203
7.3.10 Factors Controlling the Soil CO 2 Fluxes – Summing up
Soil temperature and soil moisture are the main factors that control the soil CO 2
fluxes. Higher soil temperature facilitates enhanced microbial activity in the pedosphere and leads to higher soil CO 2 effluxes. Soil moisture in most of the studies has
been found to play a negative role on the soil CO 2 effluxes (Fig. 7.3b). Lesser magnitude of soil CO 2 fluxes were observed during high tide sessions and vice-versa.
The higher the residence time of the tidal water the lower was the CO 2 fluxes as
during this time sediment-water CO 2 exchange took place at a higher rate than the
soil to atmosphere CO 2 exchange. Soil rich in organic carbon are usually found to
emit more CO 2 as this organic carbon was used as resource by the microbial community to feed upon and release CO 2 (Fig. 7.3b). Higher nutrients like N, P, Fe usually led to higher effluxes of CO 2 , however, exceptions were observed in rare cases
where slow metabolic rate of the microbes are held accountable for lower fluxes
despite having higher nutrients.
7.4 Air-Water CO 2 Fluxes from the Adjacent Water Bodies
of Mangroves
7.4.1 Basic Global Scenario
Amongst the three types of CO 2 fluxes taken into consideration in this chapter,
quantification of air-water CO 2 flux is perhaps one of the most challenging endeavors due to several intrinsic complicacies in delineating the bio-physical factors driving these fluxes. A substantial part of the carbon assimilated by the mangrove
vegetation finds its way to the adjacent water bodies by phenomenon like tidal flushing, pore water drainage, litter fall and so forth. More than 50% of the fixed carbon
in the terrestrial compartment of mangroves enters the adjacent water bodies either
in the form of dissolved inorganic carbon (DIC) or dissolved organic carbon (DOC)
and particulate organic carbon (POC) as well (Bouillon et al. 2008). Again, a major
part of these DOCs are also re-mineralized to DIC (Bouillon et al. 2008). Tidal
export of DIC, DOC and POC to the near shore sea waters accounts for a considerable amount of carbon trapped in the mangroves, out of which a fair share of DIC is
converted to CO 2 and they are eventually emitted to the atmosphere back again
(Bouillon et al. 2008).
In this chapter, we have only taken into account those studies which directly
measured the CO 2 flux in the air-water interface (the lateral flux of DIC or DOC
from the mangrove waters to the coastal seas is kept outside the ambit of this chapter). Table 7.3 shows that quite a many works have been done in the estuarine and
7 CO 2 Fluxes in Mangrove Ecosystems
7.3.10 Factors Controlling the Soil CO 2 Fluxes – Summing up
Soil temperature and soil moisture are the main factors that control the soil CO 2
fluxes. Higher soil temperature facilitates enhanced microbial activity in the pedosphere and leads to higher soil CO 2 effluxes. Soil moisture in most of the studies has
been found to play a negative role on the soil CO 2 effluxes (Fig. 7.3b). Lesser magnitude of soil CO 2 fluxes were observed during high tide sessions and vice-versa.
The higher the residence time of the tidal water the lower was the CO 2 fluxes as
during this time sediment-water CO 2 exchange took place at a higher rate than the
soil to atmosphere CO 2 exchange. Soil rich in organic carbon are usually found to
emit more CO 2 as this organic carbon was used as resource by the microbial community to feed upon and release CO 2 (Fig. 7.3b). Higher nutrients like N, P, Fe usually led to higher effluxes of CO 2 , however, exceptions were observed in rare cases
where slow metabolic rate of the microbes are held accountable for lower fluxes
despite having higher nutrients.
7.4 Air-Water CO 2 Fluxes from the Adjacent Water Bodies
of Mangroves
7.4.1 Basic Global Scenario
Amongst the three types of CO 2 fluxes taken into consideration in this chapter,
quantification of air-water CO 2 flux is perhaps one of the most challenging endeavors due to several intrinsic complicacies in delineating the bio-physical factors driving these fluxes. A substantial part of the carbon assimilated by the mangrove
vegetation finds its way to the adjacent water bodies by phenomenon like tidal flushing, pore water drainage, litter fall and so forth. More than 50% of the fixed carbon
in the terrestrial compartment of mangroves enters the adjacent water bodies either
in the form of dissolved inorganic carbon (DIC) or dissolved organic carbon (DOC)
and particulate organic carbon (POC) as well (Bouillon et al. 2008). Again, a major
part of these DOCs are also re-mineralized to DIC (Bouillon et al. 2008). Tidal
export of DIC, DOC and POC to the near shore sea waters accounts for a considerable amount of carbon trapped in the mangroves, out of which a fair share of DIC is
converted to CO 2 and they are eventually emitted to the atmosphere back again
(Bouillon et al. 2008).
In this chapter, we have only taken into account those studies which directly
measured the CO 2 flux in the air-water interface (the lateral flux of DIC or DOC
from the mangrove waters to the coastal seas is kept outside the ambit of this chapter). Table 7.3 shows that quite a many works have been done in the estuarine and
7 CO 2 Fluxes in Mangrove Ecosystems