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M. Naeem et al.
16.1 Introduction
Eutrophication is the process by which a water body acquires
a high concentration of nutrients, especially phosphates and
nitrates. These nutrients promote excessive growth of algae.
As the algae die, a huge amount of organic matter is acted
upon by decomposing organisms that deplete the available
oxygen of water, causing suffocation and the death of aquatic
fauna and flora. In the middle of the twentieth century, eutrophication was recognized as a problem for the first time.
Since then, the biologists have been studying it extensively
in order to prevent further eutrophication of vital bodies of
water around the world (Khan and Ansari 2005; Yang et al.
2008; Ansari et al. 2011). Although it is a natural slow-aging
process, many human activities have led to widespread eutrophication in rivers, streams, lakes, and oceans around the
world. When eutrophication is accelerated, it becomes a severe problem, adversely affecting the quality of water and
the diverse organisms living therein. Eutrophication, caused
by human activities, is known as “nutrient pollution.” Mineral nutrients runoff from the agricultural farms is a leading cause of eutrophication worldwide. Furthermore, surface
runoffs, dust and organic debris, excreta and exudates of
animals also raise the nutrient content in the water bodies.
The decomposition of biodegradable pollutants releases hazardous elements which often threaten the biodiversity in the
water body. The eutrophication-accelerated plant and animal
biomass that develops in the water body often becomes a
nuisance. As the nutrients enter the water supply, they result
in an outburst of plant growth in water, specifically that of
algae, known as algal bloom. Eutrophication-affected lakes
and rivers often turn bright green or red according to the type
of algae forming the algal bloom. Algal blooms severely reduce the available oxygen in the water and, hence, ultimately
lead to loss of animal species in these water bodies owing
to suffocation. For instance, there is a gigantic dead zone,
which lacks animal life in the Gulf of Mexico because of
eutrophication. For several decades, the attempts have been
made to prevent eutrophication of water bodies around the
world (Ansari et al. 2011).
16.1.1 Types of Aquatic Systems
Based on nutrient status and productivity, aquatic systems
can be classified into the following three types:
a. Oligotrophic system: a water body with poor nutrient status and productivity
b. Mesotrophic system: a water body with intermediary or
moderate nutrient status and productivity
c. Eutrophic system: a water body with high nutrient status
and productivity
These three systems demarcate a biomass gradient that
ranges from nutrient-poor to nutrient-rich water bodies, supporting low (oligotrophic), medium (mesotrophic), and high
(eutrophic) biomass habitats. Nixon (1995) explained the
process of eutrophication in terms of increase in the rate of
supply of organic matter to the ecosystem. This definition
has gained worldwide acceptance and may be the most frequently used quantitative measure of eutrophication. In estuaries, organic matter occurs in the form of particulate organic
matter (POM), e.g., plant debris, detritus, phytoplankton, and
as dissolved organic matter (DOM), e.g., humics, mucopolysaccharides, peptides, and lipids. The distinction between
POM and DOM depends on the methods used to separate the
two fractions (e.g., filtration, ultrafiltration, centrifugation,
dialysis). In addition, the rate of supply of different forms
of organic matter is highly variable in natural ecosystems
and is significantly affected by the factors such as land use
characteristics of the watershed (rural, agricultural, urban),
hydrology, and climatology. (Paerl 1997; Guo et al. 1999).
Allochthonous organic matter (AOM) is transported into the
estuary primarily from watershed runoff and river inflow
(usually the primary source) or from coastal waters through
tidal inlets (secondary source). AOM is generated within the
system, mostly through photosynthesis by primary producformation of calcium carbonate can control the fate of nutrients in water bodies added by
anthropogenic activities. Magnesium is essential for chlorophyll synthesis and, thus, acts as a
limiting factor for the growth of phytoplankton. Therefore, depletion of magnesium reduces
the phytoplankton population. As an essential element, therefore, Mg often limits the growth
of primary producers such as algae, other aquatic plants, cyanobacteria, and photosynthetic
bacteria. The regulation effects of iron should be considered besides nitrogen and phosphorus
during the treatment of eutrophication of lakes. Studies of algal spectral properties under
different iron supply would be meaningful for determining the bloom and developing the
remote sensing warning system of lake eutrophication. The present review covers the definition and concept and types of eutrophication, adverse effects of eutrophication on quality and
functioning of aquatic ecosystems, causes and consequences of eutrophication, and the task
of mineral nutrients in the process of eutrophication.
Keywords
Algal bloom · Eutrophication · Nitrogen · Nutrient loading · Phosphorus · Potassium
M. Naeem et al.
16.1 Introduction
Eutrophication is the process by which a water body acquires
a high concentration of nutrients, especially phosphates and
nitrates. These nutrients promote excessive growth of algae.
As the algae die, a huge amount of organic matter is acted
upon by decomposing organisms that deplete the available
oxygen of water, causing suffocation and the death of aquatic
fauna and flora. In the middle of the twentieth century, eutrophication was recognized as a problem for the first time.
Since then, the biologists have been studying it extensively
in order to prevent further eutrophication of vital bodies of
water around the world (Khan and Ansari 2005; Yang et al.
2008; Ansari et al. 2011). Although it is a natural slow-aging
process, many human activities have led to widespread eutrophication in rivers, streams, lakes, and oceans around the
world. When eutrophication is accelerated, it becomes a severe problem, adversely affecting the quality of water and
the diverse organisms living therein. Eutrophication, caused
by human activities, is known as “nutrient pollution.” Mineral nutrients runoff from the agricultural farms is a leading cause of eutrophication worldwide. Furthermore, surface
runoffs, dust and organic debris, excreta and exudates of
animals also raise the nutrient content in the water bodies.
The decomposition of biodegradable pollutants releases hazardous elements which often threaten the biodiversity in the
water body. The eutrophication-accelerated plant and animal
biomass that develops in the water body often becomes a
nuisance. As the nutrients enter the water supply, they result
in an outburst of plant growth in water, specifically that of
algae, known as algal bloom. Eutrophication-affected lakes
and rivers often turn bright green or red according to the type
of algae forming the algal bloom. Algal blooms severely reduce the available oxygen in the water and, hence, ultimately
lead to loss of animal species in these water bodies owing
to suffocation. For instance, there is a gigantic dead zone,
which lacks animal life in the Gulf of Mexico because of
eutrophication. For several decades, the attempts have been
made to prevent eutrophication of water bodies around the
world (Ansari et al. 2011).
16.1.1 Types of Aquatic Systems
Based on nutrient status and productivity, aquatic systems
can be classified into the following three types:
a. Oligotrophic system: a water body with poor nutrient status and productivity
b. Mesotrophic system: a water body with intermediary or
moderate nutrient status and productivity
c. Eutrophic system: a water body with high nutrient status
and productivity
These three systems demarcate a biomass gradient that
ranges from nutrient-poor to nutrient-rich water bodies, supporting low (oligotrophic), medium (mesotrophic), and high
(eutrophic) biomass habitats. Nixon (1995) explained the
process of eutrophication in terms of increase in the rate of
supply of organic matter to the ecosystem. This definition
has gained worldwide acceptance and may be the most frequently used quantitative measure of eutrophication. In estuaries, organic matter occurs in the form of particulate organic
matter (POM), e.g., plant debris, detritus, phytoplankton, and
as dissolved organic matter (DOM), e.g., humics, mucopolysaccharides, peptides, and lipids. The distinction between
POM and DOM depends on the methods used to separate the
two fractions (e.g., filtration, ultrafiltration, centrifugation,
dialysis). In addition, the rate of supply of different forms
of organic matter is highly variable in natural ecosystems
and is significantly affected by the factors such as land use
characteristics of the watershed (rural, agricultural, urban),
hydrology, and climatology. (Paerl 1997; Guo et al. 1999).
Allochthonous organic matter (AOM) is transported into the
estuary primarily from watershed runoff and river inflow
(usually the primary source) or from coastal waters through
tidal inlets (secondary source). AOM is generated within the
system, mostly through photosynthesis by primary producformation of calcium carbonate can control the fate of nutrients in water bodies added by
anthropogenic activities. Magnesium is essential for chlorophyll synthesis and, thus, acts as a
limiting factor for the growth of phytoplankton. Therefore, depletion of magnesium reduces
the phytoplankton population. As an essential element, therefore, Mg often limits the growth
of primary producers such as algae, other aquatic plants, cyanobacteria, and photosynthetic
bacteria. The regulation effects of iron should be considered besides nitrogen and phosphorus
during the treatment of eutrophication of lakes. Studies of algal spectral properties under
different iron supply would be meaningful for determining the bloom and developing the
remote sensing warning system of lake eutrophication. The present review covers the definition and concept and types of eutrophication, adverse effects of eutrophication on quality and
functioning of aquatic ecosystems, causes and consequences of eutrophication, and the task
of mineral nutrients in the process of eutrophication.
Keywords
Algal bloom · Eutrophication · Nitrogen · Nutrient loading · Phosphorus · Potassium