51
mixed- species seagrass beds and adjacent barren areas of back-reef carbonate sediments (Miyajima et al. 1998, 2001b). Thus, seagrass meadows may generally have
an ecosystem function of increasing the storage of OC in sediment to at least twice
the extent of storage observed under the same oceanographic conditions in the
absence of seagrass. It should be noted that sediment in unvegetated zones neighboring seagrass meadows often contains a significant amount of OC exported from
the seagrass meadow (Kennedy et al. 2010) and cannot be considered equivalent to
sediment prior to colonization by seagrasses. The OC concentration in the original
unvegetated sediment would have been even lower than that in sediment in zones
adjacent to meadows. Therefore, the influence of seagrass meadows on sediment
OC stock would be greater than expected from the comparison described above.
Based on a compilation of more than 200 datasets from 88 seagrass meadows
worldwide, Kennedy et al. (2010) also reported that the actual OC concentration in
0
50
100
OC loading
(µmol m )
Deposition-resuspension cycles
Fluid mud incinerators
Erosion-deposition cycles
Soil formation
Terrestrial OC &
clastic sediment
Plankton production
Plankton
production
a
0
50
100
OC loading
(µmol m )
Production, accumulation, and
preservation of OC
Mangrove &
salt marsh Seagrass
Coral reef
& seagrass
Reef development &
accumulation of OC+IC
Terrestrial OC &
clastic sediment
Plankton production
Plankton
production
b
Terrestrial OC
Petrogenic OC
Marine OC
Fig. 2.6 Carbon sequestration as an ecosystem function of coastal vegetated ecosystems (CVEs)
from a sediment source-sink perspective (Blair and Aller 2012). (a) Schematic representation of
the serial transport-reaction system from the watershed to the coastal ocean in the absence of the
CVEs. The shallow coastal sedimentary system plays a role as a “fluid mud incinerator”, in which
OC delivered from the watershed is efficiently oxidized and remineralized via deposition–
resuspension cycling (modified from Fig. 4 of Blair and Aller (2012)). (b) Establishment of CVEs
converts a portion of the coastal sedimentary system into a site of efficient OC sequestration via
their own primary production and sediment accumulation/stabilization functions. Development of
coral reefs also enhances OC sequestration by providing favorable habitats for CVEs (Watanabe
and Nakamura (2018) in this volume). Bar graphs below the diagrams show the typical spatial
changes in OC loading of surface sediment and the fractions of OC attributed to marine, terrestrial,
and “petrogenic” (ancient crustal) organic matter. The advent of CVEs is thus assumed to have
considerably altered the global carbon cycle
2 Carbon Sequestration in Sediment as an Ecosystem Function of Seagrass Meadows
mixed- species seagrass beds and adjacent barren areas of back-reef carbonate sediments (Miyajima et al. 1998, 2001b). Thus, seagrass meadows may generally have
an ecosystem function of increasing the storage of OC in sediment to at least twice
the extent of storage observed under the same oceanographic conditions in the
absence of seagrass. It should be noted that sediment in unvegetated zones neighboring seagrass meadows often contains a significant amount of OC exported from
the seagrass meadow (Kennedy et al. 2010) and cannot be considered equivalent to
sediment prior to colonization by seagrasses. The OC concentration in the original
unvegetated sediment would have been even lower than that in sediment in zones
adjacent to meadows. Therefore, the influence of seagrass meadows on sediment
OC stock would be greater than expected from the comparison described above.
Based on a compilation of more than 200 datasets from 88 seagrass meadows
worldwide, Kennedy et al. (2010) also reported that the actual OC concentration in
0
50
100
OC loading
(µmol m )
Deposition-resuspension cycles
Fluid mud incinerators
Erosion-deposition cycles
Soil formation
Terrestrial OC &
clastic sediment
Plankton production
Plankton
production
a
0
50
100
OC loading
(µmol m )
Production, accumulation, and
preservation of OC
Mangrove &
salt marsh Seagrass
Coral reef
& seagrass
Reef development &
accumulation of OC+IC
Terrestrial OC &
clastic sediment
Plankton production
Plankton
production
b
Terrestrial OC
Petrogenic OC
Marine OC
Fig. 2.6 Carbon sequestration as an ecosystem function of coastal vegetated ecosystems (CVEs)
from a sediment source-sink perspective (Blair and Aller 2012). (a) Schematic representation of
the serial transport-reaction system from the watershed to the coastal ocean in the absence of the
CVEs. The shallow coastal sedimentary system plays a role as a “fluid mud incinerator”, in which
OC delivered from the watershed is efficiently oxidized and remineralized via deposition–
resuspension cycling (modified from Fig. 4 of Blair and Aller (2012)). (b) Establishment of CVEs
converts a portion of the coastal sedimentary system into a site of efficient OC sequestration via
their own primary production and sediment accumulation/stabilization functions. Development of
coral reefs also enhances OC sequestration by providing favorable habitats for CVEs (Watanabe
and Nakamura (2018) in this volume). Bar graphs below the diagrams show the typical spatial
changes in OC loading of surface sediment and the fractions of OC attributed to marine, terrestrial,
and “petrogenic” (ancient crustal) organic matter. The advent of CVEs is thus assumed to have
considerably altered the global carbon cycle
2 Carbon Sequestration in Sediment as an Ecosystem Function of Seagrass Meadows