181
In this chapter, we discussed previous investigations of air–water CO 2 fluxes that
used several methods in shallow coastal ecosystems. Empirical measurements using
multiple methods revealed that autotrophic seagrass meadows can be a sink of
atmospheric CO 2 over the course of a year. Also, macroalgal beds can directly
absorb atmospheric CO 2 . In coral reefs, the relative rate of photosynthesis and calcification is the key factor that determines whether these ecosystems are net sinks or
sources of atmospheric CO 2 .
Statistical prediction methods may be practical for quantifying the effect of the
interactions between regulating factors on the air–water CO 2 flux and also provide
information on the spatial and temporal variability of the fluxes.
Studies exploiting carbon isotopes have demonstrated that the CO 2 flux between
the atmosphere and seagrass water-films may contribute to the uptake of atmospheric CO 2 by eelgrass beds. Determining the pathways of CO 2 absorption via this
process should be addressed in future studies of air–aquatic ecosystem CO 2 fluxes.
Accurate quantification of air–aquatic ecosystem CO 2 fluxes over local, regional,
and global scales is essential for assessing the role of shallow coastal ecosystems in
mitigating the effects of anthropogenic CO 2 emissions. Fluxes should be measured
at dense spatiotemporal scales in various types of shallow coastal ecosystems for
this purpose. We propose two strategies for this extensive data collection.
The first approach is to build observation facilities based mainly on the eddy covariance method around the world and to conduct long-term measurements over annual
and decadal time scales (e.g., FLUXNET in terrestrial ecosystems). The observation
facilities should be deployed in various types of ecosystem (i.e., seagrass meadows,
mangroves, saltmarshes, macroalgal beds, coral reefs, tidal flats, and urbanized systems). A combination of multiple methods such as the bulk formula method and the
floating chamber method will be necessary to complement the eddy-covariance CO 2
flux estimates by assessing details of the pertinent mechanisms.
The second approach is to develop simple, low-cost, and easy-to-use methods for
non-specialists and organizations. This approach will facilitate filling gaps in the
spatial and temporal coverage of the data. Statistical prediction is a candidate
method in this respect, although the accuracy of statistical predictions should be
enhanced in future studies. Because the accuracy of statistical predictions can be
improved with empirical data, the concurrent use of both of these approaches will
promote the quantification of CO 2 exchanges in blue carbon ecosystems at national
and global scales.
References
Akhand A, Chanda A, Manna S et al (2016) A comparison of CO 2 dynamics and air-water fluxes
in a river-dominated estuary and a mangrove-dominated marine estuary. Geophys Res Lett
43:726–735
Akhand A, Chanda A, Das S, Hazra S, Kuwae T (2018) CO 2 fluxes in mangrove ecosystems. In:
Kuwae T, Hori M (eds) Blue carbon in shallow coastal ecosystems: carbon dynamics, policy,
and implementation. Springer, Singapore, pp 185–221
6 Air–Water CO 2 Flux in Shallow Coastal Waters: Theory, Methods…
In this chapter, we discussed previous investigations of air–water CO 2 fluxes that
used several methods in shallow coastal ecosystems. Empirical measurements using
multiple methods revealed that autotrophic seagrass meadows can be a sink of
atmospheric CO 2 over the course of a year. Also, macroalgal beds can directly
absorb atmospheric CO 2 . In coral reefs, the relative rate of photosynthesis and calcification is the key factor that determines whether these ecosystems are net sinks or
sources of atmospheric CO 2 .
Statistical prediction methods may be practical for quantifying the effect of the
interactions between regulating factors on the air–water CO 2 flux and also provide
information on the spatial and temporal variability of the fluxes.
Studies exploiting carbon isotopes have demonstrated that the CO 2 flux between
the atmosphere and seagrass water-films may contribute to the uptake of atmospheric CO 2 by eelgrass beds. Determining the pathways of CO 2 absorption via this
process should be addressed in future studies of air–aquatic ecosystem CO 2 fluxes.
Accurate quantification of air–aquatic ecosystem CO 2 fluxes over local, regional,
and global scales is essential for assessing the role of shallow coastal ecosystems in
mitigating the effects of anthropogenic CO 2 emissions. Fluxes should be measured
at dense spatiotemporal scales in various types of shallow coastal ecosystems for
this purpose. We propose two strategies for this extensive data collection.
The first approach is to build observation facilities based mainly on the eddy covariance method around the world and to conduct long-term measurements over annual
and decadal time scales (e.g., FLUXNET in terrestrial ecosystems). The observation
facilities should be deployed in various types of ecosystem (i.e., seagrass meadows,
mangroves, saltmarshes, macroalgal beds, coral reefs, tidal flats, and urbanized systems). A combination of multiple methods such as the bulk formula method and the
floating chamber method will be necessary to complement the eddy-covariance CO 2
flux estimates by assessing details of the pertinent mechanisms.
The second approach is to develop simple, low-cost, and easy-to-use methods for
non-specialists and organizations. This approach will facilitate filling gaps in the
spatial and temporal coverage of the data. Statistical prediction is a candidate
method in this respect, although the accuracy of statistical predictions should be
enhanced in future studies. Because the accuracy of statistical predictions can be
improved with empirical data, the concurrent use of both of these approaches will
promote the quantification of CO 2 exchanges in blue carbon ecosystems at national
and global scales.
References
Akhand A, Chanda A, Manna S et al (2016) A comparison of CO 2 dynamics and air-water fluxes
in a river-dominated estuary and a mangrove-dominated marine estuary. Geophys Res Lett
43:726–735
Akhand A, Chanda A, Das S, Hazra S, Kuwae T (2018) CO 2 fluxes in mangrove ecosystems. In:
Kuwae T, Hori M (eds) Blue carbon in shallow coastal ecosystems: carbon dynamics, policy,
and implementation. Springer, Singapore, pp 185–221
6 Air–Water CO 2 Flux in Shallow Coastal Waters: Theory, Methods…