1. Hydrologic Cycle, Properties of Water, Factors affecting Life in Water
Lecture 05 Water
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 days
Oceans 3,100 years

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. Impacted by absolute humidity – amount of water vapor in atmosphere
Dew
Condensation of water on surfaces cooled by radiation of heat to atmosphere
Impacted by absolute humidity – amount of water vapor in atmosphere
Fog: Forms at dew point on nucleation sites, small particles
Important source of moisture in summer along California coast – some other dry environments

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

12. 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

13. 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

16. Depth % of surface light 1 cm 73 1 meter 44,5 10 meters 22.2
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

17. http://staffwww. fullcoll

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

19. Dissolves at surface (diffusion): function of temperature
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

22. 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

23. 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

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

25. 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

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

28. 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

29. Life on earth depends on water and its properties
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