211
In all the above four studies, sampling was done in the Lothian Island of
Sundarban, however, in the later two studies of Ganguly et al. (2008) and Ray et al.
(2011), study sites like Sajnekhali Sanctuary and Bonnie Camp which are located
amidst the dense mangrove cover of Sundarbans were covered under the ambit of
sampling. This observation gave a strong indication that the atmosphere-biosphere
CO 2 fluxes could exhibit high spatial as well as temporal variability.
Moreover, since the method adopted was flux gradient technique (in these studies), it was quite reasonable to argue that regional fluxes within the Sundarban might
vary substantially depending upon the site and the mangrove vegetation in its surrounding. Based on these hints, Chanda et al. (2013a, b) carried out their measurements in three sites of the Sundarban mangroves, especially to delineate the spatial
variability of CO 2 fluxes throughout the Indian part of Sundarbans. Both in the short
term study of Chanda et al. (2013a) and the study over a complete annual cycle
(Chanda et al. 2013b), significant spatial variability in the atmosphere-biosphere
CO 2 fluxes were observed. The variability in the species composition along with the
canopy density was found to be the principal regulating factors of the fluxes.
However, the relationship between the atmosphere-biosphere CO 2 fluxes and photosynthetically active radiation (PAR) was found to be same in all the three sites.
7.5.2.4 Sundarbans Acting As a Strong Sink for CO 2
In order to characterize the fluxes above the canopy with more certainty, a flux
tower has been set up beside the station Bonnie camp and it was fitted with sensors
and sonic anemometers to measure CO 2 flux by eddy covariance technique. Rodda
et al. (2016) reported the annual mean flux to be −2.5 ± 0.2 g CO 2 m
−2
day
−1
from
this tower, which was comparable to the short term observations of Chanda et al.
(2013a) but much less than that observed by the year round data of Chanda et al.
(2013b). Thus it can be inferred that discrete data sets taken in certain specific days
of each month cannot necessarily portray the true scenario and it can substantially
overestimate or underestimate the fluxes.
However, the findings of Rodda et al. (2016) affirmed that Sundarbans at present
is acting as a strong sink for CO 2 and its efficient management and prevention of
forest encroachment can enable the policymakers to combat substantially the effect
of anthropogenic emissions. In this regard, Ray and Jana (2017) carried out a significant work as they simultaneously measured the CO 2 fluxes over the metropolis
of Kolkata, a thermal power plant belt (both lying close to Sundarbans) and the
Sundarban mangroves. They observed that almost 95% of the emissions made by
the thermal power plant belt was consumed by Sundarban’s net photosynthetic
uptake rate, hence, proving again the potential of Sundarban mangroves to combat
CO 2 emission.
7 CO 2 Fluxes in Mangrove Ecosystems
In all the above four studies, sampling was done in the Lothian Island of
Sundarban, however, in the later two studies of Ganguly et al. (2008) and Ray et al.
(2011), study sites like Sajnekhali Sanctuary and Bonnie Camp which are located
amidst the dense mangrove cover of Sundarbans were covered under the ambit of
sampling. This observation gave a strong indication that the atmosphere-biosphere
CO 2 fluxes could exhibit high spatial as well as temporal variability.
Moreover, since the method adopted was flux gradient technique (in these studies), it was quite reasonable to argue that regional fluxes within the Sundarban might
vary substantially depending upon the site and the mangrove vegetation in its surrounding. Based on these hints, Chanda et al. (2013a, b) carried out their measurements in three sites of the Sundarban mangroves, especially to delineate the spatial
variability of CO 2 fluxes throughout the Indian part of Sundarbans. Both in the short
term study of Chanda et al. (2013a) and the study over a complete annual cycle
(Chanda et al. 2013b), significant spatial variability in the atmosphere-biosphere
CO 2 fluxes were observed. The variability in the species composition along with the
canopy density was found to be the principal regulating factors of the fluxes.
However, the relationship between the atmosphere-biosphere CO 2 fluxes and photosynthetically active radiation (PAR) was found to be same in all the three sites.
7.5.2.4 Sundarbans Acting As a Strong Sink for CO 2
In order to characterize the fluxes above the canopy with more certainty, a flux
tower has been set up beside the station Bonnie camp and it was fitted with sensors
and sonic anemometers to measure CO 2 flux by eddy covariance technique. Rodda
et al. (2016) reported the annual mean flux to be −2.5 ± 0.2 g CO 2 m
−2
day
−1
from
this tower, which was comparable to the short term observations of Chanda et al.
(2013a) but much less than that observed by the year round data of Chanda et al.
(2013b). Thus it can be inferred that discrete data sets taken in certain specific days
of each month cannot necessarily portray the true scenario and it can substantially
overestimate or underestimate the fluxes.
However, the findings of Rodda et al. (2016) affirmed that Sundarbans at present
is acting as a strong sink for CO 2 and its efficient management and prevention of
forest encroachment can enable the policymakers to combat substantially the effect
of anthropogenic emissions. In this regard, Ray and Jana (2017) carried out a significant work as they simultaneously measured the CO 2 fluxes over the metropolis
of Kolkata, a thermal power plant belt (both lying close to Sundarbans) and the
Sundarban mangroves. They observed that almost 95% of the emissions made by
the thermal power plant belt was consumed by Sundarban’s net photosynthetic
uptake rate, hence, proving again the potential of Sundarban mangroves to combat
CO 2 emission.
7 CO 2 Fluxes in Mangrove Ecosystems