259
tively. The amount of outflow has been reported to be about 30% of the fallen shoot
in dense eelgrass beds and about 70% in sparse eelgrass beds (Hemminga and
Duarte 2000). Therefore, the amounts of outflow shoots (drifting leaves) from the
dense and sparse eelgrass beds are estimated to be 0.49 and 0.58 kg DW m
−2
year
−1
,
respectively. Note that the rate of shoot flowing out is larger for the sparse eelgrass
bed, whereas that of fallen shoot is larger in the dense eelgrass bed.
Next, we consider eelgrass-derived organic matter that flows out as suspended
particles. Eelgrass-derived organic matter that has become fine particles due to fragmentation or decomposition is stirred up by water flow and resuspended in the water
column. The suspended particles are transported by the currents and some flow out
of the eelgrass bed, while the rest settle again within the eelgrass bed when conditions become calm. According to a sediment trap survey in the eelgrass beds around
Ikuno Island, the amount of suspended organic matter (including small leave fragments) that flowed out of the eelgrass bed was 0.015 kg DW m
−2
year
−1
. This corresponds to 0.3% of the eelgrass production, or about 3% of the amount that flowed
out as drifting leaves.
9.4 Fate of Eelgrass-Derived Organic Carbon in Eelgrass
vBeds
In the previous sections, we described the sedimentation, decomposition, and outflow of eelgrass leaves. However, to evaluate carbon storage in eelgrass beds, it is
necessary to quantify the development of eelgrass (including death and leave loss).
In this section, we introduce a numerical model of the population dynamics of eelgrass and describe the mass balance within the eelgrass bed estimated by the model
simulation.
9.4.1 Modeling the Growth and Withering Process of Eelgrass
The basic idea of the numerical eelgrass growth models is similar to low trophic
ecosystem models targeting phytoplankton; they mathematically express that
growth by photosynthesis depends on environmental factors such as solar radiation,
water temperature, and nutrient concentrations. Because eelgrass is divided into an
aboveground part composed of blades and a sheath and a belowground part composed of rhizomes and fibrous roots, most models calculate biomasses of the
aboveground part and the belowground part (Verhagen and Nienhuis 1983, Bach
1993, Bocci et al. 1997, Zharova et al. 2001). Here, we introduce a model developed
by Tarutani et al. (2011), which they modified from the relatively simple and highly
versatile model of Bocci et al. (1997).
Figure 9.7 shows the outline of the eelgrass growth model. In this model, we
calculate the biomasses of the aboveground and belowground parts, and the amount
9 Quantifying the Fate of Captured Carbon: From Seagrass Meadows to the Deep Sea
tively. The amount of outflow has been reported to be about 30% of the fallen shoot
in dense eelgrass beds and about 70% in sparse eelgrass beds (Hemminga and
Duarte 2000). Therefore, the amounts of outflow shoots (drifting leaves) from the
dense and sparse eelgrass beds are estimated to be 0.49 and 0.58 kg DW m
−2
year
−1
,
respectively. Note that the rate of shoot flowing out is larger for the sparse eelgrass
bed, whereas that of fallen shoot is larger in the dense eelgrass bed.
Next, we consider eelgrass-derived organic matter that flows out as suspended
particles. Eelgrass-derived organic matter that has become fine particles due to fragmentation or decomposition is stirred up by water flow and resuspended in the water
column. The suspended particles are transported by the currents and some flow out
of the eelgrass bed, while the rest settle again within the eelgrass bed when conditions become calm. According to a sediment trap survey in the eelgrass beds around
Ikuno Island, the amount of suspended organic matter (including small leave fragments) that flowed out of the eelgrass bed was 0.015 kg DW m
−2
year
−1
. This corresponds to 0.3% of the eelgrass production, or about 3% of the amount that flowed
out as drifting leaves.
9.4 Fate of Eelgrass-Derived Organic Carbon in Eelgrass
vBeds
In the previous sections, we described the sedimentation, decomposition, and outflow of eelgrass leaves. However, to evaluate carbon storage in eelgrass beds, it is
necessary to quantify the development of eelgrass (including death and leave loss).
In this section, we introduce a numerical model of the population dynamics of eelgrass and describe the mass balance within the eelgrass bed estimated by the model
simulation.
9.4.1 Modeling the Growth and Withering Process of Eelgrass
The basic idea of the numerical eelgrass growth models is similar to low trophic
ecosystem models targeting phytoplankton; they mathematically express that
growth by photosynthesis depends on environmental factors such as solar radiation,
water temperature, and nutrient concentrations. Because eelgrass is divided into an
aboveground part composed of blades and a sheath and a belowground part composed of rhizomes and fibrous roots, most models calculate biomasses of the
aboveground part and the belowground part (Verhagen and Nienhuis 1983, Bach
1993, Bocci et al. 1997, Zharova et al. 2001). Here, we introduce a model developed
by Tarutani et al. (2011), which they modified from the relatively simple and highly
versatile model of Bocci et al. (1997).
Figure 9.7 shows the outline of the eelgrass growth model. In this model, we
calculate the biomasses of the aboveground and belowground parts, and the amount
9 Quantifying the Fate of Captured Carbon: From Seagrass Meadows to the Deep Sea