Water Quality Variables and Their Impact on Ecosystems
Introduction
Any physical, chemical, or biological property of
water that effects natural ecological systems or
influences water use by humans is a water quality
variable.
There are literally hundreds of water quality
variables, but for a particular water use, only a few
variables usually are of interest.
Drinking water must not have excessive
concentrations of minerals, it must be free of toxins,
and it must not contain disease organisms.
Water for livestock does not have to be of human
drinking water quality, but it must not cause sickness
or death in animals.
Excessive concentrations of minerals in irrigation
water have adverse effects on plants, and irrigation
water also must be free of toxic substances.
Water for industry also must be of adequate quality
for the purposes for which it is used.
Density of water:
The density of liquid water increases as temperature
rises reaching maximum density of 1.000 g/cm
3
at
3.98
0
C. Further warming causes the density of water
to decrease
One cubic meter of pure water at 10
0
C weighs
999.70 kg; the same volume weighs 995.65 kg at 30
0
C.
The relationship between salinity and density
reveals that water at 20
0
C with 30 g/L salinity has a
density of 1.0210 g/cm
3
as compared to 0.99821
g/cm
3
for freshwater at the same temperature. This
is a weight difference of 22.79 kg/m
3
.
Differences in density related to salinity commonly
cause density stratification in estuaries where rivers
run into the sea.
Temperature of water:
•
Temperature is a measure of the internal thermal
energy content of water.
•
Heat content (the amount of thermal energy) is a
function of temperature and volume.
•
A liter of boiling water (100
0
C) in a beaker has a high
temperature but small heat content when compared
to water at 20
0
C in a reservoir of million m
3
volume.
•
Water temperature in small lakes and in ponds
closely follows air temperature.
•
Because water can store much heat, larger bodies of
water require time to warm up in the spring and to
cool down in the autumn. Therefore, the
temperature of large reservoirs and lakes tend to lag
air temperatures.
•
Stream temperature is effected by many factors such
as slope and turbulence, precipitation, and forest
cover. Nevertheless, there usually is a relatively good
correlation between air temperature and stream
temperature especially for smaller streams.
Effect of temperature and density on lakes:
•
Heat is absorbed more strongly and more quickly within
the upper layer of water than in lower layers. The
transfer of heat from upper to lower layers of water
depends mainly upon mixing by wind.
•
Density of water is dependent upon water temperature.
Ponds and lakes may stratify thermally, because heat is
absorbed more rapidly near the surface making the
upper waters warmer and less dense than the deeper
waters.
•
Stratification
occurs when differences in density
between upper and lower strata become so great
that the two strata cannot be mixed by the wind
•
The stratum between the upper layer and the lower
layer has a marked temperature difference. which
drops at a rate of at least 1
0
C/m. The depth of this
layer may fluctuate depending upon weather
conditions.
•
At the end of winter in a lake or pond, the water
column has a relatively uniform temperature.
Although heat is absorbed at the surface on sunny
days, there is little resistance to mixing by wind and
the entire volume circulates and warms.
•
As spring progresses, the upper stratum heats more
rapidly than heat is distributed from the upper
stratum to the lower stratum by mixing
•
Most large lakes do not destratify until autumn when
air temperatures decline and surface waters cool.
The difference in density between upper and lower
strata decreases until wind mixing causes the entire
volume of water in a lake or pond to circulate and
destratify.
•
There are several other patterns of lake stratification
and periods of free circulation in lakes
•
Small water bodies with average depths of 1 m or
less often thermally stratify during daylight hours, but
they destratify at night when the upper layers cool by
conduction.
•
The stability of thermal stratification in a water body
is related to the amount of energy required to mix its
entire volume to a uniform temperature. The greater
the energy required, the more stable is stratification.
•
In tropical region, some large deep lakes tend to be
permanently stratified, but most occasionally
destratify as the result of weather events.
•
Events that can lead to sudden destratification of
water bodies are strong winds that supply enough
energy to cause complete circulation, cold, dense
rain falling on the surface that sinks through the
warm upper layer.
•
The density of water varies with salinity, so
stratification may occur in areas where waters of
different salt contents converge. Where rivers
discharge into the ocean, freshwater will tend to float
above the salt water because it is less dense.
•
Stratification has a clear effect on lakes’ water
quality. For example, light penetration into the
lower layer is inadequate for photosynthesis.
Organic particles settle into the Lower layer, and
microbial activity causes dissolved oxygen
concentrations to decline and carbon dioxide
concentrations to increase.
•
Lower layer water often is of low quality, and
sudden destratification of lakes with mixing of
Lower layer water with upper layers of water can
lead to water quality deterioration.
Water quality variables play a crucial role in natural ecological systems and human water use. Factors like mineral concentrations, toxins, and disease organisms affect the suitability of water for various purposes such as drinking, livestock, irrigation, and industrial use. Density and temperature of water also influence its properties, with salinity affecting density stratification in estuaries. Monitoring and managing these water quality variables are essential for maintaining healthy water ecosystems and sustainable water use practices.
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Presentation Transcript
Any physical, chemical, or biological property of water that effects natural ecological systems or influences water use by humans is a water quality variable. There are literally hundreds of water quality variables, but for a particular water use, only a few variables usually are of interest.
Drinking concentrations of minerals, it must be free of toxins, and it must not contain disease organisms. Water for livestock does not have to be of human drinking water quality, but it must not cause sickness or death in animals. Excessive concentrations of minerals in irrigation water have adverse effects on plants, and irrigation water also must be free of toxic substances. Water for industry also must be of adequate quality for the purposes for which it is used. water must not have excessive
Density of water: The density of liquid water increases as temperature rises reaching maximum density of 1.000 g/cm3at 3.980C. Further warming causes the density of water to decrease One cubic meter of pure water at 10 999.70 kg; the same volume weighs 995.65 kg at 30 0C. 0C weighs
The relationship between salinity and density reveals that water at 200C with 30 g/L salinity has a density of 1.0210 g/cm3as compared to 0.99821 g/cm3for freshwater at the same temperature. This is a weight difference of 22.79 kg/m3. Differences in density related to salinity commonly cause density stratification in estuaries where rivers run into the sea.
Temperature of water: Temperature is a measure of the internal thermal energy content of water. Heat content (the amount of thermal energy) is a function of temperature and volume. A liter of boiling water (1000C) in a beaker has a high temperature but small heat content when compared to water at 200C in a reservoir of million m3volume.
Water temperature in small lakes and in ponds closely follows air temperature. Because water can store much heat, larger bodies of water require time to warm up in the spring and to cool down in the temperature of large reservoirs and lakes tend to lag air temperatures. Stream temperature is effected by many factors such as slope and turbulence, precipitation, and forest cover. Nevertheless, there usually is a relatively good correlation between air temperature and stream temperature especially for smaller streams. autumn. Therefore, the
Effect of temperature and density on lakes: Heat is absorbed more strongly and more quickly within the upper layer of water than in lower layers. The transfer of heat from upper to lower layers of water depends mainly upon mixing by wind. Density of water is dependent upon water temperature. Ponds and lakes may stratify thermally, because heat is absorbed more rapidly near the surface making the upper waters warmer and less dense than the deeper waters.
Stratification occurs when differences in density between upper and lower strata become so great that the two strata cannot be mixed by the wind The stratum between the upper layer and the lower layer has a marked temperature difference. which drops at a rate of at least 10C/m. The depth of this layer conditions. may fluctuate depending upon weather
At the end of winter in a lake or pond, the water column Although heat is absorbed at the surface on sunny days, there is little resistance to mixing by wind and the entire volume circulates and warms. has a relatively uniform temperature. As spring progresses, the upper stratum heats more rapidly than heat is distributed from the upper stratum to the lower stratum by mixing
Most large lakes do not destratify until autumn when air temperatures decline and surface waters cool. The difference in density between upper and lower strata decreases until wind mixing causes the entire volume of water in a lake or pond to circulate and destratify. There are several other patterns of lake stratification and periods of free circulation in lakes
Small water bodies with average depths of 1 m or less often thermally stratify during daylight hours, but they destratify at night when the upper layers cool by conduction. The stability of thermal stratification in a water body is related to the amount of energy required to mix its entire volume to a uniform temperature. The greater the energy required, the more stable is stratification.
In tropical region, some large deep lakes tend to be permanently stratified, destratify as the result of weather events. but most occasionally Events that can lead to sudden destratification of water bodies are strong winds that supply enough energy to cause complete circulation, cold, dense rain falling on the surface that sinks through the warm upper layer.
The stratification may occur in areas where waters of different discharge into the ocean, freshwater will tend to float above the salt water because it is less dense. density of water varies with salinity, so salt contents converge. Where rivers
Stratification has a clear effect on lakes water quality. For example, light penetration into the lower layer is inadequate for photosynthesis. Organic particles settle into the Lower layer, and microbial activity causes concentrations to decline and carbon dioxide concentrations to increase. dissolved oxygen Lower layer water often is of low quality, and sudden destratification of lakes with mixing of Lower layer water with upper layers of water can lead to water quality deterioration.
