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estimated global carbon stock of 4.2–8.4 Pg (Fourqurean et al. 2012). The carbon
stock in mangroves is much higher than that observed in tidal marshes (Hinson et al.
2017). Factors like intricate root systems up to great depths, high sedimentation
rates, and waterlogged soils free from risk of fires, along with anoxic soils in mangroves result in substantially high rate of net carbon burial compared to any other
terrestrial forests (Mcleod et al. 2011; Alongi 2012; Breithaupt et al. 2012). Due to
these intrinsic features of the mangrove ecosystems, these ecosystems are eyed as
one of the cheapest options towards mitigating climate change (Siikamäki et al.
2012; Murdiyarso et al. 2015) by means of two approaches. A school of thought
insists that successful and effective reforestation of mangroves can substantially
offset the effects of increase in greenhouse gas concentrations in the atmosphere
(Pendleton et al. 2012; Van Lavieren et al. 2012), whereas, some scientists opined
that restoration of existing mangroves can also serve the climate by preventing a
substantial quantity of carbon being emitted to the atmosphere by various natural
biogeochemical pathways during natural or man-made degradation of mangroves
(Alongi and Mukhopadhyay 2015). In recent days, these ideas in turn have renewed
interest on topics like carbon sequestration and biogeochemical cycles of the mangrove forest with special emphasis on their CO 2 flux characteristics and net carbon
capture (Bouillon et al. 2008; Breithaupt et al. 2012).
7.1.3.2 CO 2 Flux in the Mangrove Ecosystem
CO 2 flux denotes the rate of exchange of carbon in the form of CO 2 per unit time per
unit area amongst the several pools of an ecosystem or between ecospheres, by
means of physico-chemical, biological or anthropogenic activities. The CO 2 trapped
by photosynthetic activities of mangroves remains as the live biomass in the mangrove trees which might have different fates like (i) part of the biomass produced
can be consumed by fauna, either directly or after export to the aquatic system, (ii)
carbon can be deposited deep into the sediment, where it is stored for longer periods
of time, (iii) carbon can be re-mineralized and either emitted back to the atmosphere
as CO 2 , or can be exported as dissolved inorganic carbon (DIC), (iv) carbon can be
exported to adjacent ecosystems in organic form (dissolved or particulate) where it
can either be deposited in sediments, mineralized, or used as a food source by faunal
communities (IUCN 2009) (Fig. 7.1). Thus several biogeochemical processes take
place within the mangrove ecosystem which completes the dynamics of carbon and
all the pathways leading to its different speciation (like organic carbon, carbonate
ion, bicarbonate ion, aqueous CO 2 etc.). However, in this chapter we have concentrated exclusively on the CO 2 flux mechanisms that take place within a mangrove
ecosystem. The term ‘CO 2 flux within mangroves’ can be broadly classified into
three categories, namely: (i) air-vegetation/atmosphere-biosphere CO 2 flux (which
mainly denotes the CO 2 exchange between the mangrove canopy and the overlying
atmosphere); (ii) soil CO 2 flux/air-soil CO 2 exchange (which denotes the CO 2
A. Akhand et al.
estimated global carbon stock of 4.2–8.4 Pg (Fourqurean et al. 2012). The carbon
stock in mangroves is much higher than that observed in tidal marshes (Hinson et al.
2017). Factors like intricate root systems up to great depths, high sedimentation
rates, and waterlogged soils free from risk of fires, along with anoxic soils in mangroves result in substantially high rate of net carbon burial compared to any other
terrestrial forests (Mcleod et al. 2011; Alongi 2012; Breithaupt et al. 2012). Due to
these intrinsic features of the mangrove ecosystems, these ecosystems are eyed as
one of the cheapest options towards mitigating climate change (Siikamäki et al.
2012; Murdiyarso et al. 2015) by means of two approaches. A school of thought
insists that successful and effective reforestation of mangroves can substantially
offset the effects of increase in greenhouse gas concentrations in the atmosphere
(Pendleton et al. 2012; Van Lavieren et al. 2012), whereas, some scientists opined
that restoration of existing mangroves can also serve the climate by preventing a
substantial quantity of carbon being emitted to the atmosphere by various natural
biogeochemical pathways during natural or man-made degradation of mangroves
(Alongi and Mukhopadhyay 2015). In recent days, these ideas in turn have renewed
interest on topics like carbon sequestration and biogeochemical cycles of the mangrove forest with special emphasis on their CO 2 flux characteristics and net carbon
capture (Bouillon et al. 2008; Breithaupt et al. 2012).
7.1.3.2 CO 2 Flux in the Mangrove Ecosystem
CO 2 flux denotes the rate of exchange of carbon in the form of CO 2 per unit time per
unit area amongst the several pools of an ecosystem or between ecospheres, by
means of physico-chemical, biological or anthropogenic activities. The CO 2 trapped
by photosynthetic activities of mangroves remains as the live biomass in the mangrove trees which might have different fates like (i) part of the biomass produced
can be consumed by fauna, either directly or after export to the aquatic system, (ii)
carbon can be deposited deep into the sediment, where it is stored for longer periods
of time, (iii) carbon can be re-mineralized and either emitted back to the atmosphere
as CO 2 , or can be exported as dissolved inorganic carbon (DIC), (iv) carbon can be
exported to adjacent ecosystems in organic form (dissolved or particulate) where it
can either be deposited in sediments, mineralized, or used as a food source by faunal
communities (IUCN 2009) (Fig. 7.1). Thus several biogeochemical processes take
place within the mangrove ecosystem which completes the dynamics of carbon and
all the pathways leading to its different speciation (like organic carbon, carbonate
ion, bicarbonate ion, aqueous CO 2 etc.). However, in this chapter we have concentrated exclusively on the CO 2 flux mechanisms that take place within a mangrove
ecosystem. The term ‘CO 2 flux within mangroves’ can be broadly classified into
three categories, namely: (i) air-vegetation/atmosphere-biosphere CO 2 flux (which
mainly denotes the CO 2 exchange between the mangrove canopy and the overlying
atmosphere); (ii) soil CO 2 flux/air-soil CO 2 exchange (which denotes the CO 2
A. Akhand et al.