3. The Nature of Water

Question 1

What is a bathymetric map?

Answer 1

A depth profile (like a topographic map for lakes)

Question 2

Give the simple methodological approach for measuring bathymetry

Answer 2

• get a basic outline from topographic map
• establish gridded transects (grid of lake depths)
• Use SONAR etc to create contours

Question 3

“depth” in freshwater ecology is denoted as:

Answer 3

“z”

Question 4

Lake volume (V) can be calculated using the area between the ____ _____. Explain the process

Answer 4

contour lines

1. calculate the area at each depth
2. use depth-specific areas to calculate layer volumes
3. plot area vs depth –> create an absolute hypsographic curve

Question 5

What’s the difference between an absolute and a relative hypsographic curve?

Answer 5

absolute= true measurements are used
relative= absolute values are converted to relative values

Question 6

Relative Hypsographic curves plot ___ vs ___

Answer 6

relative depth (%)
vs
Relative area (%)

Question 7

What is fetch? What is it calculated as?

Answer 7

The maximum length of a lake
= the distance b/w the 2 most distant points
or
max length + 1/2 width is sometimes used

Question 8

Effective fetch=

Answer 8

measures the lake length in the prevailing wind direction (not necessarily max length)

Question 9

Why is fetch important?

Answer 9

It’s fundamental for mixing! Helps us understand wind dynamics, wave height, and mixing in lakes

Question 10

The shoreline development index (DL) is a measure of:

Answer 10

the spatial irregularity of a lake

Question 11

If a lake has a high shoreline development index, what does that indicate?

Answer 11

• highly dendritic
• a higher degree of near-shore habitat
• numerous bays: may differ from the main lake in terms of temp, water chem, and light penetration

Question 12

What is water residence time (retention time)? How is it calculated?

Answer 12

= the average amount of time for a water molecule in a lake to fully turn over

WRT (yrs)= Volume/ water loss from lake

Question 13

Liquid water is most dense at __ degrees C, where is has a density of __

Answer 13

3.98
1.00g/mL

Question 14

It’s unusual that water’s solid state is less dense than the liquid state. What causes this?

Answer 14

hydrogen bonding of water!
the structure of the water molecule fosters an uneven distribution of elecromagnetic charge (molecular polarity)

Question 16

T/F
Water has approx as many H-bonds as it does covalent bonds

Answer 16

true
(this is very unique)

Question 17

The hydrogens in H2O have a net __ charge and the oxygen has a net __ charge
This uneven distribution enables ___ bonds

Answer 17

H= net positive charge
O= net negative charge

hydrogen bonds

Question 18

Why does ice float?

Answer 18

The hydrogen bonds enable a lattice-like structure; causes ice to be very rigid, forcing space between water molecules (so ice expands). Air pockets= floats

Question 19

Below 0 degrees, each water molecule has an average of __ hydrogen bonds
- this increases spacing/ rigidity of adjacent molecules, lowering its density and weight
Above 0 degrees, each water molecule has an average of __ hydrogen bonds
- enhances fluidity of water

Answer 19

Freezing= 4 per molecule

Above 0= 3.4 per molecule (less)

Question 20

The lattice-like structure of ice breaks down as you increase the temperature, which ___(inc/dec) density

Answer 20

increases

Question 21

What’s one major implication of H2O density for aquatic life?

Answer 21

Depth refugia!
Fish etc can live through the winter underneath the ice. If it froze from the bottom, they wouldn’t survive

Question 22

Specific Heat Capacity=

Answer 22

the amount of heat (in calories) needed to raise 1g of a substances mass by 1 degree C

Question 23

_____ _____ cause the heat capacity of water to be much greater than in most other liquids (and air!).

Answer 23

hydrogen bonds

Question 24

What is water’s specific heat capacity? What implications does this have?

Answer 24

4.2J/kgK

• water bodies act as a ‘buffer’ for temp changes (eg coast climates have a more stable temp)
• lakes warm and cool more gradually than the surrounding land

Question 25

Latent Heat of Melting=

Answer 25

the amount of energy required from the enviro to change ice to liquid water

Question 26

T/F

Water has a high:
- specific heat capacity
- latent heat of melting
- latent heat of vaporization
- latent heat of fusion

Answer 26

true for all

Question 27

Latent heat of vaporization=

Answer 27

the amount of energy required from the environment to evaporate water

Question 28

Latent heat of fusion=

Answer 28

the amount of energy that must be lost to the enviro for the fusion of water from liquid to solid state at 0 degrees C

Question 29

Which are more soluble in water: polar or non-polar gas molecules?

Answer 29

Polar gas molecules (CO2)= far more soluble in water than non-polar molecules (N2, O2)

Question 30

T/F

Higher water temperature allows for more gases to dissolve in the water column

Answer 30

FALSE

HIGHER TEMP DECREASES SOLUBILITY FOR GASES
warmer water= less gas can be dissolved in it b/c the molecular motion increases, ‘kicking’ the gas molecules out

Question 31

T/F
Higher water temp allows for more solids to dissolve in the water

Answer 31

TRUE
solids increase their solubility with increasing temp (b/c of the polarity created by H bonds)

Question 32

Viscosity=

Answer 32

the resistance of its molecules to being moved relative to one another (how easily it is for the liquid to flow)

Question 33

In general, viscosity __(inc/dec) with decreasing temperature. Why is this true for water?

Answer 33

increases
(harder for something to flow in cold temps)
- b/c of the increasing strength of H-bonds

Question 34

Viscous forces increase close to surfaces as a result of friction. In flowing water, what does this create?

Answer 34

A Boundary Layer!
= a layer of water surrounds any fixed surface in flowing water (a thin layer that’s not flowing)

Question 35

-

Answer 35

• the flow of water in a stream channel
• the depletion of nutrients and CO2 in the ‘stagnant’ water masses immediately adjacent to photosynthetic organisms

Question 36

List a consequence of each following property of water
1. density change with temp change
2. high heat capacity
3. viscosity change with temp change
4. gas saturation with temp change

Answer 36

1. density change with temp change: stratification
2. high heat capacity: aquatic systems are buffered
3. viscosity change with temp change: rate of falling; viscosity and boundary layers
4. gas saturation with temp change: cool water holds more oxygen

Question 37

Pure water both scatters and ___ solar radiation

Answer 37

absorbs

Question 38

Does water scatter or absorb the following light:
- Infrared photons (heat)
- Low energy red photons
- Higher energy blue photons

Answer 38

infrared= absorbed almost instantly

red= absorbed relatively easily

blue= transmitted and scattered