352
was indirectly calculated as the residual value of the global carbon budget and the
mangrove and tidal marsh contributions were excluded from the oceans’ uptake rate
(Le Quéré et al. 2018).
However, even when we subtract these two estimates from the total SCE uptake
rate, the CO 2 exchange rate (−669 Tg C year
−1
) is still higher than the soil carbon
accumulation rate. The estimate for macroalgal beds ranged from −4202 to 202 Tg
C year
−1
, with a mean of −913 Tg C year
−1
, contributing to the high net uptake rate.
We should note that only one study investigated macroalgal beds (Ikawa and Oechel
2015) and thus this ecosystem type has a considerable spatial uncertainty as a global
estimate, although the study included 3 years of observational data gathered using
the state-of-the-art eddy covariance technique.
Studies dealing with a suite of key processes for air–water CO 2 fluxes, such as
carbonate chemistry and organic carbon dynamics, are still scarce in SCEs (but see
Maher and Eyre 2012; Tokoro et al. 2014; Watanabe and Kuwae 2015), although
recent studies have begun to address the abundance and burial rates for both organic
and inorganic carbon in sediments and soils (e.g., Mazarrasa et al. 2015; Fodrie
et al. 2017; Macreadie et al. 2017; Howard et al. 2018). In particular, even though
SCEs are significant organic carbon reservoirs, they can also be net emitters of CO 2
to the atmosphere through air–sea gas exchange, depending on the organic and
inorganic carbon dynamics (Regnier et al. 2013), as autochthonous calcification
increases the CO 2 concentration in water (Ware et al. 1992; Watanabe and
Nakamura 2018).
Nevertheless, our results should help to encourage discussions regarding the
uncertainty in the current estimates of global carbon cycling for both terrestrial and
marine ecosystems. In addition, our findings also reveal the necessity for more
research on carbon dynamics to improve our understanding of the potential functioning of SCEs for climate change mitigation.
13.3 Toward Strengthening Science and Technology
13.3.1 Current Status
Ecosystem management can be effective for maintaining multiple ecosystem
services in a sustainable manner (Hori et al. 2018). However, problems often
arise when decision-makers (e.g., governmental and administrative agencies)
have to make policy decisions without scientific and technological knowledge
(Russell- Smith et al. 2015). Thus, it is important that policy-making organizations
are closely connected with the science and engineering researchers assessing
changes in ecosystem status.
Blue carbon initiatives are moving from the advocating stage with reports from
the United Nations Environmental Programme (UNEP) (Nellemann et al. 2009) and
the International Union for Conservation of Nature (Laffoley and Grimsditch 2009)
T. Kuwae and M. Hori
was indirectly calculated as the residual value of the global carbon budget and the
mangrove and tidal marsh contributions were excluded from the oceans’ uptake rate
(Le Quéré et al. 2018).
However, even when we subtract these two estimates from the total SCE uptake
rate, the CO 2 exchange rate (−669 Tg C year
−1
) is still higher than the soil carbon
accumulation rate. The estimate for macroalgal beds ranged from −4202 to 202 Tg
C year
−1
, with a mean of −913 Tg C year
−1
, contributing to the high net uptake rate.
We should note that only one study investigated macroalgal beds (Ikawa and Oechel
2015) and thus this ecosystem type has a considerable spatial uncertainty as a global
estimate, although the study included 3 years of observational data gathered using
the state-of-the-art eddy covariance technique.
Studies dealing with a suite of key processes for air–water CO 2 fluxes, such as
carbonate chemistry and organic carbon dynamics, are still scarce in SCEs (but see
Maher and Eyre 2012; Tokoro et al. 2014; Watanabe and Kuwae 2015), although
recent studies have begun to address the abundance and burial rates for both organic
and inorganic carbon in sediments and soils (e.g., Mazarrasa et al. 2015; Fodrie
et al. 2017; Macreadie et al. 2017; Howard et al. 2018). In particular, even though
SCEs are significant organic carbon reservoirs, they can also be net emitters of CO 2
to the atmosphere through air–sea gas exchange, depending on the organic and
inorganic carbon dynamics (Regnier et al. 2013), as autochthonous calcification
increases the CO 2 concentration in water (Ware et al. 1992; Watanabe and
Nakamura 2018).
Nevertheless, our results should help to encourage discussions regarding the
uncertainty in the current estimates of global carbon cycling for both terrestrial and
marine ecosystems. In addition, our findings also reveal the necessity for more
research on carbon dynamics to improve our understanding of the potential functioning of SCEs for climate change mitigation.
13.3 Toward Strengthening Science and Technology
13.3.1 Current Status
Ecosystem management can be effective for maintaining multiple ecosystem
services in a sustainable manner (Hori et al. 2018). However, problems often
arise when decision-makers (e.g., governmental and administrative agencies)
have to make policy decisions without scientific and technological knowledge
(Russell- Smith et al. 2015). Thus, it is important that policy-making organizations
are closely connected with the science and engineering researchers assessing
changes in ecosystem status.
Blue carbon initiatives are moving from the advocating stage with reports from
the United Nations Environmental Programme (UNEP) (Nellemann et al. 2009) and
the International Union for Conservation of Nature (Laffoley and Grimsditch 2009)
T. Kuwae and M. Hori