Classification of lakes

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Classification of lakes
By
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth Science,
University of Mysore
Mysore

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Introduction:
When we see a beautiful lake in any place, we feel
happy and remember it for ever.
Some locations are popular because of the
existence of a large lake in it.
Tourists are attracted due to lakes which have
boating, swimming and a good landscape around.
You may be aware that a lake is a large body of
natural water collected in a depression.

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It differs from a pond/ tank due to its larger size,
presence of biotic life and many other ecological
factors.
Though a reservoir is similar to a lake, it
comprises less habitat and is mostly man-made.
On our Earth, a body of water is considered a lake
when it is inland, not part of the ocean, is larger
and deeper than a pond.

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The presence of a lake, in any region, greatly
influences the life of the people living adjacent to
it.
Lakes are helpful in controlling weather and local
climate. Lakes are helpful for creating irrigation
facilities and recreation.
In some places, lakes are good sources for water
supply for drinking.

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Lakes occupy about 1.8 % of the earth’s surface.
About 280 000 cu.km of water exists on earth in
the form of lakes.
This is 0.19% of the total volume of water in the
hydrosphere. There are about 304-million
standing water bodies existing . About 91 percent
of the lakes have 1 hectare (2.5 acres) or less area
in coverage.
Small lakes are much more numerous than big
lakes.

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Streams of watershed are the feeding sources to
lakes.
In addition, about 800 000 artificial lakes and
reservoirs are also present in different parts of the
world.
Every lake, is unique in terms of its size,
morphometry, water availability, water chemistry,
physics, hydrology and biology.

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Lakes are good refuge for enormous variety of
flora and fauna.
Majority of the lakes on earth are freshwater lakes
and most of them lie in the Northern Hemisphere.
More than 60% of the world’s lakes are in Canada
due to its deranged drainage system.
Finland is known as the land of thousand lakes
comprising 1,87, 888 lakes out of which about
60,000 are large in dimensions.

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The Minnesota of the US is known as the land of
ten thousand lakes.
Lakes differ in their size from small ones to very
large ones covering thousands of sq.km area.
The depth may be ranging from a few metres to
more than 100m.
The largest lake by area is the Caspian sea. The
deepest lake is the Lake Baikal in Siberia.

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Lake Baikal, which is 25-30 million years old, is
deepening at a faster rate than it is being filled by
erosion and may be destined over millions of
years to become attached to the global ocean.
The Red Sea, for example, is thought to have
originated as a rift valley lake.

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Lake basins are formed due to endogenous
geological processes like tectonism and
volcanism and exogenous activities like
landslides, glaciation, solution, river and wind
action.
The major role played by lakes and reservoirs is
the regulation of stream flow.
Some lakes lie at an elevated portions of the
earth, and others are far below the sea level.

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Lake Titicaca, in South America, is 3,812 metres
above mean sea level.
The Dead Sea, located between Israel and Jordan,
lies about 400 metres below mean sea level. Lake
Eyre, the largest lake in Australia, is at about 16
metres below mean sea level.
The formation of lakes, their physic-chemical
conditions and their biotic life are studied under
the subject limnology.

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Limnology is the scientific study of in-land waters
(both saline and fresh), specifically lakes, ponds
and rivers (both natural and manmade), including
their biological, physical, chemical, and
hydrological aspects.
Every lake is characterized by
a) its basin, which is the depression holding the
water
b) Its maximum depth of water
c) Its volume of water
d) Its surface area
e)Rate of Infow and outflow of water

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f) Quality of water
g) Total dissolved load of nutrients and
sediments
h) Biotic species and their density
A lake’s watershed refers to the catchment zone.
The landuse and landcover of the catchment zone
have a great role to play in the pollutant load of
the lakes.

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Some lakes are artificial lakes and are constructed
for hydro-electric power generation, aestetic
purposes, recreational purposes, industrial use,
agricultural use or domestic water supply.
When there are more number of lakes, people
have a tendency to classify them.
Classification helps us to understand and visualize
the relationships and helps us to communicate.

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The simplest classification is the dimension of a
lake. Whether a lake is small, big or very large.
There are several type, kinds and categories of
lakes in the world.
Lakes are classified on the basis of
a) Origin
b) Trophic levels
c) Mixing of water.
d) Nature of Inflow-outflow.

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Based on origin, lakes are classified into:
a) Tectonic lakes
b) Lakes formed due to landslides:
c) Salt lakes
d) Oxbow lakes:
e) Crater lakes
f) Sinkhole lakes:
g) Lakes formed due to erosion:
h) kettle lake.
i) Artificial lake:
j) Fjord lake:

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Tectonic lakes are formed due to tectonic uplift of
a mountain range.
These actions can create bowl-shaped depressions
that accumulate water and form lakes.
The most notable examples are probably the Great
Lakes of North America.
Next comes the Lakes formed due to landslides:
Lakes are also formed due to landslides or land
subsidence.
Eg. The Sun Lakes of Washington.

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Salt lakes are formed when there is no natural
outlet or where the water evaporates to contain
more salt content in it.
Examples of salt lakes include the Great Salt
Lake, the Aral Sea and the Dead Sea.
Oxbow lakes are Small, crescent-shaped lakes
formed along the meandering river courses. The
slow-moving river forms a sinuous horseshoe
bend like water body which is detached from the
river through a narrow neck. This forms a bow-
shaped lake.

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Crater lakes are formed due to volcanic craters
and calderas.
An example is the Crater Lake in Oregon.
Sinkhole lakes come into existence as a result of
sinkhole activity. Example: Lake Jackson in
Florida, USA,
Lakes are also formed due to erosion:

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Glacial lakes are formed due to melting of glacier,
like a kettle lake.
Next comes, Artificial lake:
A lake is also created by flooding land behind a
dam. It is normally called as an impoundment or
reservoir.
Typical example is the Hirakud Dam in India.
Fjord lake: A lake in a glacially eroded valley that
has been eroded below sea level.

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Classification based trophic levels:
This classification is based on the productivity of
the lakes or some might say on the relative
nutrient richness of the lake.
Trophic level states a Waterbody’s Ability To
Support Plants, Fish, and Wildlife.
The richness in nutrient level is called as
Productivity.
It is the basis for the trophic concept of
classification.

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The lake water is also reflected in this parameter
as nutrient poor means super clear water in lakes
and nutrient rich means very poor water clarity in
lakes.
There are Four Water Chemistry Parameters used
to Determine the Trophic State.
They are: Chlorophyll, Phosphorous, nitrogen and
transparency.

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a) Chlorophyll — is the dominant green pigment
found in most algae (the microscopic plant-like
organisms living in a water body). Chlorophyll
enables algae to use sunlight to make food.
b) Phosphorus — is a nutrient necessary for the
growth of algae and aquatic plants. It’s found in
many forms in water body sediments and
dissolved in the water.

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c) Nitrogen — is also a nutrient necessary for the
growth of algae and aquatic plants.
When total nitrogen is in low supply , low
biological productivity can be expected.
Like phosphorus, nitrogen can be a limiting
nutrient.
d) Water clarity — refers to the clearness or
transparency of water.

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Lakes are classified into 8 categories as:
a) oligotrophic lakes
b) Mesotrophic
c) Eutrophic and
d) Dystrophic lakes
e) Acidotrophic lakes
f) Alkalitrophic lakes
g) Argillotrophic lakes
h) Siderotrophic lakes.

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Oligotrophic lakes are characterized by the
following features:
a) Very low concentrations of those nutrients
required for plant growth
b) Low productivity
c) small populations of phytoplankton,
zooplankton, attached algae, macrophytes
(aquatic weeds), bacteria, and fish.
d) very little consumption of oxygen
e) good water clarity (a deep Secchi disk
reading, averaging about 10 meters or 33 feet)
f) few suspended algae

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g) low chlorophyll readings (average about 1.7
mg/m3)
h) Sandy or rocky bottom.
Oligotrophic lakes have
a) nice clean water,
b) no weed problems and
c) poor fishing.
d) deep with cold water.

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They seldom exist in populated areas. When
the population is high, there will be heavy use
of chemicals.
That tends to eventually shift these lakes out of
the oligotrophic category.
Let us see the extreme end type, Eutrophic
lakes:
These are in contrast to the oligotrophic lakes.
They are
a) rich in plant nutrients and hence,
b) their productivity is high.

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c) produce high numbers of phytoplankton
(suspended algae)
d) poor Secchi disk readings (average about 2.5
meters or 8.0 feet).
e) high numbers of zooplankton and minnows
and other small fish that feed on the
zooplankton.
f) Contain considerable amount of organic
sediments.
g) Depletion of oxygen from the lower depths
of these lakes.

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h) Chlorophyll concentrations averaging about
14 mg/m3 or higher.
i) Phosphorus concentration averages
something over 80 mg/m3.
Eutrophic lakes are often relatively shallow and
often have weed beds.
The weed beds are common because of the
availability of nutrients and light to the shallow
portions of these lakes, but also because the
accumulated organic sediments provide the "soil"
for their roots.

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Fishing is often quite good in eutrophic lakes.
After all, as the oligotrophic lake ages, it
gradually accumulates nutrients and sediments,
and moves toward and eventually into the
eutrophic stage.
This natural eutrophication process commonly
takes thousands of years and involves both the
physical filling of the lake and chemical
enrichment of the lake water.

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Mesotrophic lakes:
The mesotrophic lake is intermediate in most
characteristics between the oligotrophic and
eutrophic stages.
Production of the plankton is intermediate so we
have some organic sediment accumulating and
some loss of oxygen in the lower waters.
The oxygen may not be entirely depleted except
near the bottom (the relative depth of the lake has
a bearing on this).

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Let us compare some of these parameters:
Total
Phosphorus
(mg/m3)
Chlorophyll
a (mg/m3)
Secchi
Disk
Depth
(m)
Oligotrophic 8 1.7 9.9
Mesotrophic 26.7 4.7 4.2
Eutrophic 84.4 14.3 2.45
Oligotrophic and eutrophic represent the two
extreme ends and mesotrophic is somewhere in
the middle of the trophic continuum of
productivity.

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As the eutrophic lakes continue to age and
accumulate both nutrients and sediments, some
characteristics reach their extreme levels and
finally, the lakes become really bad. These lakes
are categorized as hypereutrophic.
Such lakes are often relatively shallow lakes with
much accumulated organic sediment. They have
extensive, dense weed beds and often
accumulations of filamentous algae.

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Their water clarity is poor with Secchi disk depths
usually less than 0.5 meter (about 1.6 feet).
The phosphorus concentration is high, often above
100 mg/m3 and the chlorophyll may be over 50
mg/m3. Thus, the hypereutrophic lake represents
the extreme ranges for the eutrophic lake shown
here.
It is obvious to say that these lakes are not very
desirable for human enjoyment.

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Hypereutrophic lakes are often subjected to many
human activities.
Such activities are those that add nutrients to the
water entering the lake from the watershed.
These activities include poorly located and poorly
functioning septic systems, industrial effluents,
urban runoff and some agricultural practices that
fail to control nutrient runoff.

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Dystrophic Lakes:
In the trophic level based classification of lakes,
the level changes from oligotrophic through
eutrophic largely due to result of the production
and accumulation of organic matter.
The organic matter is generated within the lake as
a result of inorganic nutrients supplied largely
from the watershed.

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The dystrophic lakes are developed from the
accumulation of organic matter derived from
outside the lake.
In this case, the watershed is often forested and
there is an input of organic acids (e.g. humic
acids) from the breakdown of leaves and
evergreen needles.
This is followed by a series of processes resulting
in a lake having low in pH (acid) in water and
often has moderately colored (yellow/brown)
water.

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These lakes are poor in plankton production and
have sparse fish populations largely because of
the acid conditions and have low nutrient
concentrations.
The other type are very simple types.
Acidotrophic lakes show low production with low
P and N, but pH<5.5
Alkalitrophic lakes show high production with
high calcium.
Argillotrophic lakes show low production with
high clay turbidity.

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Siderotrophic lakes show low production with
high iron.
Classification based on mixing cycles of water:
The next system of classification is based on the
extent to which the water is mixed and the number
of times during the year. It is also based on water
circulation pattern in a year. This is commonly
refered to as "Turn-over cycle of the lake”.

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In many lake basins the water has notable
patterns of circulation. This circulation is mostly a
vertical mixing of the water. It has been called an
"over-turn" or "turn-over" of the lake.
The circulation or mixing is usually wind driven
and is facilitated when the lake has a uniform
temperature from top to bottom.

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Since we refer to these periods of water exchange
as periods of mixing, limnologists have used the
noun mixis and the adjective mictic in the
classification system.
Because mixing is a function of temperature and
wind.
The types of lakes which belong to this category
are:
a) Amixis,
b) Holomixis and
c) Meromixis.

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Amixis lakes are characterized by a lack of
mixing: some lakes never circulate.
These amictic lakes are usually ice covered
throughout the year.
These lakes are under the polar ice caps (at the
North and South Poles of our globe) or high
mountain lakes where the temperature is mostly
below freezing.

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Holomixis lakes:
They show full mixing. This is typical situation
where the winds mix the "whole" lake water once
or more annually.
The third type is Meromixis lake:
These show partial or incomplete mixing. Some
lakes have one or more periods of annual mixing.
The force of the wind mixes the water of the lake.

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Once uniform density is reached, strong winds
can mix the lake from top to bottom in most of
our lakes, unless they are unusually deep. This
period of mixing is often call the "over-turn".
Nutrients from the lower water are brought to the
upper surface. Similarly oxygen is brought from
the surface to the lower depths.
After the overturn, for a week or two, there will
be uniform temperature,
oxygen, nutrients etc. from top to bottom.

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The Sun continues to warm the surface of the
water and the winds begin to lessen in intensity
and most of heat is absorbed in the first few
centimeters. The surface water temperature
increases and becomes lighter and "floats" on the
more dense water below.
This heating of the surface water continues and
eventually forms an upper layer of warm water.
It acts as a layer of insulation, absorbing the heat
from the sun and preventing the lower water from
getting any heat.

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We call this layer as epilimnion (epi - on top,
limnion - layer).
Below the epilimnion, the temperature of the
water drops rapidly for about 2 meters (6-7 feet)
and then remains about the same to the bottom.
This middle layer is called as metalimnion (meta
- middle, limnion - layer) and it is about two
meters thick with rapidly decreasing temperature
and increasing density.

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Below the metalimnion we have the cold, much
more dense layer called hypolimnion (hypo -
below, limnio - layer).
In a deep lake, the hypolimnion can be a very
large volume, a large percent of the lake, and the
reverse is true in a shallow lake.
Lets look at the holomictic lakes, those lakes that
mix entirely at least during one period a year.

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We have four types of holomictic lakes :
a) Oligomictic lakes.
b) Polymictic lakes
c) Monomictic lakes
d) Dimictic lakes
In Oligomictic lakes - mixing is unusual,
irregular and of short duration, these lakes are
relative few in number and are mostly tropical.
The Polymictic lakes have many periods of
mixing annually, even ap- proaching continuous

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mixing and are influenced more by daily
temperature changes than seasonal.
Monomictic lakes Mono means one, so these
lakes have one regular period of mixing during
the year.
Warm monomictic lakes are usually those sub-
tropical lakes that have a long summer and a short
winter. They are stratified most of the year and
then for a short period in the winter the
stratification breaks down and the lakes can mix.

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Dimictic lakes:
Di means two. The Dimictic lakes show mixing
twice a year , both in the spring and in the fall.
This category covers the lakes in the temperate
zones of our globe and includes the majority of
our lakes.
Oligomictic lakes:
These lakes are usually located in the tropics and
have poor (oligo) mixing.
The mixing is irregular, or sporadic and usually of
short duration.

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These lakes are usually warm throughout, but the
surface waters are even warmer, creating some
stratification.
Only occasional, and maybe rare, cooling of the
surface waters allow any chance of mixing.
Polymictic lakes:
As the word signifies, Poly means many. These
are the lakes which show many mixing periods
even to the extent that they are mixed nearly
continuously throughout the year. These lakes are
often small, shallow and in tropical or at least
warmer climates or at higher altitudes.

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The temperature changes are often influenced
more by cooling of the surface at night and
warming during the day.
Meromixus lakes:
Meromictic lakes would probably be typical
dimictic lakes;
Their periods of mixing usually are incomplete.
These lakes, over time, have developed a deep
layer of water that has a much greater amount of
material in solution than does the upper waters.

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These solutes, substances in solution, cause these
lower waters to have a greater density that resists
mixing. Thus when temperature of the water is
uniform from top to bottom, we still have a
density gradient that limits the normal mixing
only to the depth where the currents encounter
this dense lower layer.
The concentration of substances in the lower
depths accumulate usually over an extended time.

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Lakes may have one natural outflow in the form
of a river or stream, which maintain a lakes's
average level by allowing the drainage of excess
water.
Some may not have an outlet but lose water
solely by evaporation or underground seepage or
both. They are termed endorheic lakes.
Endorheic lakes are almost terminal or closed
lakes. A lake which has no significant outflow,
either through rivers or underground diffusion.

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Any water within an endorheic basin leaves the
system only through evaporation or seepage.
Examples are, Lake Eyre in central Australia and
the Aral Sea in central Asia.
Another type is the Ephemeral lake: A seasonal
lake that exists as a body of water during only part
of the year.
The Intermittent lake is one lake with no water
during a part of the year.

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The last category is Shrunken lake. This is closely
related to former lakes. A shrunken lake is one
which has drastically decreased in size over
geological time.
Lake Agassiz, which once covered much of
central North America, is a good example of a
shrunken lake.
Lakes are valuable ecosystems on earth.
Protection of lake ecosystems involve a lot of
restoration measures.

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These require a thorough understanding of lakes,
their environmental conditions and dynamic
changes.
There are some more classifications exit on lakes.
Let us see them in due course of time.
Lakes are valuable ecosystems on earth.
Protection of lake ecosystems involve a lot of
restoration measures. These require a thorough
understanding of lakes, their environmental
conditions and dynamic changes.

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The city of Mysore is blessed with a good number
of lakes.
It is also due these lakes, the city is pleasant all
through the year.
The beauty of a city lies in its composition with a
good number of natural or artificial ecosystems,
like rivers, lakes, canals and reservoirs.
Mysore lakes are much varied in their origin.
Some are natural lakes and many are artificial
lakes constructed by the Maharaja’s of Mysore to
create water resources to meet the local demands.

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The city is growing day-by-day.
Most of the lakes which were along the periphery
of the city in those days, are now in the middle of
the city. Imagine their fate today.
Urbanisation in any part of the world will always
become a threat to natural ecosystems if they are
closer to each other. Lakes of Mysore are no
exceptions.
But, careful planning of restoring their conditions
will certainly help to preserve them and conserve
the water and aquatic life.

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Several Research findings have also come out
over the years about these lakes.
Sometimes, the algal blooms create a big problem
in some parts which are being continuously
attended to.
The inflow of water is not regular, which is one of
the reasons for deterioration of the quality.
People are gradually becoming cautious to avoid
polluting these lakes.

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Authorities at all levels have taken steps to protect
them. Many NGOs, Environmentalist and
naturalists are showing utmost care in maintaining
these lakes.
Lake ecosystem needs a through understanding to
solve its ever-growing environmental problems.
We see in several other cities, that the lakes have
already died out to accommodate bus-stands and
other infrastructures.

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Creating an artificial lake itself is an expensive
affair.
Closing a lake is an easy affair.
Every one can not create a lake.
But alteast the existing lakes should be preserved.
Let us protect these ecosystems.

Classification of lakes

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