difficult to establish a linear dose-response relationship under in situ condition
(Håkanson 1980). In human-impacted rivers, eutrophication and metal pollution
generally occur simultaneously. Thus, for an accurate measurement of river health,
it is important to understand how the ecosystem responds toward human
perturbations.
As a solution of this problem, Jaiswal and Pandey (2019a) developed an “ecological response index (ERI)” which is able to quantitatively predict ecosystem
response to C eutrophication and metal pollution in large rivers. The index was
developed using carbon and its response determinant (fluorescein diacetate hydrolytic assay, FDAase) and a sum of six heavy metal concentrations in an empirical
relationship as below (Jaiswal and Pandey 2019a):
Ecological Response Index ¼
FDAase  qM
P n
i¼1
M i
ð Þ
where FDAase ¼ fluorescein diacetate hydrolytic activity; qM ¼ microbial quotient;
and (M i ) ¼ concentration of i
th metal.
The ERI, as a quantitative predictor of eutrophy and metal pollution, was
validated using Carlson’s trophic state index (TSI) (Carlson 1977), Håkanson’s
risk index (RI) (Håkanson 1980), and Duodu’s modified ecological risk index
(MRI) (Duodu et al. 2016). Strong relationships among these indices indicated that
the ERI is highly appropriate for quantitative prediction of metal pollution and
trophic state of lotic ecosystems. Based on ERI, Jaiswal and Pandey (2019a)
concluded that the ERI between 0 and 24 represents extreme metal pollution (toxic
condition), between 25 and 38 indicates combination of eutrophy and metal pollution, 39 to 77 represents hypereutrophic condition and low metal pollution, 78 to
155 indicates eutrophic condition, and 156 to 320 represents the oligotrophic state of
the river ecosystem. The ERI can be used as an alternative ecological tool for
appropriately addressing concordant changes in ecological functioning with stronger
mechanistic linkages between the causal factor and associated responses. Besides
this, it is stable, widely applicable, and cost-effective in addressing the impact of
multiple human stressors on functional shifts in riverine ecosystems.
10.6.5 Ecosystem Feedbacks
A positive feedback in an ecosystem begins when a driving force is likely to cause a
transitional shift (Jaiswal and Pandey 2019f). Positive feedbacks are self-enhancing
and are among the most prominent signature of transitional shift where the changes
in ecosystem processes are expected to lead to development of alternative stable
states (Scheffer et al. 2001). It occurs in a feedback loop leading to enhance the
magnitude of even small perturbations. Positive feedbacks are widespread in nature
10 Ecosystem Responses to Pollution in the Ganga River: Key Issues to Address. . .
243
(Håkanson 1980). In human-impacted rivers, eutrophication and metal pollution
generally occur simultaneously. Thus, for an accurate measurement of river health,
it is important to understand how the ecosystem responds toward human
perturbations.
As a solution of this problem, Jaiswal and Pandey (2019a) developed an “ecological response index (ERI)” which is able to quantitatively predict ecosystem
response to C eutrophication and metal pollution in large rivers. The index was
developed using carbon and its response determinant (fluorescein diacetate hydrolytic assay, FDAase) and a sum of six heavy metal concentrations in an empirical
relationship as below (Jaiswal and Pandey 2019a):
Ecological Response Index ¼
FDAase  qM
P n
i¼1
M i
ð Þ
where FDAase ¼ fluorescein diacetate hydrolytic activity; qM ¼ microbial quotient;
and (M i ) ¼ concentration of i
th metal.
The ERI, as a quantitative predictor of eutrophy and metal pollution, was
validated using Carlson’s trophic state index (TSI) (Carlson 1977), Håkanson’s
risk index (RI) (Håkanson 1980), and Duodu’s modified ecological risk index
(MRI) (Duodu et al. 2016). Strong relationships among these indices indicated that
the ERI is highly appropriate for quantitative prediction of metal pollution and
trophic state of lotic ecosystems. Based on ERI, Jaiswal and Pandey (2019a)
concluded that the ERI between 0 and 24 represents extreme metal pollution (toxic
condition), between 25 and 38 indicates combination of eutrophy and metal pollution, 39 to 77 represents hypereutrophic condition and low metal pollution, 78 to
155 indicates eutrophic condition, and 156 to 320 represents the oligotrophic state of
the river ecosystem. The ERI can be used as an alternative ecological tool for
appropriately addressing concordant changes in ecological functioning with stronger
mechanistic linkages between the causal factor and associated responses. Besides
this, it is stable, widely applicable, and cost-effective in addressing the impact of
multiple human stressors on functional shifts in riverine ecosystems.
10.6.5 Ecosystem Feedbacks
A positive feedback in an ecosystem begins when a driving force is likely to cause a
transitional shift (Jaiswal and Pandey 2019f). Positive feedbacks are self-enhancing
and are among the most prominent signature of transitional shift where the changes
in ecosystem processes are expected to lead to development of alternative stable
states (Scheffer et al. 2001). It occurs in a feedback loop leading to enhance the
magnitude of even small perturbations. Positive feedbacks are widespread in nature
10 Ecosystem Responses to Pollution in the Ganga River: Key Issues to Address. . .
243