Lecture 08 Water
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Transcript of Lecture 08 Water
Lecture 08Water
Hydrologic Cycle, Properties of Water, Factors affecting Life in
Water
• Over 71% of the earth’s surface is covered by water:– Oceans contain 97%.– Polar ice caps and glaciers contain 2%.– Freshwater in lakes, streams, and ground water make up
less than 1%.
• Precipitation infiltration (or surface runoff) groundwater– Special issue as we create hard surfaces– Special value of wetlands
• Water returns to atmosphere via:– Transpiration: evaporation from internal
surfaces of leaves, etc.– Evapotranspiration: movement from plant and
ground surfaces to atmosphere
The Hydrologic Cycle
• Turnover time is the time required for the entire volume of a reservoir to be renewed.– Atmosphere 9 days– Rivers 12-20 days– Oceans 3,100 years
http://digital.films.com/PortalViewVideo.aspx?xtid=47289&psid=0&sid=0&State=&title=Liquid Assets: The Big Business of Water&IsSearch=N&parentSeriesID=
Evaporation – Loss of Water from Organism to Atmosphere
• Important for terrestrial organisms
–Provides cooling
–Represents major loss of water.
• Greatest in dry climates – water vapor in air less – where ‘humidity’ is lower
–Concentration gradient greater• Cooling from evaporation greatest in
dry climates.
Bonds formed between water molecules – break and reform – like velcro
Unequal sharing of electron in water molecule results in positively and negatively charged regions
• Cohesive and adhesive• Viscous• High specific heat• High heat of vaporization• Greatest density is as a
cold liquid, less dense as solid
• Solvent• Properties altered by
dissolved substances
• Changes in density with temperature
• Greatest density at 4C
• Ice floats – expands due to intermolecular interactions
• Develops layers of stratification– Surface waters warmed (in summer)– Deeper waters cool– Thermocline – region of rapid change in temp.
with depth
Penetration of Water by Light• % of surface light at various depths:•
Depth % of surface light
1 cm 73
1 meter 44.5
10 meters 22.2
100 meters 0.53
•varies with turbidity – assume clear water•Different wavelengths penetrate water to different degrees – blue penetrates the furthest
http://staffwww.fullcoll.edu/tmorris/elements_of_ecology/images/light_spectral_absorption_water.jpg
• Estimation of turbidity of water using senchi disc
• Turbidity is a function of suspended plankton growth and amount particulate matter in water
• Oxygen and Depth • Dissolves at surface (diffusion): function of temperature• Reaches minimal concentration between surface and ~ 1000
meters depth• Anoxic or Anaerobic = ?
– Certain deep waters– Consequence of metabolic activity
Gasses dissolved in water: Enter and move by diffusion
Oxygen - solubility function of – Temperature – greater at lower temperatures– Salinity – more soluble in fresh water– Atmospheric pressure
• Carbon dioxide – creates carbonic acid
pH and water – acids and bases
• Due to dissociation of water molecules into Hydrogen and hydroxyl ions
• pH is a measure of hydrogen ion concentration
• Impacted by dissolved substances – organic materials, gasses, salts
Acidity – concentration of hydrogen ions
• pH is a measure of hydrogen ion concentration
• Acid = substance which increases [H+]
• Base = substance which decrease [H+]
Acids and Bases
• Acid: excess of H+ ions • Base: excess of OH- ions
pH is a measure of H+ ion concentration on a log scale:
pH = -log [H+]• lower number indicates a higher
hydrogen ion concentration or a more acidic condition
Buffers
• A buffer _______________________– sort of like a chemical shock absorber
• Important in living systems – pH is critical to maintenance of life processes
• CO2 is absorbed from atmosphere• Enters rain water and diffuses directly into
surface waters– Creates moderately acidic condition but also
some buffering capacity
• Other atmospheric gasses may increase acidity of rain water: = acid rain– Sulfur oxides sulfuric acid– Nitrogen oxides nitric acid
• Strong acids, overcome buffering capacity, create acidic bodies of water
• Particular problem for areas with granite substrate• http://digital.films.com/PortalViewVideo.aspx?xtid=44017&psid=0&sid=0&State=&title=The%20Weather%20Video%20Clip
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%20Environment&IsSearch=Y&parentSeriesID=• http://digital.films.com/PortalViewVideo.aspx?xtid=44363&psid=0&sid=0&State=&title=The
%20Adirondacks&IsSearch=Y&parentSeriesID=&loid=124929
• Summary• Life on earth depends on water and its
properties• Water is a polar compound
– Ends of each molecule have different charges
• Water is a solvent for ionic solids – salts which dissociate into positively and negatively charged ions
• pH is a measure of H+ ion concentration– Lower pH means higher H+ ion concentration
• Light is quickly absorbed by water meaning is in only available at the surface of bodies of water
• Water is much more viscous than air