4.3.1 Carbon Dioxide Fluxes and Net Ecosystem
Exchange
Several micrometeorological flux towers were erected for the
long-term monitoring of GHGs fluxes over different
ecosystems in India by the Indian Space Research Organisation (ISRO) as part of the Geosphere-Biosphere Program.
These sites include a mixed deciduous teak forest in Betul
over central India (Jha et al. 2013); a mangrove forest in
Sundarbans on the east coast of India, flanked by the Bay of
Bengal (Jha et al. 2014; Rodda et al. 2016); a mixed
deciduous forest in Haldwani over north India (Watham
et al. 2014; Ahongshangbam et al. 2016); and a tropical
moist deciduous sal forest in Barkot over north India
(Watham et al. 2017; Pillai et al. 2019).
Being deciduous in nature, the carbon exchange at the
Betul forest is observed to be strongly influenced by the
availability of the leaves. It is seen to act as a sink in winter
with a maximum value of NEE being −300 µgC m
−2 s
−1 in
the daytime. However, the sink strength is drastically
reduced to −24 µgC m
−2 s
−1 in the dry months of summer
due to leaf dehiscence. Annual NEE, GPP and TER of the
Betul forest were not available at the time of writing this
report.
The Sundarbans mangrove acted as a net sink of CO 2
with annual NEE of −249 ± 20 gC m
−2 y
−1 . Soil–CO 2
emission from this ecosystem was found to vary between 18
and 28 µgC m
−2 s
−1 . It remains positive throughout the year
with a close dependency on the soil temperature (Chanda
et al. 2014). Annual GPP and TER of this ecosystem were
1271 gC m
−2 y
−1 and 1022 gC m
−2 y
−1 , respectively. Sink
strength varied widely between −72 µgC m
−2 s
−1 in summer and −120 µgC m
−2 s
−1 in winter.
The 9-year-old man-made mixed forest at Haldwani acted
as a net CO 2 source during the leafless months of winter,
quite contradictory to Betul and Sundarbans (Watham et al.
2014). Subsequently, it transformed into a sink during the
growing months from April to September. The monthly
mean daily total NEE of this ecosystem was 0.35 gC m
−2
d
−1 , in January. It became slightly negative at −0.38 gC
m
−2 d
−1 in February and grew farther negative continuously
to −5.74 gC m
−2 d
−1 in September. The annual NEE of this
ecosystem was unavailable at the moment to quantify the
yearlong total carbon exchange. The GPP of Barkot forest
was observed to vary from 5.38 gC m
−2 d
−1 in December to
12.42 gC m
−2 d
−1 in September. This shows the gross carbon exchange to be stronger in monsoon compared to winter. The annual mean daily GPP of this ecosystem was
7.98 gC m
−2 d
−1 . However, annual NEE is required for
estimating the actual carbon sequestration by this ecosystem.
Based on a three-year-long EC measurement during 2014–
2016, the mixed forest at Kosi-Katarmal, Almora (20.05° N,
79.05° E, 1217 m amsl), acted as a net sink of atmospheric
CO 2 with the average daily NEE being −3.21 gC m
−2 d
−1
(Mukherjee et al. 2018). In another study, CO 2 exchange of
a wheat field was measured by an EC system at Modipuram,
north India, by the ISRO (Patel et al. 2011). Maximum
daytime uptake and nighttime release of CO 2 by this
ecosystem were observed to vary markedly during different
stages of the crop growth. During the anthesis stage of the
crop, maximum midday uptake and nighttime release were
−26.78 gC m
−2 d
−1 and 3.45 gC m
−2 d
−1 , respectively.
Due to reduced leaf area index (LAI), midday uptake drastically reduced to −19.00 gC m
−2 d
−1 in the senescence
stage. However, the nighttime release remained unaltered.
Subsequently, in the mature stage daytime uptake further
plummeted below −11.22 gC m
−2 d
−1 . The annual estimates of NEE, GPP and TER will be required to draw
conclusion on the actual carbon sequestration of this wheat
field.
The Indian Institute of Tropical Meteorology (IITM),
Pune, also established a few flux towers over different
ecosystems under the aegis of the MetFlux India project,
initiated and funded by the Ministry of Earth Sciences
(MoES), Government of India. These sites include a
semievergreen moist deciduous forest in Kaziranga National
Park over Northeast India (Deb Burman et al. 2017, 2019;
Sarma et al. 2018), a mangrove forest in Pichavaram
(Gnanamoorthy et al. 2019) on the southeast coast of India
by the Bay of Bengal and an evergreen coniferous forest
over the eastern Himalayan range in Darjeeling (Chatterjee
et al. 2018) in Northeast India. In addition to the GHG
fluxes, CO 2 concentration in seawater and atmosphere is also
measured in two islands, in Agatti in the Lakshadweep
Islands over the Arabian Sea (Kumaresan et al. 2018) and
Port Blair in the Andaman and Nicobar Islands over the Bay
of Bengal as part of the MetFlux India network. The
ecosystem at Kaziranga has an annual GPP of 2110 gC
m
−2 y
−1 with a prominent seasonal variation primarily
governed by the plant leaf phenology (Deb Burman et al.
2017). It is also reported that cloudiness during the Indian
summer monsoon months drastically reduces the availability
of the photosynthetically active radiation at this ecosystem
which in turn affects its carbon sequestration activity negatively (Deb Burman et al. 2020b). The mangrove forest of
Pichavaram in Tamil Nadu registered a NEE maximum (ca.
−11.40 gC m
−2 d
−1 ) during the month of January.
Annual GPP and ecosystem respiration (TER) were estimated to be 1466 gC m
−2 y
−1 and 1283 gC m
−2 y
−1 ,
respectively (Gnanamoorthy et al. 2020). Based on a twomonth observation at a high-altitude Himalayan evergreen
forest near Darjeeling, Chatterjee et al. (2018) estimated
springtime CO 2 flux for the year 2015. These authors observed
a maximum NEE reaching up to −10.37 gC m
−2 d
−1
.
4 Observations and Modeling of GHG Concentrations and Fluxes …
81
Exchange
Several micrometeorological flux towers were erected for the
long-term monitoring of GHGs fluxes over different
ecosystems in India by the Indian Space Research Organisation (ISRO) as part of the Geosphere-Biosphere Program.
These sites include a mixed deciduous teak forest in Betul
over central India (Jha et al. 2013); a mangrove forest in
Sundarbans on the east coast of India, flanked by the Bay of
Bengal (Jha et al. 2014; Rodda et al. 2016); a mixed
deciduous forest in Haldwani over north India (Watham
et al. 2014; Ahongshangbam et al. 2016); and a tropical
moist deciduous sal forest in Barkot over north India
(Watham et al. 2017; Pillai et al. 2019).
Being deciduous in nature, the carbon exchange at the
Betul forest is observed to be strongly influenced by the
availability of the leaves. It is seen to act as a sink in winter
with a maximum value of NEE being −300 µgC m
−2 s
−1 in
the daytime. However, the sink strength is drastically
reduced to −24 µgC m
−2 s
−1 in the dry months of summer
due to leaf dehiscence. Annual NEE, GPP and TER of the
Betul forest were not available at the time of writing this
report.
The Sundarbans mangrove acted as a net sink of CO 2
with annual NEE of −249 ± 20 gC m
−2 y
−1 . Soil–CO 2
emission from this ecosystem was found to vary between 18
and 28 µgC m
−2 s
−1 . It remains positive throughout the year
with a close dependency on the soil temperature (Chanda
et al. 2014). Annual GPP and TER of this ecosystem were
1271 gC m
−2 y
−1 and 1022 gC m
−2 y
−1 , respectively. Sink
strength varied widely between −72 µgC m
−2 s
−1 in summer and −120 µgC m
−2 s
−1 in winter.
The 9-year-old man-made mixed forest at Haldwani acted
as a net CO 2 source during the leafless months of winter,
quite contradictory to Betul and Sundarbans (Watham et al.
2014). Subsequently, it transformed into a sink during the
growing months from April to September. The monthly
mean daily total NEE of this ecosystem was 0.35 gC m
−2
d
−1 , in January. It became slightly negative at −0.38 gC
m
−2 d
−1 in February and grew farther negative continuously
to −5.74 gC m
−2 d
−1 in September. The annual NEE of this
ecosystem was unavailable at the moment to quantify the
yearlong total carbon exchange. The GPP of Barkot forest
was observed to vary from 5.38 gC m
−2 d
−1 in December to
12.42 gC m
−2 d
−1 in September. This shows the gross carbon exchange to be stronger in monsoon compared to winter. The annual mean daily GPP of this ecosystem was
7.98 gC m
−2 d
−1 . However, annual NEE is required for
estimating the actual carbon sequestration by this ecosystem.
Based on a three-year-long EC measurement during 2014–
2016, the mixed forest at Kosi-Katarmal, Almora (20.05° N,
79.05° E, 1217 m amsl), acted as a net sink of atmospheric
CO 2 with the average daily NEE being −3.21 gC m
−2 d
−1
(Mukherjee et al. 2018). In another study, CO 2 exchange of
a wheat field was measured by an EC system at Modipuram,
north India, by the ISRO (Patel et al. 2011). Maximum
daytime uptake and nighttime release of CO 2 by this
ecosystem were observed to vary markedly during different
stages of the crop growth. During the anthesis stage of the
crop, maximum midday uptake and nighttime release were
−26.78 gC m
−2 d
−1 and 3.45 gC m
−2 d
−1 , respectively.
Due to reduced leaf area index (LAI), midday uptake drastically reduced to −19.00 gC m
−2 d
−1 in the senescence
stage. However, the nighttime release remained unaltered.
Subsequently, in the mature stage daytime uptake further
plummeted below −11.22 gC m
−2 d
−1 . The annual estimates of NEE, GPP and TER will be required to draw
conclusion on the actual carbon sequestration of this wheat
field.
The Indian Institute of Tropical Meteorology (IITM),
Pune, also established a few flux towers over different
ecosystems under the aegis of the MetFlux India project,
initiated and funded by the Ministry of Earth Sciences
(MoES), Government of India. These sites include a
semievergreen moist deciduous forest in Kaziranga National
Park over Northeast India (Deb Burman et al. 2017, 2019;
Sarma et al. 2018), a mangrove forest in Pichavaram
(Gnanamoorthy et al. 2019) on the southeast coast of India
by the Bay of Bengal and an evergreen coniferous forest
over the eastern Himalayan range in Darjeeling (Chatterjee
et al. 2018) in Northeast India. In addition to the GHG
fluxes, CO 2 concentration in seawater and atmosphere is also
measured in two islands, in Agatti in the Lakshadweep
Islands over the Arabian Sea (Kumaresan et al. 2018) and
Port Blair in the Andaman and Nicobar Islands over the Bay
of Bengal as part of the MetFlux India network. The
ecosystem at Kaziranga has an annual GPP of 2110 gC
m
−2 y
−1 with a prominent seasonal variation primarily
governed by the plant leaf phenology (Deb Burman et al.
2017). It is also reported that cloudiness during the Indian
summer monsoon months drastically reduces the availability
of the photosynthetically active radiation at this ecosystem
which in turn affects its carbon sequestration activity negatively (Deb Burman et al. 2020b). The mangrove forest of
Pichavaram in Tamil Nadu registered a NEE maximum (ca.
−11.40 gC m
−2 d
−1 ) during the month of January.
Annual GPP and ecosystem respiration (TER) were estimated to be 1466 gC m
−2 y
−1 and 1283 gC m
−2 y
−1 ,
respectively (Gnanamoorthy et al. 2020). Based on a twomonth observation at a high-altitude Himalayan evergreen
forest near Darjeeling, Chatterjee et al. (2018) estimated
springtime CO 2 flux for the year 2015. These authors observed
a maximum NEE reaching up to −10.37 gC m
−2 d
−1
.
4 Observations and Modeling of GHG Concentrations and Fluxes …
81