I. Properties of Water

A. Bonding -- dipole moment

high __dipole
moment__; electrons associate with O with a higher probability than
with
H

H-O-H
angle is 104.5 degrees

hydrogen bonds

good
**solvent**
for salts and polar organic molecules

B. Characteristics of water

1. specific heat

- capacity to absorb thermal energy per unit change in temperature

- water takes 1 cal/g to raise the temperature 1 degree C

2. latent heat of vaporization

- amount of thermal energy needed to change from water to gas

- for water this is 540 cal/g

- for heat of sublimation (ice to gas) is 679 cal/g

3. latent heat of fusion

- amount of thermal energy needed to be removed to change 1 g. of
material
from liquid (water) to solid (ice)

- for water this is79.7 cal/g

So these attributes make
water a **good thermal buffer**

4. density – See Figure 2-3 in Wetzel

- Density = rho = r
= g x cm^{-3}

- Temperature of maximum
density is 3.98 degrees C

- Ice lattice has more space
and so ice less dense

- Density vs. temperature -
nonlinear

Density-temperature relationship is affected by:

a) dissolved salts -- increased density with increasing salts

b) particulates

c) dissolved gases

d) pressure -- increase of pressure decreases the temperature of
maximum
density.

5. Viscosity – water is 775 times density of air and more viscous; [viscosity decreases as temperature increases]

6. Surface tension high

II. Thermal Stratification

A. Layering

1. epilimnion -- upper mixed layer -- warmer water (less dense)

2. metalimnion --
middle layer -- where temperature changes

- thermocline is the __plane__
where dT/dz is maximum

3. hypolimnion -- lower layer -- cooler water (more dense)

HOW ARE THESE LAYERS FORMED?

B. Seasonal cycles for a temperate lake

1. winter

reverse stratification or inverse stratification cold water is on top of warmer water

2. early spring

spring turnover or overturn

Isothermal

3. late spring –

incipient
stratification

Resistance to mixing proportional to d(r)/dz

4. early to mid-summer

summer stratification

Why is hypolimnion temperature in summer often more than 4 degrees C?

5. early fall

6. fall overturn

7. return to winter and inverse stratification

8. complex summer temperature profiles

C. Factors affecting the mixing cycle

1. morphology

fetch

thermal bars -- in a large lake with shallow water nearshore, the shallow area will warm faster

2. geography

3. water clarity

4. weather

III. Patterns of stratification

holomictic --

depth-time diagram of isotherms

A. Dimictic
--

2. warm monomictic

C. Special considerations in tropical lakes

D. Polymictic

2. warm polymictic

E. Oligomictic

F. Amictic

G. Meromictic (mero=partial)

mixolimnion
-- shallow layer that mixes

monimolimnion
-- deep layer that doesn't mix

pycnocline
-- region of maximum density change

chemocline
-- region of change in density due to change in salinity; dissolved
salts
or organics

1. **ectogenic**
-- external event brings salt water into a freshwater lake or
freshwater
into a saline lake

2. **crenogenic**
-- submerged saline springs release dense water to deep portions of
lake
basins

3. **biogenic**
-- accumulation of salts due to decomposition in the sediments,
sinking
organic matter,

and photosynthetic precipitation of carbonate

H. Patterns of lake mixing types

- Updated version of figure 6-7 in Wetzel from Hutchinson and Loffler, 1956

IV. Resistance to mixing and stability

A. Resistance to mixing proportional to dr
/dz

B. Stability
– the resistance to mixing; the
amount of work that would be required to mix an entire lake to uniform
density without adding

or subtracting heat in the process.

1. Whole lake
stability
– determines if the whole lake will mix; is the amount of energy
required
to mix the entire lake to uniform density
(KJ/cm^{3})

z_{max}

a. S = 1/A_{0 } S
(r_{z} – r_{average})
(z - z _{raverage}) (A_{z})
dz

Z_{0}

where S is
actually an integral symbol (apparently non-existent on my html font
file
for now!)

where A_{o} = the surface area in cm

A_{z} = the area at some depth z (in cm)

r_{average} = the final or mean
density
that would result if the lake were completely mixed

r_{z} = the density at depth z

z_{raverage} = the depth (cm) where
the final (mixed) mean density exists prior to mixing

z_{max} = maximum depth in cm

z_{0} = surface or zero depth

2. Richardson’s
stability
– determines whether or not two fluids will mix

a. Ri = (g x dr/dz) / r_{average}
(du/dz)^{2}

Where g = acceleration of gravity

r = density

u = horizontal velocity

b. Ri > 0.25 then no mixing -- numerator dominates

c. Ri < 0.25 then will mix -- denominator dominates (energy of
mixing)

C. Heat in lakes

1. Annual heat budget
(Birgean heat budget) – record of the heat content of the lake

- Winter heat income – amount
of heat required to warm a
dimictic
lake from winter stratification to isothermal mixing in spring

- Summer heat income – amount
of heat required to heat the
lake
from spring mixing to its maximum summer heat content

A = Area at depth z

T_{s} = maximum summer temperature at depth z

T_{w} = minimum winter temperature at depth z

2. Analytical heat budget – budget based on identification of all the sources and sinks for heat to or from a lake

D. Streams and Heat