allochthonous organic matter and stabilize the sediment. The burial efficiency of
OC in marine sediment is constrained principally by (i) structural recalcitrance of
accumulated organic matter, (ii) enhancement of OC preservation through organic–
mineral interactions, and (iii) the length of the oxygen exposure time in the reactive
layer of sediment. We discuss how these mechanisms contribute to and constrain
OC sequestration in seagrass sediments. From the sediment source–sink perspective,
long-term carbon sequestration capacity can be viewed as an emergent property of
coastal vegetated ecosystems such as seagrass meadows. Sequestration of OC also
depends on the nature of the OC supplied, which is largely determined by the origin
of the OC. The major sources of OC to seagrass meadow sediments are reviewed
and classified in terms of their mode of transport and degradability in the early
diagenetic process. The available methods of evaluating various OC sources,
including recently developed environmental DNA techniques, are also critically
reviewed. Finally, available data are compiled on the concentration and burial rate
of OC in seagrass meadow sediments and a tentative global estimate of the longterm (~1000 years) OC sequestration rate in seagrass meadows as 1.6–9.4 Tg C
year
−1
is provided. This is lower than previous estimates of the global OC burial rate
in seagrass meadows.
T. Miyajima (*)
Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan
e-mail: miyajima@aori.u-tokyo.ac.jp
M. Hamaguchi
National Research Institute of Fisheries and Environment of Inland Sea, Japan Fisheries
Research and Education Agency, Hatsukaichi, Hiroshima, Japan