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Lecture 08 Water

Lecture 08 Water. 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%.

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Lecture 08 Water

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  1. Lecture 08Water Hydrologic Cycle, Properties of Water, Factors affecting Life in Water

  2. 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%.

  3. 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

  4. 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

  5. http://digital.films.com/PortalViewVideo.aspx?xtid=47289&psid=0&sid=0&State=&title=Liquid Assets: The Big Business of Water&IsSearch=N&parentSeriesID=

  6. 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.

  7. Unequal sharing of electron in water molecule results in positively and negatively charged regions Bonds formed between water molecules – break and reform – like velcro

  8. 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

  9. 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

  10. Penetration of Water by Light • % of surface light at various depths: • varies with turbidity – assume clear water • Different wavelengths penetrate water to different degrees – blue penetrates the furthest

  11. http://staffwww.fullcoll.edu/tmorris/elements_of_ecology/images/light_spectral_absorption_water.jpghttp://staffwww.fullcoll.edu/tmorris/elements_of_ecology/images/light_spectral_absorption_water.jpg

  12. Estimation of turbidity of water using senchi disc Turbidity is a function of suspended plankton growth and amount particulate matter in water

  13. 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

  14. 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

  15. 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

  16. Acidity – concentration of hydrogen ions • pH is a measure of hydrogen ion concentration • Acid = substance which increases [H+] • Base = substance which decrease [H+]

  17. 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

  18. Buffers • A buffer _______________________ • sort of like a chemical shock absorber • Important in living systems – pH is critical to maintenance of life processes

  19. 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%20Collection&IsSearch=Y&parentSeriesID=&loid=111194 • http://digital.films.com/PortalViewVideo.aspx?xtid=10780&loid=32209&psid=0&sid=0&State=&title=The%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

  20. 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

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