Limnology!

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Limnology!
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Limnology

• the oceanography of lakes
• Study of the functional relationships and
  productivity of freshwater communities, as they
  are regulated by the dynamics of their physical,
  chemical, and biotic environments

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Limnology

• Term limnology derived from Greek word limne
  meaning pool, marsh, or lake
• The science arose from from lake investigation
• mid-1800s - Henry David Thoreaus observations
  from Walden Pond (nice lake)

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Limnology

• Gradually grew to encompass all inland waters
• Today includes standing water (lentic habitats)
  as well as running water (lotic habitats)

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Physical Limnology

• Unique properties of water - important role in
  penetration, distribution of light, heat
• Water movements (waves, currents)
• Geology of basin (origin, morphology, leaching
  minerals)

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Chemical Limnology

• Inorganic , organic compounds
• Closely allied to geology (leaching)
• Distribution often related to water movements

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Biological Limnology

• Base is photosynthesis - primary productivity
• Regulated by, and may regulate, physical and
  chemical factors

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Limnology

• Everything becomes interconnected
• Add in further complications resulting from human
  relations and impacts
• Very complicated science

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Properties of Water

• Unique characteristics of water regulate the
  chemical, physical, and metabolic activities in
  freshwater systems

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Properties of Water

• 1) non-linear relationship between temperature
  and density
• 2) high specific heat
• 3) viscosity-density relationship
• 4) high surface tension

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Structure of Water Molecule

• 3 atoms arranged into non-linear molecule
• 104.5 angle

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Structure of Water Molecule

• Polar molecule with weak charges
• Allows for weak hydrogen bonding between adjacent
  water molecules

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Structure of Water Molecule

• Each water molecule can have hydrogen bonds with
  as many as 4 other water molecules

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Structure of Water Molecule

• Structure most obvious in ice
• Creates tetrahedral pattern
• Lots of space between molecules
• Low density - it floats

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Temperature-Density

• Non-linear
• Maximum density at 4C
• Lower density at higher and lower temperatures
• Hydrogen bonding and molecular movement

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Specific Heat

• Or heat capacity - high for water
• Amount of heat energy required to raise unit mass
  1C
• Because of hydrogen bonding

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Specific Heat

• Temperature changes occur more gradually in lakes
  than in terrestrial environs
• Lakes can buffer climate of nearby land masses
• Warmer in winter, cooler in summer

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Viscosity-Density Relation

• Viscosity - resistance to flow
• Viscosity of water increases as density increases
• It doubles as temp decreases from 25C to 0C

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Viscosity-Density Relation

• Change not apparent to human eye
• Profound effect on movements of microscopic
  plants and animals, and sinking of particles in
  lakes

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High Surface Tension

• Hydrogen bonding interrupted at air-water
  interface
• molecules exert an inward adhesion to the liquid
  phase
• Molecules at surface resist being pulled apart

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High Surface Tension

• Allows objects that would normally sink in water
  to be supported on the surface
• Mercury is the only liquid with a higher surface
  tension
• Increases slightly with increased salinity,
  decreases with increased temperature, addition of
  organic compounds