EXERCISE 3
Physical Characteristics:
Lake Models
The hydrodynamics of water movement is an
integral component of a functional lake system.
The importance of water movements and associated turbulence either has been underestimated or neglected in a large majority oflimnological
investigations. Consideration must be given to
the effects of water movements on stratification
and on the distribution of temperature, dissolved
gases and nutrients, and biota.
The various laboratory exercises outlined
below are based on a simple and rather naive
model of a lake. Thus you should bear in mind
constantly that you are studying only a model
and not an actual lake. Furthermore, many of
the formulas are simplified accordingly. Some
virtues of models are:
1. Size is reduced to manageable proportions.
2. Complexity is reduced to such an extent that
mechanisms and processes may be appreciated readily and intuitively understood.
3. Experimentation is facilitated, whereas it may
LAKE MODEL 1: TEMPERATE LAKE
Purpose
be difficult and/or expensive with a natural
system.
On the other hand, unjustifiable extrapolations
to natural conditions can be made from the
model when the observer is not careful to distinguish between the two. In the experiments outlined here, for example, if the sides and bottom
of the aquarium were not insulated, there
would be more rapid heat exchange between the
model "lake" and its surroundings than ever
would be the case in nature. Likewise, the
amount of energy supplied by the heat lamp in
relation to the depth of water is much higher than
in natural situations. The reason for the modification is, of course, to accelerate the process.
These and similar points should be stressed in
your report(s}.
These exercises are based on and modified
from material prepared by Mortimer (1951) and
Vallentyne (1967).
Caution: Take care not to splash water on the
heat lamp-otherwise, EXPLOSION!
Thermally induced density stratification commences in the spring and persists through
the summer for moderately deep lakes in the Temperate Zone. These conditions will be
illustrated in this lake model. It is instructive in this exercise to separate the actions of
sun and wind, and to that extent the model is unnatural. The exercise also illustrates the
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Physical Characteristics:
Lake Models
The hydrodynamics of water movement is an
integral component of a functional lake system.
The importance of water movements and associated turbulence either has been underestimated or neglected in a large majority oflimnological
investigations. Consideration must be given to
the effects of water movements on stratification
and on the distribution of temperature, dissolved
gases and nutrients, and biota.
The various laboratory exercises outlined
below are based on a simple and rather naive
model of a lake. Thus you should bear in mind
constantly that you are studying only a model
and not an actual lake. Furthermore, many of
the formulas are simplified accordingly. Some
virtues of models are:
1. Size is reduced to manageable proportions.
2. Complexity is reduced to such an extent that
mechanisms and processes may be appreciated readily and intuitively understood.
3. Experimentation is facilitated, whereas it may
LAKE MODEL 1: TEMPERATE LAKE
Purpose
be difficult and/or expensive with a natural
system.
On the other hand, unjustifiable extrapolations
to natural conditions can be made from the
model when the observer is not careful to distinguish between the two. In the experiments outlined here, for example, if the sides and bottom
of the aquarium were not insulated, there
would be more rapid heat exchange between the
model "lake" and its surroundings than ever
would be the case in nature. Likewise, the
amount of energy supplied by the heat lamp in
relation to the depth of water is much higher than
in natural situations. The reason for the modification is, of course, to accelerate the process.
These and similar points should be stressed in
your report(s}.
These exercises are based on and modified
from material prepared by Mortimer (1951) and
Vallentyne (1967).
Caution: Take care not to splash water on the
heat lamp-otherwise, EXPLOSION!
Thermally induced density stratification commences in the spring and persists through
the summer for moderately deep lakes in the Temperate Zone. These conditions will be
illustrated in this lake model. It is instructive in this exercise to separate the actions of
sun and wind, and to that extent the model is unnatural. The exercise also illustrates the
31