Daphnia enjoys a P-rich lifestyle and encounters potential P deficiency when cellular
P declines (Elser et al. 2000). Thus, the population of Daphnia, which can be used as
an indicator of P eutrophy, will decline sharply under N-rich condition. These
studies have led to conclude that the shifts in nutrient stoichiometry can be used as
an alternative response indicator of shifting ecosystem structure and functioning
driven by increasing natural and anthropogenic perturbations.
10.6.3 Diatom-TEP Linkages
Diatoms, a highly diverse group of photosynthetic protists and widely used indicators of environmental shifts, are producers of transparent exopolymeric particles
(TEP). The diversity and abundance of these primary producers are affected by
absolute nutrient concentrations, stoichiometry, ionic strength, pH, light penetration,
and temperature (Potapova and Charles 2003). The abundance of diatoms is often
negatively influenced by high concentrations of nutrients because only some species
can grow in nutrient-rich condition. The species adapted to high nutrient concentrations remain generally accommodative to heterogeneous habitats by dominance
transference (Pandey et al. 2017). As already mentioned, the N/P/Si ratio is the
most important factor that drives the diatoms diversity and abundance. The decrease
in N/P ratio decreases the species diversity although P-loving diatoms proliferate
rapidly (Pandey et al. 2017). Increased N/Si ratio leads to Si limitation with potential
effects on the quantity (cell number and biomass) as well as quality (composition of
biomass) of diatom assemblages (Davidson and Gurney 1999). Alterations in the
abundance of specific diatom species, assemblage, and cellular metabolic states
affect the microbial trophic transfer and population of meso-zooplankton (Miralto
et al. 1999) with overall effects on carbon export and biogeochemical cycling.
Diatoms produce acidic polysaccharides in the form of transparent exopolymeric
particles (TEP). The size of TEP ranges from >0.4 μm to <200 μm and is stained
with the Alcian blue. Diatoms with C 4 photosynthetic pathway are prolific in carbon
capture and storage under excess N supply and may accumulate excessive carbon
(Riebesell et al. 2007). To maintain a normal physiological state (C/N ratio, for
instance), the excessive carbon is excreted in the form of acidic polysaccharides
which are ultimately converted into TEP. Because of their ability to form coagulates
and aggregates, the TEP play an important role in the regulation of DOC-POC pump
and carbon sequestration. Additionally, high-density particles such as heavy metals
get aggregated enhancing the density of TEP and consequent sedimentation of
nutrients, metals, and pathogens (Passow et al. 2001). The results of a recent study
(Pandey et al. 2017) reveal that to cope up with changing nutrient concentrations and
their stoichiometric ratio, the diatoms increase the production of TEP which
enhances the sedimentation and removal of turbidity and other harmful components.
This is an important mechanism responsible for high self-purification capacity of the
Ganga River (Pandey et al. 2017). The study further shows that to compensate the
reduction in TEP under excessive human pressure, the diatom tends to accommodate
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D. Jaiswal et al.
P declines (Elser et al. 2000). Thus, the population of Daphnia, which can be used as
an indicator of P eutrophy, will decline sharply under N-rich condition. These
studies have led to conclude that the shifts in nutrient stoichiometry can be used as
an alternative response indicator of shifting ecosystem structure and functioning
driven by increasing natural and anthropogenic perturbations.
10.6.3 Diatom-TEP Linkages
Diatoms, a highly diverse group of photosynthetic protists and widely used indicators of environmental shifts, are producers of transparent exopolymeric particles
(TEP). The diversity and abundance of these primary producers are affected by
absolute nutrient concentrations, stoichiometry, ionic strength, pH, light penetration,
and temperature (Potapova and Charles 2003). The abundance of diatoms is often
negatively influenced by high concentrations of nutrients because only some species
can grow in nutrient-rich condition. The species adapted to high nutrient concentrations remain generally accommodative to heterogeneous habitats by dominance
transference (Pandey et al. 2017). As already mentioned, the N/P/Si ratio is the
most important factor that drives the diatoms diversity and abundance. The decrease
in N/P ratio decreases the species diversity although P-loving diatoms proliferate
rapidly (Pandey et al. 2017). Increased N/Si ratio leads to Si limitation with potential
effects on the quantity (cell number and biomass) as well as quality (composition of
biomass) of diatom assemblages (Davidson and Gurney 1999). Alterations in the
abundance of specific diatom species, assemblage, and cellular metabolic states
affect the microbial trophic transfer and population of meso-zooplankton (Miralto
et al. 1999) with overall effects on carbon export and biogeochemical cycling.
Diatoms produce acidic polysaccharides in the form of transparent exopolymeric
particles (TEP). The size of TEP ranges from >0.4 μm to <200 μm and is stained
with the Alcian blue. Diatoms with C 4 photosynthetic pathway are prolific in carbon
capture and storage under excess N supply and may accumulate excessive carbon
(Riebesell et al. 2007). To maintain a normal physiological state (C/N ratio, for
instance), the excessive carbon is excreted in the form of acidic polysaccharides
which are ultimately converted into TEP. Because of their ability to form coagulates
and aggregates, the TEP play an important role in the regulation of DOC-POC pump
and carbon sequestration. Additionally, high-density particles such as heavy metals
get aggregated enhancing the density of TEP and consequent sedimentation of
nutrients, metals, and pathogens (Passow et al. 2001). The results of a recent study
(Pandey et al. 2017) reveal that to cope up with changing nutrient concentrations and
their stoichiometric ratio, the diatoms increase the production of TEP which
enhances the sedimentation and removal of turbidity and other harmful components.
This is an important mechanism responsible for high self-purification capacity of the
Ganga River (Pandey et al. 2017). The study further shows that to compensate the
reduction in TEP under excessive human pressure, the diatom tends to accommodate
240
D. Jaiswal et al.