Limnology!

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

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)

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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