The analysis of the available annual NEE data from across
the country reveals that the maximum carbon uptake (maximum negative NEE value on a diurnal scale) takes place
typically in monsoon to early winter in most of the places,
except in the Kaziranga forest in Northeast India. This site is
characterized by maximum uptake (large negative NEE
values) during the pre-monsoon time, while the minimum
values typically occur in the winter. Kosi-Katarmal in north
India sequesters maximum carbon during the late monsoon,
though significant amount of carbon is also sequestered
during the pre-monsoon time. The reason for this unusual
behavior is thought to be arising partly due to the leaf
phenology and partly driven by the regional climate variability. For example, the northeast region of India receives a
significant amount of rainfall (driven by nor’westers) during
the early summer and high sunshine (compared to the cloudy
days during the monsoon time) days resulting in the
increased uptake of carbon by the vegetation. The kharif
(rainfed) sesame crop cultivated at Barkachha, Uttar Pradesh, in the Indo-Gangetic Plain over north India sequesters
maximum CO 2 during monsoon, whereas the sequestration
activity is seen to be severely affected by the drought
(Deb Burman et al. 2020a).
4.3.2 Methane Fluxes
The Sundarbans mangrove forest acted as a net source of
atmospheric CH 4 with average daily flux being
150.2 ± 248.9 mg m
−2 d
−1 (Jha et al. 2014). Methane
source was enhanced at Sundarbans during summer months
due to the elevated temperature and moisture contents.
Another study by Mukhophadhya et al. (2001) estimates the
CH 4 source from Sundarbans mangroves to lie within 4.5–
8.9 µg m
−2 s
−1 . The methane flux has also been measured in
the Pichavaram mangrove forest. Purvaja and Ramesh
(2001) used static chamber and reported methane emission
in the range of 47.2–324.5 mg m
−2 d
−1 .
Methane flux from Indian rice paddy fields is reported to
vary from 2.4 to 660.0 mg m
−2 d
−1 (Parashar et al. 1991;
Lal et al. 1993; Adhya et al. 1994). Total CH 4 emission from
an irrigated rice paddy field in New Delhi was reported to be
0.275–0.372 g m
−2 . Fertilizers such as urea, ammonium
sulfate and potassium nitrate increased the CH 4 emission,
while dicyandiamide helped reduce it (Ghosh et al. 2003).
Intermittently irrigated rice paddy fields were seen to emit
less CH 4 compared to the continuously flooded fields (Jain
et al. 2000). A dry land rice cultivation in Varanasi, north
India, was reported to be a sink of CH 4 with an average
growing season uptake of 8.4 mg m
−2 d
−1 (Singh et al.
1997). According to these authors in dry tropical ecosystems, N availability is remarkably low, and this may be the
reason for high CH 4 uptake rates in these ecosystems.
Furthermore, these dry soils are well drained and permeable,
and it has been clearly demonstrated that CH 4 consumption
is diffusion-limited (Dörr et al. 1993). A recent study showed
potential for CH 4 emission by changing rice cultivation
practice from conventional transplanting (CT) to system of
rice intensification (SRI) in India (Oo et al. 2018). Inland
water bodies such as lakes, ponds, open wells, rivers, springs
and canals are known to emit CO 2 and CH 4 to the atmosphere. Total CH 4 flux from multiple such ecosystems in
India measured using flux chambers ranged from 0.16 to
834 mg m
−2 d
−1 (Selvam et al. 2014). Additionally, the CO 2
flux from these systems was measured to lie between 0.34
and 3.15 gC m
−2 d
−1 (Selvam et al. 2014).
4.3.3 Carbon Inventory of the Indian Forests
The total carbon stored in Indian forests, including forest
soil, is estimated to be in the range of 8.58–9.6 PgC
(Ravindranath et al. 2008). According to Chhabra and
Dadhwal (2004), 3.8–4.3 PgC is stored as Indian forest
phytomass, approximately 10% of the global forest phytomass carbon pool. Several studies assessed the influence of
land use change on forest carbon (Ravindranath et al. 1997;
Kaul et al. 2009). Kaul et al. (2009) estimated that net carbon
flux attributable from land use change decreased from a
source level of 5.65 Tg C yr
−1 during 1982–1992 to a sink
level of 1.09 Tg C yr
−1 during 1992–2002. It indicates that
Indian forests became a sink of atmospheric carbon due to
the regeneration and afforestation efforts.
4.3.4 Agricultural Ecosystem
Apart from the natural vegetation, agricultural ecosystems
also contribute significantly to the GHGs fluxes. Specifically,
the rice paddy fields are known to emit significant amounts of
CH 4 owing to the anaerobic conditions prevalent during the
times when the fields are inundated with potentially warm
water (Adhya et al. 2000). Moreover, the net emission from
the agricultural ecosystems depends strongly on the agricultural practices such as applications of fertilizers, manure,
pesticides, crop residue, straw and flooding of the agricultural
field (Debnath et al. 1996; Singh et al. 1996; Bhatia et al.
2005). Indian Agricultural Research Institute (IARI) has
several flux measurement systems across India for measuring
the emissions from different agricultural fields.
4.3.5 Other Observations
Several satellites provide derived values of GPP, NEE and
TER from space observations. Such products have also been
82
S. Chakraborty et al.
the country reveals that the maximum carbon uptake (maximum negative NEE value on a diurnal scale) takes place
typically in monsoon to early winter in most of the places,
except in the Kaziranga forest in Northeast India. This site is
characterized by maximum uptake (large negative NEE
values) during the pre-monsoon time, while the minimum
values typically occur in the winter. Kosi-Katarmal in north
India sequesters maximum carbon during the late monsoon,
though significant amount of carbon is also sequestered
during the pre-monsoon time. The reason for this unusual
behavior is thought to be arising partly due to the leaf
phenology and partly driven by the regional climate variability. For example, the northeast region of India receives a
significant amount of rainfall (driven by nor’westers) during
the early summer and high sunshine (compared to the cloudy
days during the monsoon time) days resulting in the
increased uptake of carbon by the vegetation. The kharif
(rainfed) sesame crop cultivated at Barkachha, Uttar Pradesh, in the Indo-Gangetic Plain over north India sequesters
maximum CO 2 during monsoon, whereas the sequestration
activity is seen to be severely affected by the drought
(Deb Burman et al. 2020a).
4.3.2 Methane Fluxes
The Sundarbans mangrove forest acted as a net source of
atmospheric CH 4 with average daily flux being
150.2 ± 248.9 mg m
−2 d
−1 (Jha et al. 2014). Methane
source was enhanced at Sundarbans during summer months
due to the elevated temperature and moisture contents.
Another study by Mukhophadhya et al. (2001) estimates the
CH 4 source from Sundarbans mangroves to lie within 4.5–
8.9 µg m
−2 s
−1 . The methane flux has also been measured in
the Pichavaram mangrove forest. Purvaja and Ramesh
(2001) used static chamber and reported methane emission
in the range of 47.2–324.5 mg m
−2 d
−1 .
Methane flux from Indian rice paddy fields is reported to
vary from 2.4 to 660.0 mg m
−2 d
−1 (Parashar et al. 1991;
Lal et al. 1993; Adhya et al. 1994). Total CH 4 emission from
an irrigated rice paddy field in New Delhi was reported to be
0.275–0.372 g m
−2 . Fertilizers such as urea, ammonium
sulfate and potassium nitrate increased the CH 4 emission,
while dicyandiamide helped reduce it (Ghosh et al. 2003).
Intermittently irrigated rice paddy fields were seen to emit
less CH 4 compared to the continuously flooded fields (Jain
et al. 2000). A dry land rice cultivation in Varanasi, north
India, was reported to be a sink of CH 4 with an average
growing season uptake of 8.4 mg m
−2 d
−1 (Singh et al.
1997). According to these authors in dry tropical ecosystems, N availability is remarkably low, and this may be the
reason for high CH 4 uptake rates in these ecosystems.
Furthermore, these dry soils are well drained and permeable,
and it has been clearly demonstrated that CH 4 consumption
is diffusion-limited (Dörr et al. 1993). A recent study showed
potential for CH 4 emission by changing rice cultivation
practice from conventional transplanting (CT) to system of
rice intensification (SRI) in India (Oo et al. 2018). Inland
water bodies such as lakes, ponds, open wells, rivers, springs
and canals are known to emit CO 2 and CH 4 to the atmosphere. Total CH 4 flux from multiple such ecosystems in
India measured using flux chambers ranged from 0.16 to
834 mg m
−2 d
−1 (Selvam et al. 2014). Additionally, the CO 2
flux from these systems was measured to lie between 0.34
and 3.15 gC m
−2 d
−1 (Selvam et al. 2014).
4.3.3 Carbon Inventory of the Indian Forests
The total carbon stored in Indian forests, including forest
soil, is estimated to be in the range of 8.58–9.6 PgC
(Ravindranath et al. 2008). According to Chhabra and
Dadhwal (2004), 3.8–4.3 PgC is stored as Indian forest
phytomass, approximately 10% of the global forest phytomass carbon pool. Several studies assessed the influence of
land use change on forest carbon (Ravindranath et al. 1997;
Kaul et al. 2009). Kaul et al. (2009) estimated that net carbon
flux attributable from land use change decreased from a
source level of 5.65 Tg C yr
−1 during 1982–1992 to a sink
level of 1.09 Tg C yr
−1 during 1992–2002. It indicates that
Indian forests became a sink of atmospheric carbon due to
the regeneration and afforestation efforts.
4.3.4 Agricultural Ecosystem
Apart from the natural vegetation, agricultural ecosystems
also contribute significantly to the GHGs fluxes. Specifically,
the rice paddy fields are known to emit significant amounts of
CH 4 owing to the anaerobic conditions prevalent during the
times when the fields are inundated with potentially warm
water (Adhya et al. 2000). Moreover, the net emission from
the agricultural ecosystems depends strongly on the agricultural practices such as applications of fertilizers, manure,
pesticides, crop residue, straw and flooding of the agricultural
field (Debnath et al. 1996; Singh et al. 1996; Bhatia et al.
2005). Indian Agricultural Research Institute (IARI) has
several flux measurement systems across India for measuring
the emissions from different agricultural fields.
4.3.5 Other Observations
Several satellites provide derived values of GPP, NEE and
TER from space observations. Such products have also been
82
S. Chakraborty et al.