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Teaching the “Broken” Water Cycle: A Reality Check
Cornelia Harris & Kim [email protected] ; [email protected]
Research & Education based on Ecosystem Ecology
The water cycle in textbooks
Does this help students analyze their water cycle?
How do you think the local water cycle has been altered (or “broken”)?
We have changed nearly all of the links in the water cycle
Why are forested streamflows lower in the summer?
Changes in evaporation and transpiration
• Transpiration is often overlooked in importance
• About half of rain and snow that falls on the Hudson Valley is evaporated or transpired before it reaches the sea
• A mature tree transpires ~50 gallons of water a day in the summer
Investigation: Investigation: stomata slides & stomata slides & bags on treesbags on trees
Water Budget of a Leaf
Input from stem
Output - transpiration
Use - water is used in the plant for photosynthesis and movement of important elements
Question: I wonder…. Hypothesis (statement that I can test): Results: Date bags put on branches: Date bags collected:
Is your hypothesis correct? Explain.
1 2 3 4
Bag # Amount of water (mL)
Area of 2 leaves (cm2) calculate area with graph paper
Amount evaporated per square centimeter (mL/cm2) divide column 2 by column 3
Changes in evaporation and transpiration
• Modifying vegetation can have huge effects on streamflow
Changes in evaporation and transpiration
• Half of the 800 trillion gallons of water used each year in irrigation is “lost” to the air
Deforestation & Transpiration
2000: Rondonia region of western Brazil, images from NASA
Deforestation & Transpiration
2008: Rondonia region of western Brazil, images from NASA
Borneo
UNEP
Reduced Infiltration
• Impermeable surfaces have large impact
• Other changes to the land surface affect infiltration (plowing, loss of leaf litter, etc.)
Reduced Infiltration
Baltimore Ecosystem Study
Water quality is also affected by decreased infiltration
Investigation: Investigation: infiltration ratesinfiltration rates
Where does the rain in your
schoolyard go?
Cover type 1: Where does the rain go?
Prediction Result
Cover type 2: Where does the rain go?
Prediction Result
Cover type 3: Where does the rain go?
Prediction Result
Most of the water that f alls on my schoolyard
goes_______________________________.
Or in your neighborhood?Name ______________________ Date __________
Mapping Your Neighborhood
What are the surfaces like in your neighborhood? Use this activity to find out!
Materials: pen or pencil, colored pencils/crayons, measuring cup, water
1. What is the difference between a permeable and an impermeable surface? __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
2. Describe your neighborhood. Does it have lots of grass or trees? Houses? Apartments? __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
3. Are there more permeable or impermeable surfaces in your neighborhood? __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
4. When it rains, where does the water go? ____________________________________________________________________________________________________________________________________________________________
Try this: Go outside and walk around your neighborhood. You don’t have to map the whole neighborhood, but try to do one city block if you can. Look at all the features: trees, sidewalks, houses, streets, etc. Look for gutters or rain grates on the side of the street.
Try to decide how much of your neighborhood is covered (in percent) by each of the following:
Grass/trees/other plants: _______________
Sidewalks/driveways/streets: _______________
Houses/other buildings: _________________
Other: ________________
Create a map of your neighborhood. Label your drawing carefully and use colored pencils/crayons to show different types of surface cover. For example, you can use green for all the grass and trees, brown for the houses, and black for the sidewalks and streets.
Finally, test the different surface types in your neighborhood. Get a measuring cup and fill it with one cup of water. Pour the water on the different surfaces, one cup per surface. Fill out the chart below with your results!
Surface What happened to the water? Explain where the water went. Grass/trees/other plants
Sidewalks/streets/driveways
Houses/other buildings
Other: _______________
Based on the information you collected, where does most of the water in your neighborhood go when it rains? ____________________________________
Impermeable
Permeable
“Runoff Worksheet”
“Runoff Worksheet”
Increased runoff
• ~1 million dams around the world
• Dams double the time it takes for stream water to reach the sea
• Dams hold back ¼ of the sediment from reaching the sea
How many dams exist around the world?
Lack of sediment accumulation has severe
consequences for wetlands and the
mainland
Wetlands around New Orleans, Louisiana
After Katrina
Before Katrina NASA
www.edf.org
Dams often make grotesque patterns
of water flow
Source: Swaney et.al 2006
Dams in the Hudson River Watershed
Dams of New Yorkhttp://www.dec.ny.gov/pubs/42978.html
Normal Water Flow Has Been Obstructed by Dams
Several of the world’s great rivers no longer reach the sea
•Nile (6X as much flow as the Hudson)•Colorado (0.9X)•Murray-Darling (0.7X)•Yellow (2.3X)•Ganges-Brahmaputra (59X)
http://visibleearth.nasa.gov
Lake Powell
Grand CanyonHoover Dam
Glen Canyon Dam
Lake Mead
Gulf of California
Other ecological effects of dams• Block migratory species• May release water that is low
in temperature and oxygen• Alter habitat up- and
downstream of the dam
Agricultural Water Use
Irrigation is the major consumptive use of water in most parts of the world = 80% of all water consumed in North America
Cost generally low since withdrawals are subsidized
Groundwater depletion
•Happening around the world in arid and semiarid areas•Declines can be rapid and dramatic•Dries up springs and small streams
Ogallala Aquifer
• Before 1940s, water couldn’t be accessed if it was below 70-80 feet
• Technology allowed wells to extract water from more then 3,000 feet
• By 1990, sixteen million acres of the high plains were irrigated with water from Ogallala
• Some areas: more than 150 foot declines www.unwater.org
3rd UN World Water Development Report, 2009
Humans even alter precipitation!
• Humans affect fog water inputs
• Air pollution may affect rainfall amounts
• Water quality (“acid rain”)
Moving water across watersheds
• Water doesn’t cross watershed boundaries in a textbook, but it does in the real world– New York City (390 billion
gallons/yr)– Chicago (600 billion gallons/yr)– Common for irrigation and
cities globally• This translocated water can
move species around
Moving water across watersheds in bottles
• 1978: 415 million gallons• 2001: 5.4 billion gallons (43 billion sixteen-
ounce bottles)... An increase of 1300%
Water ‘Footprint’
3rd UN World Water Development Report, 2009
Opportunities to teach the real water cycle
• Humans materially affect the water cycle• You are connected to the water cycle (and affect
it)– Where does your drinking water come from?– Where does your sewage go?– How do local activities (even on the school grounds)
affect the water cycle?– Are there concerns with how the water cycle is
treated locally?– If so, how could the community do better?
Conclusions from these lessons
• The cycle is a “messy web” and humans have large effects on all parts of the water cycle.
• This is just one example of how human activities (partially) control the character of the global ecosystem
• We need to exercise responsibility with this control
• Fresh waters contain remarkable biodiversity• That biodiversity is badly endangered
Resources
http://water.usgs.gov/data/
Familiar reasons “to care” about water
Source: www.4.bp.blogspot.com Source: www.impactlab.com
Yann Arthus-Bertrand
The forgotten piece…
Fresh waters are hotspots of
diversity (bars) and
endangerment (lines)
although fresh waters cover <1% of the
Earth’s surface, they contain 10% of known
animal species, and 1/3 of vertebrate
species
Des
crib
ed s
peci
es/m
illio
n km
20
10000
20000
30000
40000
Impe
riled
spe
cies
/mill
ion
km2
0
200
400
600
800
1000All species
marine land freshwater0
1000
2000
3000
4000
5000
0
100
200
300
400
500
600Vertebrates
www.feow.org Similar to amphibians, invertebrates, mussels…
Freshwater organisms are more imperiled than their terrestrial counterparts
Birds and mammals(n=1182)
Extinct (GX, GH) Critically imperiled (G1)Imperiled (G2)Vulnerable (G3)Secure (G4, G5)
Freshwater fish(n=798)
Freshwater insects(n=1046)
Crayfish and mussels(n=609)
Source: http://jrscience.wcp.muohio.edu/western/fishid/Orange-throat__amp__Rainbo.html
Source: www.iz.carnegiemnh.org
