190
7.1.3.2.1 Atmosphere-Biosphere CO 2 Fluxes in Mangroves
The ‘Atmosphere-biosphere’ CO 2 fluxes mainly take place due to photosynthetic
activities during the day time and respiration activities during the night time above
the canopy of any forest. Various kinds of micrometeorological techniques are
deployed to measure this kind of gaseous exchange; however, comparatively lesser
attention has been paid to the marine-terrestrial interface regimes like mangrove
forests till date (Wofsy and Harris 2002; Barr et al. 2010). Among the different types
of micrometeorological methods two approaches are commonly used namely:
‘Flux-gradient method’ and ‘Eddy covariance method’. The Flux-gradient theory is
based on the assumption that any turbulent transfer of any trace gas is analogous to
molecular diffusion and that the turbulent flux is directly proportional to mean vertical mixing ratio gradient and constant known as eddy diffusivity (Baldocchi et al.
1988). These eddy diffusivities in turn are usually computed by either aerodynamic
method or the Bowen ratio energy balance technique (Kanemasu et al. 1979).
However, now-a-days the eddy covariance technique is being unanimously implemented throughout the globe to measure the CO 2 exchange above the canopy by
using 3D sonic anemometers and open path CO 2 /H 2 O gas analyzer (Baldocchi
2008). Owing to the simplicity of this approach and feasibility to monitor fluxes
continuously over diurnal to annual scale, a network of more than 140 sites has been
established throughout the world under the umbrella named FLUXNET (Baldocchi
et al. 2001). In all these sites continuous measurement of CO 2 , water vapor and heat
fluxes are being monitored to develop an intercomparable data set and provide a
platform of ground-truth data to validate the satellite sensors mounted on the NASA
Terra Satellite (Baldocchi et al. 2001).
7.1.3.2.2 Soil CO 2 Fluxes in Mangroves
Soil CO 2 fluxes mainly results due to production of CO 2 in mangrove soils by means
of mostly microbial activity during organic matter mineralization and root respiration (Chen et al. 2012; Lovelock et al. 2011). The organic compounds that enter the
pedosphere as decaying roots, root exudates, litter, microbial biomass etc. undergoes decomposition by a multitude of micro- and meso-fauna (Oades 1998). Due to
regular flushing of seawater, this decomposition in the mangroves mainly takes
place by reducing other electron acceptors substituting the O 2 (i.e., O 2 → NO 3
−
→ Mn
oxyhydroxides → Fe oxyhydroxides → SO 4
2−
→ CO 2 ) and leading to a decreased
rate of decomposition due to lower energetic yield (Alongi et al. 2001; Neue et al.
1997). In other words, when the microorganisms oxidize the organic C using O 2 ,
NO 3
−
, Mn
4+
, Fe
3+
, and SO 4
2−
as electron acceptors the CO 2 flux to the atmosphere
takes place from the soils surface (Kristensen et al. 2008).The soil respired CO 2 is
considered to be the second largest terrestrial carbon flux (Raich and Schlesinger
1992), out of which forest soils may account for 30–80% of the total ecosystem
respiration (Luo and Zhou 2006). Soil temperature, moisture and various other
A. Akhand et al.
7.1.3.2.1 Atmosphere-Biosphere CO 2 Fluxes in Mangroves
The ‘Atmosphere-biosphere’ CO 2 fluxes mainly take place due to photosynthetic
activities during the day time and respiration activities during the night time above
the canopy of any forest. Various kinds of micrometeorological techniques are
deployed to measure this kind of gaseous exchange; however, comparatively lesser
attention has been paid to the marine-terrestrial interface regimes like mangrove
forests till date (Wofsy and Harris 2002; Barr et al. 2010). Among the different types
of micrometeorological methods two approaches are commonly used namely:
‘Flux-gradient method’ and ‘Eddy covariance method’. The Flux-gradient theory is
based on the assumption that any turbulent transfer of any trace gas is analogous to
molecular diffusion and that the turbulent flux is directly proportional to mean vertical mixing ratio gradient and constant known as eddy diffusivity (Baldocchi et al.
1988). These eddy diffusivities in turn are usually computed by either aerodynamic
method or the Bowen ratio energy balance technique (Kanemasu et al. 1979).
However, now-a-days the eddy covariance technique is being unanimously implemented throughout the globe to measure the CO 2 exchange above the canopy by
using 3D sonic anemometers and open path CO 2 /H 2 O gas analyzer (Baldocchi
2008). Owing to the simplicity of this approach and feasibility to monitor fluxes
continuously over diurnal to annual scale, a network of more than 140 sites has been
established throughout the world under the umbrella named FLUXNET (Baldocchi
et al. 2001). In all these sites continuous measurement of CO 2 , water vapor and heat
fluxes are being monitored to develop an intercomparable data set and provide a
platform of ground-truth data to validate the satellite sensors mounted on the NASA
Terra Satellite (Baldocchi et al. 2001).
7.1.3.2.2 Soil CO 2 Fluxes in Mangroves
Soil CO 2 fluxes mainly results due to production of CO 2 in mangrove soils by means
of mostly microbial activity during organic matter mineralization and root respiration (Chen et al. 2012; Lovelock et al. 2011). The organic compounds that enter the
pedosphere as decaying roots, root exudates, litter, microbial biomass etc. undergoes decomposition by a multitude of micro- and meso-fauna (Oades 1998). Due to
regular flushing of seawater, this decomposition in the mangroves mainly takes
place by reducing other electron acceptors substituting the O 2 (i.e., O 2 → NO 3
−
→ Mn
oxyhydroxides → Fe oxyhydroxides → SO 4
2−
→ CO 2 ) and leading to a decreased
rate of decomposition due to lower energetic yield (Alongi et al. 2001; Neue et al.
1997). In other words, when the microorganisms oxidize the organic C using O 2 ,
NO 3
−
, Mn
4+
, Fe
3+
, and SO 4
2−
as electron acceptors the CO 2 flux to the atmosphere
takes place from the soils surface (Kristensen et al. 2008).The soil respired CO 2 is
considered to be the second largest terrestrial carbon flux (Raich and Schlesinger
1992), out of which forest soils may account for 30–80% of the total ecosystem
respiration (Luo and Zhou 2006). Soil temperature, moisture and various other
A. Akhand et al.