Transcript The Water Cycle

The Water Cycle
Therese Camilleri
St. Michael School Scout Group
Therese Camilleri VSL
St. Michael School Scout Group
Therese Camilleri VSL
St. Michael School Scout Group
The Role of Water for Living
Organisms
Without water, the other nutrient
cycles would not exist in their
present forms and current forms on
earth would not exist.
Water determines the type of
organisms in terrestrial systems.
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The Role of Water for
Living Organisms
The flow of water in an out
of an aquatic ecosystem
affects physical conditions for
organisms by influencing
temperature, salinity, and
availability of nutrients.
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St. Michael School Scout Group
How the Water is Cycled in the
Ecosphere
Main process of the water cycle
Evaporation
Transpiration
Condensation
Precipitation
Infiltration
Percolation
Runoff
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Evaporation
Conversion of water into air vapor
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Evaporation Cont
Water cycle is powered by energy from
the sun and gravity.
Solar energy evaporates water from
oceans, streams, lakes, soil, and
vegetation.
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St. Michael School Scout Group
Evaporation Cont
Percent of water vapor in atm. includes
84% from oceans
16% from land
Amount of water vapor entering the
atmosphere is amount of water returning
to earths surface.
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Transpiration
Evaporate from leaves of water, extracted
from soil by roots, and transported
through the plant.
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Condensation
Conversion of water vapor
into droplets of liquid water.
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Precipitation
Rain, sleet, hail, and snow.
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Water Vapor
Amount of water vapor air can hold
depends on temperature.
Warm air is capable of holding more
water vapor than cold air.
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Humidity
Absolute Humidity
Amount of water vapor found in a
certain mass of air.
Usually expressed as grams of water
per kilogram of air.
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Humidity Cont
Relative Humidity
The amount of water vapor in a
certain mass of air.
Expressed as a percentage of the
maximum amount it could hold at
that temperature.
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Example of Relative Humidity
Example: Relative humidity of
60% at 27 degrees Celsius means
that each kg of air contains 60%
of the maximum amount of water
vapor it could hold at that
temperature.
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St. Michael School Scout Group
Infiltration
The movement of water
into soil
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Percolation
Downward flow of water
through soil and permeable rock
formations to groundwater
storage areas called aquifers.
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Runoff
Downslope surface
movement back to the sea to
resume the cycle.
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Water Vapor to
Precipitation
Winds and air masses transport
water vapor over earth’s surfaces.
This water vapor condenses into tiny
droplets that form clouds as a result
of falling temperatures.
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Water Vapor to Precipitation Cont
Precipitation will then occur
only if the air has
condensation
For condensation to occur
the temperature must be at
dew point.
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St. Michael School Scout Group
Precipitation to Runoff
77% of precipitation falls to the sea,
the rest falls to land.
Some of the precipitation becomes
locked in glaciers
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Precipitation to Runoff cont
Most of the precipitation becomes
surface runoff flowing into streams and
lakes which eventually carry water
back to the oceans where it starts all
over again.
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Surface Runoff
Replenishes streams and lakes.
Causes soil erosion.
Water dissolves many nutrient
compounds which makes it a
major medium for transporting
nutrients.
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St. Michael School Scout Group
Percolation
Some of the water returning to the
land soaks into (infiltrates) the soil
and porous rock and then percolates
downward, dissolving minerals from
porous rocks on the way.
This water is stored as groundwater
in the pores and cracks of rocks.
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St. Michael School Scout Group
Percolation Cont
Where the pores are joined, a network of water
to flow through the porous rock.
Aquifer: water-laden rock
Water table: level of the earth’s land crust to
which it is filled.
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Percolation Cont
This underground water flows slowly
downhill through rock pores and
seeps out into streams and lakes or
comes out in springs.
 This water evaporates or reaches
the sea to continue the cycle.
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St. Michael School Scout Group
Humans Influence the Water
Cycle
Humans intervene in the water cycle
in three main ways:
 We withdraw large quantities of fresh
water.
We clear vegetation from land.
We modify water quality
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St. Michael School Scout Group
Humans Influence the Water
Cycle cont
We withdraw large quantities
of fresh water from streams,
lakes, and underground
sources.
This has led to depletion or
intrusion of ocean salt water into
underground water supplies
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St. Michael School Scout Group
Humans Influence the Water
Cycle cont
We clear vegetation from land for
agriculture, mining, road and building
construction and other activities.
This increases runoff and reduces
infiltration that recharges groundwater
supplies.
Increases the risk of flooding and
accelerates soil erosion and landslides.
Therese Camilleri VSL
St. Michael School Scout Group
Therese Camilleri VSL
St. Michael School Scout Group
Bibliography
 http://www.learner.org/exhibits/weather/watercycle.html
 http://www.epa.gov/OGWDW/kids/cycle.html
 http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Wate
rcycle.shtml
 http://www.sensorland.com/HowPage037.html
 http://www.ph-measurement.co.uk/home.htm
 http://sjr.state.fl.us/programs/outreach/conservation/landscape/images/phb
arp6.jpg
 http://old.jccc.net/~pdecell/chemistry/phscale.html
 http://www.epa.gov/airmarkets/acidrain/ph.html
 http://www.css.cornell.edu/faculty/hmv1/watrshed/CDIB354.gif
 http://www.nwd-wc.usace.army.mil/nwp/gifs/pics/transpiration.gif
 http://www.dutchstandard.com/droplet.gif
 Miller, G. Tyler Jr. Living in the Environment. Pacific Grove;
Brooks/Cole Publishing Company, 2000.
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St. Michael School Scout Group