WATER CYCLE PROCESSES

Transcription

1 WATER CYCLE PROCESSES OBJECTIVES Identify when heat energy or gravitational energy is gained or lost during water cycle processes Assess how heat energy affects water s state of matter Explain how the force of gravity influences the movement of water TOPICS Water cycle Energy TEKS ALIGNMENT Grade 2 Science: 1A, 2A, 2B, 2C, 2D, 2E, 2F, 4A, 5A, 5B, 6A, 7B, 8C Grade 3 Science: 1A, 2A, 2F, 3A, 3C, 4A, 5B, 5C, 6A, 6C, 8B Grade 4 Science: 1A, 2A, 2B, 2C, 2D, 2F, 4A, 5A, 5B, 6A, 6D, 7C, 8B Grade 5 Science: 1A, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 3A, 4A, 5A, 5B, 6A, 8B BACKGROUND MATERIAL Individual water molecules are constantly moving from one water reservoir to another in a system known as the water cycle. The water cycle is not literally a circle, even though it is often shown as a circle in pictures. A cycle is a group of events that repeat themselves, and that is what the processes of the water cycle do. In the water cycle, water is neither created nor destroyed, it just moves to different reservoirs through a series of processes. There are nine different processes in the water cycle: evaporation, condensation, precipitation, runoff, infiltration, percolation, transpiration, freezing and melting. Water is unique because it is the only substance on earth that naturally occurs in three states of matter: solid, liquid and gas. Ice is the solid form of water. Water in lakes, rivers and streams is a liquid. Water vapor in the atmosphere is a gas. Earth s water changes between these three states. The state of matter that water exists in at any particular time depends on heat energy from the sun. Water gains heat energy as it melts, evaporates or transpires, and it loses heat energy as it freezes or condenses.

2 Gravitational energy is a type of potential energy that a body possesses due to the force of gravity. Water gains gravitational energy as it rises into the atmosphere and loses gravitational energy as it falls from the sky, flows downhill or infiltrates into the soil. Locally, humans can have profound effects on water cycle processes. Prior to large-scale settlement in the San Antonio River Basin, most of the land was open grassland, with areas of brush and trees along rivers and streams. Because of overgrazing by livestock and the suppression of wildfires in rural areas, much of the natural grassland has disappeared and has been replaced with trees and brush especially mesquite. Mesquite and other trees are able to withdraw hundreds of gallons of groundwater daily through transpiration. In urban areas, increases in impervious cover have reduced infiltration and increased run-off. Overgrazing by livestock and the effects of urbanization have reduced the infiltration capacity of soils, causing less infiltration into aquifers and more surface runoff and soil erosion. KEY TERMS Basin is a depression in the earth s surface. A body of water, such as a lake or river is often located in the bottom of the basin. Condensation is the water water vapor becomes liquid water. Water vapor loses heat energy when it condenses. Evaporation is the water liquid water becomes water vapor. Liquid water gains heat energy when it evaporates. Freezing is the water cycle process by which liquid water becomes solid ice. Liquid water loses heat energy when it freezes. Gravitational Energy is stored energy that an object has because of its position. Gravitational energy is due to the force of gravity, and it is caused by the attraction of all other objects to the mass of the Earth. Heat Energy is the energy that an object has because of the motion of its atoms and molecules. The more an object s atoms and molecules move, the more heat energy it has. Impervious Cover is any type of material on the ground surface that prevents water from infiltrating. Examples are asphalt, concrete, brick or metal. Infiltration is the water liquid water enters the soil due to the force of gravity. Water loses gravitational energy when it infiltrates into the soil. Melting is the water cycle process by which solid ice becomes liquid water. Water gains heat energy when it melts. Percolation is the water liquid water flows through the soil due to the force of gravity. Water loses gravitational energy when it percolates through the soil.

3 Precipitation is the water water in the atmosphere falls back to Earth as rain, snow, sleet or hail due to the force of gravity. Water loses gravitational energy when it falls from the atmosphere. Runoff is the water cycle process by which water flows over the soil surface due to the force of gravity. Water loses gravitational energy when it runs off the soil surface. Transpiration is the water plants remove water from the soil through their roots and transfer it into the atmosphere through tiny openings in their leaf surfaces. Plants lose heat energy and keep themselves cool by transpiration. Water gains heat energy during transpiration. Water Table is the top of the water surface of groundwater that is at atmospheric pressure; the boundary, underground between the area that is saturated with water and the area above it that is unsaturated. PROCEDURES A. Start by asking the students to reflect on what they know about the water cycle. What do they know about the major processes in the water cycle: evaporation, condensation, precipitation, infiltration, runoff, percolation and transpiration? For reference, you can use the image on Student Sheet 1. B. You can proceed with the following activities in any number of ways. If the class is small enough, you might do each activity as one demonstration for the class. Alternatively, you could set up stations around the classroom and ask the students to make observations independently before coming back together as a group to discuss them. MATERIALS 1. Evaporation, Condensation, and Melting **For younger groups, this should be done as a demonstration regardless of class size** a. Fill the heat-tolerant glass container half full of water and put it on top of the hot plate. b. Lay the wire mesh over the top of the glass container. c. Put the hot plate to the highest setting. d. Fill the plastic cup with ice, and place it on top of the wire mesh. Two ring stands One 9 oz. or larger plastic cup One hot plate One heat-tolerant glass container Wire mesh or a toaster rack Ice One stalk of celery with the leaves still attached One plastic sandwich bag One water glass Three plastic shoe boxes Two heat lamps (clamp on light and reflector with 100 W bulb) Some garden soil Student worksheet e. Observe what happens to the water inside of the glass container that is sitting on the hot plate. f. Observe what happens to the side of the plastic cup. g. Observe what happens to the ice inside the plastic cup.

4 2. Transpiration **Set-up should be completed the day before for best results** a. Fill the water glass three-fourths full of water. b. Place the celery in the glass of water, put a sandwich bag over the top part of the celery stalk, and fasten the bag around the stem by zipping it or using a twist tie. c. Clip the lamp to a ring stand, and lower the lamp so that it is about 6 inches above the celery. Make sure that the plastic bag does not touch the light bulb! Then turn on the heat lamp. d. Observe what happens in the bag over time. 3. Precipitation, Infiltration and Surface Runoff a. Place gardening soil into a plastic shoebox until the shoebox is half full. b. Slowly pour water onto the soil. c. Observe what happens to the water as you pour it on the soil and note where it moves. d. Continue to add water to the soil, until the soil cannot hold any more water. e. Observe what happens to the water and where it goes in relation to the soil. 4. Precipitation, Infiltration and Percolation a. Fill a plastic shoebox to within an inch of the rim with gardening soil. b. Dig a hole in the soil an inch or two deep. c. Slowly pour water onto the soil, but do not pour it directly in the hole. d. Continue to pour water in the soil until the soil is completely saturated with water. e. Observe what happens to the hole over time. 5. Precipitation, Infiltration and Evaporation a. Fill a plastic shoebox to within an inch or two of the rim with gardening soil or sand. b. Clip the heat lamp to a ring stand, such that the top of the lamp is about 6 inches above the shoebox. c. Turn on the lamp. d. Pour water into the soil until it becomes saturated and cannot hold any more water. e. Over time, observe what happens to the water on the soil surface in the shoebox. C. When the students are finished completing all five activities, they should complete the table found on Student Sheet 2 with their observations and descriptions of the changes in energy during each process. GUIDING QUESTIONS How were the models good representations of what happens in the real world? How is the real world different from what you saw in the models? Does water gain or lose energy when it condenses? What type of energy does it gain or lose? Does water gain or lose energy when it melts? What type of energy does it gain or lose? How much water do you think hundreds of mesquite trees can transfer into the atmosphere by the process of transpiration, and what effect might this process have on groundwater? Does water gain or lose energy when precipitation occurs? What type of energy does it gain or lose?

5 Around your home or school, where does water infiltrate into the ground, and where does it not infiltrate into the ground? How does the type of surface on the ground (e.g. asphalt vs. trees) affect infiltration? What happens to water when it cannot soak into the ground, or when it can no longer soak into the soil? When water is added to soil, you learned that it percolates through the soil via gravity and can be distributed to other places in the ground. What do you think happens to water when people pump it out of the ground? What do you think is more protected from evaporation, water in the ground or water in a lake or swimming pool? EVALUATION Have the students draw and label a diagram of the water cycle processes that take place in the San Antonio River Basin, explain whether each process gains or loses energy, and explain what type of energy or force is involved in moving water during the process.

6 STUDENT SHEET 1

7 STUDENT SHEET 2

8 REFERENCES Black, P. E Watershed Hydrology, Second Edition. Ann Arbor Press, Chelsea, MI. 449pp. Schlesinger, W. H Biogeochemistry: An Analysis of Global Change, Second Edition. Academic Press, San Diego, CA. 588pp. U.S. Geological Survey Groundwater Atlas of the United States: Oklahoma, Texas. U.S.G.S Publication HA 730-E. Wetzel, R. G Limnology, Second Edition. Saunders College Publishing, Orlando, FL. 857pp.