(Disclaimer: these are
lecture outlines with some figures; these are not lecture
Some lake types:
-volcanism - collapsed craters, filled blowholes, lava dams
-earthquakes and landslide - Lake Reelfoot, TN
SOLUTION - sinkhole (solution) lakes, collaspsed saltdomes
RIVER - oxbows
Natural Lakes versus Artificial Reservoirs
How might RESERVOIRS (impoundments) and LAKES differ based on:
Drainage basin area to lake surface area Flushing rate Sedimentation, turbidity Water level
MATTER IN WATER
* inorganic ions (such as ....?)
* free organic molecules (such as ....?)
* inorganic particles (such as ....?)
cells and multicellular organisms
Measurements used to characterize matter in water:
<2 µm 14 days to sink 5 cm water
Silt 2-20 µm 3.5 days
Sand 20-2000 µm 1.5 second
In aquatic systems, how does
the rate of settling depend on the mechanical energy of
the water (water movement)?
In a reservoir like Lake Allatoona, would you expect a gradient in suspended solids from the incoming streams to the dam?
Both dissolved and suspended
solids can be measured gravimetrically
Which is likely to weigh more in an typical surface freshwater sample?
Which is more likely to interfere with light transmission through water?
Estimating dissolved solids:
Much of the fraction that is dissolved, can be estimated by conductivity (specific conductance) - the capacity of a solution to conduct electrical current. Estimates total dissolved ions. Why?
What will happen to the transmission of light as more solids are suspended in water?
How then could to amount of suspended substances be estimated indirectly?
Given this, will suspended solids affect temperature in natural waters? How?
Summary of matter in water:
Fate of light in aquatic systems:
* Reflection - prevented from entering water by air-water surface interface
* Scattering - suspended
particles reflect light at a massive array of angles
* Absorption - diminution
of light by transformation. What is light energy
typically transformed into upon being absorbed (or is the
energy simply destroyed)?
Light entering pure water:
Light entering lake water with other matter:
* silts and clays - reds and oranges more likely to be scattered - How do color and clarity differ from water with high concentrations of organic compounds?
* phytoplankton chlorophyll -
What color is not absorbed by chlorophyll a?
properties in water (usefulness depends on question
measures intensity of light scattered at 90°.
Units are Nepholometic
Turbidity Units (NTU's).
How are vertical illumination and turbidity related?
What would a deflection in the line indicate?
Why might it be important
to measure vertical illumination?
Compensation depth - Respiration exceeds photosynthesis within a cell at about 1% of incident surface light (the photic zone is the region from the surface to where 99% of light has disappeared).
Visibility can be used to
depth and trophic
What factors affect these estimate?
TWO SUMMARY POINTS:
* high specific heat
* high specific gravity
Why is there a temperature difference between lake inputs
Sources of heat:
* transfer of heat from air
How should heat energy be distributed vertically within a lake (what should a temperature-depth profile look like)?
Major sources of water movement in lakes:
* internal waves
Thermal stratification is a function of water movement and heat distribution
Lake types based on mixing vs.
How will thermal stratification
change as a lake becomes more eutrophic?
Quantifying the intensity of thermal stratification - Relative Thermal Resistance to Mixing (RTRM)
= Density of Upper Layer -
Density of Lower Layer
Density at 5°C - Density at 4°C
RTRM is a
relative, non-dimensional value used to:
- Identify the depth of the thermocline and assess the relative strength of stratification. A "strongly stratified lake" typically has an RTRM max > 80 (when calculated in 1 meter depth increments).
- RTRM can be summed to calculate Σ RTRM, an estimate of total stratification intensity.
So depth of light penetration is important in determining depth of thermal stratification. How can we test this idea in Lake Allatoona?
What are the ecological consequences of thermal stratifcation?