The Water Cycle
In this presentation you will: Explore the importance of water Investigate how water is recycled Examine the impact of acid rain
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The Water Cycle
Water is vital to life on Earth for two main reasons. Firstly, it makes up 70% of living organisms. Secondly, it provides an environment for those organisms that live in water. It is therefore important to understand the way in which water cycles through the atmosphere and living things in its various forms.
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In the presentation you will explore the importance of water to living organisms. You will also investigate how water is recycled and examine the impact of acid rain.
The Water Cycle
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The Importance of the Water Cycle
Water evaporates into the atmosphere from the land and sea. Plants and animals then use and re-use water and release water vapor into the air.
Once in the air, water vapor circulates and condenses to form clouds and precipitation (rain), which fall back to Earth. This sequence of events is known as the water, or hydrologic cycle.
Condensation
EvaporationRain
The Water Cycle
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Our Water is Millions of Years Old
At one time or another, all the water molecules on the planet have been in an ocean, a river, a plant, an animal, a cloud, a raindrop or a glacier!
Another interesting fact is that the water we drink today is the same water that the dinosaurs drank millions of years ago!
The Water Cycle
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Evaporation
Evaporation is the changing of a liquid to a gas. During the evaporation process, impurities in the water are left behind. As a result the water vapor that enters the atmosphere is cleaner.
Water can evaporate into the atmosphere from raindrops, seas, lakes, water pools, soil, snow, heated buildings and living organisms.
The Water Cycle
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Factors that Affect Evaporation
The amount of natural evaporation that takes place is affected by wind. The warmer and drier the wind, the higher the rate of evaporation.
Low air pressure helps to promote evaporation, but the main factor is temperature. Water evaporates more quickly at higher temperatures.
The Water Cycle
Condensation
Condensation is the process by which water vapor changes its physical state from a vapor to a liquid. Water vapor condenses onto small airborne particles to form dew, fog or clouds.
The most active particles that come from clouds are sea salts, atmospheric ions caused by lightning, and combustion products containing sulfurous and nitrous acids.
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The Water Cycle
Heat added in calories per gram of water
Condensation and Energy
Condensation is brought about by the cooling of the air or by increasing the amount of vapor in the air to its saturation point, that is, the point when the water vapor in the atmosphere is at its maximum level for the existing temperature.
When water vapor condenses back to its liquid state, the same large amount of heat energy that was needed to make the vapor is released into the environment.
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Ice
Melting
WaterBoiling
Steam
The Water Cycle
Sublimation
Sublimation is the conversion between the solid and the gaseous phases of matter, withno intermediate liquid stage. In the water cycle, it is most often used to describe the process of snow and ice changing into water vapor in the air without first melting into water.
The opposite of sublimation is ‘deposition’, where water vapor changes directly into ice – such as snowflakes and frost.
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The Water Cycle
The Conditions Needed for Sublimation
Sublimation occurs more readily when certain weather conditions are present, such as low relative humidity and dry winds.
Sublimation also occurs at higher altitudes where the air pressure is lower than at lower altitudes. Energy, such as strong sunlightis needed.
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The Water Cycle
1
Windy conditions increase the rate of evaporation and condensation.
Answer True or False.
Question
The Water Cycle
2
When water vapor condenses, no energy change occurs.
Answer True or False.
Question
The Water Cycle
3
What is sublimation?
Question
A) The conversion of a liquid to a gas.
B) The conversion of a gas to a liquid.
C) The conversion of a gas to a solid.
D) The conversion of a solid to a gas.
The Water Cycle
Precipitation
Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow or hail. It is the primary connection in the water cycle that provides for the delivery of atmospheric water to the Earth. Most precipitation falls as rain.
Clouds contain water vapor and cloud droplets, which are small drops of condensed water. These droplets are way too small to fall as precipitation, but they are large enough to form visible clouds.
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The Water Cycle
The Conditions Needed for Precipitation
Most of the condensed water in clouds does not fall as precipitation because their fall speed is not large enough to overcome updrafts which support the clouds.
For precipitation to happen, tiny water droplets must first condenseonto even tinier dust, salt or smoke particles which act as a nucleus or central point. Water droplets grow as a result of the additional condensation of water vapor when the particles collide. When the droplet’s fall velocity is greater than the cloud updraft velocity, then it will fall out of the cloud as precipitation.
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Highfall
velocity
Lowupdraftvelocity
Precipitation occurs
Lowfall
velocity
Highupdraftvelocity
No precipitation
The Water Cycle
The Formation of Snow
Sometimes, precipitation-sized drops are formed through a process that leads to the rapid growth of ice crystals at the expense of the water vapor present in the cloud. These crystals may fall as snow, or melt and fall as rain.
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The Water Cycle
Transpiration
Transpiration is a biological process that occurs mostly during the day. Water inside plants is transferred from the plant to the atmosphere as water vapor though numerous individual leaf openings called stomata.
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The Water Cycle
The Effect of Vegetation on Soil Evaporation
Vegetation generally slows evaporation from the soil. Vegetation that shades soil reduces the wind velocity. Evaporation from vegetation also reduces the amount of direct evaporation from the soil or from snow or ice cover.
The absorption of water into plant roots offsets the general effects that vegetation has in retarding evaporation from the soil. As a result, forest vegetation tends to have more moisture than the soil beneath the trees.
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The Water Cycle
Surface Run-off
Run-off is flow from a drainage basin (the area drained by a main river and its tributaries) that appears in surface streams. The flow is made up partly of:
Part of the subsurface flow enters the stream quickly, while the remaining portion may take a longer period before joining the water in the stream.
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• surface run-off that infiltrates the surface soils and moves towards the stream
• precipitation that falls directly on the stream
• groundwater runoff from deep percolation (filtering) through the soil.
The Water Cycle
Infiltration
Infiltration into the ground is the transition from surface water to groundwater. The infiltration rate will depend mainly upon the soil or rock permeability. Infiltrated water may reach groundwater.
Groundwater tends to move slowly, so in some cases, it can take up to thousands of years to return as surface water. Due to the force of gravity, the water returns to the land surface at lower elevation than where it infiltrated.
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The Water Cycle
Percolation
This is the downward movement of water through soil and rock. Percolation occurs beneath the root zone (the depth of soil penetrated by crop roots.)
Ground water percolates through the soil in the same way that water fills a sponge. It moves from space to space along fractures in rock or through sand or gravel. The terms infiltration and percolation are often used interchangeably.
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The Water Cycle
4
Which of the following is necessary for rain drops to form?
Question
A) A low fall speed.
B) A large updraft.
C) Tiny particles of dust, salt or smoke.
D) All of the above.
The Water Cycle
5
Which of the following is the most likely outcome of deforestation?
Question
A) An increase in the amount of evaporation from the soil.
B) A decrease in the amount of evaporation from the soil.
C) A reduction in wind velocity near the soil surface.
D) An increase in the amount of shading.
The Water Cycle
Acid Rain
Unpolluted rain has a slightly acidic pH or 5.6 (7 is neutral and greater than 7 is alkaline). This is because carbon dioxide and water in the air react together to form carbonic acid. Acid rain can have a pH of around 4.
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The Water Cycle
What Causes Acid Rain?
The main causes of acid rain are sulfur dioxide (SO2) and nitrogen oxide gases (NOX). These are mainly produced by electric power stations that rely on burning fossil fuels such as coal.
Road transport and factories also contribute to the acid rain problem. The gases react in the atmosphere to form sulfuric and nitric acid. The rate of these reactions is increased by increasing sunlight.
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SO2 - Other
NOX – Roadtransport
SO2 – Industry
SO2 – Powerstations NOX – Other
NOX –Industry
NOX –Power
stations
The Water Cycle
Wet Deposition
Acid rain is also known as acid deposition or acid precipitation. There are two types of acid deposition – wet and dry.
Wet deposition refers to acidic rain, fog or snow. Sulfur dioxide and nitrogenoxide dissolve very easilyin water and can be transported long distanceswhen they become part of rain water, snow and fog.
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As this acidic water flows over and through the ground, it affects a variety of plants and animals.
Sulfur Dioxide (SO2)
NitrogenOxide (NOX)
SO2 & NOX
Acid snow Acid rain
The Water Cycle
Dry Deposition
Dry deposition refers to acidic gases and particles that are carried by wind. The wind carries these dry particles over buildings, soils, crops and even into the air we breathe.
We could even ingest some of these contaminants when we eat food which has been in contact with polluted dust and gas.
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About half the acidity in the atmosphere falls to earth as dry deposition.
Sulfur Dioxide (SO2)
NitrogenOxide (NOX)
SO2 & NOX
Dry deposition
The Water Cycle
6
What is the pH of acid rain?
Question
A) 4.5
B) 5.6
C) 7.0
D) 14.0
The Water Cycle
Buffering
Normal precipitation - such as rain, sleet, or snow - reacts with alkaline chemicals, or non-acidic materials, that can be found in air, soils, bedrock, lakes, and streams. These reactions usually neutralize natural acids. Neutralizing materials are called buffers since they ‘absorb’ or neutralize some degree of acidity.
The strength of these effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved and the types of fish, trees and other living things that rely on the water.
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The Water Cycle
When does Acid Rain Cause Damage?
If precipitation becomes too acidic due to human contamination or in media with smaller buffer capacities, neutralizing materials may not be able to neutralize all of the acids and the drop in pH can destroy the ecological balance.
Over time, these neutralizing materials can be washed away by acid rain resulting in damage to crops, trees, lakes, rivers and animals.
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The Water Cycle
How Acid Rain Affects Lakes
Lakes can also be damaged by acid rain. Fish die off as their food becomes toxic and this results in a food shortage for birds. Alternatively, the birds die from eating toxic fish and insects.
Acid rain can kill fish even before they are born. When fish eggs come into contact with the acid an entire generation can be killed.
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Fish usually only die when the level of acidity in the lake is high. When the level of acidity is lower, they become sick, suffer stunted growth, or lose their ability to reproduce.
The Water Cycle
Land Plants
Acid rain can also damage and destroy plants.
Some species are more sensitive to acid rain than others. Among the most sensitive are lichens, mosses, fungi, and aquatic plants.
Some plants are directly affected by acid rain since it strips away the waxy protective layer of leaves and causes alterations in the metabolism processes, like photosynthesis.
Lichens Mosses Fungi Aquatic Plants
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The Water Cycle
Land Plants
This makes it very difficult to demonstrate that the real cause of a forest’s death is pollution, since there are different agents other than pollution that actually kill the plants.
However, in cases with highly contaminating concentrations, there are clear symptoms of defoliation and discoloration that can be related to acid contamination.
As result of the alterations caused by acid rain, plants lose leaves and suffer a gradual weakening process, becoming more vulnerable to plagues, diseases and water deficiency.
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The Water Cycle
How Acid Rain Affects Architecture
When sulfur pollutants fall on the surfaces of buildings (especially those made out of sandstone or limestone), they react with the minerals in the stone to form a powdery substance that can be washed away by rain. This powdery substance is called gypsum.
Some living organisms are alsomade of calcium carbonate, such as coral skeletons and the shells of marine organisms. Acid rain destroys these structures in much the same way it damages buildings.
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The Water Cycle
People Under Acid Rain
Acid rain affects humans too.
The toxic materials released into water by acid rain can cause poisonous levels of mercury in the fish we eat.
Acidic drinking water reacts with water pipes dissolving the metal, causing damage to the kidneys and liver.
The effects of acid rain may affect people directly too. High levels of nitrogen oxides in the air obstruct breathing systems, raising the cases of pneumonias and bronchitis.
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The Water Cycle
7
What effect can acid rain have on trees?
Question
A) They can lose their leaves.
B) They can be more susceptible to disease.
C) Their growth can be stunted due to lack of photosynthesis.
D) All of the above.
The Water Cycle
8
Which of the following can be aggravated by acid rain?
Question
A) Bronchitis
B) Liver damage
C) Kidney damage
D) All of the above
The Water Cycle
Summary
After completing this presentation you should be able to:
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Explain the importance of water
Identify the stages of the water cycle
Recognize how certain conditions can affect the water cycle
Identify the causes of acid rain
Describe the impact of acid rain on the environment
