In Varanasi region, the autochthonous carbon varies between 256.6 and 567.8 kg C
ha
À1 . Across the river length, the autochthonous input contributes $102.58 Gg of
organic C annually (Singh and Pandey 2019). Comparative studies of Goldstein and
Galbally (2007) and Hallquist et al. (2009) show that, at global scale, the total
organic carbon (TOC) deposition increased from 305–645 to 950 Tg over a period
of only 2 years. The Ganga River in Varanasi region receives ~110.8–558.6 tons
organic carbon through atmospheric deposition, ~1421.55 tons DOC through surface runoff, and 364.0–1456.3 tons organic carbon through Assi drain (Yadav and
Pandey 2017a). Basin-scale extrapolation showed that the basin receives $1.81 Tg
TOC each year through atmospheric deposition of which $4.26 Gg is added directly
on to the river surface (Singh and Pandey 2019). Surface runoff exports 16.16 to
26.90 Tg TOC and 9.19 to 16.46 Tg DOC, whereas the point sources add over
110 Gg of TOC to the river annually (Singh and Pandey 2019).
Studies show that a large amount of carbon in rivers and streams comes from
terrigenous sources (Pandey et al. 2014a; Siddiqui et al. 2019b). Because nonpoint
source C of terrestrial origin is flushed mainly through monsoon season runoff, this
C is largely transported to the sea. The Ganga River leads to a burial of
~1.1 Â 10
12 mol sediment-driven organic carbon each year in the Bengal Fan
which is $10% of the global organic carbon burial flux in the continental margins
(France-Lanord and Derry 1997). At global scale, rivers export $611 Tg carbon per
year (Cole et al. 2007) from which the contribution from South Asian rivers alone is
$7% (42.9 Tg year
À1 ) (Patra et al. 2013). The Ganga-Brahmaputra with $7 Tg C
year
À1 contributes the largest share in global DOC export to the oceans (361 Tg
year
À1 ) (Patra et al. 2013).
10.3 Ecosystem Responses to Pollution and Eutrophy
10.3.1 Shifts in Microbial Enzyme Activity
The riverbed sediments, an important component of riverine ecosystem, are a
biologically active and comparatively stable zone and support benthic communities
which play an important role in ecosystem functions including biogeochemical
cycling, secondary production, carbon metabolism, and sedimentation of carbon,
nutrients, and heavy metals (Covitch et al. 2004). Recent studies have established
that sediment microbial extracellular enzymes (EEs) can be used as an indicator of
carbon and nutrient limitation/acquisition and to uncover the influence of regionalscale anthropogenic stressors (Sinsabaugh et al. 2009; Yadav and Pandey 2017b;
Jaiswal and Pandey 2018, 2019e). The substrate-specific nature of EEs makes them
important tools to investigate the functional profile of microbial communities as
influenced by human-induced alterations (Sinsabaugh and Linkins 1990). The EE
activities show quantifiable and instantaneous response (for instance, toward substrates and toxicants) even to small alterations in the ecosystems (Paerl et al. 2003).
As the microbes play vital role in mediating the biogeochemical cycles and
10 Ecosystem Responses to Pollution in the Ganga River: Key Issues to Address. . .
225
ha
À1 . Across the river length, the autochthonous input contributes $102.58 Gg of
organic C annually (Singh and Pandey 2019). Comparative studies of Goldstein and
Galbally (2007) and Hallquist et al. (2009) show that, at global scale, the total
organic carbon (TOC) deposition increased from 305–645 to 950 Tg over a period
of only 2 years. The Ganga River in Varanasi region receives ~110.8–558.6 tons
organic carbon through atmospheric deposition, ~1421.55 tons DOC through surface runoff, and 364.0–1456.3 tons organic carbon through Assi drain (Yadav and
Pandey 2017a). Basin-scale extrapolation showed that the basin receives $1.81 Tg
TOC each year through atmospheric deposition of which $4.26 Gg is added directly
on to the river surface (Singh and Pandey 2019). Surface runoff exports 16.16 to
26.90 Tg TOC and 9.19 to 16.46 Tg DOC, whereas the point sources add over
110 Gg of TOC to the river annually (Singh and Pandey 2019).
Studies show that a large amount of carbon in rivers and streams comes from
terrigenous sources (Pandey et al. 2014a; Siddiqui et al. 2019b). Because nonpoint
source C of terrestrial origin is flushed mainly through monsoon season runoff, this
C is largely transported to the sea. The Ganga River leads to a burial of
~1.1 Â 10
12 mol sediment-driven organic carbon each year in the Bengal Fan
which is $10% of the global organic carbon burial flux in the continental margins
(France-Lanord and Derry 1997). At global scale, rivers export $611 Tg carbon per
year (Cole et al. 2007) from which the contribution from South Asian rivers alone is
$7% (42.9 Tg year
À1 ) (Patra et al. 2013). The Ganga-Brahmaputra with $7 Tg C
year
À1 contributes the largest share in global DOC export to the oceans (361 Tg
year
À1 ) (Patra et al. 2013).
10.3 Ecosystem Responses to Pollution and Eutrophy
10.3.1 Shifts in Microbial Enzyme Activity
The riverbed sediments, an important component of riverine ecosystem, are a
biologically active and comparatively stable zone and support benthic communities
which play an important role in ecosystem functions including biogeochemical
cycling, secondary production, carbon metabolism, and sedimentation of carbon,
nutrients, and heavy metals (Covitch et al. 2004). Recent studies have established
that sediment microbial extracellular enzymes (EEs) can be used as an indicator of
carbon and nutrient limitation/acquisition and to uncover the influence of regionalscale anthropogenic stressors (Sinsabaugh et al. 2009; Yadav and Pandey 2017b;
Jaiswal and Pandey 2018, 2019e). The substrate-specific nature of EEs makes them
important tools to investigate the functional profile of microbial communities as
influenced by human-induced alterations (Sinsabaugh and Linkins 1990). The EE
activities show quantifiable and instantaneous response (for instance, toward substrates and toxicants) even to small alterations in the ecosystems (Paerl et al. 2003).
As the microbes play vital role in mediating the biogeochemical cycles and
10 Ecosystem Responses to Pollution in the Ganga River: Key Issues to Address. . .
225