Eutrophication occurs when an aquatic
ecosystem becomes enriched with nutrients, causing an increased growth of
photosynthetic bacteria and the development of dense mats of floating plants
such as Nile cabbage and water hyacinths in lakes and lower reaches of rivers.
Waters with low salt concentrations are called
oligotrophic and the salts are the limiting factor for plant growth. On the
other hand, waters with high concentrations of salt are called eutrophic and
there is much limitation on growth.
Eutrophication can occur naturally as the
lakes grow old and filled with sediments. However, human activities can speed
up the rate of eutrophication through the discharge of chemical nutrients
(phosphates and nitrates) into the water systems. This will bring large impacts
to the environment and living organisms.
Leaching of nutrients from the soil into the
waterways causes populations of algae and photosynthetic bacteria to grow very
rapidly. Algal blooms occur where the water becomes densely populated with
species of blue-green bacteria. The density of these blooms increases to a
point where light is unable to penetrate into the water. The algae deep in the
the lake are therefore unable to photosynthesise, and die.
of Eutrophication (Refer Appendix 1.1)
The increased nutrients promote rapid growth
of algae when they are deposited in rivers and lakes. This explosive growth of
algae is called an algal bloom. Some algae produce toxins that are harmful to
higher forms of life. This can cause problems along the food chain and affect other
animals that feed on them.
The densely populated algae cover the water
surface and block sunlight from penetrating into the water. Photosynthetic
marine plants under the water surface are unable to carry out photosynthesis.
Thus, the marine plants die and the aquatic animals lose their food sources and
habitats. The food chains and ecosystem change.
The death of algae and other photosynthetic
organisms encourages the growth of decomposing organisms especially saprophytic
bacteria or detritus. Decomposition process may use up large quantity of oxygen
to decompose the dead organisms. This reduces the oxygen content in the water
and the biochemical oxygen demand (BOD) of the water is increased. The higher
the BOD value, the more polluted the water as the dissolved oxygen level
decreases, leaving none for aquatic organisms. As a consequence, all aerobic
life which requires oxygen in the water to live dies. Their bodies add to the
organic material available for the decomposers and so the situation worsens.
1.3 Causes of Eutrophication
Eutrophication may happen quite naturally.
However, sources of human pollution have made eutrophication increasingly
common, and are leading to the death of many rivers and ponds. The salts
necessary for eutrophication are largely nitrates and phosphates which are
needed for photosynthesis. They come from different sources:
Leaching from the surrounding land – This slow
natural process involves the removal of salts caused by floods and the flow of
water from lakes or rivers. Drainage of water can wash excess nutrients off the
land into the water systems. In addition, lakes naturally accumulate sediments and
minerals as they grow old, which contribute to the explosive growth of phytoplankton
and cyanobacterial, thus causing dense growth of algal blooms.
Fertilizers from agricultural fields – Inorganic
fertilizer is applied to farmland to replace the nutrients in the soil and to
increase the crop yield. Fertilizers contain nitrates and phosphates which are
highly soluble and they are readily leached into the soil. These nutrients are
quickly run off into lakes and rivers if the soil can
no longer assimilate the high concentration of nutrients, causing an
increase in nutrient levels in the water. Photosynthesis of aquatic plant life
is increased, causing algal blooms.
Direct sewage discharge and industrial
waste – In some developing nations, sewage water is directly discharged into
water bodies such as rivers, lakes and oceans. As a result, it introduces large
amount of chemical nutrients which stimulates the dense growth of algal blooms
and other aquatic plants that can threaten the survival of aquatic life. Even if
it is discharged into the water after treatment, it can still cause the
accumulation of excess nutrients, ultimately bringing about eutrophication.
Run-off of animal waste – Animal wastes
that are pumped into the river or lake form a massive food supply for
decomposing organisms. These decomposers use up much of the oxygen to decompose
the sewage and this results in death of the waterway.
Aquiculture – Aquiculture is a technique
of growing shellfish, fish and aquatic plants (without soil) in water
containing dissolved nutrients. If aquiculture is not properly managed, the
unconsumed food particles together with the fish excretion can significantly
increase the levels of nitrogen and phosphorous in the water, thus results in excessive
growth of microscopic floating plants.
1.4 Effects of Eutrophication
Threatens the survival of fish and other
aquatic life forms – The increased nutrients in aquatic ecosystems causes the
phytoplankton and other photosynthetic plants to grow explosively, which
results in algal blooms. The algal blooms limit the amount of dissolved oxygen
required for respiration by the aquatic plants and animals. When the dissolved
oxygen reaches hypoxic levels, the animal and plant species under the water
suffocate to death. In extreme cases, the anaerobic conditions encourage the
growth of bacteria that produces toxins which are deadly to the marine mammals
and birds. Decomposition of dead plant life will use up the dissolved oxygen
too. The growth of phytoplankton also reduces light penetration into the lower
depths of the water. This can bring about aquatic dead zones, loss of aquatic
life and it also lessens biodiversity.
Deterioration of water quality and decline
in the availability of clean drinking water – Algal blooms produce toxic and
once the water reaches the anaerobic conditions, the growth of more toxic
bacterial is promoted. The impact is extensive deterioration of water quality
and limits the access to safe drinking water. The explosive growth of algal
blooms and photosynthetic bacteria in the waters can also block water systems, thus
limiting the availability of piped water.
Affects living organisms’ health – The
cyanobacteria, also referred to as dinoflagellates generates red tide, thus releases
very powerful toxins with high poison levels in the water. It can cause death
in humans and animals even at the least concentration when ingested in drinking
water. Besides, freshwater algal blooms can threaten livestock health. The
toxic compounds can make their way up the food chain, contributing to various
negative health impacts such as cancers. For instance, the shellfish accumulate
the poison in their muscles and can poisons humans upon consumption. High
nitrogen concentration in drinking water can inhibit blood circulation in
infants, a condition known as blue baby syndrome.
Endangers fishing – The extensive growth
of aquatic plants such as algae, Nile cabbage and water hyacinths makes it
difficult to set the fishing nets in water and the floating plants will also
limit the mobility of boats and other fishing vessels.
Degradation of recreational opportunities
– The algal blooms and other floating aquatic plants reduces the transparency
and navigation in the water, which will lessen the recreational values
especially for boating and swimming. Nile cabbage, algal blooms, and water
hyacinth can spread over the entire surface of the shores and can even float
into the land area.
1.2 Ways to reduce Eutrophication
Composting – Composting is a practice of
converting organic matter such as food residues and decaying vegetation into
compost manure. The nutrients in the compost manure are deficient of the high
concentration of nitrates and phosphates that feed the algae and other microbes
in water bodies. Manure decompose slowly so that the nutrients are not readily
leached away. All the essential elements are broken down and synthesized by the
plants thereby not creating the cycle of eutrophication.
Proper treatment and breakdown of sewage
before it is released into the rivers and lakes – This method can reduce the
amount of nutrients being disposed into the water.
Reducing pollution – To control
eutrophication, industries and municipalities should reduce the pollution of
water by stop discharging waste into water systems so as to reduce the amount
of toxins and nutrients ended up in the waters that feed the algae and other
Strengthening laws and regulations against
non-point pollution – According to EPA, non-point pollution presents the most
serious challenge in the management of nutrient entry into water systems. By controlling
nutrient sources and minimizing non-point pollution, the amount of nutrients
entering the aquatic ecosystems is lessened, thereby reduce eutrophication.
Ultrasonic Irradiation – The use of
ultrasonic irradiation is a mechanism which has been exploited as an
alternative solution to control algal blooms. The process works by causing cavitation
which produces free radicals that will destroy algae cells. Still, research is
still underway to determine the uniqueness of its use in controlling the
Install mixing devices in lakes – Mixing
of stagnant water, for example by air bubbling, enhance vertical mixing of phytoplankton,
which can decrease the formation of surface blooms of buoyant cyanobacteria. Increasing
the water flow through lakes or estuaries also reduces water residence time and
inhibits cyanobacteria blooms.
1.3 Examples of Eutrophication
In 2007, for instance, more than 2 million
residents of Wuxi, China could not access piped drinking water for more than a
week due to severe attack by algal blooms on Lake Taihu.
In 2011, Lake Erie experienced the largest
harmful algal bloom in its recorded history, with a peak intensity over three
times greater than any previously observed bloom. Land use, agricultural
practices, and meteorological conditions may all have contributed to
exacerbating the algal bloom. Weak lake circulation has led to abnormally long
residence times that incubated the bloom. Uncommonly warm and quiescent
conditions in late spring and summer after bloom makes the algae to remain near
the top of the water column and prevented flushing of nutrients from the
system. (Refer Appendix 1.2)
According to the latest HELCOM assessment
on eutrophication, in 2007-2011 almost the entire open Baltic Sea was assessed
as being eutrophied and only the open Bothnian Bay was assessed as being
unaffected by eutrophication. Number of phytoplankton increases, especialy
cyanobacteria because of the increases in nutrient concentrations and due to
the changes in the seasonal availability. Cyanobacteria bloom (Nodularia
spumigena) in the western Baltic. (Refer Appendix 1.3)
Deforestation is the extensive removal of
trees from large tracts of land for logging, agriculture, development and
grazing operations. Forests are formed over millions of years. Although they
cover only a relatively small percentage of the surface of the Earth, they are
important in absorbing carbon dioxide from the atmosphere for photosynthesis and
in maintaining species diversity because they are the homes of an estimated 50
to 90 percent of all land-dwelling species.
Long before the advent of highly
mechanized logging practices, people were practising shifting cultivation. They
cut and burn trees, then till ashes into the soil. The nutrient-rich ashes can
sustain crops for one to several seasons. Afterward, heavy leaching causes the
soil infertile, thereby abandon the cleared plots. When shifting cultivation is
practised on small, widely scattered plots, a forest ecosystem does not
necessarily suffer extensive damage. But soil fertility declines with
increasing in population size. Then, larger areas are cleared, and plots are
cleared again at shorter intervals.
At one time, tropical forests cloaked
regions that were, collectively, twice the size of Europe. However, as the time
goes by, poverty and greed have driven people to ever-increasing destruction of
these vital ecosystems. By 1980, around 44% of all the tropical rainforest had
been cleared, and in the 1990s, this destruction is continuing at the rate of
around 35 acres every minute. If it continues at this rate, in about 90 years’
time, there may be no tropical rainforests left.
2.2 Importance of Forests
Forests help control soil erosion,
flooding, and the accumulation of sediments that can clog rivers, lakes, and
reservoirs by intervening in the downstream flow of water
Forests function as habitat of various
flora and fauna. – Nearly half of all known species live in forests, including
80 percent of biodiversity on land. That variety is especially rich in tropical
rain forests, from rare parrots to endangered apes, but forests teem with life
around the planet: Bugs and worms work nutrients into soil, bees and birds
spread pollen and seeds, and keystone species like wolves and big cats keep
hungry herbivores in check.
Forests are housing plants which produce
food and pharmaceutical products. – Forests provide a wealth of natural
medicines and increasingly inspire synthetic spin-offs. The asthma drug
theophylline comes from cacao trees, for example, while a compound in eastern
red cedar needles has been found to fight MRSA, a type of staph infection that
resists many antibiotic drugs. About 70 percent of all known plants with
cancer-fighting properties occur only in rain forests.
Forests help in regulating world’s climate.
– Large forests can influence regional weather patterns and even create their
own microclimates. The Amazon, for example, generates atmospheric conditions
that not only promote regular rainfall there and in nearby farmland, but
potentially as far away as the Great Plains of North America.
Forests help in regulating the amount of
carbon dioxide and oxygen in our atmosphere. – They do this by taking in carbon
dioxide and giving out oxygen during photosynthesis. A
single mature, leafy tree is estimated to produce a day’s supply of oxygen for
anywhere from 2 to 10 people. Phytoplankton are more prolific, providing half
of Earth’s oxygen, but forests are still a key source of quality air.
Forests serve as water catchment areas. – The
watersheds of forested regions absorb, hold, and then release water gradually. Their
leaves slow down the rate of evaporation and the rate at which water reaches
the soil. Forests catches runoff rather than letting it flow across the
surface, but they can’t absorb all of it. Water that gets past their roots
trickles down into aquifers, replenishing groundwater supplies that are
important for drinking, sanitation and irrigation around the world.
Keep us cool. – By growing a canopy to hog
sunlight, trees also create vital oases of shade on the ground. Urban trees
help buildings stay cool, reducing the need for electric fans or air
conditioners, while large forests can tackle daunting tasks like curbing a
city’s “heat island” effect or regulating regional temperatures.
Keep Earth cool. – Trees absorb CO2 that
fuels global warming. Plants always need some CO2 for photosynthesis, but
Earth’s air is now so thick with extra emissions that forests fight global
warming just by breathing.
2.3 Causes of Deforestation
demand for tropical hardwoods as timber, lumber and building materials – As
human population increases around the world, more trees are being cut down to
fulfil the need of wood supply for construction of buildings.
demand for paper for newsprint, photocopiers, printers and office consumption –
Wood based industries like paper, match-sticks and furniture also need a
substantial amount of wood supply.
demand for firewood and charcoal as fuels. – Wood can be used as fuel,
therefore trees are chopped for supplies.
of land for farms, cattle ranches, plantations, cropland, agricultural land and
grazing land. – Because of overgrowing demand for food products, many trees are
cut down to grow crops and for cattle grazing. Increase in global demand for
commodities, such as palm oil and soybeans, makes the industrial-scale
producers to clear the forests at an alarming speed. Even when efforts are made
to replenish barren plantations, the infertile soil is not able to produce the
same biodiversity it once was.
of land for the construction of new roads and towns – With the expansion of populations
and cities, more land is needed to establish housing and settlements. Therefore,
forest land is cleared. Road construction can lead to deforestation by
providing an entryway to previously remote land.
Effects of Deforestation
Leads to soil erosion, landslides and
flash floods. – Clearing of trees causes the loss of leaves to protect the soil
from the impact of raindrops and wind. Therefore, the soil is exposed directly
to the force of the rain and wind, and it will rapidly become barren. Deforestation
also causes the loss of tree roots to hold the soil and the stability of the
soil is affected. When it rains for a long period of time during rainy seasons,
the top layer of soil loosens and can be washed away by the rainwater easily,
especially on steep slopes. This leads to soil erosion and even landslides. The
eroded soil is carried away by water and may deposited in rivers. Moreover,
rainwater will flow quickly into the river during heavy rainfall because there
is no retention of water by plant roots and water catchment areas. Due to
silting in the rivers, the water flow is blocked. Thus, water flows inland and
causes flash floods in low areas. Flash floods may cause loss of lives and
properties. Soil erosion may lead to depletion of minerals for the land too. Thus,
the land cannot be used for cultivation.
Loss of biodiversity, – Deforestation
leads to the loss of habitats for many species of flora and fauna, and the
animals are forced to move to new locations. Several species are finding it
hard to survive or adapt to new habitats. Some of them are even pushed to
extinction. It also causes local extinction of species of trees. As a result,
it reduces biodiversity and the source of food and valuable medicines for
Climatic changes. – Destruction of forests
increases the amount of carbon dioxide (a greenhouse gas) in the atmosphere as
less photosynthesis takes place, and so leads to global warming or greenhouse
effect, as well as the chances of disastrous changes in climate. This will
contribute to the melting of the polar icecaps and shifting patterns of wind
and rainfall which have huge impact on agriculture throughout the world. In the
larger picture, deforestation alters rates of evaporation, transpiration,
runoff, and regional patterns of rainfall. In the logged-over regions, annual
precipitation declines, and rain swiftly drains away from the exposed,
nutrient-poor soil. The regions are now hotter and drier, and soil fertility
and moisture have plummeted. In time, sparse grassland or desertlike conditions
might prevail instead of the formerly rich, forested biomes. Tropical forests
absorb much of the sunlight reaching the equatorial regions of the Earth’s
surface. Deforested land is shinier and it reflects more incoming energy back
into space. Trees release water vapour in the air, which is compromised on with
the lack of trees. Trees also provide the required shade that keeps the soil
moist. This leads to the imbalance in the atmospheric temperature further
making conditions for the ecology difficult.