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H. Dutta
3.2 Eutrophication
3.2.1 Algal Blooms
Algal blooms are dense aggregations of phytoplankton cells of one or more species
and accumulate in water until their growth is checked by resource depletion. Nutrient
availability is the primary requirement for their buildup because phytoplanktons grow
by taking up dissolved nutrients and incorporating them into biomass (Assmy and
Smetacek 2009). When excessive nutrients accumulate in the aquatic ecosystems the
phytoplankton community shifts to bloom-forming algae. This persistent condition
of surface waters is called eutrophication (Smith 1990; Carpenter 2005). Eutrophication leads to predictable increment of the biomass of algae in both freshwater
and marine ecosystems (Smith 2003) and occurs due to nitrogen and phosphorus
enrichment (Johnson et al. 2007; Frumina and Gildeeva 2014). Globally, total nitrogen input has been strongly correlated with phytoplankton production in estuarine
and marine waters, whereas total phosphorus input has been strongly correlated with
phytoplankton production in freshwaters (Anderson et al. 2002). The concentration
of nutrients prior to its outbreak determines the magnitude of the bloom peak (Assmy
and Smetacek 2009). The potential sources of nutrients that stimulate algal blooms are
atmospheric deposition, sewage, groundwater flow, as well as runoff and discharge
from agriculture and aquaculture (Anderson et al. 2002). Examples of blooms due
to nutrient loading can be cited from U.S. mainland estuaries (Chesapeake Bay and
the Albemarle-Pamlico Estuarine System), Inland Sea of Japan, the Black Sea, and
Chinese coastal waters (Anderson et al. 2002), coastal waters of Lee County, Florida
(Lapointe and Bedford 2007) and Gulf of Mexico (Henrichs et al. 2015).
3.2.2 Cyanobacteria as a Problem
The increment of cyanobacterial dominance in phytoplankton communities worldwide has been linked with eutrophication (Smith 2003). Cyanobacteria are the oldest
oxygen evolving organisms of the earth and have played an important role in shaping the present biosphere (Paerl and Paul 2012). They are the most ancient group of
phytoplanktons and form harmful algal blooms in freshwater, estuarine, and marine
ecosystems (O’Neil et al. 2012). Certain cyanobacterial species form massive surface growths that produce toxins, deplete oxygen and alter food webs. Such bacteria
are benefitted by nutrient enrichment (eutrophication), and hydrologic modifications
like water withdrawal, reservoir construction (Paerl and Huisman 2009). Examples
of cyanobacteria that secrete potent toxins are Microcystis, Anabaena, and Nodularia
and blooms of these species can give rise to severe problems (Assmy and Smetacek
2009). The toxic and non-toxic strains of several bloom-forming cyanobacteria occur
together and cannot be distinguished visually (Davis et al. 2009).
H. Dutta
3.2 Eutrophication
3.2.1 Algal Blooms
Algal blooms are dense aggregations of phytoplankton cells of one or more species
and accumulate in water until their growth is checked by resource depletion. Nutrient
availability is the primary requirement for their buildup because phytoplanktons grow
by taking up dissolved nutrients and incorporating them into biomass (Assmy and
Smetacek 2009). When excessive nutrients accumulate in the aquatic ecosystems the
phytoplankton community shifts to bloom-forming algae. This persistent condition
of surface waters is called eutrophication (Smith 1990; Carpenter 2005). Eutrophication leads to predictable increment of the biomass of algae in both freshwater
and marine ecosystems (Smith 2003) and occurs due to nitrogen and phosphorus
enrichment (Johnson et al. 2007; Frumina and Gildeeva 2014). Globally, total nitrogen input has been strongly correlated with phytoplankton production in estuarine
and marine waters, whereas total phosphorus input has been strongly correlated with
phytoplankton production in freshwaters (Anderson et al. 2002). The concentration
of nutrients prior to its outbreak determines the magnitude of the bloom peak (Assmy
and Smetacek 2009). The potential sources of nutrients that stimulate algal blooms are
atmospheric deposition, sewage, groundwater flow, as well as runoff and discharge
from agriculture and aquaculture (Anderson et al. 2002). Examples of blooms due
to nutrient loading can be cited from U.S. mainland estuaries (Chesapeake Bay and
the Albemarle-Pamlico Estuarine System), Inland Sea of Japan, the Black Sea, and
Chinese coastal waters (Anderson et al. 2002), coastal waters of Lee County, Florida
(Lapointe and Bedford 2007) and Gulf of Mexico (Henrichs et al. 2015).
3.2.2 Cyanobacteria as a Problem
The increment of cyanobacterial dominance in phytoplankton communities worldwide has been linked with eutrophication (Smith 2003). Cyanobacteria are the oldest
oxygen evolving organisms of the earth and have played an important role in shaping the present biosphere (Paerl and Paul 2012). They are the most ancient group of
phytoplanktons and form harmful algal blooms in freshwater, estuarine, and marine
ecosystems (O’Neil et al. 2012). Certain cyanobacterial species form massive surface growths that produce toxins, deplete oxygen and alter food webs. Such bacteria
are benefitted by nutrient enrichment (eutrophication), and hydrologic modifications
like water withdrawal, reservoir construction (Paerl and Huisman 2009). Examples
of cyanobacteria that secrete potent toxins are Microcystis, Anabaena, and Nodularia
and blooms of these species can give rise to severe problems (Assmy and Smetacek
2009). The toxic and non-toxic strains of several bloom-forming cyanobacteria occur
together and cannot be distinguished visually (Davis et al. 2009).