208
7.4.8 Soil Surface Topography
Sippo et al. (2016) pointed out that earlier study like Bouillon et al. (2008) assumed
a constant ratio between mangrove soil surface and water or even study like Borges
et al. (2003) assumed the total water area to the total mangrove area, however, in
reality the area of water-air interface varies substantially within a tidal cycle. Thus
Sippo et al. (2016) inferred that high resolution digital elevation model (DEM) measurements of water surface should be also performed to reduce the uncertainties in
the global estimates of air-water CO 2 fluxes from the mangrove adjacent water
bodies.
7.4.9 Factors Controlling the Air-Water CO 2 Fluxes –
Summing up
Salinity is one of the principal factors that govern the air-water CO 2 fluxes. Usually
higher salinity implies higher dominance of seawater which is lean in pCO 2 and
hence leads to lower effluxes of CO 2 from water surface. On the other hand, lower
salinity value indicates more freshwater abundance or mangrove pore water which
is rich in pCO 2 and leads to higher effluxes of CO 2 (Fig. 7.3c). Higher total suspended matter or turbidity of the water column usually prevents the penetration of
PAR within the water mass and hence delimits photosynthetic activity which in turn
leads to heterotrophy or enhances the CO 2 source potential of the water body. Tidal
cycle is another important factor as it regulates the mixing of freshwater and sea
water in the mangrove adjoining areas. Usually high tide phases experience lesser
abundance of pCO 2 (water) leading to lesser magnitude of water to air CO 2 flux and
vice-versa. Among the physical forcing factors, wind speed plays one of the most
important roles in regulating the magnitude of fluxes. Higher wind speed always
facilitates higher exchange of any gas in the air-water interface, hence higher CO 2
flux is observed in high wind conditions and vice-versa (Fig. 7.3c). Bottom generated shear and turbulence usually leads to good mixing of the entire water column
and it brings organic material rich water to the surface which in turn leads to higher
mineralization and higher air-water CO 2 fluxes towards the atmosphere. Lastly the
effect of rain has been also found to play a crucial role. Rain usually facilitates more
runoff and more draining mangrove pore water to the estuarine systems. Thus, usually during rainy season or monsoon phase, higher effluxes of CO 2 is observed to
take place towards atmosphere.
A. Akhand et al.
7.4.8 Soil Surface Topography
Sippo et al. (2016) pointed out that earlier study like Bouillon et al. (2008) assumed
a constant ratio between mangrove soil surface and water or even study like Borges
et al. (2003) assumed the total water area to the total mangrove area, however, in
reality the area of water-air interface varies substantially within a tidal cycle. Thus
Sippo et al. (2016) inferred that high resolution digital elevation model (DEM) measurements of water surface should be also performed to reduce the uncertainties in
the global estimates of air-water CO 2 fluxes from the mangrove adjacent water
bodies.
7.4.9 Factors Controlling the Air-Water CO 2 Fluxes –
Summing up
Salinity is one of the principal factors that govern the air-water CO 2 fluxes. Usually
higher salinity implies higher dominance of seawater which is lean in pCO 2 and
hence leads to lower effluxes of CO 2 from water surface. On the other hand, lower
salinity value indicates more freshwater abundance or mangrove pore water which
is rich in pCO 2 and leads to higher effluxes of CO 2 (Fig. 7.3c). Higher total suspended matter or turbidity of the water column usually prevents the penetration of
PAR within the water mass and hence delimits photosynthetic activity which in turn
leads to heterotrophy or enhances the CO 2 source potential of the water body. Tidal
cycle is another important factor as it regulates the mixing of freshwater and sea
water in the mangrove adjoining areas. Usually high tide phases experience lesser
abundance of pCO 2 (water) leading to lesser magnitude of water to air CO 2 flux and
vice-versa. Among the physical forcing factors, wind speed plays one of the most
important roles in regulating the magnitude of fluxes. Higher wind speed always
facilitates higher exchange of any gas in the air-water interface, hence higher CO 2
flux is observed in high wind conditions and vice-versa (Fig. 7.3c). Bottom generated shear and turbulence usually leads to good mixing of the entire water column
and it brings organic material rich water to the surface which in turn leads to higher
mineralization and higher air-water CO 2 fluxes towards the atmosphere. Lastly the
effect of rain has been also found to play a crucial role. Rain usually facilitates more
runoff and more draining mangrove pore water to the estuarine systems. Thus, usually during rainy season or monsoon phase, higher effluxes of CO 2 is observed to
take place towards atmosphere.
A. Akhand et al.