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carbon reservoirs and providing direct net uptake of atmospheric CO 2 , in light of
human systems–ecosystem interactions. Namely, if we view the land and a SCE as
an integrated system, with appropriate management of both wastewater treatment
and SCE, we will be able to not only suppress CO 2 release but also capture and store
carbon.
11.1 Introduction
Recent research has demonstrated that the sediment of shallow coastal ecosystems
(SCEs), such as mangroves, salt marshes, tidal flats, seagrass meadows, estuaries,
and embayment, is important as a marine carbon reservoir (e.g., Nellemann et al.
2009; McLeod et al. 2011; Fourqurean et al. 2012; Duarte et al. 2013; Miyajima
et al. 2015, 2017; Endo and Otani 2018; Inoue 2018; Miyajima and Hamaguchi
2018). Moreover, coastal ecosystems with high primary productivity, such as seagrass meadows, can serve as net sinks for atmospheric CO 2 (i.e., total CO 2 uptake
minus total CO 2 release is positive; Smith 1981; Tokoro et al. 2014).
From the viewpoint of mitigating climate change, the net uptake of atmospheric
CO 2 through the exchange of CO 2 at the air–water interface is a direct process,
whereas the suppression of CO 2 emission to the atmosphere by carbon storage in the
marine ecosystem is an indirect process (Fig. 11.1). Although these are two completely different processes, both are effective for mitigating climate change. There
is controversy as to which is more important, but ecosystems that show both net
uptake of atmospheric CO 2 and long-term storage of carbon are desirable.
However, because ecosystems are dynamic natural systems characterized by
complex fluctuations in biological communities and environmental conditions,
atmospheric CO 2 uptake and carbon storage do not occur at constant rates. The CO 2
gas exchange at the air–water interface fluctuates through absorption and emission
phases and the amount of carbon stored in the ecosystem increases and decreases
over time (Tokoro et al. 2014, 2018). Therefore, in considering the effectiveness of
ecosystem-based technology measures such as mitigation of climate change through
the use of blue carbon ecosystems, setting a specified time and space of interest in
advance is important to judge whether atmospheric CO 2 is taken up or whether carbon is stored. As the temporal and spatial scales of the processes increase, the measure becomes more effective and more reliable.
The effect of human activity cannot be ignored at longer time scales. The geophysical setting of SCEs is often at the boundary between land and sea, making
them socioeconomically important features. As a result, the carbon cycle of many
SCEs has changed significantly over time due to the load of nutrients and organic
matter (green carbon), freshwater use, and topographic modification (Bauer et al.
2013; Regnier et al. 2013). In particular, because nutrient loading and wastewater
T. Kuwae et al.
carbon reservoirs and providing direct net uptake of atmospheric CO 2 , in light of
human systems–ecosystem interactions. Namely, if we view the land and a SCE as
an integrated system, with appropriate management of both wastewater treatment
and SCE, we will be able to not only suppress CO 2 release but also capture and store
carbon.
11.1 Introduction
Recent research has demonstrated that the sediment of shallow coastal ecosystems
(SCEs), such as mangroves, salt marshes, tidal flats, seagrass meadows, estuaries,
and embayment, is important as a marine carbon reservoir (e.g., Nellemann et al.
2009; McLeod et al. 2011; Fourqurean et al. 2012; Duarte et al. 2013; Miyajima
et al. 2015, 2017; Endo and Otani 2018; Inoue 2018; Miyajima and Hamaguchi
2018). Moreover, coastal ecosystems with high primary productivity, such as seagrass meadows, can serve as net sinks for atmospheric CO 2 (i.e., total CO 2 uptake
minus total CO 2 release is positive; Smith 1981; Tokoro et al. 2014).
From the viewpoint of mitigating climate change, the net uptake of atmospheric
CO 2 through the exchange of CO 2 at the air–water interface is a direct process,
whereas the suppression of CO 2 emission to the atmosphere by carbon storage in the
marine ecosystem is an indirect process (Fig. 11.1). Although these are two completely different processes, both are effective for mitigating climate change. There
is controversy as to which is more important, but ecosystems that show both net
uptake of atmospheric CO 2 and long-term storage of carbon are desirable.
However, because ecosystems are dynamic natural systems characterized by
complex fluctuations in biological communities and environmental conditions,
atmospheric CO 2 uptake and carbon storage do not occur at constant rates. The CO 2
gas exchange at the air–water interface fluctuates through absorption and emission
phases and the amount of carbon stored in the ecosystem increases and decreases
over time (Tokoro et al. 2014, 2018). Therefore, in considering the effectiveness of
ecosystem-based technology measures such as mitigation of climate change through
the use of blue carbon ecosystems, setting a specified time and space of interest in
advance is important to judge whether atmospheric CO 2 is taken up or whether carbon is stored. As the temporal and spatial scales of the processes increase, the measure becomes more effective and more reliable.
The effect of human activity cannot be ignored at longer time scales. The geophysical setting of SCEs is often at the boundary between land and sea, making
them socioeconomically important features. As a result, the carbon cycle of many
SCEs has changed significantly over time due to the load of nutrients and organic
matter (green carbon), freshwater use, and topographic modification (Bauer et al.
2013; Regnier et al. 2013). In particular, because nutrient loading and wastewater
T. Kuwae et al.