DR. SAJJAN M. B.
DEPT. OF ZOOLOGY
RAJE RAMRAO COLLEGE, JATH. 416404
Unit 2: Freshwater Biology 10
1. Lakes
a. Lake as an Ecosystem
b. Lake Morphometry
c. Physico-chemical characteristics
i. Light ii. Temperature
iii. Thermal Stratification iv. Dissolved solids
v. Carbonates vi. Bicarbonates
vii. Phosphates and Nitrates viii. Turbidity
ix. Dissolved gases (Oxygen Carbon dioxide)
x. Nutrient Cycle – (Nitrogen, Sulphur and Phosphorus)
2. Streams
a. Different stages of stream development
b. Physico-chemical Environment
c. Adaptation of hill stream fishes
Important Lakes
1. Yercaud Lake:-
2 Lake Superior :
3 Lake Baikal :
Classification of Lakes
2. Eutrophic lakes and
3 Dystrophic lakes.
1. Oligotrophic lakes
1 They are young lakes
2 They have great depths
3 The water is transparent
4 They are poor in organic materials
5 They have low electrolyte content
6 They have low pH
7 They are poor in N2 P and Ca.
8 Oxygen is abundant.
9 They have low fertility.
10 They have low nutrients.
11 They are poor in fauna and flora.
2. Eutrophic lakes
Eutrophic lakes are characterised by-
1 They are shallow
2 They are rich in phosphorus.
3 They are rich in organic materials.
4 They have low electrolyte content
5 They have high fertility.
6They are rich in flora and fauna
7 They are rich in plankton.
3 Dystrophic lakes
Dystrophic lakes are characterised by-
1 They may be deep or shallow.
2 They are rich in humus.
3 They have high concentration of humic acid.
4 They are rich in P, N2 and Ca
5 They have high organic content.
6 They have poor in electrolyte content
7 Oxygen content is very low or absent.
8 They are poor in flora and fauna.
9 Fauna includes insect larvae and deep water animals
Classification of Lakes (On the basis of duration of availability of water)
Classification of Lakes (On the basis of Salinity)
3. Fresh water lakes 4. Saline lakes
1. Temporary lakes
Lakes may exist temporarily filling up the small depressions of undulating ground after a heavy shower. In this kind of lakes, Evaporation > Precipitation.
Example: Small lakes of deserts.
2. Permanent lakes
In this kind of lakes, Evaporation < Precipitation. These lakes are deep and carry more water than could ever be evaporated.
Example: Great Lakes of North America, East African Rift Lakes.
3. Fresh water lakes
Most of the lakes in the world are fresh-water lakes fed by rivers and with out-flowing streams e.g. Great Lakes of North America.
4. Saline lakes
Salt lakes (also called saline lakes) can form where there is no natural outlet or where the water evaporates rapidly and the drainage surface of the water table has a higher-than-normal salt content.
Examples of salt lakes include Great Salt Lake, the Aral Sea and the Dead Sea.
Lakes Formed by Earth Movement
Man-made lakes
1. Tectonic lakes
Due to the warping (simple deformation), subsidence (sliding downwards), bending and fracturing (splitting) of the earth’s crust, tectonic depressions occur.
Such depressions give rise to lakes of immense sizes and depths.
They include Lake Titicaca, and the Caspian Sea.
2. Rift valley lakes
A rift valley is formed when two blocks of earth move apart letting the ‘in between’ block slide downwards. Or, it’s a sunken land between two parallel faults.
Rift valleys are deep, narrow and elongated. Hence the lakes formed along rift valleys are also deep, narrow and very long.
Water collects in troughs (Valley in the rift) and their floors are often below sea level.
example is the East African Rift Valley which runs through Zambia, Malawi, Tanzania, Kenya and Ethiopia, and extends along the Red Sea to Israel and Jordan over a total distance of 3,000 miles.
It includes such lakes as Lakes Tanganyika, Malawi, Rudolf, Edward, Albert, as well as the Dead Sea 1,286 feet below mean sea level, the world’s lowest lake.
3. Lakes Formed by Glaciation
Cirque lakes or tarns
4. Rock-hollow lakes
The advance and retreat of glaciers can scrape depressions in the surface where water accumulates; such lakes are common in Scandinavia, Patagonia, Siberia and Canada.
These are formed by ice-scouring (eroding) when ice sheets scoop out (dig) hollows on the surface.
Such lakes of glacial origin are abundant in Finland – Land of Lakes. It is said that there are over 35,000 glacial lakes in Finland.
5. Lakes Formed by Volcanic Activity
Crater and caldera lakes
During a volcanic explosion the top of the cone may be blown off leaving behind a natural hollow called a crater.
In dormant or extinct volcanoes, rain falls straight into the crater or caldera which has no superficial outlet and forms a crater or caldera lake.
Examples: Lonar in Maharashtra and Krakatao in Indonesia.
6. Lakes Formed by Erosion
Karst lakes
7. Wind-deflated lakes
8. Lakes Formed by Deposition
Lakes due to river deposits
9. Lakes due to Marine deposits
10. Lakes due to damming of water
Lakes formed by these processes are also known as barrier lakes. Landslides, avalanches may block valleys so that rivers are dammed. Such lakes are short-lived.
Example: Lakes that are formed in Shiwaliks (Outer Himalayas). Dehradun (all Duns) were lakes few centuries ago.
11. Man-made lakes
Besides the natural lakes, man has now created artificial lakes by erecting a concrete dam across a river valley so that the river water can be kept back to form reservoirs.
Example: Lake Mead above the Hoover Dam on the Colorado River, U.S.A.
Man’s mining activities, e.g. tin mining in West Malaysia, have created numerous lakes.
Functions / Uses of Lakes
Means of communication
Large lakes like the Great Lakes of North America provide a cheap and convenient form of transport for heavy and bulky goods such as coal, iron, machinery, grains and timber.
The Great Lakes-St. Lawrence waterways penetrate more than 1,700 miles into the interior. They are thus used as the chief arteries of commerce.
Economic and industrial development
The Great Lakes-St. Lawrence waterways were responsible for the development of the interior wheat farms and lakeside industries.
Water storage
Example: Kolleru lake in Andhra Pradesh.
Hydro-electric power generation
Artificial lakes like Hirakud.
Agricultural purposes
Many dams are built across artificial lakes.
Bhakra Nangal Dam. Its reservoir, known as the “Gobind Sagar Lake” and Hirakud Dam (Odisha) on the Mahanadi in India.
Regulating river flows
Hoover Dam on the River Colorado and the Bhakra and Nangal Dams on the Sutlej in India.
The Hirakud dam was originally conceived as a flood control measure. But the project is criticized for doing more damage than good.
Source of food
Many large lakes have important supplies of protein food in the form of freshwater fish. Sturgeon is commercially caught in the Caspian Sea, salmon and sea trout in the Great Lakes.
Source of minerals
Salt lakes provide valuable rock salts. In the Dead Sea, the highly saline water is being evaporated and produces common salt. Borax is mined in the salt lakes of the Mojave Desert.
Tourist attraction and health resorts
Lake Chilka, Leh, Dead Sea etc..
Characteristics of Lakes :
1 A lake is a large body of standing water body.
2 It has no connection with sea
3 It has stable environmental factors.
4 Thermal Stratification:
Characteristics of Lakes
1. Salinity:
2. pH:
3. Water Current:
4. Pressure, Density:
Dissolved salts increase the density of water.
The density of freshwater is much less than seawater .
5. Transparency:
6. Oxygen:
a. Direct diffusion of atmospheric oxygen
b. water plants and phytoplankton release O2 by photosynthesis
a. By the respiration of aquatic plants and animals
b. By the decomposition of dead organism
c, By mixing of water of low O2 content
7. Carbon-Dioxide:
2) Aquatic animals and plants release CO2 by respiration
2) By the lime depositing bacteria
8. Temperature:
Thermal Stratification:
A) Summer Stratification:- In summer there are three distinct layers namely
Epilimnion:-
1. It is upper layer of water
2. It is the warmer layer
3. The temperature of this layer fluctuates with the temperature of the atmosphere. It will be about 270C to 210C
4. In this layer the water is continuously stirred by wind
Hypolimnion:-
1. It is the bottom layer
2. The water of this layer is cool
3. The temperature is between 50C and 70C
4. The water of this layer is stagnant
Thermocline or Metalimnion:-
1. It is the middle layer
2. The temperature is intermediate between the temperature of the upper layer and that of the lower layer
3. It is characterised by a gradation of temperature from top to the bottom
4. The temperature of the thermocline is 210C at upper level and 70C at the lower level
5. It decreases gradually from the upper level to the lower level
Winter Stratification:
Diagram- Winter Stratification in freshwater system
9. Light:-
10. Dissolved solids
Refer to any minerals, salts, metals, cations or anions dissolved in water. Total dissolved solids comprise inorganic salts &some small amounts of a organic matter that are dissolved in water.
11. Carbonates
A salt that is often formed by the reaction of carbon dioxide with another chemical substance.
-The carbonates tend to be soft soluble in hydrochloric acid & have a marked anisotropy in many physical properties as a result of the carbonate ion . The carbonate minerals a contain the anionic complex which is a triangular .
Nutrient Cycle
Lake as an ecosystem-�A lake is a suitable example for ecosystem. It is a lentic fresh water ecosystem. It contains shallow standing water. The lake ecosystem is formed of abiotic and biotic factors.�
Abiotic factors-
The abiotic factors of the lake ecosystem are water, CO2, O2, inorganic compounds, organic compounds, light, temperature, pressure, pH. Etc
Flora of Lakes:-
The plant community of the lakes constitutes the producers. It is grouped into four types. They are-
1. Phytoplankton: Navicula, Asterione, Richterilla, Closterium, Nitzschia, Fragilaria, Microcystis, Volvex, Eudorina, Euglena, Anabaena, Ceratium, Ehornia etc.
2 Floating Plants :Pistia, Lemna, Echornia, Wolfia etc.
3 Submerged Plants :Utricularia, Ceratophyllum, Hydrilla, Vallisneria, Chara etc.
4 Rooted Plants :Nymphaea, Nelambo, Sagittaria, Typha, Marsilea etc.
Lake Fauna :
The fauna of lake constitutes the consumer of the lake ecosystem. They are-
1 Benthos 2 Periphyton 3 Plankton 4 Nekton 5 Neuston
1 Benthos: Organism living at the bottom are called benthos.
eg. Lamellidons, Pila, Planorbis, Turtles, Saccobranchus, Earthworm etc.
2 Periphyton: Organism attached to the plants or clinging to water plants are called Perophytoneg. Vorticella, Stentor, Hydra, Planeria, Leeches, Nymphs of damsel fly, Snails etc.
3 Plankton: Planktons are small animals and plants those power of self-locomotion are so limited that they cannot overcome water currents. Planktons are of two types.
a Phytoplankton: These are plant plankton. They contain chlorophyll. They carry out photosynthesis. Hence they are called producers. eg. Navicola, Asterionella, Richteriella, Clasterium, Fragillaria, Microsystis, Volvex, Eudorina, Euglena, Anabaena, Ceratium, Chlamydomonas, etc.
b Zooplankton: These are animal plankton. Eg. Daphnia, Cyclops,
4 Nekton: Nekton are swimmers. Eg. Amoeba, Paramoecium, Hydra, Planeria, Miracidium, Brachionus, Limnicola, Huridinaria
Arthropods: Cladpcerans like Dahnia, ceriodaphnia, Copepods likes Cyclops, nymphs of dragonflies, mayflies and caddisflies Insects like Nepa, Notonecta, Belosoma, Ranatra, HydrometraCybister etc.
Mollusca: Lamellidans, Limnaea, Planorbis, Pila etc.
Fishes: Catla, Tilapia, Saccobranchus, Ophipcephalus, Clarias, etc.
Amphibia: Frog, Tadpoles etc.
Reptiles: Natrix, Turtles etc
Birds: Pond herons, cattle herons, water ducks, cormorants etc.
5 Neuston: These are Organisms surviving at air-water interface. They includes floating plants and animals.
Eg. Wolffia, lemna, Pistia, Eichornia, water strides, diving beetles etc.
The animal neuston are of two types.
aEpineuston: These are animals surviving on top of air-water interface.
eg. Water striders.
bHyponeuston: These are animals which spend most of the time onthe underside of the air-water interface and obtain much of their food from within water,
eg, diving beetles, Notonecta, water spiders, whirling beetles.
���Biotic factors�The biotic factors of the lake ecosystem are producers, consumers and reducers.
Producers
Consumers
e.g. Zooplankton (cyclops, daphnia, larvae of chironomus etc), Dysticus (insect), Lymnaea(snail) etc.
E.g. small fishes, frogs.
Reducers or decomposers
Lake Morphometry -
This method involves placing a grid pattern over a lake map and counting the squares (of a known dimension) from the grid, to determine lake surface area Step 1: Trace the lake map on a piece of graph paper or draw a square grid on top of a copy of the map, as illustrated in Figure A-1.
Step 2: Count all the squares that fall within the shoreline of the lake. At the shoreline, count only those squares that are more than half inside the lake shoreline area. Do not count squares that are more than one-half outside the lake boundary
Step 3: Using the map scale, determine the area represented by one square. For example, suppose the map scale shows that 1 inch represents 1000 feet and the squares of the grid are one-half inch on a side.
Using this information, we can see that each square represents a measurement of 500 feet per side [ 0.5 x 1000 = 500 ft.].
Therefore, the area of one square would equal 250,000 square feet [ 500 x 500 = 250,000 sq ft ].
Step 4: The area of the lake, in square feet, would be equal to the number of squares counted from the grid (N) X 250,000. To convert the area from square feet to acres by dividing 43,560. ✪ N X 250,000 = lake surface area 43,560 in acres lake surface area = N X 250,000 /43,560 (43,560 is the conversion factor for converting square feet to acres.)
Lake surface area can be measured with a bathymetric map using any of the following techniques:
2.One of the most accurate methods is to use a planimeter to trace the shoreline contour of a lake. This hand-held instrument is designed for measuring the area of a shape as drawn on a two-dimensional plane. Using the tracer point of a planimeter, you can carefully follow the outermost contour of a bathymetric map. The planimeter calculates the area of the shape in planimeter units (PU) while tracing its outline. Once you have the area in planimeter units you can compare it with the scale of the map to convert the PU to the lake’s actual surface area.
3. Digital tablets or computer scanners can also be used to trace or scan a bathymetric image. Once the image is digitally memorized (i.e., traced or scanned), computer mapping software can be used to calculate surface area.
2. Stream:
A stream is a body of water with a detectable current that moves across the country between banks.
It is also characterized by a particular profile which includes beginning with steep gradients, no floodplain, a little shifting of channels and evolving into streams with low gradients, wide floodplain, and extensive meanders.
Different Types of Streams
When a stream leaves an area that is relatively steep and enters one that is almost entirely flat, this is called an alluvial fan.
Streams normally gather smaller streams as they move along, and the smaller streams that join the main flow are called tributaries. Occasionally, there can also be distributaries, which are smaller streams that actually flow outward.
These distributaries most often find their way back together and form a single valley, but when they instead fan out over a broad area, the result is an alluvial fan.
Alluvial fans form when a stream leaves a canyon and flows out to a lowland that is essentially flat. The sediment generated by the canyon’s erosion means the stream will have a very large load by the time it arrives on the flatland.
The flatland is a little steeper at the mouth of the canyon, and the Badwater Road Alluvial Fan in Death Valley, California, is a perfect example.
2. Braided Streams
Usually found close to very high mountains, braided streams have multiple channels that continuously branch and join along the entire length of the stream, which in turn creates numerous longitudinal bars between the channels.
Also known as anastomosing, it is not the same thing as alluvial fans because the channels do not form into fan shapes or distributaries.
They are called braided streams because the pattern resembles hair tresses that are braided together. Moreover, they tend to rejoin very quickly and their flow is concentrated on a narrow valley that has no actual floodplain.
There is a Providence Canyon in Georgia that has a small stream on the bottom, and it demonstrates what braided streams look like.
Although the eastern part of the United States has very few braided streams, they can be found frequently in the large rivers that cross the Great Plains from the Rocky Mountains. It is also common for more streams to form whenever the water levels recede.
3. Deltas
Deltas result when streams enter a standing body of water, usually an ocean. If the body of water is able to move the sediment as fast as it arrives, deltas will not form. Deltas are like alluvial fans in one aspect because there are distributary channels which spread out from a single channel.
The Nile delta is perhaps one of the most famous deltas on the planet, and before it was used frequently for irrigation, many more active distributaries were present.
In fact, any time a stream reaches a standing body of water, even if it isn’t an ocean, a delta will form. The delta will eventually fill the lake entirely with sediment, even though they have a life expectancy when they are man-made reservoirs.
Deltas usually form the shape of a triangle, which is another reason for their name, and the river usually subdivides into other small rivers before flowing into the sea; an example of this is the Mississippi Delta.
4. Ephemeral Streams
Ephemeral streams flow for a short time only, usually after the snow melts or there is a massive rainstorm; in other words, any time there is an increase in the amount of watershed on the earth. These are small streams with channels that are usually dry during the year.
Contrary to what some people think, there is a difference between ephemeral streams and intermittent streams. Ephemeral streams are very shallow and have a lot less flow than intermittent streams, and they are actually dry throughout most of the year. In recent years, areas that have experienced less-than-normal rainfall can exhibit ephemeral characteristics because they can form these types of streams.
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5. Intermittent Streams
Intermittent streams are those streams that usually flow during the wet season – usually winter through spring – but which are typically dry during the hot summer months. They flow for part or most of the year, but they do not always carry water during the dry season.
Also called seasonal streams, they are supplemented by the runoff from rainfall or other types of precipitation, and they only flow during certain times of the year, usually as a result of groundwater which provides enough water for the flow of the stream to be maintained.
6. Meandering Streams
A meandering stream consists of large loops that flow across a wide flat floodplain and is surrounded by valley walls. If the mountains are too close to the sea, you usually don’t find these types of streams. They are always found in relatively flat areas – including floodplains – as well as places where the sediment is made mostly of muds, fine sands, and silts.
Some scientists are unsure whether meandering streams are depositional or erosional because it is obvious that they both erode sediment and deposit it; however, most of them concur that they are mostly erosional, due to their energy versus load ratio.
Meandering streams grow laterally through erosion – outside the bend – and through the deposit of sediment inside of the bend. If the loops get too big and develop friction, meaning they consume too much energy, the stream will find a shortcut that is less taxing, resulting in a part of the old channel being abandoned. In this case, an oxbow lake will form.
7. Perennial Streams
Perennial streams have water flowing through them all year long, and the source of the water can be either surface water, groundwater, or both. This doesn’t mean that there is water in every inch of its bed, but at least part of the stream will have some water in it.
These are permanent streams, and they rely on normal amounts of rainfall for their existence. Also, the aquatic bed is located below the water table for most of the year with a perennial stream, and they are very well-defined channels as well.
8. Straight Channel Streams
Sometimes, streams are not perfectly straight, but have no major twists and turn about them, and these are called straight channel streams. These types of streams are confined to a single channel, and their banks and valley walls are essentially the same things.
Often found in canyons that aren’t very deep, but whose walls can be steep, straight channel streams tend to occur towards the heads of the rivers and any place that crosses a high ridge. If you’ve ever visited the Grand Canyon and seen the Colorado River, you’ve seen a straight channel stream.
Straight streams do not have to have gorges or canyons that are thousands of feet deep, but they all have valley walls that go inward steeply right to the edge of the water, meaning there is no actual floodplain.
Straight streams are also purely erosional, and the resulting sediment moves quickly downstream because of the energy of the flowing water. They also usually have very large
Adaptations to Hill Stream Fishes
Unit 3: Endocrinology 10
a. Study of endocrine glands – Anatomy and histology
b. Hormones- Nature, role, regulation and disorders with reference to the following thyroid gland, parathyroid gland, adrenal gland and islets of Langerhans.
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