Teaching the “Broken” Water
Cycle: A Reality Check
Cornelia Harris & Kim Notin
harrisc@caryinstitute.org ; notink@caryinstitute.org
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:
stomata slides &
bags on trees
Output - transpiration
Water Budget
of a Leaf
Input from stem
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:
1
Bag #
2
Amount of
water (mL)
3
Area of 2 leaves
(cm2)
calculate
area with graph
paper
Is your hypothesis correct? Explain.
4
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:
infiltration rates
Cover type 1:
Where does the rain go?
Prediction
Cover type 2:
Where does the rain go?
Prediction
Where does the
rain in your
schoolyard go?
Result
Result
Cover type 3:
Where does the rain go?
Prediction
Result
Most of the water that falls 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!
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.
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: _______________
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
Grass/trees/other plants
What happened to the water? Explain where the water went.
Sidewalks/streets/driveways
Houses/other buildings
Other: _______________
Sidewalks/driveways/streets: _______________
Houses/other buildings: _________________
Other: ________________
Based on the information you collected, where does most of the water in your neighborhood go when it rains?
____________________________________
 Permeable
 Impermeable
“Runoff Worksheet”
“Runoff Worksheet”
Increased runoff
• ~1
million
the
How
manydams
damsaround
exist around
world
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
Lack of sediment
accumulation has severe
consequences for
wetlands and the
mainland
After Katrina
www.edf.org
Wetlands around New Orleans, Louisiana
Before Katrina
NASA
Dams often make
grotesque patterns
of water flow
Dams in
the
Hudson
River
Watershed
Dams of New York
http://www.dec.ny.gov/pubs/42978.html
Source: Swaney et.al 2006
Normal Water Flow Has Been Obstructed by Dams
Several of the world’s great rivers no
longer reach the sea
Lake Powell
Glen Canyon Dam
•Nile (6X as much flow as
the Hudson)
•Colorado (0.9X)
•Murray-Darling (0.7X)
•Yellow (2.3X)
•Ganges-Brahmaputra
(59X)
Grand Canyon
Hoover Dam
Lake Mead
Gulf of
California
http://visibleearth.nasa.gov
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 sixteenounce 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
Yann Arthus-Bertrand
Source: www.impactlab.com
Source: www.4.bp.blogspot.com
The forgotten piece…
1000
All species
800
30000
20000
2
2
600
400
10000
200
0
0
5000
Vertebrates
600
4000
500
3000
400
300
2000
200
1000
100
0
0
marine
land
freshwater
Imperiled species/million km
although fresh waters
cover <1% of the
Earth’s surface, they
contain 10% of known
animal species, and
1/3 of vertebrate
species
40000
Described species/million km
Fresh waters are
hotspots of
diversity (bars)
and
endangerment
(lines)
Similar to amphibians, invertebrates, mussels…
www.feow.org
Freshwater organisms are more imperiled
than their terrestrial counterparts
Extinct (GX, GH)
Critically imperiled (G1)
Imperiled (G2)
Vulnerable (G3)
Secure (G4, G5)
Birds and mammals
(n=1182)
Freshwater fish
(n=798)
Freshwater insects
(n=1046)
Crayfish and mussels
(n=609)
Source:
http://jrscience.wcp.muohio.edu/western/fishid/Orangethroat__amp__Rainbo.html
Source: www.iz.carnegiemnh.org