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
Water Budget of a Leaf Input from stem Output - transpiration Use - water is used in the plant for photosynthesis and movement of important elements
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 York http://www.dec.ny.gov/pubs/42978.html
Several of the worlds 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 Canyon Hoover 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 couldnt 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
Humans even alter precipitation! Humans affect fog water inputs Air pollution may affect rainfall amounts Water quality (acid rain)
Moving water across watersheds Water doesnt 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 3 rd 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