213
other mangroves. However, it is worth mentioning that the soil temperature in
Sundarbans varied between 13.9 and 36.8 °C, and throughout this entire range, soil
CO 2 fluxes were found to increase, i.e. a positive exponential relationship was
observed between the soil CO 2 effluxes and soil temperature.
Lovelock (2008) on the contrary mentioned about a drop in soil CO 2 fluxes above
26 °C in many of the Australian mangroves. Such phenomenon did not take place in
Sundarbans. In many studies (Leopold et al. 2013; Chen et al. 2014) negative fluxes,
i.e. CO 2 fluxes towards the soil were observed due to the presence of biofilms.
However, in Sundarbans no such biofilms were noted to exist in the selected study
sites at least.
The effect of tides was the same in Sundarbans as observed in other mangroves
i.e., higher soil CO 2 effluxes during low tides and vice-versa.
7.5.2.8 Spatial Variability of Air-Water CO 2 Flux
Like soil CO 2 effluxes, very few air-water CO 2 flux oriented studies have been conducted in Sundarbans. Biswas et al. (2004) reported the air-water CO 2 fluxes for the
first time in the year 2004. They chose the study sites to be the sea mouths of three
main distributaries flowing in the Sundarbans. The fluxes ranged from −0.02 to
0.05 g CO 2 m
−2
day
−1
(having a mean of 0.01 g CO 2 m
−2
day
−1
), which was several
orders less than that observed in the forest floor or above canopy fluxes. Thus the
sink strength of the Sundarban mangrove ecosystem as a whole was not compromised due to the air-water CO 2 fluxes. However, in this study the spatial variability
was not discussed in details.
In order to address this issue, Akhand et al. (2013) carried out a short term work
and a long term work throughout one complete annual cycle (Akhand et al. 2016)
trying to characterize the spatial variability of air-water CO 2 fluxes in the inner,
middle and outer estuarine stations. Both these studies observed that the inner estuarine stations were substantial sources of CO 2 , whereas, the outer estuarine stations
behaved as sinks of carbon, leading to lower mean effluxes from the air-water interface. It was found that the organic matter rich waters leading to re-mineralization to
CO 2 was abundant in inner estuarine stations, whereas, in the outer estuarine stations, where the seawater lean in organic matter content diluted the mangrove
exported water mass ultimately resulting in lower water pCO 2 .
Incidentally the air-water CO 2 fluxes observed in the Sundarban waterways were
fairly low compared to the results obtained in other mangrove waters of the world.
It is worth mentioning that the estuary (namely Matla Estuary) where the study was
undertaken happened to be an enclosed estuary, with very limited perennial supply
of freshwater. This might have led to the greater dominance of sea water in the
Sundarban mangroves (Indian part), however, observations like this emphasizes to
take into account the spatial variability of CO 2 fluxes within a mangrove adjacent
water mass, as up-scaling a single stationed data from any mangrove water body
might highly overestimate the fluxes taking place at the air-water interface.
7 CO 2 Fluxes in Mangrove Ecosystems
other mangroves. However, it is worth mentioning that the soil temperature in
Sundarbans varied between 13.9 and 36.8 °C, and throughout this entire range, soil
CO 2 fluxes were found to increase, i.e. a positive exponential relationship was
observed between the soil CO 2 effluxes and soil temperature.
Lovelock (2008) on the contrary mentioned about a drop in soil CO 2 fluxes above
26 °C in many of the Australian mangroves. Such phenomenon did not take place in
Sundarbans. In many studies (Leopold et al. 2013; Chen et al. 2014) negative fluxes,
i.e. CO 2 fluxes towards the soil were observed due to the presence of biofilms.
However, in Sundarbans no such biofilms were noted to exist in the selected study
sites at least.
The effect of tides was the same in Sundarbans as observed in other mangroves
i.e., higher soil CO 2 effluxes during low tides and vice-versa.
7.5.2.8 Spatial Variability of Air-Water CO 2 Flux
Like soil CO 2 effluxes, very few air-water CO 2 flux oriented studies have been conducted in Sundarbans. Biswas et al. (2004) reported the air-water CO 2 fluxes for the
first time in the year 2004. They chose the study sites to be the sea mouths of three
main distributaries flowing in the Sundarbans. The fluxes ranged from −0.02 to
0.05 g CO 2 m
−2
day
−1
(having a mean of 0.01 g CO 2 m
−2
day
−1
), which was several
orders less than that observed in the forest floor or above canopy fluxes. Thus the
sink strength of the Sundarban mangrove ecosystem as a whole was not compromised due to the air-water CO 2 fluxes. However, in this study the spatial variability
was not discussed in details.
In order to address this issue, Akhand et al. (2013) carried out a short term work
and a long term work throughout one complete annual cycle (Akhand et al. 2016)
trying to characterize the spatial variability of air-water CO 2 fluxes in the inner,
middle and outer estuarine stations. Both these studies observed that the inner estuarine stations were substantial sources of CO 2 , whereas, the outer estuarine stations
behaved as sinks of carbon, leading to lower mean effluxes from the air-water interface. It was found that the organic matter rich waters leading to re-mineralization to
CO 2 was abundant in inner estuarine stations, whereas, in the outer estuarine stations, where the seawater lean in organic matter content diluted the mangrove
exported water mass ultimately resulting in lower water pCO 2 .
Incidentally the air-water CO 2 fluxes observed in the Sundarban waterways were
fairly low compared to the results obtained in other mangrove waters of the world.
It is worth mentioning that the estuary (namely Matla Estuary) where the study was
undertaken happened to be an enclosed estuary, with very limited perennial supply
of freshwater. This might have led to the greater dominance of sea water in the
Sundarban mangroves (Indian part), however, observations like this emphasizes to
take into account the spatial variability of CO 2 fluxes within a mangrove adjacent
water mass, as up-scaling a single stationed data from any mangrove water body
might highly overestimate the fluxes taking place at the air-water interface.
7 CO 2 Fluxes in Mangrove Ecosystems