10.2.2 Nutrient Loading
Nitrogen (N) and phosphorus (P) are considered as most critical nutrients because
their demand to supply ratios generally lie at unity or below. Because of this reason,
they become limiting nutrients for phytoplankton growth. Excessive input of these
nutrients, although increases food production and stimulates plant growth, causes
detrimental effects on surface waters including rivers. Rivers receive nutrients from
the airshed, in the form of atmospheric deposition (AD), and watershed in the form
of leaching and runoff (Pandey et al. 2014a; Bellmore et al. 2018). A global-scale
study has shown that during the period of 1860–2005, the reactive N (Nr) deposition
has increased from $15 Tg to 187 Tg which could be doubled by 2050 (Galloway
et al. 2008). Further, AD adds over 3.7 Tg of P annually at global scale (Tipping
et al. 2014). Studies show AD-N input range between 1.54 and 40 kg ha
À1 year
À1 in
inland water bodies of the world (Edokpa et al. 2015; Bellmore et al. 2018) and
between 12 and 38 kg ha
À1 year
À1 in many parts of India (Pandey 2011; Pandey and
Pandey 2013; Siddiqui et al. 2019b). It varies between 9.72 and 42.85 kg ha
À1 year
À1
in the Ganga River, an amount high enough to change the Ganga River ecology
(Singh and Pandey 2019). Basin-scale extrapolation of a recent study shows that
through AD, $2.77 Tg DIN and $0.13 Tg DRP are deposited in the basin
and ~ 5.31 Gg DIN and 0.37 Gg DRP are added directly on the Ganga River surface
annually (Singh and Pandey 2019). Additionally, the river receives a large amount of
nutrients from tributaries and sub-tributaries (Mishra et al. 2016; Yadav and Pandey
2017a).
In Ganges basin, over 2723 MLD municipal sewage is generated, out of which
only ~1200 MLD is flushed to the river after treatment. These urban effluents add
~13.28 Gg DIN and 5.29 Gg of DRP annually into the river. Surface runoff also adds
huge amount of nutrient to surface waters. A sub-watershed-scale estimation in
Varanasi region shows that agricultural land adds ~403, 186, and 24 Gg year
À1 ;
woodland adds ~67, 30, and 19 Gg year
À 1; and built-up area adds ~11, 55, and
34 Gg year
À1 of NO 3
À , NH 4
+ , and DRP, respectively, through surface runoff. The
basin-scale extrapolation of these data shows that the river receives ~193 to 1181 Gg
DIN and ~59 to 218 Gg DRP annually through surface runoff. The river transports
~31.58 Gg of DIN and 3.97 Gg of DRP annually to the Bay of Bengal (Singh and
Pandey 2019). These overall quantitative estimations show that, along with the point
sources, the nonpoint sources also add a large amount of nutrients to the Ganga River
across its length which needs proper attention and management.
10.2.3 Carbon Enrichment
Along with point sources, the atmospheric deposition and surface runoff are important regulators of autochthonous and allochthonous C pool in the Ganga River
(Pandey et al. 2014a, 2015a; Siddiqui et al. 2019b; Siddiqui and Pandey 2019b).
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Nitrogen (N) and phosphorus (P) are considered as most critical nutrients because
their demand to supply ratios generally lie at unity or below. Because of this reason,
they become limiting nutrients for phytoplankton growth. Excessive input of these
nutrients, although increases food production and stimulates plant growth, causes
detrimental effects on surface waters including rivers. Rivers receive nutrients from
the airshed, in the form of atmospheric deposition (AD), and watershed in the form
of leaching and runoff (Pandey et al. 2014a; Bellmore et al. 2018). A global-scale
study has shown that during the period of 1860–2005, the reactive N (Nr) deposition
has increased from $15 Tg to 187 Tg which could be doubled by 2050 (Galloway
et al. 2008). Further, AD adds over 3.7 Tg of P annually at global scale (Tipping
et al. 2014). Studies show AD-N input range between 1.54 and 40 kg ha
À1 year
À1 in
inland water bodies of the world (Edokpa et al. 2015; Bellmore et al. 2018) and
between 12 and 38 kg ha
À1 year
À1 in many parts of India (Pandey 2011; Pandey and
Pandey 2013; Siddiqui et al. 2019b). It varies between 9.72 and 42.85 kg ha
À1 year
À1
in the Ganga River, an amount high enough to change the Ganga River ecology
(Singh and Pandey 2019). Basin-scale extrapolation of a recent study shows that
through AD, $2.77 Tg DIN and $0.13 Tg DRP are deposited in the basin
and ~ 5.31 Gg DIN and 0.37 Gg DRP are added directly on the Ganga River surface
annually (Singh and Pandey 2019). Additionally, the river receives a large amount of
nutrients from tributaries and sub-tributaries (Mishra et al. 2016; Yadav and Pandey
2017a).
In Ganges basin, over 2723 MLD municipal sewage is generated, out of which
only ~1200 MLD is flushed to the river after treatment. These urban effluents add
~13.28 Gg DIN and 5.29 Gg of DRP annually into the river. Surface runoff also adds
huge amount of nutrient to surface waters. A sub-watershed-scale estimation in
Varanasi region shows that agricultural land adds ~403, 186, and 24 Gg year
À1 ;
woodland adds ~67, 30, and 19 Gg year
À 1; and built-up area adds ~11, 55, and
34 Gg year
À1 of NO 3
À , NH 4
+ , and DRP, respectively, through surface runoff. The
basin-scale extrapolation of these data shows that the river receives ~193 to 1181 Gg
DIN and ~59 to 218 Gg DRP annually through surface runoff. The river transports
~31.58 Gg of DIN and 3.97 Gg of DRP annually to the Bay of Bengal (Singh and
Pandey 2019). These overall quantitative estimations show that, along with the point
sources, the nonpoint sources also add a large amount of nutrients to the Ganga River
across its length which needs proper attention and management.
10.2.3 Carbon Enrichment
Along with point sources, the atmospheric deposition and surface runoff are important regulators of autochthonous and allochthonous C pool in the Ganga River
(Pandey et al. 2014a, 2015a; Siddiqui et al. 2019b; Siddiqui and Pandey 2019b).
224
D. Jaiswal et al.