313
areas from estuaries to shelves will be accelerated in the future due to an increase in
atmospheric CO 2 concentration and increased nutrient loads (Andersson and
Mackenzie 2004).
11.4.2 Revaluation of Stored Carbon
Many studies on the importance of blue carbon ecosystems and their conservation
are based on the premise that if the ecosystem degrades or disappears, all of the
carbon stored will be mineralized and released into the atmosphere as CO 2 (e.g.,
McLeod et al. 2011). This assumption, however, is a worst case scenario and clearly
overestimates emissions (Pendleton et al. 2012; Macreadie et al. 2014; Lovelock
et al. 2017). Thus, further research is needed to examine the relationship between
the degree of degradation or extinction of the ecosystem and indices such as the
ecosystem area, vegetation biomass, net ecosystem production rate, and amount of
carbon storage (Kuwae and Hori 2018).
As green carbon is stored in SCEs together with blue carbon, there is room for
discussion as to whether the land-derived green carbon should also be included in
the blue carbon storage function. It may be reasonable to include green carbon if the
decision is based on the site where carbon is stored. Similarly, it may be reasonable
to exclude green carbon if it is based on the site where CO 2 is first captured from the
atmosphere. Indeed, some studies have estimated the contribution of blue carbon
and green carbon separately (Middelburg et al. 1997; Kennedy et al. 2010; Dubois
et al. 2012; Miyajima et al. 2015; Watanabe and Kuwae 2015; Kubo and Kanda
2017). Likewise, there needs to be discussion as to whether particulate blue carbon
(POC) and macrophyte drifts that flow out of the SCE and are stored at the seabed
of the shelf or the open ocean is also included as SCE blue carbon storage (KrauseJensen and Duarte 2016; Duarte and Krause-Jensen 2017; Abo et al. 2018).
11.4.3 Mitigation of Climate Change Through Wastewater
Treatment
In this chapter, we noted that CO 2 emission from human-impacted SCEs is suppressed because carbon flowing into the SCE has been largely removed by wastewater treatment. This means that CO 2 that would be emitted from the sea surface is
instead emitted from the wastewater treatment plant. In other words, if we view the
land and SCE as an integrated system, the amount of CO 2 taken up by the SCE may
be canceled out by the emission from decomposition of organic matter in the open
aeration tank of the wastewater treatment plant. However, by appropriate management of wastewater treatment, we are able to suppress CO 2 emission from the treatment plant or capture carbon (Fig. 11.8). For example, the generated sludge can be
11 CO 2 Uptake in the Shallow Coastal Ecosystems Affected…
areas from estuaries to shelves will be accelerated in the future due to an increase in
atmospheric CO 2 concentration and increased nutrient loads (Andersson and
Mackenzie 2004).
11.4.2 Revaluation of Stored Carbon
Many studies on the importance of blue carbon ecosystems and their conservation
are based on the premise that if the ecosystem degrades or disappears, all of the
carbon stored will be mineralized and released into the atmosphere as CO 2 (e.g.,
McLeod et al. 2011). This assumption, however, is a worst case scenario and clearly
overestimates emissions (Pendleton et al. 2012; Macreadie et al. 2014; Lovelock
et al. 2017). Thus, further research is needed to examine the relationship between
the degree of degradation or extinction of the ecosystem and indices such as the
ecosystem area, vegetation biomass, net ecosystem production rate, and amount of
carbon storage (Kuwae and Hori 2018).
As green carbon is stored in SCEs together with blue carbon, there is room for
discussion as to whether the land-derived green carbon should also be included in
the blue carbon storage function. It may be reasonable to include green carbon if the
decision is based on the site where carbon is stored. Similarly, it may be reasonable
to exclude green carbon if it is based on the site where CO 2 is first captured from the
atmosphere. Indeed, some studies have estimated the contribution of blue carbon
and green carbon separately (Middelburg et al. 1997; Kennedy et al. 2010; Dubois
et al. 2012; Miyajima et al. 2015; Watanabe and Kuwae 2015; Kubo and Kanda
2017). Likewise, there needs to be discussion as to whether particulate blue carbon
(POC) and macrophyte drifts that flow out of the SCE and are stored at the seabed
of the shelf or the open ocean is also included as SCE blue carbon storage (KrauseJensen and Duarte 2016; Duarte and Krause-Jensen 2017; Abo et al. 2018).
11.4.3 Mitigation of Climate Change Through Wastewater
Treatment
In this chapter, we noted that CO 2 emission from human-impacted SCEs is suppressed because carbon flowing into the SCE has been largely removed by wastewater treatment. This means that CO 2 that would be emitted from the sea surface is
instead emitted from the wastewater treatment plant. In other words, if we view the
land and SCE as an integrated system, the amount of CO 2 taken up by the SCE may
be canceled out by the emission from decomposition of organic matter in the open
aeration tank of the wastewater treatment plant. However, by appropriate management of wastewater treatment, we are able to suppress CO 2 emission from the treatment plant or capture carbon (Fig. 11.8). For example, the generated sludge can be
11 CO 2 Uptake in the Shallow Coastal Ecosystems Affected…