teaching the broken water cycle: a reality check cornelia harris & kim notin...

Teaching the “Broken” Water Cycle: A Reality Check

Cornelia Harris & Kim Notinharrisc@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: 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