269
about 30,000 tons (40.9%) accumulated on the seabed in the Seto Inland Sea and
about 6000 tons (8.3%) flowed out and accumulated in the deep sea.
Thus, the total amount of carbon accumulated in the Seto Inland Sea and the deep
sea is about 36,000 tons per year. We estimate that this amount accumulates yearly
and is stored in the seabed, assuming that no additional mineralization occurs in the
sediment after the first year. In other words, the eelgrass beds in the Seto Inland Sea
can be regarded as having 36,000 tons of potential carbon storage capacity annually.
The eelgrass bed area estimated from the satellite image used in the model was
about 19,000 ha, so the carbon storage capacity of the eelgrass beds is about 1.9 tons
ha
−1
. The annual carbon uptake of artificial (reforested and afforested) Cryptomeria
japonica forests was estimated to be about 2.3 tons ha
−1
(Forestry Agency of Japan),
so the eelgrass beds in the Seto Inland Sea have a potential carbon sequestration and
storage capacity comparable to that of cedar plantations. In addition, most of the
eelgrass-derived organic carbon was accumulated in the shallow water of the Seto
Inland Sea, with only about one-sixth accumulated in the deep sea. Thus far, organic
carbon sequestered in shallow coastal waters was not thought to be stored unless it
settled in the deep sea, but our case study suggests that much more is stored in shallow coastal waters.
The carbon storage capacity of eelgrass beds described in this chapter was based
on a value estimated over 1 year. However, some issues remain to be clarified, such
as the storage period of organic carbon in the sediment. Therefore, it is necessary to
improve our knowledge of the decomposition process of eelgrass-derived organic
carbon accumulated in the sediment when we discuss the carbon storage function at
longer time scales of several decades to a century. Moreover, the model calculations
introduced here were based on various assumptions, and the reproducibility was not
sufficiently verified due to the difficulty of acquiring data in the actual sea area.
Thus, future research is needed to improve the accuracy of the estimates reported
here.
To date, there were individual models that dealt with seagrass growth, material
circulation in seagrass meadows, and tracking drifting leaves. The model presented
in this chapter is a combination of these, using seagrass growth models, material
circulation models, and drifting leave tracking models. This is the first model to
estimate the carbon storage capacity of seagrass meadows by tracking seagrassderived carbon from the meadows through shallow coastal waters to the deep sea.
References
Aioi K (1980) Seasonal changes in the standing crop of eelgrass (Zostera marina L.) in Odawa
Bay, central Japan. Aquat Bot 8:343–354
Bach HK (1993) A dynamic model describing the seasonal variations in growth and the distribution of eelgrass (Zostera marina L.). I. Model theory. Ecol Model 65:31–50
Bocci M, Coffaro G, Bendoricchio G (1997) Modelling biomass and nutrient dynamics in eelgrass
(Zostera marina L.): applications to the Lagoon of Venice (Italy) and Øresund (Denmark). Ecol
Model 102:67–80
9 Quantifying the Fate of Captured Carbon: From Seagrass Meadows to the Deep Sea
about 30,000 tons (40.9%) accumulated on the seabed in the Seto Inland Sea and
about 6000 tons (8.3%) flowed out and accumulated in the deep sea.
Thus, the total amount of carbon accumulated in the Seto Inland Sea and the deep
sea is about 36,000 tons per year. We estimate that this amount accumulates yearly
and is stored in the seabed, assuming that no additional mineralization occurs in the
sediment after the first year. In other words, the eelgrass beds in the Seto Inland Sea
can be regarded as having 36,000 tons of potential carbon storage capacity annually.
The eelgrass bed area estimated from the satellite image used in the model was
about 19,000 ha, so the carbon storage capacity of the eelgrass beds is about 1.9 tons
ha
−1
. The annual carbon uptake of artificial (reforested and afforested) Cryptomeria
japonica forests was estimated to be about 2.3 tons ha
−1
(Forestry Agency of Japan),
so the eelgrass beds in the Seto Inland Sea have a potential carbon sequestration and
storage capacity comparable to that of cedar plantations. In addition, most of the
eelgrass-derived organic carbon was accumulated in the shallow water of the Seto
Inland Sea, with only about one-sixth accumulated in the deep sea. Thus far, organic
carbon sequestered in shallow coastal waters was not thought to be stored unless it
settled in the deep sea, but our case study suggests that much more is stored in shallow coastal waters.
The carbon storage capacity of eelgrass beds described in this chapter was based
on a value estimated over 1 year. However, some issues remain to be clarified, such
as the storage period of organic carbon in the sediment. Therefore, it is necessary to
improve our knowledge of the decomposition process of eelgrass-derived organic
carbon accumulated in the sediment when we discuss the carbon storage function at
longer time scales of several decades to a century. Moreover, the model calculations
introduced here were based on various assumptions, and the reproducibility was not
sufficiently verified due to the difficulty of acquiring data in the actual sea area.
Thus, future research is needed to improve the accuracy of the estimates reported
here.
To date, there were individual models that dealt with seagrass growth, material
circulation in seagrass meadows, and tracking drifting leaves. The model presented
in this chapter is a combination of these, using seagrass growth models, material
circulation models, and drifting leave tracking models. This is the first model to
estimate the carbon storage capacity of seagrass meadows by tracking seagrassderived carbon from the meadows through shallow coastal waters to the deep sea.
References
Aioi K (1980) Seasonal changes in the standing crop of eelgrass (Zostera marina L.) in Odawa
Bay, central Japan. Aquat Bot 8:343–354
Bach HK (1993) A dynamic model describing the seasonal variations in growth and the distribution of eelgrass (Zostera marina L.). I. Model theory. Ecol Model 65:31–50
Bocci M, Coffaro G, Bendoricchio G (1997) Modelling biomass and nutrient dynamics in eelgrass
(Zostera marina L.): applications to the Lagoon of Venice (Italy) and Øresund (Denmark). Ecol
Model 102:67–80
9 Quantifying the Fate of Captured Carbon: From Seagrass Meadows to the Deep Sea