STRATIFICATION IN LAKES

C E N T E R F O R B I O T E C H N O L O G Y A N D

M I C R O B I O L O G Y

P R E S E N T E D B Y

A D A M K H A N C # 3 4

7 T H S E M E S T E R

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INTRODUCTION OF LAKES

A lake is an area, filled with fresh or salt water of

considerable size,localized in a basin, that is

surrounded by land.

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TYPES OF LAKE

There are two types of lakes

Eutrophic lakes

Those that are shallow, saucer-like ones called eutrophic lakes

Oligotrophic lakes

usually, turbid water and deep, steep-sided ones called oligotrophic

lakes with clear water.

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Oligotrophic

Low biomass

High diversity

Complex food web

Oxic waters

Cold-water fish present

High aesthetic quality

No taste or odor problems

Eutrophic

High biomass

Low diversity

Simple food chain

Anoxic bottom waters

Cold-water fish absent

Low aesthetic quality

Taste and odor problems

Rough fish abundant

Toxic algae present

EFFECTS OF EUTROPHICATION

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LAKE

DARAL LAKE VALLEY LALKOO

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STABILITY OF LAKE STRATIFICATION

Stable stratification results when waters of differing densities are

positioned vertically in order of their density

In other words, more density (heavier) water lies below less dense

(lighter) water

Energy is required to break down this density gradient

Stability of stratification is the energy required to uniformly mix a

stratified lake.

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THERMAL ZONES IN A STRATIFIED

LAKE

Temperature oC

6 8 10 12 14 16 18 20 22 24 26

Dep

th (

m)

0

1

2

3

4

5

6

7

8

9

10

11

12

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Scattering and absorption of light

give lake part of its characteristic

color

Clean water - blue color

More and bigger particles scatter

longer wavelengths and absorb

shorter wavelengths

Blue-green, green, yellow

LAKE COLOR

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STRATIFICATION OF LAKES

Lake divided vertically into 3 regions

Epilimnion

Metalimnion(thermocline)

Hypolimnion

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Epilimnion –top of the lake

uniformly warm layer mixed by wind

Metalimnion – middle layer

Intermediate zone where temperature drops rapidly with

increasing depth

Also referred to as thermocline - plane between two depths

between which temperature change is greatest

.

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HYPOLIMNION

THE BOTTOM LAYER.

uniformly cool lower layer unaffected by wind

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CHEMISTRY OF LAKES - OXYGEN

o Oxygen is the second most abundant element in the

atmosphere (20%)

But is only weakly soluble in water (10 ppm)

o Most aquatic organisms require 4-5 mg/L for survival

So… oxygen can be a limiting factor in aquatic systems

The absence of oxygen can allow other chemicals like H2S to

build up. 13

LAKE CHEMISTRY - OXYGEN

Sources

Atmosphere

Photosynthesis

o 6CO2 + 6H20 + light C6H12O6 + O2

Sinks

Respiration

Chemical oxidation

Gas bubbles

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NUTRIENT LIMITATION

The growth of algae and higher aquatic plants in lakes is

regulated by conditions of light and temperature and the

availability of those inorganic nutrients required to

support growth. The element most often in limiting

supply is phosphorus, P.

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LAKE CLASSIFICATION BY

CIRCULATION

• Amixis refers to a lake that does not ever turnover; called an

amictic lake.

• Holomixis refers to lake turnover. The frequency of mixis over

annual to decadal time scales is used in classifying lakes.

• Dimictic lakes follow the pattern described for temperate lakes;

spring and fall turnovers.

• Oligomictic lakes turnover every few years.

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Cold monomixis:colder lakes that inverse stratify only under winter ice cover and mix the remainder of the year.

Warm monomixis:

warmer lakes that mix during winter (never freeze over) and stratify in summer.

• MONOMICTIC LAKES TURNOVER ONCE.

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MICROBIAL FAUNA IN LAKES

Microbes include bacteria, bacteria-like organisms called

archaea, viruses, protozoa, helminths, and protists.

Cyanobacteria are an important group of plants often appearing a dominant

part of the phytoplankton of lakes and reservoirs. They tend to form a

dense surface bloom rising to the surface

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THANKS

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