Water Cycle

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Transcript Water Cycle

Water Cycle
Water Quality
About the Hydrologic Cycle
• Hydrology is the study of movements and
characteristics of water.
• The hydrologic cycle has a profound effect upon
climate prediction.
• Water is vital for life so we must understand
where to find water and how water supplies cycle
through the Earth.
W h e r e ’s t h e W a t e r ?
FIGURE 11.2 The distribution of water on Earth. [Data from J. P. Peixoto and M. Ali Kettani, “The Control
of the Water Cycle.” Scientific American (April 1973): 46; E. K. Berner and R. A. Berner, Global
Environment. Upper Saddle River, N.J.: Prentice Hall, 1996, pp. 2–4.]
The Water Cycle
Flows and Reservoirs
• Precipitation: water vapor condenses into tiny drops
that form clouds, eventually fall as rain or snow
• Infiltration: when precipitation soaks into the ground
through particles of soil or cracks
• Runoff: precipitation that doesn’t infiltrate moves over
the land surface, eventually collecting in streams and
• Evaporation/Transpiration: liquid water transforming
into gaseous water (water vapor) from surface water
(evaporation) or plants (transpiration)
• Sublimation: solid water (ice) transforming directly
into gaseous water (without becoming liquid)
Water Quality
• We will be going on a field trip to test water
• What is ‘Clean’ water?
• Why is water quality important?
• What impacts water quality?
Water Quality Tests
Dissolved Oxygen (DO)
Biochemical Oxygen Demand (BOD)
Total Dissolved Solids (TDS) and Salinity
Total Coliform Bacteria
• Water temperature changes much more
slowly than air temperature.
• How would water body size affect
temperature? How about vegetation near the
water? How about flowing vs. standing water?
• Why do we care about temperature?
– Warm water holds less oxygen, but produces
conditions that require more oxygen.
• A relative measure of water’s alkalinity/acidity.
• Chemically a measure of the number of
hydrogen ions.
• pH scale is logarithmic, so substances at the
far ends are extremely acidic or alkaline.
• Natural factors that influence pH
– Decomposing organic materials release carbon
dioxide, creating carbonic acid.
• Human factors that influence pH
– Releases of sulfur dioxide, nitrogen oxides and
carbon dioxide all can form acid rain.
• Why should we care about pH? How does it
influence water quality?
Dissolved Oxygen (DO)
• Water holds a reasonably large amount of
dissolved oxygen, which is essential for life.
• Dissolved oxygen is influenced by salinity,
agitation and turbulence, temperature,
minerals, plant life, and organic wastes.
– How do you think these factors influence DO?
Biochemical Oxygen Demand (BOD)
• Decomposing organic materials consume
• High BOD indicates pollution.
• Low BOD suggests good water quality.
• Nitrogen is an abundant element.
• Nitrogen is considered a nutrient because it is
essential for plant growth.
• How could plant growth impact water quality?
• Eutrophication is enrichment with nutrients.
– Eutrophication can be both a natural and humaninduced phenomenon.
Total Dissolved Solids (TDS)
and Salinity
• Water is a universal solvent, so it may contain a
wide range of substances.
– Examples include calcium, sodium, phosphorus, iron,
• Some solids in water are essential to maintaining
• High concentrations may lower water quality by
increasing turbidity.
• Salinity is a measure of specific type of dissolved
solid, namely, salts.
• Turbidity is a measure of how cloudy water
– It is a measure of how much light passes through
the water caused by light scattering solid particles.
• Do you think that if turbidity is low (water is
clearer) that it is automatically healthier?
Total Coliform Bacteria
• Coliform bacteria is generally nonpathogenic
and lives throughout the environment.
• Fecal coliform lives in the intestines of warm
blooded animals and helps to digest food.
• The presence of fecal coliform indicates that
pathogenic bacteria is present also.
• Testing for specific pathogenic bacteria takes a
lot of time and may be difficult.
– How might we solve this problem?
Water Quality
• For many of the indicators we will be testing
for there are national standards determined
by the Environmental Protection Agency.
• Water quality standards are based on the use.
– Drinking water, recreation, and fishing each have
different standards.
• Do you think there is a magic formula that
creates high quality water?