The Water Cycle The Earth has a limited amount of water The water on Earth moves from the Earth to the sky and back to the Earth in a cycle. This is called the water cycle

Steps of the Water Cycle 1. Evaporation 2. Condensation 3. Precipitation 4. Collection

The Cause of Phase Changes in Water Cycle Kinetic Theory: All atoms and molecules move When energy (thermal) is added, atoms move faster Atoms and Molecules are naturally attracted to one another They want to form bonds However, when enough energy is added to these atoms, the bonds they form aren’t strong enough to hold them together When this happens, the atoms undergo a phase change

Phase Changes Solid= little energy added, molecules stay together Liquid= more energy added, molecules bond and break bonds Gas=too much energy, molecules can’t keep bonds

1) Evaporation Evaporation: process of turning liquid into gas. Water (H2O) : thermal energy added to liquid water in lakes, rivers, oceans by radiation from sun and turns into a gas (water vapor) In water cycle, the step where H2O enters the atmosphere

Remember!!! When a gas is heated, the molecules will speed up As they speed up, they occupy more space and thus become lighter and unable to form bonds Lighter (hotter) gases tend to rise “Hot Air Rises” Principle

2) Condensation Condensation: process of turning gas into liquid Thermal energy is removed and water molecules begin forming bonds Causes formation of clouds

Remember!!! When a gas is cooled, the molecules will slow down As they slow down, they occupy less space and thus become heavier and able to form bonds Heavier (colder) gas tend to sink “Hot Air Rises” Principle

How to Clouds Form? The amount of water vapor in the atmosphere is called relative humidity. As temperature and pressure go down, molecules lose heat energy, they slow down and go from gas (vapor) to liquid When this occurs, the water vapor has reached its Dew Point: temperature at which the water vapor begins to form liquid water In the atmosphere, the little droplets of water form clouds by sticking to particles in the air called condensation nuclei (ex. dust, smoke, salt) What happens if you increase temperature and pressure?

3) Precipitation Precipitation: tiny water droplets combine to form bigger droplets that the atmosphere can’t hold, so the water falls Examples: rain, snow, sleet, and hail

4) Collection/Runoff When water falls back to earth as precipitation, it may fall back in the oceans, lakes or rivers or it may end up on the land surface

Quiz Time! During which water cycle step does H2O enter the atmosphere? a) Evaporation b) Condensation c) Precipitation d) Transportation How does H2O return to Earth’s surface from the atmosphere?

Quiz Time! Which step of the water cycle is represented by letter B? a) Evaporation b) Condensation c) Precipitation d) Transportation

Erosion Erosion: Loss of topsoil Agents: Water (rivers, floods, glaciers) Wind Gravity Effects of Erosion: Loss of farmland (fertile soil) Destruction of property (landslides) Negative impact on wildlife (fish, plants) Rate of erosion: how quickly erosion occurs

Factors Affecting Rate of Erosion Soil erosion increases with: Smaller soil particles that are loosely compacted Sand vs. Soil Areas with less vegetation Roots hold onto soil preventing erosion Clear cutting, tree thinning, or fires increase erosion Areas with steep slopes (Gravity)

What area has the least erosion? Areas that are flat with heavy vegetation experience little erosion

Types of Water Surface Water Ground Water Local Water

Surface Water Water that sits or flows above the earth Including lakes, oceans, rivers, and streams.

Ground Water Water that flows or seeps downward and accumulates in the ground Supplies springs and wells. The point where water begins to collect is called the water table

Local Water Rural (country) areas have a shortage due to falling water table Phoenix & Tucson Currently: water is abundant due to CAP Future: Water shortages due to growth

Water Issues How Much Water Is There?

3 Factors that Affect Water Quantity 1) Population Growth More people create greater demands for water 2) Precipitation Levels 3) Drought “Water is the true wealth in a dry land" --Wallace Stegner Water resources become less dependable Water bodies become depleted Reservoirs are low

3 Factors that Affect Water Quality 1) Acid Rain 2) Agriculture 3) Factories and Chemical Pollutants

1) Acid Rain When fossil fuels are burned, sulfur and nitrogen gases are released into the air These pollutants chemically combine with water forming sulfuric acid and nitric acids

Effects of Acid Rain Damages Plants, Animals, and Buildings

2) Agriculture Crops and Cows Chemical fertilizers and animal manure runs off and is washed into ponds, rivers, & groundwater Crops: Fertilizers Rich in nutrients (Nitrogen, Phosphorus, Potassium) which increase algae growth when entering the water supply When algae dies, bacteria decompose dead material and use up oxygen in water causing other organisms (fish, plant life) to die

2) Agriculture Cows: Manure Manure (poop) carries bacteria into the water supply which multiply and use up the oxygen in the water

3) Factories and Chemical Pollutants Factories: Metals from mining & gasoline refineries Homes: Detergents, cleaning products Highway Runoff: fuels, oil

Water Management: Dams and Reservoirs Provide water storage for run-off Dams & reservoirs along Salt and Verde Rivers supply irrigation & drinking water for metro Phoenix area Disrupts river system

Tapping Groundwater Using ground water drops the water table This leads to water shortages This also leads to contaminations from pesticides and fertilizers

Ground Water Contamination

Treated Wastewater Treated wastewater - sewage, industrial wastewater, or other effluent that is treated to a level necessary for its intended usage. Used to – Irrigate golf courses, lawns Cool power plants Irrigate crops