3. The Nature of Water Flashcards
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
Latent Heat of Melting=
the amount of energy required from the enviro to change ice to liquid water
T/F
Water has a high:
- specific heat capacity
- latent heat of melting
- latent heat of vaporization
- latent heat of fusion
true for all
Latent heat of vaporization=
the amount of energy required from the environment to evaporate water
Latent heat of fusion=
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
Which are more soluble in water: polar or non-polar gas molecules?
Polar gas molecules (CO2)= far more soluble in water than non-polar molecules (N2, O2)
T/F
Higher water temperature allows for more gases to dissolve in the water column
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
T/F
Higher water temp allows for more solids to dissolve in the water
TRUE
solids increase their solubility with increasing temp (b/c of the polarity created by H bonds)
Viscosity=
the resistance of its molecules to being moved relative to one another (how easily it is for the liquid to flow)
In general, viscosity __(inc/dec) with decreasing temperature. Why is this true for water?
increases
(harder for something to flow in cold temps)
- b/c of the increasing strength of H-bonds
Viscous forces increase close to surfaces as a result of friction. In flowing water, what does this create?
A Boundary Layer!
= a layer of water surrounds any fixed surface in flowing water (a thin layer that’s not flowing)
-
- the flow of water in a stream channel
- the depletion of nutrients and CO2 in the ‘stagnant’ water masses immediately adjacent to photosynthetic organisms
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
- density change with temp change: stratification
- high heat capacity: aquatic systems are buffered
- viscosity change with temp change: rate of falling; viscosity and boundary layers
- gas saturation with temp change: cool water holds more oxygen
Pure water both scatters and ___ solar radiation
absorbs
Does water scatter or absorb the following light:
- Infrared photons (heat)
- Low energy red photons
- Higher energy blue photons
infrared= absorbed almost instantly
red= absorbed relatively easily
blue= transmitted and scattered
