“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
Gradually grew to encompass all inland
waters
Today includes standing water (lentic
habitats) as well as running water (lotic
habitats)
Unique characteristics of
water regulate the chemical,
physical, and metabolic
activities in freshwater
systems
1) non-linear relationship
between temperature and
density
2) high specific heat
3) viscosity-density
relationship
4) high surface tension
5) 3 atoms arranged into nonlinear molecule
6) 104.5° angle
Structure of Water Molecule
Each water molecule can
have hydrogen bonds with
as many as 4 other water
molecules
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
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
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
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
Limnology
(lentic = lakes and ponds; lotic = streams and rivers)
Lake Zones
Limnology: light
Limnology: light
WATER CLARITY
Causes and significance
Causes
•Turbidity (Suspended solids)
•Plankton blooms
•Pollutants
Significance
•Reduces light penetration
•Reduces Photosynthesis
•Reduses feeding efficiency of fishes
Heating and cooling
Sources of heat:
1.Direct solar radiation (most important)
2.Groundwater and springs
3.Ground (minor)
Losses of heat:
1.Thermal radiation (primary)
2.Conduction
3.Evaporation
4.Outflow
Temperature Cycles & Lake Stratification
Most lakes mix during some seasons and
become stratified during other seasons.
These terms refer to the vertical circulation
of water: Mixing = circulation, Stratification =
lack of mixing (development of layers)
The mixing pattern has a large effect on
lake chemistry and the biota
Lakes have traditionally been classified
according to their annual mixing pattern or
mixing regime (amictic, monomictic, dimictic,
etc.)
Temperate zone Dimictic Lake
Stratified
Mixing
Mixing
Stratified
Thermal zones in a stratifed lake
Metalimnion
Mixing and Stratification
ESSENTIALS 0F A THERMAL PROFILE: WHAT
DOES IT MEAN?
Thermal stratification
-Effects vertical circulation of water
and reduces mixing of deep and
surface water
•Prevents up welling of nutrients
•Concentrates pollution
Unstratified lake
-Allow nutrients to react shallow
water
-Nutrients and light allowed for
photosynthesis