Probably the most significant thermal anomaly is thermal expansion. Because of
orientation of the water molecules, the most compact configuration occurs at 4
C.
Thus, the most dense water will be 4
C. This results in deep temperate climate lakes
having a fairly constant temperature of 4
C on the bottom. Furthermore, ice, the
solid state of water, is less dense than water and therefore floats on the surface. Water
is the only substance whose solid state floats on its liquid surface. This is very
important in our environment since if this were not the case ice would form at the
bottom of all deep lakes and this ice would never thaw. Such a circumstance would
severely restrict biological activity in the bottom of the lake and result in a buildup of
layers of sediments and ice in the bottom of all lakes.
There are several non-thermal properties of water that are also peculiar to it. The
first one to be considered is its solvent power. More elements and compounds
dissolve in water than in any other liquid. This is very important in making nutrients
available to biological life in the water, whose food must be waterborne. In addition,
the materials dissolved in the water help to maintain the osmotic pressure of the
aquatic organisms.
Water also has a very high ionizing power as a result of its high dielectric
constant, which helps to reduce the force of attraction between atoms or molecules
in the liquid. This is important in providing soluble nutrients to aquatic organisms
and also affects cell permeability.
Only mercury has a higher surface tension than water. The value for distilled
water is 7.5 Â 10
À6 N/m (75 dynes/cm), whereas for mercury it is 43.6 Â l0
À6 N/m.
This creates a tough, thin elastic film on the surface of the liquid and results in the
formation of drops. It also affects capillarity, which controls the rise of liquid in the
soil. The surface film of a lake actually forms a habitat for certain organisms known
as pleuston. Microscopic pleuston are called neuston. Those living on the upper
surface of the interface film are called epineuston, and those on the underside are
called hyponeuston. The pleuston include the water striders, the mosquito larvae,
certain snails, and other organisms. Some organisms that do not live in the surface
film nonetheless deposit their eggs there. Thus the surface film of water is a very
special habitat to certain organisms.
The viscosity or resistance to flow of water varies with its temperature. This
affects lake mixing, particularly during the summer, when the surface of the lake is
warm and more readily mixed by the wind. It also affects the flotation of organisms
in the euphotic zone (the area through which sunlight penetrates). This is important
in maintaining balanced algal growths and in differentiating between the species that
may be present at certain times of the year as a function of temperature.
Water is considered a noncompressible fluid, although precise measurements
show that it is very slightly compressible. For all intents and purposes, it may be
considered a noncompressible fluid for either measurement purposes or for the
aquatic organisms living therein.
From all these physical and chemical parameters, it may be seen that water is very
important in sustaining life. It is the author’s belief that water is the most important
factor in maintaining life on earth and that if scientists want to determine whether or
6 Basic Hydrology, Water Resources, and DAF Boat Plant for Lake Restoration
235
orientation of the water molecules, the most compact configuration occurs at 4
C.
Thus, the most dense water will be 4
C. This results in deep temperate climate lakes
having a fairly constant temperature of 4
C on the bottom. Furthermore, ice, the
solid state of water, is less dense than water and therefore floats on the surface. Water
is the only substance whose solid state floats on its liquid surface. This is very
important in our environment since if this were not the case ice would form at the
bottom of all deep lakes and this ice would never thaw. Such a circumstance would
severely restrict biological activity in the bottom of the lake and result in a buildup of
layers of sediments and ice in the bottom of all lakes.
There are several non-thermal properties of water that are also peculiar to it. The
first one to be considered is its solvent power. More elements and compounds
dissolve in water than in any other liquid. This is very important in making nutrients
available to biological life in the water, whose food must be waterborne. In addition,
the materials dissolved in the water help to maintain the osmotic pressure of the
aquatic organisms.
Water also has a very high ionizing power as a result of its high dielectric
constant, which helps to reduce the force of attraction between atoms or molecules
in the liquid. This is important in providing soluble nutrients to aquatic organisms
and also affects cell permeability.
Only mercury has a higher surface tension than water. The value for distilled
water is 7.5 Â 10
À6 N/m (75 dynes/cm), whereas for mercury it is 43.6 Â l0
À6 N/m.
This creates a tough, thin elastic film on the surface of the liquid and results in the
formation of drops. It also affects capillarity, which controls the rise of liquid in the
soil. The surface film of a lake actually forms a habitat for certain organisms known
as pleuston. Microscopic pleuston are called neuston. Those living on the upper
surface of the interface film are called epineuston, and those on the underside are
called hyponeuston. The pleuston include the water striders, the mosquito larvae,
certain snails, and other organisms. Some organisms that do not live in the surface
film nonetheless deposit their eggs there. Thus the surface film of water is a very
special habitat to certain organisms.
The viscosity or resistance to flow of water varies with its temperature. This
affects lake mixing, particularly during the summer, when the surface of the lake is
warm and more readily mixed by the wind. It also affects the flotation of organisms
in the euphotic zone (the area through which sunlight penetrates). This is important
in maintaining balanced algal growths and in differentiating between the species that
may be present at certain times of the year as a function of temperature.
Water is considered a noncompressible fluid, although precise measurements
show that it is very slightly compressible. For all intents and purposes, it may be
considered a noncompressible fluid for either measurement purposes or for the
aquatic organisms living therein.
From all these physical and chemical parameters, it may be seen that water is very
important in sustaining life. It is the author’s belief that water is the most important
factor in maintaining life on earth and that if scientists want to determine whether or
6 Basic Hydrology, Water Resources, and DAF Boat Plant for Lake Restoration
235