1. Limnology!

2. 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

3. Limnology • Term “limnology” derived from Greek word “limne” meaning pool, marsh, or lake • The science arose from from lake investigation • mid-1800s - Henry David Thoreau’s observations from Walden Pond (nice lake)

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

5. 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)

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

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

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

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

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

11. Structure of Water Molecule • 3 atoms arranged into non-linear molecule • 104.5° angle

12. Structure of Water Molecule • Polar molecule with weak charges • Allows for weak hydrogen bonding between adjacent water molecules

13. Structure of Water Molecule • Each water molecule can have hydrogen bonds with as many as 4 other water molecules

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

15. Temperature-Density • Non-linear • Maximum density at 4°C • Lower density at higher and lower temperatures • Hydrogen bonding and molecular movement

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

17. 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

18. Viscosity-Density Relation • Viscosity - resistance to flow • Viscosity of water increases as density increases • It doubles as temp decreases from 25°C to 0°C

19. Viscosity-Density Relation • Change not apparent to human eye • Profound effect on movements of microscopic plants and animals, and sinking of particles in lakes

20. 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

21. 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