Wheres the water now: an introduction to the hydrologic cycle

1
Wheres the water now? an introduction to the
hydrologic cycle

• Critical concepts for today
• Open vs closed system
• Flux
• Residence time

2
gt4.5 BYA The sun and planets of our solar system
condensed from clouds of gasses and materials
3
gt4.5 BYA Planetesimals formed as lumps of gas
and dust in the clouds, giving rise to planets
4
Earths early atmosphere was formed by outgassing
of H2O, CO, CH4, NH3, N2, HCl, S2 The ability of
a planet to hold onto its gases depends upon
gravity. To escape Earths gravity, a molecule
(like NASAs rockets, must have an outward
velocity of 25,000 mile/hr (11 km/s)
5
Water Question Did the H20 come entirely from
condensation of vapor? Or from bombardments of
ice-bearing plantesimals?
6
Open vs Closed Systems

• System a group of interrelated and interacting
  objects and phenomena.
• Open system allows both matter and energy to
  flow across its boundaries
• Closed system can exchange energy but not matter
  across its boundaries
• Isolated system does not allow either energy or
  matter to cross its boundaries

Image From http//earthobservatory.nasa.gov/Newsr
oom/NewImages/images.php3?img_id4231
7
From http//earthobservatory.nasa.gov/Newsroom/Ne
wImages/images.php3?img_id4231
From http//earthobservatory.nasa.gov/Newsroom/Ne
wImages/images.php3?img_id4231
8
Hydrologic Cycle the interesting story of how
water gets around Processes
Precipitation The change of atmospheric water
vapor to liquid (rain) or solid (snow hail)
Evaporation The exchange of water from a liquid
to a vapor
Runoff The total amount of water flowing into a
stream, or other body of water (Surface Water)
Infiltration The movement of liquid water
downward from the land surface into and through
the soil and rock. (Ground water)
Transpiration The release of water into the
atmosphere by plant and animal cells
Image From Miller, Living in the Environment
9
Hydrologic Cycle the interesting story of how
water gets around

• A tale that includes
• Reservoirs (Stocks)
• Amount of water in each reservoir
• Residence Time
• How much water gets moved between each
  reservoir/unit time

Image from www.nps.gov/yose/ news/graphics/
10
Residence Time
Total Amount Volume
Residence Time
Amount Added (or lost) / Time
This is one of THE MOST important measurements
and concepts in Environmental Science
11
Average Residence Time of Undergraduate Student _at_
Wesleyan

• Total number of students (reservoir or stock)
• Students added (or leaving) each year (flux)

2700 (students) / 675 (students enter (and
leave) each year)
4 years Average residence time
12
Water Reservoirs (Stocks)
What will be the major reservoirs in this group?
13
Calculating Residence Time

• How much is in a reservoir? (Note absolute
  numbers will vary in different books.)

What is the rate of inflow or outflow flux What
do you think the residence times will be in these
different reservoirs?
14
Water Cycle -Botkins Keller
Numbers are in thousand cubic kilometers/
year Figure from Botkins and Keller
15
What is the residence time of water in the Ocean?
What is the residence time of water in the ocean?

• What do you need to know?
• Vol of ocean
• Vol of ocean 1,321 x 106 km3
• Amount of water entering (or leaving) the
  ocean/year 505 x 103 km3/yr
• 1,321 x 106 km3 / 505 x 103 km3/yr 2.6 x 103
  yr (2,600 yr )
• 2.6 x 103 yr average residence time of water
  in the ocean!

16
Youre turn

• Calculate the residence time of water
• In the atmosphere
• On continents

From http//www.units.muohio.edu/dragonfly/com/wo
lfpup.jpg
17
Calculating Residence Time
Numbers in figure are in thousand cubic
kilometers/ year (Figure from Botkins and Keller)
18
Other examples of residence time?
19
Residence Time on an International Scale An
Example

• CFCs in the atmosphere
• Residence time of 80 years
• Antarctic ozone hole recognized 1985
• Montreal protocol signed in 1987
• Reduction of global CFC emissions to 50 of 1986
  emissions
• Most industrial countries stopped production by
  1995
• Estimates are that stratospheric ozone levels
  will return to pre-1980 levels by 2050