lec 3

Question 1

what is a bathymetric map? what is the process of making one?

Answer 1

u know those geographic models of mountains n shit. flip it upside and u got a map of lakes and their depths

to make one u gotta:
1. start w basin outline (aerial imagery or topography)
2. depth sounder + GPS to determine depth at diff areas)
ISOBATH are contour lines

Question 2

what are the basic physical metrics of a lake? what is the diff bw absolute and relative measures?

Answer 2

• lake area (A)
• max depth (z)
• lake volume (V)
  assuming a normal shape u can roughly calc V using A*depth
  alternatively u can find depth by doing (V/A)

absolute is lake specific, whereas relative uses averages of diff lakes (see notes for graphs)

Question 3

what is fetch? how can u measure it? (2 ways)

Answer 3

fetch is the “max length” of a lake, but technically its more a measure of wind - we just incl it bc wind dynamics are important for stratification etc

most simple method involves measuring distance bw two points

effective fetch is the length bw two points in the direction the wind is moving

Question 4

what is the shoreline development index?

Answer 4

basically its a measure of how fucky wucky a lake is looking

the formula is L/[2(piA)^1/2]
that looks fucked up but i cant incl pics so just check notes

1 means perfect circle and above (around 3.5) means dendritic aka a fucky wucky shape

higher shoreline development is assoc w shallowness, which has implications for light, heat, phytoplankton prod, etc

Question 5

what is water residence time (WRT)? how does WRT compare for moving vs still bodies of water? how do we calc it? what is the relevance of WRT?

Answer 5

the avg amount of time it takes for water in a lake to fully “turn over” ie come in and leave

moving bodies (rivers and streams) have low WRT while still bodies (lakes, oceans) have high WRT

WRT is calc using (V/water lost)

WRT is relevant for nutrient levels, pollution abatement, etc

Question 6

most times solids are more dense than liquids, yet ice floats in water. why?

bonus: what is deepwater refugia?

Answer 6

liquid water is most dense at 4 degrees C –> since water freezes at 0 degrees, it will be less dense than cold water that is around 4 degrees.

low density in ice is attributed to water’s polarity, causing hydrogen bonds. when water freezes, there is little molecular motion, leaving a little spaces that would otherwise be filled if water was in a fluid state.

deepwater refugia just refers to where animals take refuge in cold deeper waters that don’t freeze –> allow survival through winter

Question 7

water has strong bonds, resulting in many things. explain the following:
- high heat capacity
- latent heat of melting
- heat of fusion
- heat of vaporization

additionally, water is polar. what implications does this have for other polar molecules?

Answer 7

high heat capacity: water takes a lot of energy before it begins to heat, since it has so many bonds. implications are most demonstrable in seasonal changes, warming gradually in spring and conversely, losing heat gradually in fall.

same principle applies to melting, fusion, and vaporization.

Question 8

water is polar. what implications does this have for other polar molecules?

Answer 8

good at dissolving polar molecules (ex CO2) but bad at dissolving nonpolar molecules (ex. O2). water is also a good solvent for salts.