10.5 Shifts in Carbon Sequestration
Although freshwater ecosystems cover relatively less geographical area (less than
4% of the Earth’s surface), they play a critical role in the global carbon cycle because
of the high rate of respiration and carbon sequestration (Cole et al. 2007). The inland
water bodies transport huge amounts of carbon from land to the ocean and perform a
major role in carbon transit. Recent studies have shown that the inland water bodies
emit the carbon in the amount close to those absorbed by organisms on Earth’s land
surface and in oceans (Raymond et al. 2013). Further, in freshwater bodies, more
carbon is buried each year than those in vast oceanic floor (Aufdenkampe et al.
2011). Global studies have shown that every year about 2.7 billion metric tons of
carbon reaches to the inland water bodies through different sources (Raymond et al.
2013). Half of this carbon is respired and returned back to the atmosphere as CO 2
(Bastviken et al. 2011; Raymond et al. 2013), ~0.4 billion tons of carbon is buried in
bed sediments, and ~0.9 billion tons is exported to oceans (Aufdenkampe et al.
2011). Human interference such as land use change is dramatically affecting the
carbon cycle in freshwater bodies. Nutrient input to freshwater bodies increases the
algal blooms which absorb carbon from the atmosphere and increase the carbon
sequestration (Pacheco et al. 2013). However, on decomposition and respiration, this
carbon is released to the atmosphere and the cycle goes on (Bastviken et al. 2011;
Borges et al. 2015).
A worldwide study by Cole et al. (2007) reveals that ~87% of the lakes are CO 2 -
supersaturated and the average pCO 2 is about three times higher than the overlying
atmosphere. Thus, due to increasing human pressure, the surface waters may become
a source rather than a sink of atmospheric CO 2 . Recent studies have established that
this CO 2 flux from rivers and stream is enough to affect the regional C budget at
landscape scale (Raymond et al. 2013; Jaiswal et al. 2018). Amazonian rivers, for
instance, have been reported to emit CO 2 more than ten times of the amount of C
exported to the ocean (Richey et al. 2002). One of the main reason of high CO 2
efflux from rivers is in situ breakdown of young organic matter (Richey et al. 2002).
Recent studies have indicated that the human-impacted Ganga River is receiving an
increasingly high amount of carbon from terrestrial sources (Pandey et al. 2014a). In
an earlier study, conducted at land-water interface (LWI) of the Ganga River, we
found that the LWI is outgassing a huge amount of CO 2 into the atmosphere
indicating that due to increasing human perturbations many parts of the Ganga
River are now converted into a source of CO 2 (Jaiswal et al. 2018; Jaiswal and
Pandey 2019e).
The organic matter degradation and carbon cycling are controlled by microbial
extracellular enzyme (EE) activities (Sinsabaugh et al. 2009). The anthropogenic
input of carbon (allochthonous C) causes a shift in microbial community structure
and functioning, including organic matter degradation and carbon cycle. The EE
activity is influenced by human inputs such as carbon, nutrients, and heavy metals
(Pandey and Yadav 2017; Jaiswal and Pandey 2018). Carbon and nutrients act as
substrate and enhance the EE activities, while heavy metals act as toxicant and thus
10 Ecosystem Responses to Pollution in the Ganga River: Key Issues to Address. . .
235
Although freshwater ecosystems cover relatively less geographical area (less than
4% of the Earth’s surface), they play a critical role in the global carbon cycle because
of the high rate of respiration and carbon sequestration (Cole et al. 2007). The inland
water bodies transport huge amounts of carbon from land to the ocean and perform a
major role in carbon transit. Recent studies have shown that the inland water bodies
emit the carbon in the amount close to those absorbed by organisms on Earth’s land
surface and in oceans (Raymond et al. 2013). Further, in freshwater bodies, more
carbon is buried each year than those in vast oceanic floor (Aufdenkampe et al.
2011). Global studies have shown that every year about 2.7 billion metric tons of
carbon reaches to the inland water bodies through different sources (Raymond et al.
2013). Half of this carbon is respired and returned back to the atmosphere as CO 2
(Bastviken et al. 2011; Raymond et al. 2013), ~0.4 billion tons of carbon is buried in
bed sediments, and ~0.9 billion tons is exported to oceans (Aufdenkampe et al.
2011). Human interference such as land use change is dramatically affecting the
carbon cycle in freshwater bodies. Nutrient input to freshwater bodies increases the
algal blooms which absorb carbon from the atmosphere and increase the carbon
sequestration (Pacheco et al. 2013). However, on decomposition and respiration, this
carbon is released to the atmosphere and the cycle goes on (Bastviken et al. 2011;
Borges et al. 2015).
A worldwide study by Cole et al. (2007) reveals that ~87% of the lakes are CO 2 -
supersaturated and the average pCO 2 is about three times higher than the overlying
atmosphere. Thus, due to increasing human pressure, the surface waters may become
a source rather than a sink of atmospheric CO 2 . Recent studies have established that
this CO 2 flux from rivers and stream is enough to affect the regional C budget at
landscape scale (Raymond et al. 2013; Jaiswal et al. 2018). Amazonian rivers, for
instance, have been reported to emit CO 2 more than ten times of the amount of C
exported to the ocean (Richey et al. 2002). One of the main reason of high CO 2
efflux from rivers is in situ breakdown of young organic matter (Richey et al. 2002).
Recent studies have indicated that the human-impacted Ganga River is receiving an
increasingly high amount of carbon from terrestrial sources (Pandey et al. 2014a). In
an earlier study, conducted at land-water interface (LWI) of the Ganga River, we
found that the LWI is outgassing a huge amount of CO 2 into the atmosphere
indicating that due to increasing human perturbations many parts of the Ganga
River are now converted into a source of CO 2 (Jaiswal et al. 2018; Jaiswal and
Pandey 2019e).
The organic matter degradation and carbon cycling are controlled by microbial
extracellular enzyme (EE) activities (Sinsabaugh et al. 2009). The anthropogenic
input of carbon (allochthonous C) causes a shift in microbial community structure
and functioning, including organic matter degradation and carbon cycle. The EE
activity is influenced by human inputs such as carbon, nutrients, and heavy metals
(Pandey and Yadav 2017; Jaiswal and Pandey 2018). Carbon and nutrients act as
substrate and enhance the EE activities, while heavy metals act as toxicant and thus
10 Ecosystem Responses to Pollution in the Ganga River: Key Issues to Address. . .
235