3. The Nature of Water Flashcards
(39 cards)
What is a bathymetric map?
A depth profile (like a topographic map for lakes)
Give the simple methodological approach for measuring bathymetry
- get a basic outline from topographic map
- establish gridded transects (grid of lake depths)
- Use SONAR etc to create contours
“depth” in freshwater ecology is denoted as:
“z”
Lake volume (V) can be calculated using the area between the ____ _____. Explain the process
contour lines
- calculate the area at each depth
- use depth-specific areas to calculate layer volumes
- plot area vs depth –> create an absolute hypsographic curve
What’s the difference between an absolute and a relative hypsographic curve?
absolute= true measurements are used
relative= absolute values are converted to relative values
Relative Hypsographic curves plot ___ vs ___
relative depth (%)
vs
Relative area (%)
What is fetch? What is it calculated as?
The maximum length of a lake
= the distance b/w the 2 most distant points
or
max length + 1/2 width is sometimes used
Effective fetch=
measures the lake length in the prevailing wind direction (not necessarily max length)
Why is fetch important?
It’s fundamental for mixing! Helps us understand wind dynamics, wave height, and mixing in lakes
The shoreline development index (DL) is a measure of:
the spatial irregularity of a lake
If a lake has a high shoreline development index, what does that indicate?
- 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
What is water residence time (retention time)? How is it calculated?
= the average amount of time for a water molecule in a lake to fully turn over
WRT (yrs)= Volume/ water loss from lake
Liquid water is most dense at __ degrees C, where is has a density of __
3.98
1.00g/mL
It’s unusual that water’s solid state is less dense than the liquid state. What causes this?
hydrogen bonding of water!
the structure of the water molecule fosters an uneven distribution of elecromagnetic charge (molecular polarity)
T/F
Water has approx as many H-bonds as it does covalent bonds
true
(this is very unique)
The hydrogens in H2O have a net __ charge and the oxygen has a net __ charge
This uneven distribution enables ___ bonds
H= net positive charge
O= net negative charge
hydrogen bonds
Why does ice float?
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
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
Freezing= 4 per molecule
Above 0= 3.4 per molecule (less)
The lattice-like structure of ice breaks down as you increase the temperature, which ___(inc/dec) density
increases
What’s one major implication of H2O density for aquatic life?
Depth refugia!
Fish etc can live through the winter underneath the ice. If it froze from the bottom, they wouldn’t survive
Specific Heat Capacity=
the amount of heat (in calories) needed to raise 1g of a substances mass by 1 degree C
_____ _____ cause the heat capacity of water to be much greater than in most other liquids (and air!).
hydrogen bonds
What is water’s specific heat capacity? What implications does this have?
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
