Therese Camilleri St. Michael School Scout Group The Water Cycle.

Therese CamilleriSt. Michael School Scout Group

The Water Cycle

Therese Camilleri VSLSt. 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.


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.


How the Water is Cycled in the Ecosphere

Main process of the water cycleEvaporationTranspirationCondensationPrecipitationInfiltrationPercolationRunoff


Evaporation

Conversion of water into air vapor


Evaporation Cont

Water cycle is powered by energy from the sun and gravity.

Solar energy evaporates water from oceans, streams, lakes, soil, and vegetation.


Evaporation Cont

Percent of water vapor in atm. includes84% from oceans16% from land

Amount of water vapor entering the atmosphere is amount of water returning to earths surface.


Transpiration

Evaporate from leaves of water, extracted from soil by roots, and transported through the plant.


CondensationConversion of water vapor

into droplets of liquid water.


Precipitation

Rain, sleet, hail, and snow.


Water VaporAmount of water vapor air can hold

depends on temperature.Warm air is capable of holding more

water vapor than cold air.


Humidity

Absolute HumidityAmount of water vapor found in a

certain mass of air.Usually expressed as grams of water

per kilogram of air.


Humidity Cont

Relative HumidityThe amount of water vapor in a

certain mass of air.Expressed as a percentage of the

maximum amount it could hold at that temperature.


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.


InfiltrationThe movement of water

into soil


PercolationDownward flow of water

through soil and permeable rock formations to groundwater storage areas called aquifers.


RunoffDownslope surface

movement back to the sea to resume the cycle.


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.


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.


Precipitation to Runoff77% of precipitation falls to the sea,

the rest falls to land.Some of the precipitation becomes

locked in glaciers


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.


Surface RunoffReplenishes streams and lakes.Causes soil erosion.Water dissolves many nutrient

compounds which makes it a major medium for transporting nutrients.


PercolationSome 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.


Percolation ContWhere the pores are joined, a network of water

to flow through the porous rock.Aquifer: water-laden rockWater table: level of the earth’s land crust to

which it is filled.


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.


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


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


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.



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/Watercycle.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/

phbarp6.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.

Therese Camilleri St. Michael School Scout Group The Water Cycle.

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