In eutrophic, 53% in Europe and 28% in Africa.

            In the mid-20th century,
due to lack of information on eutrophication, this phenomenon in Europe and
Northern America was thought to be water pollution. Ever since then, it was
realised that this phenomenon is being distributed widely, not only in Europe
and Northern America, but across the world. According to statistics, 54% of
lakes in Asia are eutrophic, 53% in Europe and 28% in Africa. However, a study
by the CSIR has shown that in South Africa, more than 60% of the dams surveyed
were eutrophic.

            Many effects can arise due to the occurrence
of eutrophication. When this phenomenon becomes intense, undesirable effects
will follow which will not only affect the water source but also the
environment. Firstly, eutrophication will change the aquatic ecosystem. This is
said so because there will be formation of a detritus layer. Detritus layer is
layer of organic materials suspended on the seabed, piling up as more and more
organic materials suffocate and die due to lack of oxygen. Besides that,
eutrophication also changes the aquatic ecosystem into a marshy land as when dead
plants and organisms die, they sediment at the seabed, causing water to be more
turbid. This indirectly will also prevent touristic use of the lake as the
colour and smell of the lake will be unappealing. Plus, such a water source can
cause skin irritation and can also promote certain other illness, depending on
the sensitivity of a person.

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            Secondly, eutrophication also
decreases biodiversity in the ecosystem. This is said so because eutrophication
is the condition where the water surface is covered by algae and this prevents
sunlight from penetrating into the water body. As a result, plants begin to die
due to lack of oxygen. Once the producers die, the consumers will also begin to
die as the oxygen concentration in the water source further decreases. This
will also lead to a significant decrease in the fishery affairs and decrease
the quality of aquatic organisms. Unknowingly, some aquatic organisms can also
be poisonous if consumed. Not only that, if any other organisms consume water
from that particular water source, it may face a high risk of damage to the
internal body system.

Apart
from that, eutrophication can also cause new species invasion. This is due to the
change in the condition of the water source from aerobic condition to anaerobic
condition. Aerobic condition is the condition where there is sufficient supply
of oxygen while anaerobic condition is the condition where there is either
limited or no oxygen at all. Therefore, a new class of species, which can adapt
to this environment will emerge. For example, plasmodium sp. will then emerge
which will out-compete the original inhabitant species. This has been proven in
New England Salt Marshes.

Other
than that, eutrophication increases the toxicity of the water body. For
instance, anaerobic bacteria and algae can produce neurotoxins and
hepatotoxins, which are lethal to aquatic organisms, human beings and mammals. The
toxins they produce can make their way up the food chain and result in animal
mortality. An example of this is shellfish poisoning. Toxins released during
blooming of algae is taken up by shellfish such as oysters and mussels. This
will cause food to acquire toxins and hence, cause food poisoning in humans. Therefore,
eutrophication also disturbs the entire ecosystem