214
7.5.2.9 Factors Regulating Air-Water CO 2 Fluxes
Upon doing a comparative analysis between the air-water CO 2 fluxes observed in
the Sundarbans and the other mangroves throughout the world, it can be seen that
the magnitude of fluxes are quite low in Sundarbans. One of the main reasons behind
such a contrasting finding may be that Sundarbans happen to be one of the rarest
examples where the estuary is almost enclosed on the landward end and the freshwater flow is substantially less. Moreover, the area and volume of the estuaries are
fairly large which allows a huge quantity of seawater to approach during high tide
and recede during the low tide.
Very recently Rosentreter et al. (2018) after carrying out a holistic review mentioned that Sundarbans happen to be the only mangrove site in the world, where the
water mass acts as a sink for CO 2 . However, the study of Akhand et al. (2013)
showed that was a significant spatial variability in CO 2 fluxes from the inward stations towards the outward stations; the inward stations acted as mild source of CO 2
whereas the outward stations acted as sinks. Usually a strong relation between the
salinity and pCO 2 in water is seen in the mangrove waters especially while analyzing the spatial variability. However, in Sundarban (Indian part) since there is no
significant freshwater supply from the landward end such spatial relation was not
observed.
Apart from these the effect of tides were observed to be the same as in case of
other mangroves of the world; i.e., higher fluxes during low tides and vice-versa.
7.6 Summary and Conclusion
Scrutinizing the findings of all the studies related to the atmosphere-biosphere CO 2
fluxes, soil CO 2 fluxes and air-water CO 2 fluxes conducted in the global mangroves,
it can be summed up that almost all the mangrove forests that are studied throughout
the world are at present acting as significant sinks of CO 2 . However, still a lot of
endeavor needs to be taken to estimate the year round global budgets of these fluxes
and to reduce the uncertainties in the computation of these fluxes.
In this chapter we came to see that there could be various factors regulating
atmosphere-biosphere CO 2 fluxes like canopy cover, species composition, age of
the trees, ambient temperature near the canopy, rainfall, salinity regime in the forest
floor and so forth, however, all the studies did not take into account each of these
factors in the respective study sites. Much more data characterizing the fluxes with
respect to all these factors in many more mangrove sites than what could be found
at present is required to understand the CO 2 dynamics between the atmosphere and
the mangrove canopy.
The research conducted in the Sundarban mangroves highlighted that for a vast
stretch of mangroves like that of Sundarbans and especially where there lies a substantial heterogeneity in species assemblage, spatially explicit sampling is badly
needed to properly up-scale the CO 2 flux data for the entire forest stretch. However,
A. Akhand et al.
7.5.2.9 Factors Regulating Air-Water CO 2 Fluxes
Upon doing a comparative analysis between the air-water CO 2 fluxes observed in
the Sundarbans and the other mangroves throughout the world, it can be seen that
the magnitude of fluxes are quite low in Sundarbans. One of the main reasons behind
such a contrasting finding may be that Sundarbans happen to be one of the rarest
examples where the estuary is almost enclosed on the landward end and the freshwater flow is substantially less. Moreover, the area and volume of the estuaries are
fairly large which allows a huge quantity of seawater to approach during high tide
and recede during the low tide.
Very recently Rosentreter et al. (2018) after carrying out a holistic review mentioned that Sundarbans happen to be the only mangrove site in the world, where the
water mass acts as a sink for CO 2 . However, the study of Akhand et al. (2013)
showed that was a significant spatial variability in CO 2 fluxes from the inward stations towards the outward stations; the inward stations acted as mild source of CO 2
whereas the outward stations acted as sinks. Usually a strong relation between the
salinity and pCO 2 in water is seen in the mangrove waters especially while analyzing the spatial variability. However, in Sundarban (Indian part) since there is no
significant freshwater supply from the landward end such spatial relation was not
observed.
Apart from these the effect of tides were observed to be the same as in case of
other mangroves of the world; i.e., higher fluxes during low tides and vice-versa.
7.6 Summary and Conclusion
Scrutinizing the findings of all the studies related to the atmosphere-biosphere CO 2
fluxes, soil CO 2 fluxes and air-water CO 2 fluxes conducted in the global mangroves,
it can be summed up that almost all the mangrove forests that are studied throughout
the world are at present acting as significant sinks of CO 2 . However, still a lot of
endeavor needs to be taken to estimate the year round global budgets of these fluxes
and to reduce the uncertainties in the computation of these fluxes.
In this chapter we came to see that there could be various factors regulating
atmosphere-biosphere CO 2 fluxes like canopy cover, species composition, age of
the trees, ambient temperature near the canopy, rainfall, salinity regime in the forest
floor and so forth, however, all the studies did not take into account each of these
factors in the respective study sites. Much more data characterizing the fluxes with
respect to all these factors in many more mangrove sites than what could be found
at present is required to understand the CO 2 dynamics between the atmosphere and
the mangrove canopy.
The research conducted in the Sundarban mangroves highlighted that for a vast
stretch of mangroves like that of Sundarbans and especially where there lies a substantial heterogeneity in species assemblage, spatially explicit sampling is badly
needed to properly up-scale the CO 2 flux data for the entire forest stretch. However,
A. Akhand et al.