of nutrients and other pollutants. The total wastewater generation in the basin is
~8250 million liters per day (MLD), out of which, 2538 MLD is discharged directly
into the river, 4491 MLD into tributaries, and 1220 MLD on land or low-lying areas
(CPCB 2013). The Assi drain at Varanasi discharges over 66 MLD of sewage
leading to ~156 mg L
À1 chemical oxygen demand (COD) and 4060 kg day
À1
biological oxygen demand (BOD) load to the river in this region. Additionally, the
drain adds over 535 tons of dissolved inorganic nitrogen (DIN) and 133 tons of
dissolved reactive phosphorus (DRP) annually (Yadav and Pandey 2017a). In
addition to point sources, the nonpoint sources, such as agricultural runoff from
73.44% agricultural land of the basin containing residues of ~10 million tons of
fertilizers and 9000 tons of pesticides, add a sizable amount of nutrients and
pesticide to the river. A sub-watershed-scale study by Yadav and Pandey (2017a)
shows that the river in Varanasi region alone receives ~289.69 tons of DIN, 47.1 tons
of DRP, and 1421.55 tons of dissolved organic carbon (DOC) through surface runoff
and ~15.23 tons of DIN and 1.19 tons of DRP through atmospheric deposition
(AD) annually. A watershed-scale study by Pandey et al. (2016a) shows that the
Ganges basin receives ~3.32 Tg reactive nitrogen (NO 3
À + NH 4
+
) and ~173.20 Gg
phosphorus (PO 4
3À ) annually, and the inputs were relatively higher in the middle
segment which is considered as the most polluted stretch of the river (CPCB 2013).
All these sources add large amount of oxygen-demanding substances and pollutants
into the river throughout the year creating tremendous pressure on water quality and
ecosystem services such as drinking water supply, recreation, and fisheries (Pandey
et al. 2017; Jaiswal and Pandey 2019b; Siddiqui et al. 2019a).
Studies conducted on the Ganga River generally select parameters bifurcating
eutrophy and metal pollution and even without considering ecosystem-level consequences. For instance, to address trophic state, biological oxygen demand is generally considered where the sampling is restricted to the upper water column only. The
issues such as stratification of dissolved oxygen in the water column, sediment
oxygen demand (SOD), dissolved oxygen deficit (DOD), nature of oxygendemanding substances (ODS), benthic hypoxia, and ecosystem feedbacks have
been altogether ignored for this major river system of India. Similarly, for metal
pollution, the analysis of pelagic water and freshly deposited sediments are generally
considered (Siddiqui and Pandey 2019a). Some of the studies conducted in earth
sciences context have taken into account the deep sediment analysis (Verma and
Pandey 2019). Studies considering the factors of in situ metal release and its
bioavailability are altogether lacking. In particular, no data so far, except few studies
conducted in our laboratory, are available on changing state of ecosystem functions
coupling feedbacks and ecological assimilation capacity of the Ganga River. The
present review is an effort to make a critical analysis on the need for understanding
ecosystem responses coupling eutrophy and metal pollution in the Ganga River. This
has relevance because our multi-temporal, multi-scale studies suggest the need for
identifying the determinants of ecosystem responses to metal pollution and eutrophy
for integrated management of the Ganga River (Jaiswal and Pandey 2019a, c).
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D. Jaiswal et al.
~8250 million liters per day (MLD), out of which, 2538 MLD is discharged directly
into the river, 4491 MLD into tributaries, and 1220 MLD on land or low-lying areas
(CPCB 2013). The Assi drain at Varanasi discharges over 66 MLD of sewage
leading to ~156 mg L
À1 chemical oxygen demand (COD) and 4060 kg day
À1
biological oxygen demand (BOD) load to the river in this region. Additionally, the
drain adds over 535 tons of dissolved inorganic nitrogen (DIN) and 133 tons of
dissolved reactive phosphorus (DRP) annually (Yadav and Pandey 2017a). In
addition to point sources, the nonpoint sources, such as agricultural runoff from
73.44% agricultural land of the basin containing residues of ~10 million tons of
fertilizers and 9000 tons of pesticides, add a sizable amount of nutrients and
pesticide to the river. A sub-watershed-scale study by Yadav and Pandey (2017a)
shows that the river in Varanasi region alone receives ~289.69 tons of DIN, 47.1 tons
of DRP, and 1421.55 tons of dissolved organic carbon (DOC) through surface runoff
and ~15.23 tons of DIN and 1.19 tons of DRP through atmospheric deposition
(AD) annually. A watershed-scale study by Pandey et al. (2016a) shows that the
Ganges basin receives ~3.32 Tg reactive nitrogen (NO 3
À + NH 4
+
) and ~173.20 Gg
phosphorus (PO 4
3À ) annually, and the inputs were relatively higher in the middle
segment which is considered as the most polluted stretch of the river (CPCB 2013).
All these sources add large amount of oxygen-demanding substances and pollutants
into the river throughout the year creating tremendous pressure on water quality and
ecosystem services such as drinking water supply, recreation, and fisheries (Pandey
et al. 2017; Jaiswal and Pandey 2019b; Siddiqui et al. 2019a).
Studies conducted on the Ganga River generally select parameters bifurcating
eutrophy and metal pollution and even without considering ecosystem-level consequences. For instance, to address trophic state, biological oxygen demand is generally considered where the sampling is restricted to the upper water column only. The
issues such as stratification of dissolved oxygen in the water column, sediment
oxygen demand (SOD), dissolved oxygen deficit (DOD), nature of oxygendemanding substances (ODS), benthic hypoxia, and ecosystem feedbacks have
been altogether ignored for this major river system of India. Similarly, for metal
pollution, the analysis of pelagic water and freshly deposited sediments are generally
considered (Siddiqui and Pandey 2019a). Some of the studies conducted in earth
sciences context have taken into account the deep sediment analysis (Verma and
Pandey 2019). Studies considering the factors of in situ metal release and its
bioavailability are altogether lacking. In particular, no data so far, except few studies
conducted in our laboratory, are available on changing state of ecosystem functions
coupling feedbacks and ecological assimilation capacity of the Ganga River. The
present review is an effort to make a critical analysis on the need for understanding
ecosystem responses coupling eutrophy and metal pollution in the Ganga River. This
has relevance because our multi-temporal, multi-scale studies suggest the need for
identifying the determinants of ecosystem responses to metal pollution and eutrophy
for integrated management of the Ganga River (Jaiswal and Pandey 2019a, c).
222
D. Jaiswal et al.