regulating the ecosystem structure and functioning, these have been proved to be the
most suitable parameters for quantification of shift in ecosystem responses toward
alteration in organic matter (substrate) and heavy metals (inhibitors) (Sinsabaugh
et al. 2008; Jaiswal and Pandey 2018). Long-term sustainability and stability of an
ecosystem depends, in a major way, on functionally active microbial communities,
and such measurements provide the actual picture of health condition of an ecosystem. Further, because they constitute the key node connecting detritus trophic chain,
any change in their metabolism affects the whole ecosystem processes including
organic matter decomposition, nutrient cycling, and food web. Measurement of
enzyme activities requires a small quantity of sample, generally proved to be simple,
accurate, cost-effective, and rapid. Studies have shown that EE activities can be used
as an index of microbiological functional diversity and integration of these with
other physical and chemical measurements can provide important information on
which ecosystem management strategies can be keyed (Jaiswal and Pandey 2019a).
As the microbial functional diversity involves various metabolic processes, a
representative set of enzymes that control the key metabolic pathways/processes can
be used to assess the microbial response to changing carbon, nutrients, and heavy
metal concentrations. The extracellular enzyme β-D-glucosidase can be used as a
measure of C acquisition (Sinsabaugh et al. 2009) and alkaline phosphatase (AP) as a
proxy of P starvation (Duhamel et al. 2010), while protease can be used as an
indicator of N mineralization (Rejsek et al. 2008). Further, because the fluorescein
diacetate hydrolytic bioassay (FDAase) involves three major groups of enzymes
(lipases, esterases, and proteases), which contribute to organic matter decomposition, it can be used as an indicator of total microbial activity (Schnürer and Rosswall
1982). The FDAase can directly be correlated with biomass and ATP content
(Fontvieille et al. 1992). The microbial metabolic quotient (ratio of basal respiration
to substrate-induced respiration) is used as an index to measure adversities in
environmental conditions for soil microbes (Wardle 1993).
The microbial structure and functioning in aquatic ecosystems are generally
influenced by episodic events driven by stormwater and intermittent flushing of
urban-industrial effluents. Anthropogenic input of nutrients increases the autochthonous C which, along with the allochthonous C, induces EE activities. Studies have
shown that EE activities can be used as a better substitute of sediment and water
quality variables because of their direct linkages with carbon and nutrients as well as
with the concentration of toxicants in water and sediments (Hill et al. 2006; Jaiswal
and Pandey 2018). In addition to carbon and nutrients, rivers receive huge amount of
metals from natural and anthropogenic sources, a large fraction of which is deposited
in the bed sediments. Heavy metals are potentially toxic to microbial community and
influence the overall ecological structure and functioning (Jaiswal and Pandey 2018,
2019e). Organic carbon in sediment forms complex with metals and often buffers
their bioavailability and, consequently, the toxicity (Jaiswal and Pandey 2019e).
Thus, the investigations on relationships between EE activities, substrate (carbon),
and total and bioavailable metal concentration (toxicants) can provide important
cues through which the state of river health and ecotoxicological implications can be
appropriately assessed. In a recent study, we found positive correlations of EE
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D. Jaiswal et al.
most suitable parameters for quantification of shift in ecosystem responses toward
alteration in organic matter (substrate) and heavy metals (inhibitors) (Sinsabaugh
et al. 2008; Jaiswal and Pandey 2018). Long-term sustainability and stability of an
ecosystem depends, in a major way, on functionally active microbial communities,
and such measurements provide the actual picture of health condition of an ecosystem. Further, because they constitute the key node connecting detritus trophic chain,
any change in their metabolism affects the whole ecosystem processes including
organic matter decomposition, nutrient cycling, and food web. Measurement of
enzyme activities requires a small quantity of sample, generally proved to be simple,
accurate, cost-effective, and rapid. Studies have shown that EE activities can be used
as an index of microbiological functional diversity and integration of these with
other physical and chemical measurements can provide important information on
which ecosystem management strategies can be keyed (Jaiswal and Pandey 2019a).
As the microbial functional diversity involves various metabolic processes, a
representative set of enzymes that control the key metabolic pathways/processes can
be used to assess the microbial response to changing carbon, nutrients, and heavy
metal concentrations. The extracellular enzyme β-D-glucosidase can be used as a
measure of C acquisition (Sinsabaugh et al. 2009) and alkaline phosphatase (AP) as a
proxy of P starvation (Duhamel et al. 2010), while protease can be used as an
indicator of N mineralization (Rejsek et al. 2008). Further, because the fluorescein
diacetate hydrolytic bioassay (FDAase) involves three major groups of enzymes
(lipases, esterases, and proteases), which contribute to organic matter decomposition, it can be used as an indicator of total microbial activity (Schnürer and Rosswall
1982). The FDAase can directly be correlated with biomass and ATP content
(Fontvieille et al. 1992). The microbial metabolic quotient (ratio of basal respiration
to substrate-induced respiration) is used as an index to measure adversities in
environmental conditions for soil microbes (Wardle 1993).
The microbial structure and functioning in aquatic ecosystems are generally
influenced by episodic events driven by stormwater and intermittent flushing of
urban-industrial effluents. Anthropogenic input of nutrients increases the autochthonous C which, along with the allochthonous C, induces EE activities. Studies have
shown that EE activities can be used as a better substitute of sediment and water
quality variables because of their direct linkages with carbon and nutrients as well as
with the concentration of toxicants in water and sediments (Hill et al. 2006; Jaiswal
and Pandey 2018). In addition to carbon and nutrients, rivers receive huge amount of
metals from natural and anthropogenic sources, a large fraction of which is deposited
in the bed sediments. Heavy metals are potentially toxic to microbial community and
influence the overall ecological structure and functioning (Jaiswal and Pandey 2018,
2019e). Organic carbon in sediment forms complex with metals and often buffers
their bioavailability and, consequently, the toxicity (Jaiswal and Pandey 2019e).
Thus, the investigations on relationships between EE activities, substrate (carbon),
and total and bioavailable metal concentration (toxicants) can provide important
cues through which the state of river health and ecotoxicological implications can be
appropriately assessed. In a recent study, we found positive correlations of EE
226
D. Jaiswal et al.