bfsc 1st year

1. POWER RANGERNOTES LIMNOLOGY
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Limnology
1.1.1Introduction
Civilizations have depended on water bodies such as lakes, reservoirs, rivers and wetlands. Water is essential
not only to sustain human life but also to support the activities that form the basis for thriving economics.
Though the water resources are essential to human societies who could pollute and degrade and limiting their
beneficial uses. Agriculture, mining, urban development and other activities can pose risks to freshwater
bodies and hence steps have to be taken to reduce these risk factors.
Risk analysis requires knowledge of how human land use affects physical, chemical and biological characters
of the aquatic systems. One of the critical areas required to understand how human actions and natural
processes affect lakes, reservoirs, rivers and wetlands is the science called Limnology. It is a multidisciplinary
science that integrates the basic sciences (Biology, Chemistry, Physics and Geology) in order to study inland
waters as complex ecological systems.
Definition
The term Limnology is derived from Greek word; Limne means lake and logos means knowledge. Limnology
is often regarded as a division of ecology or environmental science. It is however, defined as “the study of
inland waters” (running and standing waters fresh and some times saline; natural or man made). This includes
the study of lakes, ponds, rivers, reservoirs, swamps, streams, wet lands, bogs, marshes etc. Hence, it is
commonly defined as that branch of science which deals with biological productivity of inland waters and
with all the causal influences which determine it (Welch, 1963).
Biological productivity, as used in this definition, includes its qualitative and quantitative features and its
actual and potential aspects. Under the term inland waters are included all kinds or types of water – running or
standing; fresh, salt or other physicochemical composition which are wholly or almost completely included
within the land masses. Causal influences involve various factors – physical, chemical, biological,
meteorological etc which determine the character and quantity of biological production.
History
The term Limnology was coined by Francois-Alphonse Forel (1841 – 1912) who established the field with his
studies on Lake Geneva. Interest in the discipline rapidly expanded and in 1922 August Thienemann (a
German Zoologist) and Einar Naumann (a Swedish Botanist) co-founded the International Society of
Limnology (SIL, for originally Societas Internalis Limnologiae). Forel’s original definition of limnology,
oceanography of lakes was expanded to encompass the study of all inland waters.
Welch (1935) conceived the problem of “Biological productivity” as the central theme of Limnology. He
defined Limnology as that branch of science which deals with all causal influences which determine it.
According to Schwoerbel (1987), Limnology is the science of inland waters viewed as ecosystems together
with their structures, materials and energy balance. Kiihnelt (1960) considered limnology as a sub set of
ecology along with “Oceanography” (which is concerned with marine ecosystem) and “Epheirology” (which
deals with terrestrial habitats). In short, Limnology is the study of all aquatic systems including lakes,
wetlands, marshes, bogs, ponds, reservoirs, streams, rivers etc. with regard to their physical chemical and
biological characteristics.
In addition to the above, certain other terms, like Hydrobiology, Freshwater Biology, Aquatic Biology,
Aquatic Ecology etc, are sometimes loosely used as synonymous to the word 'Limnology'. But, most of these
terms are names under which a diverse variety of subject matter is included and only a part of it is
limnological in nature.

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1.1.2 Development ofLimnology
Initiation of works in the field of Limnology could be traced back to Aristotle (384-322 BC) which consisted mostly of
strange mixtures of facts and fiction with little scientific value followed by observation of certain conspicuous
freshwater phenomena. However,significant contributions of strictly limnological nature began to appear about a
thousand nine hundred years after Aristotle with the description related to habitat, habit and life history of certain fishes,
insects and aquatic macrophytes. But, most of these were isolated accumulation of correlated observations, few of which
could be used by modern limnologists mostly for historical purposes.
Since the initiation of optics with Euclid (2000 BC) and later with the invention of microscope, there has been
significant development in the field of aquatic biology and limnology because it has not only opened the door to the
whole world of microscopic organisms, but also provided with a new and effective means of studying the various higher
types of life in water. This was followed by description of minute aquatic organisms by Anton Van Leewenhook (1632
– 1723), the pioneering classification of microscopic organisms by the Danish biologist, Otto Friedrich Muller (1786),
publication of the Treatise, “Infus Animalcules” by Ehrenberg (1838) which marks the beginning of those advances in
knowledge which occurred in the 20th century.
Peter Erasmus Muller is credited with laying the foundation stone of limnological study. Anton Fritsch could be
considered as the pioneer in lacustrine limnology for his work on lakes in the Bohemian Forest and F. Simony (1850) is
regarded, sometimes as the founder of Limnology for his discovery of thermal stratification. However,it remained
practically everything for F.A. Forel (1841- 1912), a professor in the University of Lausanne, Switzerland, to recognize
the realbiological opportunity of lake investigations and the science of limnology is indebted to him for his
comprehensive vision and complete anticipation about the future of this subject. He is regarded as the Founder and
father of Modern Limnology for his 110 publications (Chumley, 1910). It was he who took the decisive step forward
from hydrobiology to limnology through his investigations in Lake Geneva, not only from the biological point of view
but also from physical and chemical stand points, thereby formulating the concept of lake types. In addition the design
of his first programme for limnological investigations in freshwater and its subsequent execution turned out to be a
model for future researches.
Forel’s work paved the way for establishment of Limnological Society in 1887 as a component of Swiss Naturalhistory
Society (in order to promote limnological works) and later the International Commission of limnology was established
in 1890). In brief, the History of limnology could be dated back to approximately 100 years. Although certain
preliminary studies has been done on the habits, nutrition, movement, behaviour etc.,on certain aquatic organisms by
different workers during the 17th and 18th centuries, these were mostly hydrobiological works and not limnological.
True studies on the relationship of biota to freshwater could be treated as initiated from Junge (1885) and Forbes (1897)
who were the first to treat the native waters as microcosm.
Gaarder and Gran (1927) made pioneering attempts at measuring the photoautotrophic production (primary production)
by quantitative determination of oxygen produced during photosynthesis. Later the direct measurement of carbon
assimilation in the water bodies was achieved in 1952 using radio-carbon method (Steemann and Nielsen, 1952). The
estimation of trophic dynamics concept having regard to the biomass, material turn over and energy transport along the
food chain by Lindeman (1942) not only revolutionized the field of general ecology, but also gave a new direction to
Limnology (Cook,1977).
Early freshwater investigations
In 1870, Simson, published a short account of the deep water fauna of Lake Michigan. Smith and Verrill (1871) made
deep water dredging in Lake Superior and published on the invertebrates collected. In 1886, the Allis Lake laboratory, a
privately supported institution and said to be the first freshwater biological station in America, was established at
Milwaukee, Wisconsin, but its life was brief and none of its work was concerned with the general biology of the Great
lakes. In the meantime, interested workers were giving attention to some of the smaller inland lakes. Forbes made a
study of certain high lakes of the Rocky Mountains and published only on biological information concerning lakes in
western United States. During the decade of 1890 -1900, important freshwater biological stations have been found viz,
(1) the University of Minnesota at Gull Lake,Minnesota, 1893; (2) the University of Illinosis on the Illinosis River,
1894; (3) the University of Indiana at Turkey Lake, Indiana, 1895.
The stimuli of scientific interest and of the necessities of public health brought about the initiation of systematic surveys
of water supplies and of water systems in general, the Massachusette State Board of health taking the lead in about
1887. Subsequently, similar work was undertaken by various municipal and government departments, all of which

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contributed, directly and indirectly to the sum total of limnological information. Phenomenal progress of the general
subject of ecology inevitably had a constructive influence on limnology and because of its many ramifications
limnology has likewise profited from simultaneous advances of other sciences.
1.2.1 Inland waters
The inland waters which include both fresh water masses and estuarine waters of varying salt content are clearly
distinguishable from the salt waters of the oceans. The inland water masses are discrete and being isolated within the
specific land area,acquire the characteristic chemical composition of the land, by exchange between soil and water. The
oceanic water on the other hand is open and mixing together by wind action and currents and therefore more
homogeneous in chemical composition. However,the land water exchange is limited to coastalareas. The estuarine
waters are mixtures of sea and freshwater,but with the higher content of salts in the sea water (150 – 200 times that of
freshwater), are dominated by the sea water effects.
According to Hutchinson (1959), limnology is the large variety, individual and groups of inland water bodies, the
diversity being caused by the diversity of their origin as well as by the diversity of their chemistry and biology.
Types ofinland water
Frey (1960) has classified inland waters in three different ways viz, depending on whether the water is stationery or
flowing, depending on whether the water mass is natural or artificial and permanent / temporary.
I a. Flowing waters (Lotic waters)
These include creeks,streams and rivers mentioned in that sequence because of their sequence of succession also in the
same order, through the natural processes of lengthening and widening of running waters. In these,there is continuous
current of water in one direction. The organisms inhabiting these waters have complexity of adaptation towards the
increase in water current speed. It includes all forms of inland waters in which the entire body of water moves
continuously in a definite direction. The sequence of genesis is brooks, rivulets, channels and rivers.
b. Standing waters (Lentic waters)
Here,water current is not a major ecological factor; unlike in the lotic series lakes, ponds and swamps form the lentic
series. The sequence indicates the natural evolution of water masses as well lake may either be productive or non-
productive, when they are referred to as eutrophic or oligotrophic respectively. It includes all forms of inland waters –
lakes, ponds, swamps and their various integrades in which the water does not flow continuously in definite directions.
Essentially, the water remains standing, though a certain amount of water movement may occur, such as wave action,
internal currents or flow of water in the vicinity of inlets and outlets.
The sequence of genesis is as follows Lake – pond – swamp.
a. Natural bodies ofwater
Certain parts of the world are endowed with an abundance of natural waters serving human needs.
b. Artificial bodies ofwater
According to man’s needs water bodies are created artificially. It includes ponds, wells, tanks reservoirs etc.
i. Ponds
In India, even from ancient times, large ponds and wells exist serving for drinking water and also for irrigation purposes.
Types ofponds
Based on seasonalduration ponds can be classified into two types.
1. Temporary ponds
2. Seasonal ponds
Temporary ponds divided into three types,
1. Vernalponds: Water exists only in spring season.
2. VernalAutumnal pond: Water exists in those ponds during spring and autumn and they dry in summer.
3. Aestival ponds: Water persists in these ponds throughout the season but it freezes during winter.
Permanent ponds
Water persist in these ponds throughout the season but it freezer in winter.
i. Reservoirs
Rivers are blocked and reservoirs or artificial lakes are developed. These serve in generating hydroelectric power,
irrigation, fish production and recreation. These also help in flood control.

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ii. Tanks
In India there are both perennial and temporary tanks. There are some in which water remains for 6-9 months duration,
called long seasonal tanks and in some, water remains for less than 6 months, referred to as short seasonal tanks.
III a. Permanent waters
In most parts of the world where there is precipitation exceeds,the evaporation and seepage loss the waters in rivers,
lakes and ponds and are termed as permanent waters.
b. Temporary waters
Evaporation loss of water is more than the precipitation gains, as in all arid areas of the world, the water bodies dry up
usually during summer. In high latitude (30-50o), when the area is desert the rivers and streams drain into permanent or
temporary lakes. These lakes have salt differing from that of sea,the salt washed down to the lakes being predominantly
potassium and sodium carbonates and magnesium and sodium sulphates and not sodium chloride. By evaporation at
times salt concentrations in these waters exceeds that of the sea. (eg. Great salt lakes and Dead sea). The salt
concentration of Dead sea is so high that there is no life in it.
1.2.2. Distribution ofinland waters
Inland waters cover less than 2% of the earth’s surface,approximately 2.5 x 106 km2. About 20 lakes are extremely
deep (in excess of 400 m). A significant portion of the world’s freshwater is contained in lake. Some regions are very
generously supplied with lakes and streams particularly those regions once subjected to ancient glaciation. Canada and
northern United States possess an immense supply of lakes, among them the Great lakes, which constitute the greatest
body of freshwater on the globe. Portions of Europe are also noted for their generous supply of lakes and streams. In
certain regions, disappearance of inland waters during the dry season forms the basis for special biological phenomena
resulting from the intermittent character of the environments.
In India, most of the wetlands including flood plain wetlands are situated in the eastern parts of the country whereas,
reservoirs and tanks have been created mainly for irrigation are distributed throughout the country. Large rivers and
streams are well distributed in the northern and eastern region of the country. However,southern regions of the country
also have a good number of inland waters. Many of them are seasonalin nature.
Dynamics of Lotic and Lentic environment
In the lotic series, the tiny rivulet gradually deepens, widens its bed, and cuts back at its head, thus in time extending its
length and increasing its cross section to that size which justifies the designation of brook. This process continues by the
same general type of action, ultimately producing a creek and then finally a river, with all of the integrating conditions
produced in such a gradual transformation.
Faunas occupying each of the different environments must accompany these migrations or become adapted to the
gradually altering conditions or they will become extinct. These environmental migrations are very slow, in point of
time, and give ample opportunity for the characteristic organisms of particular environments to make the necessary
responses. The ultimate fate of any lotic series is the degradation of the land is the reduction of its bed to base level.
In the lentic series,natural processes work toward extinction, mainly by the gradual filling of basins.
Lake –> Pond –> Swamp
In larger lakes, natural filling takes much longer time, even many centuries also hence the filling is primarily due to :
• Wind blown materials such as dust, sand and debris of various sorts.
• Sediments brought into a lake by inflowing streams and by incoming run-off water as it flows down adjacent land
slopes.
• Wave action, cutting away exposed shores and depositing eroded material in lake basin.
• Plants, particularly the higher aquatic plants which grow in shallow water,produce deposits of organic matter.
• Accumulating remains of animal life especially shells.
Not all lakes become extinct by filling alone. Other process also contributes to this for example an outlet may cut down
its level at the point of exit from a basin, thus gradually draining the lake.
These stages in the extinction of standing waters result in a more or less definite, predictable ‘evolution of environment’
in the long run has a profound influence on the history and fate of lake organisms.
Running waters (Lotic series)
There are many different kinds of running waters,severalof them occurring, inter-connected, within a single drainage
system. The range covered within the series includes small trickles and seepages,ditches, larger fast flowing streams

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and rivers, large slow flowing rivers and canals.
The flow characteristic of any running water system are also closely connected with the geology, notably in the control
exerted by the nature and structure of rock and soil formations, and also in the relationship between the amount of
ground water and surface water flowing through the system. The basic flow pattern depends largely on the nature of this
relationship.
Most of the water on the earth is in constant circulation within what is known as ‘hydrologic cycle’. The energy utilized
within the cycle comes mainly from the sun. Water evaporates from both land and sea to be re-precipitated, usually
somewhere else. On most part of the land, precipitation exceeds evaporation, and run off towards the sea occurs.
Difference between running water and standing water
• Current : Unidirectional main current is found in running water but not in standing water.
• Depth: It is small in running water,more in standing water.
• Condition of gradient from source to mouth : In running water,physical, chemical conditions usually change from the
source to the mouth and the difference in many factors may be great between those extremes,but it is more
homogeneous in standing water.
• Water of the basin: Running water systems are very shallow and have long, complex narrow channels, but standing
water reach great depth, have broad basins.
• Permanent removal of eroded and transported materials: Constant erosion is common in running water and materials
so removed are transported to distance. Erosion occurs in standing water,but it is rarely severe,eroded materials and not
carried far away but remains within the same basins.
• Absence of prolonged stagnation: Consequence of erosion and deposition, most of the running waters tend to increase
the length of their channels with age. In standing water materials constantly being deposited tend to fill in the basin.
• Physical factor: It is more important in running water and standing water.
• Basic food materials: Most running water manufacture themselves little basic food, but depend on the contribution
from the surrounding land than the standing water.
1.3.1. Ponds, lakes, streams, river
Ponds:
Ponds are defined as small, shallow, inland standing water bodies, where rooted plants can grow over most of the
bottom. Ponds are mainly of three general classes,they are :
i. Those which represent the pond stage in the extinction of previously existing lakes
ii. Those whose basins have never been large or deep (not preceded by a lake) but or for some special reason, have
persisted in the pond stage and
iii. Those whose basins are the results of man’s activities (excavations, quarries, impoundments, etc.)
Natural process alone are constantly forming new pond basins (cut-offs from streams solution basins, beach ponds, and
many others), some of which are never more than temporary ponds from the beginning; others qualifying as permanent
ponds at least for a period in their existence.
Classification ofponds
With respect to seasonal duration, ponds are divided into two general classes
a. Permanent – those which contain some water the year round and
b. Temporary – those in which the basin contains water at certain times or seasons and becomes dry at others.
Those which occur for a limited period in spring are called Vernal ponds
Those which contain water in spring, dry up during summer, and again contain water in the autumn are called Vernal
autumnal ponds and
Those which contain some water throughout the open season but freeze to the bottom in winter have been called
Aestival ponds.
Other classifications ofponds are as follows
Natural ponds
These are perennial shallow water bodies. When a stream shifts its position it leaves behind an isolated body of standing
water which forms the "Ox-Bow" pond. In limestone regions where depressions are formed due to the solution of the
underlying strata,the water gets accumulated either by flood water or rainfall and natural ponds are formed. Sometimes

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the last remnant of a lake whose basin has become filled progressively by sedimentation in course of time is transformed
into a pond.
Artificial pond
Most of the fish ponds are semi artificial ponds. Some are constructed by erecting dams across a stream or basin and
their water level can be regulated by inflow and drainage where pisciculture is practiced. Fish pond is a shallow body of
water that can be drained completely. It is often supplied by running water,but also by spring, ground or rain water.
Pools or Temporary Ponds
They occur in depressions in the ground either at the margin of glaciers where they fill with melt water or in the vicinity
of river bed, after the floods have receded. The water thus collected usually is very shallow and measures maximum to a
few feet only. Also prolonged rainfall may form temporary small pools. All these pools dry up in some part of the year,
and as such organisms in these habitats must be able to survive in a dormant stage during dry periods and be able to
move in and out of the pools.
General Characteristics ofponds
• Ponds are small, shallow standing water bodies.
• They have calm water
• Have more vegetation
• Growth of plants can also found at the bottom
• They have outlet streams
• The movement of water is minimum
• They have slight wave action
• The average depth of water is 8 – 10 feet
• The temperature of the pond more or less changes with that of atmosphere
• Light penetrates up to the bottom
1.3.2. Lakes
Forel (1982) defined lake as a body of standing water and occupying basin and lacking continuity with the sea. He also
defined pond as a lake of small depth, and a swamp has been defined as a pond of small depth and occupied by rooted
vegetation. Carpenter (1928) formulated that the true difference between lake and pond is depth and not area
accordingly a pond is a quiet body of water where floating vegetation extends to the middle of basin in which the biota
is very similar to littoral zone of lake.
Lake Morphology
The shape of a lake basin is largely determined by its mode of origin. The depth and contour of lake bottom can be
determined by lowering a weighted line or much more quickly with an echo sounder. Physical structural components of
lakes include their shape, distribution of light, distribution of heat,and movement of water. The hydraulic retention time
(time required for all the water in the lake to pass through its outflow) is an important measure for lake pollution studies
and calculations of nutrient dynamics. The hydraulic retention time is mainly determined by the interplay between
inflow of water into the lake and the basin shape.
Lake Zonation
The following depth zones are recognized in lakes:
a. littoral zone extends from the shore just above the influence of waves and spray to a depth where light is barely
sufficient for rooted plants to grow.
b. photic (euphotic) zone is the lighted and usually well-mixed portion that extends from the lake surface down to
where the light level is 1% of that at the surface.
c.aphotic zone is positioned below the littoral and photic zones to bottom of the lake, where light levels are too low for
photosynthesis. Respiration occurs at all depths so the aphotic zone is a region of oxygen consumption. This deep, unlit
region is also known as the profundal zone.
d.compensation depth is the depth at which rates of photosynthesis and respiration are equal.
e.sublittoral zone,which is the deepest area of plant growth, is a transition between the littoral and profundal zones.
f.pelagic zone (limnetic zone) is the surface water layer in offshore areas beyond the influence of the shoreline.
Boundaries between these zones vary daily and seasonally with changing solar intensity and transparency of the water.
There is a decrease in water transparency with algal blooms, sediment inflows from rivers or shore erosion, and surface
waves.

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1.3.3. Streams and Rivers
A. STREAMS
Introduction
Streams are zones where a rapid flow of shallow water produces a shearing stress on the stream bed, resulting in a rocky
or gravel substratum covered by fully oxygenated water. Streams may vary in size from tiny rivulet to rivers. As time
goes the stream may develop into river or increase its size, whereas the size of reservoirs decreases as time passes. They
are more numerous in regions of abundant rain fall. They are temporary or permanent. Streams are closely linked to
their watersheds. The productivity of streams is often dependent on terrestrial bases,grasses and other debris. The
allocthonous materials contribute most of the food and energy to the organisms in the stream. Benthic invertebrates like
insect larvae constitute the invertebrate fauna. True plankton are almost absent in streams, and are common only in deep
slow moving stretches of rivers. All biota in streams are influenced by the unidirectional current.
Physical conditions
The annual change in stream temperature is 10 to 20°C. Although large rivers do not change in temperature very much
on a daily basis, a small unshaded stream may heat up to 10°C in a few hours on a hot summer’s day and cool by the
same amount at night. The temperature of most streams is lowest in the upland and becomes gradually warmer in the
lower reaches.
The velocity of stream water varies with the landforms. In plains, streams are slow and sluggish throughout their length.
In mountain stretches the speed of water may be rapid.
Stream water has uniform temperature and the difference between the surface and bottom is virtually negligible. The
stream follows air temperatures more closely than lake waters and the factors responsible are depth of water,current
velocity, bottom material, temperature of entering water,exposure to direct sunlight and degree of shading etc.
Extreme of turbidity occur in running water series and streams with rock beds the turbidity is minimal.
Stream systems increase their length, width and depth with increasing age. This is in distinct contrast to the reduction
processes characteristic of all standing water units.
At any position along the course of a running water system, materials eroded at that point and all materials suspended or
dissolved at the level are transported downstream with no opportunity to return. Interchanges of materials are more and
have less depth than lakes.
Chemical conditions
The dissolved oxygen supply in uncontaminated stream is high at all levels often near saturation. The polluted streams
show low dissolved oxygen due to accumulation of organic wastes. Stream which support more plants show diurnal
variation of dissolved oxygen. The level of dissolved oxygen is controlled by the slope of channel and mode of flow.
Current in streams tends to keep the pH in uniform over considerable distances. It keeps any acidity due to accumulating
free CO2 reduced. Streams waters do not develop the more intense acidities.
The dissolved solids of streams are affected by their irregular discharges. Most streams and rivers have maximum
discharge during winter rains, particulate matters, nutrients like phosphate, iron and nitrate are transported to different
parts by the flow of the streams. Streams fed by springs have more constant nutrients.
B. RIVER
River is said to be a natural stream of water usually fresh water flowing towards an ocean. In some cases river flows into
the ground or dries up completely before reaching another body of water. Usually larger streams are called rivers while
smaller streams are called creeks,brooks, rivulets, rills, and many other terms.
A river is a component of the hydrological cycle. The water within a river is generally collected from precipitation,
through surface run off, ground water recharge and release of stored water in natural reservoirs such as glacier.
Topography
The water in a river is usually confined to a channel, made up of stream bed between banks. In larger rivers there is also
a wider floodplain shaped by flood waters over-topping the channel. Flood plains may be very wide in relation to the
length of river channel. This distinction between river channel and floodplain can be indistinct especially in urban areas
where the floodplain of a river channel can become greatly developed by housing and industry.
Ecology
The flora and fauna of rivers use the aquatic habitats available, from torrential waterfalls through to lowland mires
although many organisms are restricted to the freshwaters in rivers eg salmon and Hilsa.
Flooding

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Flooding is a natural part of river cycle. The majority of the erosion of the river channels and the erosion and deposition
on the associated flood plain occur during flood stage. Human activity, however has upset the natural way flooding
occurs by walling of rivers set straight their courses and by draining of natural wetland.
Lakes
2.1.1 Lakes
Lakes origin
Lake is defined as a large body of standing water occupying a basin which does not have any connection with
sea. Approximately 1% of water is found in lakes, but the renewal time is much more rapid than the ocean.
Classification of lakes on the basis of their origin
1.Tectonic lakes
These are formed in basins created by movements of the earth’s crust by different processes.
2.Crater lakes (Volcanic lakes)
In many cases when a volcano becomes extinct, its hollow interior is filled with water by precipitation or by percolation.
They are near circular or sometimes elliptical in outline. eg, Crater lake in Oregon (USA).
3.Glacial lakes
Most common lakes are originated due to erosion and deposition associated with glacial ice movements eg. Finger lakes
of New York.
4.Basal rock dissolution lake
These are formed by the slow dissolving of soluble rock (Calcium carbonate) by water eg,clear lake in California and
Deep lake Florida (USA).
5.Oxbowlakes
An oxbow is a crescent-shaped lake lying alongside of meandering streams or rivers in the floor of a valley. The oxbow
lake is created over time as erosion and deposits of soil change the river's course. On the inside of the loop, the river
travels more slowly leading to deposition of silt. Water on the outside edges tends to flow faster,which erodes the banks
making the meander even wider. When the streams bend and are cut off from the main stream flow, an oxbow lake
results. Such lakes may be entirely cut off and become totally lentic or a little flow may persist seasonally at floods. eg,
Dal and Woolar lakes of Kashmir.
6.Fluvial lakes
These lakes are formed by river activity.
7.Aeolian lakes
These are formed by the wind activity in arid regions which may erode with broken rocks or redistribute sand which are
generally temporary.
8.Shoreline lakes
Created by irregularities or inundation along the coastline of large lakes which usually a result of long shore currents.
9.Reservoir lakes
These are man made lakes formed by the construction of dams across the streams eg, Thungabhadra reservoir in South
India, Bhakra-Nangal reservoir in north western part of India (Anthropogenic lakes).
10.Bog lakes
Bogs are best developed in the north temperate glaciated region when precipitation is abundant throughout the year,
atmospheric humidity is great. Soil temperature is low, evaporation is reduced, and run-off water is minimum having
abundant growth of plants. A typical bog lake is defined as an area of open water surrounded either wholly or by part of
true margins. Possessing peat deposits about the margins or in the bottom usually with a false bottom of very finely
divided flocculent vegetable matter.

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11.Salt lakes
There are many salt lakes throughout the world, much as saline lake waters as freshwater lakes. When climate change
become drier or geological events change drainage basins, the annual flows into lake may be greatly reduced. The lake
may seem to have a significant outflow and become a terminal or sink lake. The salts from the flowing stream are
concentrated by evaporation and are no longer flushed out through outflow eventually the lake may dry completely. In
dry climates the lakes gradually become salty.
Lake Bonneville and Lahontau of south western United States, the Great Salt Lake, Utah and lake Walker and Pyramid
in Wiveda are other examples. Salt lakes also found in areas of drier climates such as Australia, South America, East
Africa, Antarctica,Russia and dry northern side of Himalayas, South and North East America.
2.1.2 Thermal Classification oflakes
According to Hutchinson (1957), following are the classification of lakes based on changes in temperature of surface
water.
a. Amictic: No mixing of bottom and top water; lakes insulated or protected by ice-corer,there is no effect of weather
or external factors.
b. Monomictic: One mixing of the two waters during the year (most deep lakes of the world).
c. Cold monomictic: Water here at any depth never exceeds 4°C; they are ice-bound or ice-covered only in winter;
there are inverse thermal stratification top waters 0°C and bottom waters 4°C (since water at 4°C is heaviest); only one
mixing at temperatures not more than 4°C in spring / summer eg, Polar lakes.
d. Warm monomictic: Temperature of water never falls below 4°C at any depth. Direct thermal stratification top
waters 10 - 20°C and bottom waters 8 - 4°C; only one mixing in a year in a winter eg, Most subtropical deep lakes.
e. Ploymictic : Mixing is continuous, but occurs only at low temperatures.
Size of lake
Lakes differ in area from those ranges from a pond to those of great size. Lake Superior, the largest body of freshwater
flow has an area of more than 49,600 km2
. The Caspian sea with an area of 2,72,000 km2
is sometimes considered as
having the quality of lake.
Lake Chad in Africa has 64,000 km2
during wet season,but is reduced to 9,600 km2
in the dry season. Ten of the large
lakes in America including Great lakes have an combined area of about 2,03,200 km2
. However the number of lakes
whose area exceeds more than 8,000 km2
is insignificant when compared to many thousands of lakes of lesser
magnitude of 11,000 or more lakes or ponds in Michigan.
Depth oflake
Lakes vary in depth but even the deepest lake will never approaches the depth of ocean. It is important to note that the
lake Baikal has a greatest depth contains about 20% of the total volume of freshwater and it is also the deepest known
lake with a maximum depth of 1620 m. In North America, Crater lake in Oregon is about 608m. Lake Tahoe is 487m,
Lake Chelan (Washington) 457m. Seneka lake 188m, Lake Superior 393m, Lake Michigan 281m, Lake Huron 228m,
Lake Ontario 273m, Lake Erie 64m, and the last 5 lakes constitute Great lakes of America.
Lake margin
Nature of margin
The line of demarcation between land and water is the margin of the lake which depends upon a number of
circumstances.
Shore dynamics
Water is in some form of motion ranging from gentle to violent. It has a great potentiality to cause changes on the shore
against which it beats. In lake, the wave action is the principle form of water movement that cause shore changes.
Modification of the original shore line has been accomplished by two main phenomenon such as shore cutting and shore
building.
Lake bottom
The term lake bottom includes all part of bottom of lake basin from the water edge to the deepest region. All lakes of
particular region may have the same origin, may have begun the history with same material and exist at the same
climatic condition, yet the bottom material may often be different in different lakes. The kind of bottom deposits and the

10. POWER RANGERNOTES LIMNOLOGY
10
rate of deposition may depend upon the local circumstances. The nature of bottom deposits determines the biological
productivity. The principle sources of bottom materials are
i. Bodies of plankton organisms which die and sink.
ii. Plant and animal remains.
iii. Organic and inorganic materials.
iv. Silt, clay and similar materials.
v. Marl or CaCO3 precipitated produced by plants and animals.
vi. Remains of floating blanket algae.
Diversity oflake
Though all the lakes appear to be similar, there may be differences in colour, taste,hardness, turbidity and aquatic
animals and plants. With the knowledge and the modern methods of environmental analyses, the lakes posses physical,
chemical and biological diversity. According to a great diversity, lake may be stated into different forms as under :
a. Large,medium or small.
b. Deep or shallow.
c. Protected or unprotected.
d. With or without tributaries and outlets.
e. Fresh, brackish or salt.
f. Turbid or clear.
g. Acid, natural or alkaline
h. Hard,medium or soft.
i. Surrounded by bog, swamp, forest or open shores.
j. High or low in dissolved content.
k. With or without stagnation zones.
l. With mud, muck or mucky sand or false bottom.
m. With high, medium / low biological productivity.
n. With / without vegetation beds.
o. Young, mature and senescent.
2.2.1. Famous lakes
Indian lakes
Almost every region of the country is dwelt by several of lakes that add great charm to their natural characteristics.
Rajasthan and Himachal Pradesh,North-Western state and Northern state of India, respectively are undoubtedly in
possession of larger number of lakes than anywhere else in the country.
Dal lake-Jammu-Kashmir
Dal Lake is a lake in Srinagar in Jammu and Kashmir. The urban lake, which is the second largest in the state,is integral
to tourism and recreation in Kashmir and is nicknamed the "Jewel in the crown of Kashmir" or "Srinagar's Jewel". The
lake is also an important source for commercial operations in fishing and water plant harvesting.
Location : Srinagar, Jammu and Kashmir
Lake type : Warm monomictic
Surface area:18–22 square km
Average depth : 1.42 m (4.7 ft)
Catchment area : 316 square km (122 sq mi)

11. POWER RANGERNOTES LIMNOLOGY
11
Max. length : 7.44 km (4.62 mi)
Max. width : 3.5 km (2.2 mi)
Hebbal Lake- Karnataka
Hebbal Lake is located in the north of Bangalore at the mouth of National Highway 7, along the junction of Bellary road
and the outer ring road. It was one of the three lakes created in 1537 by Kempe Gowda. Like most lakes or "tanks" in
the Bangalore region it was formed by the damming natural valley systems by the construction of bunds. The spread of
the lake in a study in 2000 was found to be 75 ha with plans for extending it to make up 143 ha. The catchment area of
the lake was found to be 3750 ha. In 1974 the lake area was 77.95 ha and in 1998 it was 57.75 ha. Based on the rainfall
of the region, the annual catchment was estimated at 15.2 million cubic metres with 3.04 million cubic metres during the
Northeast Monsoon, 10.12 million cubic metres during the Southwest Monsoon and 3.28 million cubic metres in the dry
season. The storage capacity of the lake was estimated in 2000 to be 2.38 million cubic metres with desilting raising it to
4.07 million cubic metres. Sewage inflow into the lake has altered the chemistry and biology of the lake.
Powai Lake-Maharasthra
PowaiLake is an artificial lake, situated in the northern suburb of Mumbai, in the Powaivalley located downstream of
the Vihar Lake on the Mithi River. The city suburb called Powai, shares its name with the lake. Population around the
lake has substantially increased over the years.
When it was built, the lake had a water spread area of about 2.1 square kilometres (520 acres) and the depth varied from
about 3 metres (9.8 ft) (at the periphery) to 12 metres (39 ft) at its deepest. The PowaiLake has gone through many
stages of water quality degradation. The lake water which used to supply to Mumbai for drinking water has been
declared unfit to drink. The Lake still remains a tourist attraction.
Location : Mumbai
Catchment area : 6.61 km2
Max. depth :12 m
Surface elevation : 58.5 m (191.93 ft)
Settlements : Powai
Loktak lake-Manipur
Loktak Lake, the largest freshwater lake in northeastern India, also called the only Floating lake in the world due to the
floating phumdis (heterogeneous mass of vegetation, soil, and organic matters at various stages of decomposition) on it,
is located near Moirang in Manipur state,India. The etymology of Loktak is lok = "stream" and tak = "the end". This
ancient lake plays an important role in the economy of Manipur. It serves as a source of water for hydropower
generation, irrigation and drinking water supply. The lake is also a source of livelihood for the rural fisherman who lives
in the surrounding areas and on phumdis, also known as “phumshongs. Considering the ecological status and its
biodiversity values, the lake was initially designated as a wetland of international importance under the Ramsar
Convention on March 23, 1990.
Location : Manipur
Lake type : Fresh water (lentic)
Primary inflows : Manipur river and many small rivulets
Primary outflows : Through barrage for hydropower generation, irrigation, and water supply
Catchment area : 980 km2
(380 sq m)
Chilka Lake - Orrisa
Chilka (Chilika) lake is a brackish water lagoon, spread over the Puri, Khurda and Ganjam districts of Orissa state on
the east coast of India, at the mouth of the Daya River, flowing into the Bay of Bengal. It is the largest coastal lagoon in
India and the second largest lagoon in the World. It is the largest wintering ground for migratory birds on the Indian
sub-continent. The lake is home to a number of threatened species of plants and animals. The lake is an ecosystem with
large fishery resources. It sustains more than 150,000 fisher–folk living in 132 villages on the shore and islands.
Microalgae, marine seaweeds,sea grasses,fishes and crabs also flourish in the brackish water of the Chilika Lagoon.
Lake type : Brackish
Primary inflows : 35 streams including the Bhargavi, Daya,Makra, Malaguni and Nuna rivers

12. POWER RANGERNOTES LIMNOLOGY
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Primary outflows : Bay of Bengal
Catchment area : 3,560 km2
Hussian Sagar - Andhra Pradesh
Hussain Sagar (Hyderabad, India) was built by Hazrat Hussain Shah Wali in 1562, during the rule of Ibrahim Quli Qutb
Shah. It was a lake of 24 square kilo metres built on a tributary of the River Musi to meet the water and irrigation needs
of the city. There is a large monolithic statue of the Gautam Buddha in the middle of the lake which was erected in
1992.
Location: Hyderabad
Lake type: artificial lake
Max. depth: 32 ft
Surface elevation: 1,759 ft
Brahma Sarovar - Haryana
Brahma Sarovar is a water tank sacred to the Dharmic religions in Thanesar,in the state of Haryana in North India.
Dharmic religions lay emphasis on taking bath for internal and external purity.
Max. width : 1,800 ft (550 m)
Surface area :1,400 ft (430 m)
Vembanad Lake - Kerala
Vembanad Lake (Vembanad Kayal or Vembanad Kol) is India's longest lake, and is the largest lake in the state of
Kerala. It is also one of the largest lakes in India.
Max. length : 96.5 km
Max. width : 14 km
Surface area :1512 km2
Max. depth :12 m
Upper Lake - Madhya Pradesh
Upper Lake, is the largest artificial lake in Asia which lies on the Western side of the capital city of Madhya Pradesh,
Bhopal. It is a major source of drinkable water for the residents of the city, serving around 40% of the residents with
nearly 30 million gallons per day.
Location : Madhya Pradesh,Bhopal
Primary inflows : Kolans River
Catchment area : 361 km²
Surface area :31 km²
Kodaikanal Lake - Tamil Nadu
Kodaikanal Lake, also known as Kodai Lake is a manmade lake located in the Kodaikanal city in Dindigul district in
Tamil Nadu, India. The lake is said to be Kodaikanal's most popular geographic landmark and tourist attraction. Over
the years a boat club, boathouse and boat service for the public and tourists has become fully functional and is of
aesthetic significance for tourism. Boat Pageant and Flower Shows is a regular feature in the summer season which
attracts tourists.
Location : Kodaikanal, Dindigul district, Tamil Nadu
Lake type : Fresh water
Surface area :24 ha (60 acres)
Average depth : 3 m (9.7 ft)
Pushkar Lake- Rajasthan
Pushkar is an artificial lake located in the state of Rajasthan in India. It is situated near the Pushkar town in the district
of Ajmer. The lake was constructed in the 12th century with the establishment of the dam across the headwaters of the
Luni river. The pious Pushkar Lake is regarded as the sacred lake among the Hindus in India.
Osman Sagar Lake
Popularly known as the 'Gandipet', Osman Sagar Lake is the man made lake created by the dam across the Isa,a
tributary of the river Musi. It is the main source of water supply to the twin cities of Hyderabad and Secunderabad.

13. POWER RANGERNOTES LIMNOLOGY
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Bhimtal Lake
Located 22 km from Nainital, and this lake is named after the second Pandava called Bhima of the famous epic
Mahabharata. It is one of the largest lakes in the Nainital and the second largest lake in Kumaoun. The lake provides the
excellent opportunity for boating, fishing and angling.
Roopkund Lake
Roopkund Lake lies in the Chamoli district of Uttranchal at the height of 5029 meter. The lake provides the stunning
view of the Trishul peak (7122 meter) and due to its less depth it also known as the shallow lake.
2.3.1. Lakes ofthe world
Largest by continent
The largest lakes (surface area) by continent are:
• Australia - Lake Eyre (salt lake)
• Africa - Lake Victoria,also the third-largest freshwater lake on Earth. It is one of the Great Lakes of Africa.
• Antarctica - Lake Vostok (sub-glacial)
• Asia - Lake Baikal (if the Caspian Sea is considered a lake, it is the largest in Eurasia, but is divided between the two
geographic continents)
• Oceania - Lake Eyre when filled; the largest permanent (and freshwater) lake in Oceania is Lake Taupo.
• Europe - Lake Ladoga,followed by Lake Onega,both located in northwestern Russia.
• North America - Lake Michigan-Huron,which is hydrologically a single lake. However,lakes Huron and Michigan
are often considered separate lakes,in which case Lake Superior would be the largest.
• South America - Lake Titicaca, which is also the highest navigable body of water on Earth at 3,821 m above sea
level. The much larger Lake Maracaibo is considered by some to be the second-oldest lake on Earth, but since it lies at
sea level and nowadays is a contiguous body of water with the sea,others consider that it has turned into a bay.
Notable lakes
• Lake Michigan-Huron is the largest lake by surface area 117,350 km². It also has the longest lake coastline in the
world: 8,790 km. Compared to Huron and Michigan lakes, the Lake Superior alone comprises of 82,414 km². However,
Huron still has the longest coastline of 6,157 km.
• The world's smallest geological ocean, the Caspian Sea having a surface area of 394,299 km² which is greater than the
six largest freshwater lakes combined, and it's frequently cited as the world's largest lake.
• The deepest lake is Lake Baikal in Siberia, with a depth of 1,637 m and the mean depth is also the greatest in the
world (749 m). It is also the world's largest lake by volume (23,600 km³, though smaller than the Caspian Sea at 78,200
km³), and the second longest (about 630 km from tip to tip).
• The longest lake is Lake Tanganyika,with a length of about 660 km (measured along the lake's center line). It is also
the second largest by volume and second deepest (1,470 m) in the world, after lake Baikal.
Note : The world's oldest lake is Lake Baikal, followed by Lake Tanganyika (Tanzania).
• The world's highest lake is the Crater lake ofOjos del Salado,located at 6,390 m (20,965 ft). The Lhagba pool in
Tibet at 6,368 m (20,892 ft) comes second.
• The highest large freshwater lake in the world is lake Manasarovar in Tibet an autonomous region of China.
• The world's highest commercially navigable lake is Lake Titicaca in Peru and Bolivia located at 3,812 m (12,507 ft)
above sea level. It is also the largest freshwater (and second largest overall) lake in South America.
• The world's lowest lake is the Dead Sea,bordering Israeland Jordan located at 418 m (1,371 ft) below sea level. It is
also one of the lakes with highest salt concentration.
• Lake Huron has the longest lake coastline in the world of about 2980 km, excluding the coastline of its many inner
islands.
• The largest island in a freshwater lake is Manitoulin Island in Lake Huron,with a surface area of 2,766 km².
3.1.1. Nature ofInland water environment
Nature of lake environment
Lake basins with steep incline of bottom at the shore regions have margins which are less subject to changes. In lakes
with bordering low-lying swamp, bog or marsh areas,the margin shifts with elevation.
High and low water marks

14. POWER RANGERNOTES LIMNOLOGY
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The high water marks can usually be identified by ridges of debris and of certain bottom materials. Low water marks are
easily recognized from the positions of the more prominent animal an plant zones of shallow waters.
Shore dynamics
Water is restless and during calm period some form of motion varies from relatively gentle to violent. The inland lakes
the principal form of water movement produces shore changes. In lakes, particularly those of glacial origin, the shore
line is much regular and simplified. The modification of original shore line has been accompanied by two main
processes viz, shore cutting and shore building.
The shore cutting take place by the force of waves when the crest of oncoming wave is more or less to the shore line and
the final plunge of a wave lashes against the opposing land loosening a certain amount of it. If the shore is composed of
glacial drift or of soft materials, it will yield to continuously bombarding of waves. However,in regions of rocky areas
the shore cutting is slowed down but the erosion is facilitated by rock fragments which are picked by the waves.
On the other hand the shore building results from severalprocesses producing additions to the original lake margins.
Exposed sandy beaches form a beach building during summer by way of waves coming on to the gently sloping where
depth is less than the wave depth and thereby pushing and carrying ahead some of the sand. Under favorable conditions,
the end result is substantially increased breadth of beach (above water level).
Morphometry
It can be defined as the study that deals with measurement of significant morphological features of the basin of a body
of water and its included water mass is known as morphometry. Many fundamental ecological relations are directly
dependent upon structural relations of water it is necessary to make measurements of various morphological features.
Following general and morphometric information should be generated before studying structural and functional
attributes of the system.
Before taking up the morphological studies of a lake, general information regarding type, historical background,
location and general physiography should be collected.
• Type : The type of body of water viz, lake, pond, marsh, swamp, well, spring, stream,river, estuary, should be noted.
• Location : The locality, latitude, longitude and altitude at which the study area is situated should be noted from
authentic maps.
• Historical background :Collect the information pertaining to geological history of the basin and surroundings of
natural waters. For artificial bodies the construction or excavation details are of importance.
• General physiography : Salient physiographical features related to basin, bank and catchment area of the body of
water should be noted. This includes the features of bed-rock, coarse gravel, fine gravel, debris, mud, marl, peat, sand,
silt, clay, marshy, swampy etc.
The following morphometric parameters are of great importance.
1. Area:The surface area of water-spread can be calculated from a shore – line map of the body of water.
2. Bathymetry:A bathymetric or contour map is one which denotes the depth at different points in the body of water.
3. Maximum length:It is the length of line connecting two most remote extremities of the body of the water.
4. Maximum effective length:It is the length of line connecting two most remote extremities of the body of water
along which wind and wave actions occur without any kind of interruption. Maximum length and maximum effective
length may be the same in most cases.
5. Maximum width: It is the length of straight line connecting most remote transverse extremities of a body of water.
6. Maximum effective width:It is the length of straight line connecting more remote transverse extremities of a body
of water along which wind and wave actions occur without any kind of land interruption.
7. Mean width or Mean breadth ( b ) : It is equal to the area divided by maximum length ( b ) = a/l
8. Depth:It is the vertical distance between the surface and the underlying bottom.
9. Maximum depth:It is the depth measured at the deepest point.
10. Mean depth:It is calculated by dividing the volume of the body of water by its surface area
( z ) = v/a = Volume / area.
11. Outline map: Representing the outline structure of a lake in a plane surface is called outline map.
12. Topographical map: Representing various layers of lake basin on a flat surface is called topographical map.
13. Bathymetric map: Map representing the structure and lake basin is called bathymetric map. This can be derived
from outline map and topographical map.
14. Relative depth (Zr):It is the ratio of maximum depth in meters to the square root of area in hectares. Zr = a2 in
hadm /

15. POWER RANGERNOTES LIMNOLOGY
15
15. Shore line:Shore line may be measured on a map by using an instrument called rotometer.
Area of the surface and each depth contour is measured by a digitizer or a polar planimeter.
3.2.1. Physical Characteristics
Pressure
Water is a heavy substance. Pure water weighs 62.4 lb (pounds) per cubic feet at 4°C. This is a direct result of
density. Since, density changes with differences in temperature, compression, substances in solution and
substances in suspension; the weight of a cubic foot of natural water is not always the same. The pressure at
any subsurface position is the weight of the superimposed column of water plus the atmospheric pressure at
the surface. As depth increases, the pressure in water is rapidly become great, so that ultimately a crushing
effect is imposed upon objects submerged to considerable depths. This collapse under pressure is called
implosion. The pressure change in lakes and reservoirs are very small than compared to sea. In lake, having
maximum depth of 100 ft., the pressure in the deepest region is about 58 lb. per sq. in. (4 atmospheres).
Compressibility
Water is virtually incompressible. The coefficient of compressibility for each atmosphere of pressure is
usually given as 52.5 x 10- 6 at 0°C for pressures of 1 to 25 atmospheres. Lake Superior waters, suddenly
rendered absolutely incompressible, would rise in level about 23 cm and an ordinary inland lake with the
maximum depth of 100 ft. under the same circumstances, would rise about 0.25 mm. Since, increasing
pressure compresses the water, thereby increasing its density to the same slight extent, objects sink in water of
uniform temperature at essentially the same rate at all levels.
Density
Some of the most remarkable phenomena in Limnology are dependent upon density relations in water. The
density of water depends on the quantity of dissolved substances, the temperature and the pressure. With
increasing amounts of dissolved solids the density increases in a roughly linear fashion. The quantity of
dissolved solids for inland waters is usually below 1 g / l, except, for mineral waters (springs) inland salt water
bodies, and water bodies subjected to marine influence. The density difference due to chemical factors is not
more than 0.85 g /l and the density differences occurring in different zones of the same water body are usually
an order of magnitude less than this.
i) Variations due to pressure
Water at the surface, subject to a pressure of only 1 atmosphere, is considered as having a density of unity
(1.0); at a pressure of 10 atmospheres, the density is about 1.0005; at 20 atmospheres, the density is about
1.001; and at 30 atmospheres, it is about 1.0015.
ii) Variations due to Temperature
Pure water forms ice at 0°C, and steam at 100°C, but there is change in the density of the liquid due to
temperature. Water possesses the unique quality of having its maximum density at 4°C and it becomes less
dense when the temperature decreases from 4°C to freezing point. Density of water will be less during
summer and it will be high during winter. Sea water becomes heavier at 0°C. The temperature of maximum
density of sea water is 0°C, where as for fresh water it is 4°C.
iii) Changes due to dissolved substances
The total amount of dissolved substances in freshwater is less than that in sea water. Such substances usually
increase the density of water, the amount of increase depending upon the concentration of dissolved materials
and their specific gravity. Evaporation increases the density by concentrating the dissolved materials and the
dilution reduces the density.
iv) Changes due to substances in suspension
All waters contain some suspended particulate matter. The quantity and quality of these substances vary
greatly in different waters and at different times. Silt and certain other materials are heavier than water and
thus increase its weight and other material may have a specific gravity similar to that of water and cause no

16. POWER RANGERNOTES LIMNOLOGY
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significant change in weight. Density currents and related phenomena may be caused by substances in
suspension.
3.3.1. Physical characteristics
Mobility (Viscosity)
Water is an exceedingly mobile liquid. Nevertheless, it has internal friction (viscosity). This viscosity varies
with the temperature. Water is distinctly more mobile at ordinary summer temperatures than that are just
before it freezes. The viscosity changes with temperature. The response of water to wind of fixed velocity
would differ with different temperature of the water. Pressure does not cause any significant change in
viscosity.
Buoyancy is the direct outcome of density and varies with the same factors. The law of Archimedes states that
the buoyancy of an object is equal to the weight of the water it displaces. The greater the density, the greater
the buoyant force; the denser the water, the floating object will ride higher in the water. Thus, ship passing
from fresh water into sea water rises little higher, and the same ship with the same load would ride somewhat
higher in winter than in summer.
Movement of water
The principal forms of movements of water are waves, currents and seiches.
a) Waves
Waves are mainly produced by wind. They occur on every body of water in forms and magnitudes depending
upon various local conditions, such as area of open water; direction, and velocity of winds; shape of shore line
and relative amounts of deep and shallow water. The greater the expanse of water over which the wind blows
the greater the potential wave height, wave length, and wave velocity. Stevenson (1934) formulated a formula
for computing the maximum height of wave in small bodies of water as
h = 1/3 √F
h = Maximum height in water
F = Fetch of the wind in km.
In open water two types of waves are formed namely waves of oscillation and waves of translation.
 i.Waves of oscillation: In this type of wave, the water particle moves up and down but no horizontal
movement of water.
 ii.Waves of Translation: In this type of wave there is definite forward movement of water
Depth of wave action in water is of considerable limnological importance, but information about this is
lacking. It has been claimed that in the sea, wave action may exert an influence to a depth of 182 m.
b) Currents
Currents in lakes are mainly of three kinds, viz, vertical, horizontal and returning. True vertical currents
seldom occur in inland lakes, but may be present in large waters such as the Great Lakes. When present in
inland lakes, they are the result of some unusual thermal, morphological, or hydrostatic circumstance and
upwelling of water from deep water source.
Horizontal currents (undertow currents) are common in lakes. They are usually produced by wind and often
modified by the shape of shore line and form of the basin. The ratio of wind velocity to water movement
diminishes as the wind velocity increases. Also, water velocity diminishes with the increase in depth.
Returning currents are formed when water is piled up on an exposed shore as a result of an onshore wind.
Such action raises the water level at the position, and, as a result, the excess water may return underneath
along the bottom. The magnitude and duration of such currents depend upon the velocity and duration of the
wind. Steady vigorous, onshore winds may set up return currents which extend to the opposite side of the lake.
c) Tides
In inland lakes, tides are almost imperceptible, even in the Great lakes. Lake Michigan is said to have a tide of
about 5 cm. This virtually means that tides in freshwaters are so far as known is negligible phenomena in
Limnology.
d) Seiches
In lakes and along the sea coasts, oscillations of the water level occur under certain circumstances which are

17. POWER RANGERNOTES LIMNOLOGY
17
called seiches (pronounced as Saches). A seiche consists of a local, periodic rise and fall of the water level. It
is an example of standing wave in which the water particles do not travel in circular orbits but the advance and
return of the particle are in the same path. Any influence which produces a temporary, local depression or
elevation of water level may produce a seiche.
3.3.2.Seiches
Most commonly produced seiches in lakes are due to :
1. Winds, temporarily strong, which pile up water on the exposed margin of the lake
2. Sudden change in barometric pressure over a portion of the lake area
3. Earthquakes
4. Land slides
5. Sudden, very heavy rainfall at one end of lake.
The amplitude depending upon the dimensions of the lake and the intensity of the initial cause may vary from a fraction
of a centimeter in small lakes to 1 m or more in large ones. In lake Geneva, Switzerland it is reported that the amplitude
of a seiche may reach about 2 m.
Forel (1895) used the following formula for computing the period of oscillation of a seiche in a lake whose basin has
definite regularity of bottom.
t = l/√gh
where,t = time of one half oscillation in sec
l = length of axis of seiches in meters
g = acceleration of gravity (9,809 m/sec2)
h = depth of water in meters
More complicated formulas were worked out for lakes having irregular basins. Whipple (1927) presents the following
formula.
t =2 l / 3,600√dg
where,t = time of oscillations in hours
l = length of lake (or length of axis of seiche) in feet
d = mean depth in feet along axis of seiche
g = acceleration of gravity (32.66 ft/sec2)
Seiche condition in lake Erie, the calculated period is 14.4 hr.
Forms ofSeiches
Forel (1895) showed that seiches are of different forms as follows
•Longitudinal seiches - whose axis corresponds with the direction of the long axis of the lake.
•Transverse seiches - whose axis lies in the direction of one of the shorter axes of the lake.
Both longitudinal and transverse seiches are of three different forms :
a) Uninodal - having one node
b) Binodal – having tow nodes
c) Dicrotic seiche – having two beats (show as two peaks on a limnograph) due to interference of unimodal and bimodal
seiches.
d) Plurinodal – having severalnodes
Lesser forms of water motion are sometimes called seiches as for example the short–period, back and forth flow of
water though narrow channels in certain localities in very large lakes and the subsurface seiches,a type which has been
postulated as the cause of certain submerged currents in lake Erie.
Subsurface waves,sometimes produced in large bodies of water,occur where subsurface water is denser than the
overlying water. A strong localized wind starts an impulse (wave) in the underlying layer of water which moves forward
in the direction of the wind. As this wave moves along the warmer lighter water just passes over the crest of the wave
but in the opposite direction, thus producing a surface current opposite to the direction of wind.
Subsurface seiches usually arise from a temporary displacement of the thermocline by the weight of piled up surface
water on one side of a lake due to strong wind action.

18. POWER RANGERNOTES LIMNOLOGY
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3.4.1. Physical characteristics- Surface film, Temperature
Surface film
When water is exposed to air, it acts as if it were encased within an extremely thin elastic, surface membrane. This
boundary is commonly known as the surface film and is interpreted as a manifestation of unbalanced molecular action.
However,at surface film, there is a surface tension due to unbalanced attractions between water molecules at surface on
one side only and upward attraction is lacking because there are no water molecules above them.
Surface tension is maximum in pure water than in any other liquid except mercury. Surface film provides support for
organisms and miscellaneous particulate material, upper as well as under surface of surface film offers mechanized
support.
Plants are pleuston whereas animals which are associated with the surface film are termed as neuston (minute and big).
Effects of surface film
a)Beneficial effects are (i) mechanical support and (ii) respiration mainly air breathing aquatic insects.
b)Harmful effects are (i) reduction of light penetration thereby it will have effects on photosynthesis and (ii) traps the
minute organisms thereby fall easy prey to big animals.
Temperature
Temperature is one of the most important factors in an aquatic environment. In fact,it is possible that no other single
factor has so many profound influences and so many direct and indirect effects.
Diurnal and seasonal variations are very much common in freshwater environments than in marine environment. A
diurnal variation range of 4.8 to 5°C has been recorded in a tropical pond with an average depth of 3.0 m. In shallow
water bodies within an average depth of 1.5 m, the lowest night temperature was 26.6°C. The highest day time
temperature was 32°C with a variation of 5.4°C. In flowing water bodies like streams and rivers there is no such wide
fluctuations in temperature.
Lentic waters of lakes and ponds undergo thermal stratification phenomenon according to seasons. Thermal
stratification has been reported most frequently in the lakes of tropical countries such as Java,Sumatra and India.
According to temperature relations lakes have been classified into three types
1)Tropical lakes : In which surface temperature are always above 4°C.
2)Temperate lakes : In which surface temperature vary above and below 4°C.
3)Polar lakes : In which surface temperature never goes above 4°C.
Decrease in temperature cause reduction in metabolism resulting in lower rate of food consumption. Extreme higher or
lower temperature has lethal effects on the aquatic organisms. Fluctuation in temperature of water regulates the breeding
periods, gonodal activation and thermal induced migration. On the basis of their ability to tolerate thermal variations,
most fresh water organisms are classified into stenotherm and eurytherm. Stenothermic are the organisms with a narrow
range of temperature tolerance while the eurythermic are those organisms with a wide range of temperature tolerance.
Source ofheat for evaporation
a)Sun
b)Water
c)Surroundings
Inland waters are subjected to very extreme variation of temperature due to small expanse and shallow areas and get
heated rapidly during day and are cooled at night.
Rate of evaporation is determined by severalfactors such as
a)Temperature
b)Relative amount of free surface area of the water
c)Vapour pressure
d)Barometric pressure
e)Amount of wind action
f)Quality of water ie. fresh or salt
e) Thermal conductivity
The thermal conductivity of water is very low. Heat coming to a lake from the sun as partially absorbed and to some
extent conducted, but the really effective heat distribution is due to wind action in agitating the water and to a much
more limited extent, to convection currents.
f) Convection
Convection is the process of the transfer of heat by the movement of heated particles themselves. For eg, when water in
a beaker is heated by a flame placed below it, that portion of water first heated, expand and rise while the upper, colder,

19. POWER RANGERNOTES LIMNOLOGY
19
denser portion sink. If the heat supply continues for some time, there are thus set up ascending and descending currents
by means of which heat is carried all through the total water mass. This form of heat distribution is known as
convection. Most forms of artificial heating of water are of this type.
Convection does occur under the following conditions:
Cooling and sinking of surface water as when the sun sets and under conditions of falling air temperature
a) Entry of colder water from a tributary
b) Cooling of surface water with the passage of autumn into winter
c) Alterations of winds and calm conditions
d) Entry of cooler subterranean water at a high level in the basin
e) Advent of rain in temperate region
f) Cooling of the surface water by evaporation
All the plants and animals have an adaptation to certain range of temperature ie. - 200°C to the boiling point of +100°C.
Some can withstand very low temperature for a short duration in an active state and some blue green algae and bacteria
living in hot spring (mineral) condition exist at temperature up to 90°C, however they reproduce at a slightly lower
temperature.
3.4.2. a) Thermal stratification
In tropical lake, heat intake at the surface leads to the formation of a vertical temperature gradient, within
which the thermal resistance become too great for the existing winds to continue mixing the whole water
masses. The upper warmer layer is called epilimnion and the lower cooler layer is called hypolimnion. In
between the two distinct portions, a layer called thermocline.
Summer stratification
In summer, there are three distinct layers are called epilimnion (upper layer), a bottom layer called
hypolimnion and the middle layer called thermocline or metalimnion.
Epilimnion
a) It is upper layer of water.
b) It is warmer layer.
c) The temperature of this layer fluctuates with the temperature of the atmosphere. It will be about 27°C to
21°C.
Hypolimnion
a) It is the bottom layer of water.
b) At this layer, water will be cool.
c) The temp is between 5°C and 7°C.
d) It is a stagnant column of water.
Thermocline (metalimnion)
a) It is the middle layer.
b) The temperature is in between the temp of the upper layer and that of the lower layer.
c) It is characterized by a gradation of temperature from top to bottom.
d) It is also called transition zone.
In deeper lakes, a seasonal, thermal phenomenon occur which is so profound and so far reaching in its
influence that it forms, directly and indirectly the substructure upon which the whole biological framework
rests, particularly in the temperature zone. Therefore, a clear understanding of the salient features of thermal
stratification is a necessity.
Thermal relations during spring
Uniform temperature of 4°C prevails throughout the water column of the lake. Wind depresses water at
windward side and drives towards leeward side (towards the sheltered side), sinks at this end and moves at the
bottom. This results in through mixing which is known as isothermic or homothermic condition.
During summer

20. POWER RANGERNOTES LIMNOLOGY
20
As spring advances warmer winds and sun’s radiation increases surface water temperature. Water expands
above 4°C and thus water at the surface is lighter than underlying colder water. Upper layers become more
warm and lighter and no mixing can takes place. Wind drives water towards leeward and it sinks at that side
which will sink down but not reaching the bottom of the lake but will be stopped at some intermediary level
above cooler (colder) bottom water (Hypolimnion).
Currents in the upper lake will induce a counter current which is of a lesser magnitude in the bottom lake. At
this depth, the current direction will be towards the opposite side of the lake ie, windward side from leeward
to wind ward, sinks at this end and returns as the counter current at this region of lake. Thus two distinct
layers are seen at this time in the lake. Between these two layers, temperature drops suddenly, upper layer in
contact with the warmer waters of upper lake which is mixing by warmer winds and conduction.
On the other hand, the lower layers of this region is in contact with the layer which is yet to gain heat through
conduction and other processes which are themselves slow process. This separating zone between upper lake
and bottom of lake is called as Thermocline region. It is defined as a region wherein the temperature drops by
more than 1°C per meter of depth. The term of thermocline was proposed by Birge (1897). Thus, epilimnion /
upper lake is above thermocline and bottom lake / hypolimnion is below region of thermocline.
During fall (autumn)
Cold wind blow over the lake surface which cools surface water which become denser at -4°C. These denser
waters sink through lighter warmer waters to a level where it meets the waters of similar density ie. first it will
be at thermocline. Thus epilimnion gradually cools and on the other hand the hypolimnion will maintain the
same temperature. A stage will be reached when there will be no thermocline region, water freely mixes. This
mixing is called fall overturn. Mixing continuous till the temperature throughout will be at 4°C.
During winter
Cooling below 4°C will make water lighter and thus the surface waters are lighter than the warmer but denser
subsurface water. This water floats and no sinking, cooling continuous at surface till ice is formed at 0°C.
Once ice is formed at the surface wind has no effect as far as mixing is concerned a period of stagnation sets
in.
During spring
With the onset of spring, warmer sun rays and wind melt the ice cover. Now colder but lighter water will be
above warmer but denser water below. Once it attains a temperature of 4°C, it sinks down and reaches a level
of 1°C which being lighter ascends up and in turn warms up. Thus the layer of denser water increases until the
whole lake is uniformly of a same temperature. Mixing takes place now by spring winds and this is called as
spring overturn.
3.5.1. Physical characteristics- Light, Colour, Turbidity
Light
Light influences freshwater ecosystems greatly. Fresh waters contain more of suspended materials. These
suspended materials obstruct the light that penetration reaches the water. The degree of such obstruction of
light influences the productivity of the freshwater ecosystem. A shallow lake receives light to its very bottom
resulting in an abundant growth of vegetation both phytoplankton and rooted vascular plants. Light affect the
orientation and changes in position of attached species and their nature of growth and it also causes the diurnal
migration of planktonic organisms. The factors affecting the light penetration in natural waters are the
intensity at the surface, angle of contact of light with surface, differences in latitude, seasonal differences,
diurnal differences and suspended materials.
The light intensity at which oxygen production by photosynthesis and oxygen consumption by the respiration
of the plants concerned are equal is known as the compensation point, and the depth at which the
compensation point occurs is called the compensation depth.
Light exerts a great influence on many biological process of water. Most important future of water is its
transparency. This fluctuates in different seasons and water bodies such as flooding livers, mountain streams
etc. The source of light on the earth - a) Sun and b) Moon
Electromagnetic spectrum emitted by Sun (a) short gama rays (0.0001 mm) to (b) long Hertizan waves
(several km long). The Hertizan waves are the electromagnetic waves used in radio and it is pronounced as
Hertz.

21. POWER RANGERNOTES LIMNOLOGY
21
Intensity of light is the number of quanta passing through on a unit area, ie, light energy and the unit of
expression of light intensity is ‘Lux’
Wave length is the measure of light colour
nm = nanometer = mille micron 10-9
AO = 1/ton billionth of a meter
nm = 1/billionth of a meter or 10AO
Intense radiation is restricted to 300 to 1300 nm. Peak radiation distribution is in the blue green range.
Wave length heating water is 0.1 to 770 nm (infra red spectrum).
In a year the amount of radiant energy that reaches earth from the sun is 1.3x1021 k cal
Visible wave length/light : 400 to 770 nm; Ultraviolet light >286 to 400 nm
Light penetration in natural waters is affected by
a) Dissolved substances
b) Suspended substances
c) Planktonic organisms
d) Geographical features (latitude and longitude etc)
e) Meteorological conditions
f) Angle of light etc.
Methods for estimation
a) Secchi’s disc
Secchi (1865), an Italian professor employed a metallic disc for measuring the transparency of waters of
Mediterranean sea. It considered in lowering into the water a white metallic disc of 20 cm in diameter, on a
graduated rope, noting / recording the depth at which the disc disappeared then lifting the dosc and noting the
depth at which it reappeared. The average of these two readings was considered the limit of viability or Secchi
disc depth. This method was used subsequently by many investigators. Whipple modified this method by
dividing the disc into four quadrants and paintings them in such a way that two of the quadrants which were
directly opposite to each other, black and intervening ones white. He also increased the efficiency of the
method by viewing the disc, as it sank in the water through a water telescope held under the sun shade.
This method is not actual measure of light penetration, but instead merely a useful rough index of visibility
when used under standard conditions. They are (a) Clear sky (b) Sun above the head (preferably) (c) Shaded
or protected side of the boat (d)) Under a sun shade. This method has come into a wide use as a means of
comparing different waters.
Factors influencing the light penetration
1) Intensity of light at surface
This varies (a) degree of clarity of sky (b) presence of fog, dust, smoke etc and (c) time of the day/season of
the year.
2) Angle of contact with surface
Light in contact with surface part of it is reflected rest enters water and becomes refracted. Penetration
depends on angle of contact and maximum penetration when sun is at zenith.
3) Different in latitude
More remote the water mass is from equator, greater will be the departure of sun’s rays from vertical and
hence penetration varies.
4) Seasonal differences
Closely associated with latitude are the seasonal changes in the position of the sun. Only locations at or
between 23° 28i N and 23° 28i S (Tropic of cancer and Tropic of Capricorn) ever have a vertical sum. Beyond
this zone, north or south not only do locations have on regular sun but the angle changes progressively with
change of seasons.
5) Diurnal difference
Angle of light in contact with water is ever changing during day, reaches zenith at noon.

22. POWER RANGERNOTES LIMNOLOGY
22
6) Dissolved materials
One of the important factors is absorbance of light which varies with chemical substances such as (a) chloride
of Ca and Mg affect light penetration ie. Diminishes, (b) Traces of NH3 proteins, nitrate, carbohydrates etc
reduces the light penetration with respect to ultraviolet rays.
7) Suspended materials
Silt, clay etc. are effectively screen light and also the penetrations of light reduce by phytoplankton and
zooplankton.
Penetration of light in pure water
When light penetrates or enters into pure water (a) certain portion of light is absorbed and (b) some of it is
scattered in the form of deflection in all directions.
Absorption is selective in which certain wave lengths are absorbed more quickly than others.
Penetration of light in natural waters
Every quantitative determination records were only in marine waters probably because of more clarity. Here
photographic plate method used by Forel (1865) in lake Geneva at about 200 m.
3.5.2. Physical characteristics- Colour and Turbidity
Colour
Pure water bodies appear nearly black as they absorb all light components of the spectrum. The lake water containing
suspended materials is seen blue in colour due to the scattering of light by water molecules. Naturalwaters differ greatly
in colour, depending upon the materials dissolved and suspended in it.
It is a common misconception that in large water bodies, such as the oceans,the water color is blue due to the reflections
from the sky on its surface. Reflection of light off the surface of water only contributes significantly when the water
surface is extremely still, ie, mirror like, and the angle of incidence is high, as water's reflectivity rapidly approaches
near total reflection under these circumstances. Some constituents of sea water can influence the shade of blue of the
ocean and hence it can look greener or bluer in different areas.
Scattering from suspended particles also plays an important role in the color of lakes and oceans. A few tens of meters
of water will absorb all light, so without scattering, all bodies of water would appear black. Because,most lakes and
oceans contain suspended living matter and mineral particles as coloured dissolved organic matter (CDOM) and thus the
light from above is reflected upwards. Scattering from suspended particles would normally give a white color, as with
snow, but because the light first passes through many meters and the scattered light appears blue. In extremely pure
water as is found in mountain lakes, where scattering from white coloured particles is missing, the scattering from water
molecules themselves also contributes a blue color.
Turbidity
Degree of opaqueness developed in water by means of suspended water is known as turbidity. Turbidity producing
substances may be divided into two groups.
i) Settling suspended matters – those substances which in motionless water,will settle to the bottom sooner or later.
ii)Non-settling suspended matters - Finely divided solids or those materials whose specific gravity is less than water
which are in permanent.
The settling of particulate materials is by no means at a uniform rate,particularly in deeper lake having considerable
difference in temperature between the surface and the bottom layers.
Effects ofmaterials in suspension
a)Light reduction: Favourable for animals but unfavourable for plants (photosynthesis)
b)Effects of temperature: Turbid waters are warmer than clear waters. Suspended particles absorb heat more rapidly
than water itself and then radiate the heat to the surrounding water,adding to the heat content of the water.
Chemical characteristics
4.1. Dissolvedgases – Oxygen, Carbon dioxide and other dissolved gases
Dissolvedgases
No naturally occurring body of water is free of dissolved gases. Their spatial and temporal distribution is
dependent on factors such as precipitation, inflow and outflow, physical factors like temperature, movement
of water and chemical factors such as solution processes, combination and precipitation of reactions, complex

23. POWER RANGERNOTES LIMNOLOGY
23
formation etc.
Among the dissolved gases present in water, oxygen and carbon dioxide are direct indicators of biological
activity of water bodies. Gaseous nitrogen only enters the metabolic cycle of a few specific microorganisms.
Hydrogen sulphide and methane occur in small localized amounts due to bacterial activity under conditions of
low redox potential and are incorporated into the material budget of water bodies by certain bacteria.
The Liebig’s law of minimum states that the yield is dependent on whatever growth factor is at a minimum in
proportion to all the other similar factors.
Solubility of Gases in water
The solubility of gases in water decreases with increasing temperature and decrease of pressure. When a gas
comes in contact with water, it dissolves in it until a state of equilibrium is reached in which the solution and
the emission of the gas are balanced. Total solubility of gas is expressed by Henry’s law. The concentration of
a saturated solution of gas is proportional to the pressure at which the gas is supplied.
Condition affecting the solubility of gases in water
Solubility of gases differs widely even when their pressures are equal. It is therefore necessary to find out the
solubility constants.
Henry’s law is stated as :
C= K p
Where, C = Concentration of gas in solution
p = Partial pressure of gas
K= Constant of solubility
The following general conditions affect the solubility of a gas:
i. Rise in temperature reduces solubility
ii. Increasing concentration of dissolved salts diminishes solubility
iii. Rate of solubility is greater when the gases are dry than when they contain water vapour
iv. Rate of solubility is increased by wave action and other forms of surface water agitation
A. Oxygen
The main sources of dissolved oxygen in water are:
i) The atmosphere and
ii) By photosynthetic activity of aquatic plants
Atmospheric oxygen enters the aquatic system:
a) By direct diffusion at the surface and
b) Through various forms of surface water agitations such as wave action, waterfalls, and turbulences due to
obstructions.
Aquatic chlorophyll bearing plants release oxygen as a byproduct of photosynthesis, which gets distributed
into the different layers of lake water by movements. In most lakes the phytoplankton contributes the bulk of
the oxygen supply because of the huge amounts of chlorophyll of algae in the epilimnion zone. In shallow
waters like ponds and swamps the limnetic photoautotroph may be overshadowed by littoral macrophytes,
attached algae, and the benthic algal mats. In small rivulets and brooks the periphyton account for most of the
production of oxygen.
The main causes of decrease of oxygen in water are:
i. Respiration of animals and plants throughout the day and night and
ii. Decomposition of organic matter – Aerobic bacteria use up of the oxygen of water while decomposing
organic matter. Chemical oxidation of sediments also takes place. Purely chemical oxidation may also occur,
but most of the oxidative processes in aquatic habitats are probably mediated through bacterial action.
iii. Reduction due to other gases – A gas may be entirely removed from solution by bubbling another gas
through the water in which it is dissolved. In nature, gases like CO2, methane and hydrogen sulphide often
accumulate in large amounts and the excess amounts rise in the form of bubbles removing the dissolved
oxygen.

24. POWER RANGERNOTES LIMNOLOGY
24
iv. By physical process – In summer days the heat warms up the epilimnion zone of the lake, which could
account for oxygen depletion of water. The combined effects of all or some of the above mentioned processes
may completely deplete oxygen content of the system.
Diel oxygen changes in freshwaters
The concentration of oxygen in an aquatic environment is a function of biological processes such as
photosynthesis and respiration and physical processes such as water movement and temperature. Diel
variations occur in both day and night hours. Estimates of diel production can be made in natural waters by
considering night as the dark bottle and day as the clear bottle. The increase in oxygen from dawn to dusk
reflects net primary productivity. The decrease from dusk until dawn represents half the diel respiration.
Adding the oxygen that disappeared at night to the day time gain gives a sum that is daily gross primary
productivity.
B. Carbon dioxide
i) Sources of carbon dioxide in freshwater
The atmospheric carbon dioxide mixes with the water when it comes in contact with the water surface, as it
possesses the highest solubility in water. As the partial pressure of carbon dioxide in air is low, the amount
which remains in solution in water at a given temperature is also low.
1. Rainwater and inflowing ground water
Rainwater is charged with 0.55 to 0.60 mg/I CO2 as it falls towards earth. Water trickling through organic soil
may become further charged with CO2.
2. Byproduct of Decomposing Organic Matter (DOM)
Carbon dioxide is added to the water as a byproduct of decomposing organic matter which is a common
phenomenon in natural waters. Large quantities of the gas are produced in this way. It is found that carbon
dioxide is the second largest decomposition product, constituting 3 to 30 per cent of the total gas evolved.
3. Respiration of Animals and Plants
Respiratory processes produce and release carbon dioxide into the water. The quantities so added are
governed by the magnitude of aquatic flora and fauna, the relative size of the individual organism and those
factors which determine the rate of respiration.
ii) Reduction of carbon dioxide in freshwaters
The principal processes which tend to reduce the carbon dioxide supply are;
1. Photosynthesis of aquatic plants
Consumption of free CO2 in photosynthesis depends upon amount of green plants which the water supports,
duration of effective day light, transparency of water and the time of year.
Marl forming organisms
The following groups of aquatic organisms are known to form marl (=Crumble : large deposits of calcium and
magnesium carbonate) in water bodies; aquatic flowering plants like Potamogeton, Ceratophyllum,
Nymphaea, Vallisneria; many blue-green algae like Rivularia, Lyngbya nana, Lyngbya martesiana,
Colacacia. Centrosphaeria facciolaea; many species of diatoms; mollusks which form calcareous shells;
insects like Diptera larvae; the cray fishes and lime-forming bacteria. All these organisms function in the
production of the insoluble carbonates which involves carbon dioxide, calcium and magnesium. Thus the
process of lime formation binds up carbon dioxide supplied from circulation and removes the available
calcium and magnesium from the system.
Agitation of water
Agitation is a very effective method of releasing free carbon dioxide from water. It is evident from the fact
that sometimes when deeper layers of water has large amount of it, the surface water shows very little carbon
dioxide.
Evaporation
Evaporation of waters containing bicarbonates results in the loss of half-bound carbon dioxide and
precipitation of mono carbonate. The form of loss is greatest in shallow water bodies where evaporation is

25. POWER RANGERNOTES LIMNOLOGY
25
most effective.
Rise of bubbles from depths
Free carbon dioxide often accumulates in decomposing bottom deposit in such quantities that at frequent
intervals increasing internal pressure of gas exceeds the external pressure and the excess gas rises in the form
of masses of bubbles to the surface and is lost into the air.
Other dissolved gases
i) Methane
Methane, sometimes called marsh gas, is one of the products of decomposing organic matter at the bottoms of
marshes, ponds, rice field and lakes. The methane bacteria are obligate anaerobes. They decompose organic
compounds with the production of methane (CH4) through reduction of either organic or carbonate carbon.
Conditions favorable for production of methane appear at about the time the dissolved oxygen content is
exhausted. This is because methane (CH4), a compound of carbon and hydrogen burns in oxygen forming
oxides of carbon and hydrogen ie, carbon dioxide and water.
It has been found that large quantities of methane are produced in marshes and eutrophicated lakes during
summer time.
ii) Hydrogen Sulphide
Hydrogen sulphide dissolves very rapidly in water and is thus not dissipated like methane. The bottom water
of stratified eutrophic lakes may contain appreciable quantities of the very soluble gas H2S. This is especially
marked in lakes of regions of high edaphic sulfate. The reduction of sulfate to sulfide is a phenomenon largely
associated with anaerobic sediments. H2S is poisonous to aerobic organisms because it inactivates the enzyme
cytochrome oxidase.
iii) Nitrogen
Nitrogen has a low solubility in water. It is such an inert gas that the quantities which occur in lake water are
not changed by the chemical and biological processes. The atmosphere usually supplies the greater amounts of
nitrogen found in water. The minimum amount occurs in winter, since it is more soluble in cool water.
iv) Ammonia
Ammonia occurs in small amounts in unmodified natural waters. It is exceedingly soluble, 1 volume of water
dissolving 1,300 volume of ammonia at 0° C. In lakes, it is the result of the decomposition of organic matter
at the bottom. In summer, free ammonia ordinarily increases with depth.
v) Sulphur dioxide
Traces of sulphur dioxide may occur in natural waters.
vi) Hydrogen
Liberation of hydrogen in the anaerobic decomposition of lake bottom deposits seems likely. But, the amount
so formed is small.
vii) Carbon Monoxide
Carbon monoxide may occur in the bottom of the hypolimnion in small amount.
4.2.. Dissolved Solids and Dissolved Organic Matter
All waters in nature contain dissolved solids .Water is the universal solvent dissolving more different materials than any
other liquid. Natural waters come in contact with soluble substances in many ways such as mere contact with its own
basin, erosion at shore line, wind blown materials, inflow of surface waters,inflow of seepage and other forms of
subterranean waters and decay of aquatic organisms. Rain water contains 30 to 40 ppm of dissolved solids.
Solubility of solids in water
Salts are composed of ions which in the solid form are held together by ionic forces. The strong ionization of the salts
leads to the formation of hydrates with water in which the water acts as a dipole to which the ions are attached. The
solubility of solid substances is strongly dependent on the pH and the redox potential in the water. It usually increases

26. POWER RANGERNOTES LIMNOLOGY
26
with temperature and is largely independent of pressure. Most substances dissolve either in the molecular form or
dissociated into ions. Some important constituents such as humic acids, salicilic acid and ferric oxyhydrate are dispersed
in colloidal form.
Major ions in freshwaters
The major ion contents vary in different fresh waters due to five factors,which are climate, geography, topography,
biotic activity and time. These are not completely independent and they interact.
Carbonate is the principal anion in most fresh-waters. Generally carbonate occurs as bicarbonate ion with calcium in
water. Bicarbonate ion is customarily expressed as CO3 because evaporation of a known amount of calcium bicarbonate
solution leaves only the carbonate of calcium to be weighed. During evaporation, gaseous CO2 and water are lost, from
bicarbonate ions, converting them to a lesser weight of carbonate.
Alkalinity is usually a measure of carbonates. There are various compounds of carbonates with calcium, such as calcite
or aragonite which have the same chemical formula (CaCO3),but are crystallized differently. Aragonite precipitates
from thermal waters and is contained especially in the shells of freshwater mollusks. Magnetite, the carbonates of
magnesium (MgCO3) and dolomite, a double carbonate of calcium and magnesium, Ca Mg (CO3)2 are also relatively
common. Carbonates of barium (BaCO3) and strontium (SrCO3) also occur. CaCO3 is insoluble except in the presence
of acid. With carbonic acid, it becomes Ca (HCO3)2. Because of this, it seems reasonable to express alkalinity titrations
in terms of bicarbonate ions, but on the other hand, Ca(HCO3)2 is very unstable and when water is evaporated to
determine its contained dissolved salts, the bicarbonate of calcium is destroyed and only carbonate remains.
Dissolved inorganic solids
i) Nitrogen compounds
Nitrogen occurs in natural waters in the form of numerous compounds, in inorganic form as nitrate, nitrite and
ammonium and in organic form as intermediate stages of microbial protein decomposition. The most important
inorganic nitrogen compounds in water are nitrate and ammonia. Natural waters contain some ammonium salts.
Ammonium carbonate is probably the common form.
iii) Phosphorus compounds
Free phosphorus does not occur in nature, but in the form of phosphates it is abundant. Inorganic phosphorus
compounds usually occur in dissolved form only in small amounts in natural waters,often only as traces. Total
phosphorus in lake water includes two components. One is soluble phosphorus which is the phosphate form and another
one is organic phosphorus which is contained in plankton organisms and other organic matter in the water. As an
essential nutrient for primary producers, phosphorus thus acts more often than nitrogen as the growth limiting factor.
The natural inorganic phosphate content originate from atmospheric precipitation as well as from various phosphate
containing rocks especially apatite, which are flushed into the lake by tributary streams. In lakes and flowing waters
three phosphate fractions occur concurrently : soluble inorganic phosphate as orthophosphate (PO4) and polyphosphate,
soluble organic phosphate and particulate organic phosphate (organisms or detritus). These fractions make up to total
phosphate content. The losses of phosphorus occur throughout flowing water which removes both soluble and organic
form. It may also occur through removals of fish, mollusks, water plants and other organisms.
iii) Sulfur compounds
The inorganic sulfur compound occurring predominantly in natural waters is sulfate. In this form sulfur can be absorbed
by phytoplankters and other photo-autotrophs. Purely chemical processes involved in the sulfur budget of natural waters
are the oxidation of hydrogen sulfide to sulfur by molecular oxygen and also the formation of sulfides, especially iron
sulfide in the sediment. The sulfate ion, SO4 is usually second to carbonate as the principal anion is fresh waters,
although chloride sometimes surpasses it. Silica often outranks sulfate, but very little is ionized. Free or elemental sulfur
is inactive at ordinary temperature. This element can combine with both metals and non-metals to form many
compounds. Free sulfur is an important constituent of protoplasm; it is protein and specifically within those amino acids
having sulfhydryl (SH) bonding; e.g. cystine, cyseine and methionine.
When sulfur is combined with hydrogen the most reduced state is sulfide (S- -) and the most important sulfides in
limnology are the gas - hydrogen sulfide (H2S) and ferrous sulfide (FeS). Sulfates combine with hydrogen to form
sulfuric acid. With the alkali metals sulfur forms the most abundant form in lakes and streams.
Atmospheric sources of sulfate have increased with man’s industrial activities. Man now contributes about ten times
more SO2 than that the annual contribution from volcanoes. Coal combustion produces the gas maximum and copper
smelting and paper manufacturing add to it. Through precipitation and runoff water the sulfate level of some fresh water