Chapter 9 - Light and the Aquatic Ecosystem

What are the other sources of energy on Earth?

Manmade

• Uranium fission such as nuclear reactors

• Hydrogen fission (rare)

Natural

• Moon-pulled tides

• Earth’s internal heat from radioactive decay

  • Lord Kelvin: Calculated the age of Earth based on temp of Earth’s surface

• Seismic activity

What is the solar constant?

1.94 cal/cm²

Not anywhere near this; it even reaches the surface

• Measured at the Earth’s mean distance from the sun

• Functionally lost at many points

  • Scattered

  • Reflected

  • Absorbed

What is the speed of light and what does it actually mean?

299,792 km/s

• the measurement of light traveling thru diff materials

• hard speed limit of the universe

What is the speed of light composed in?

Composed of quanta of energy traveling in waves with different frequencies and wavelength

• Wavelengths measured in nanometers

• ex) would take 8 minuted to realize the sun was out if it ever happened bc of the amt of light years (299,792 km/s)

What is Planck’s Quantum theory?

Direct relationship of frequency to energy

TLDR: regarding visible light, there is almost twice as much energy in short wave light as long wave light

What are the two sources of radiation on Earth?

• Direct

• Diffuse

How is color seen on earth?

PAR: photosynthetically active range

• Chlorophyll absorbs reds and violets, reflecting greens and yellows

  • why plants look green and yellow

• Photosynthetic activity highest in violet blue and orange red lights

what is the solar constant in langley?

1.94 ly (langley) per minute

How is light reflected at the surface of a lake?

thru light bouncing= intensity is lost

• Reflectance (R):  expressed as a percentage is R X 100

  • Complicated by wind

  • Complicated by cloud cover

Why is it harder to tan in January than in the summer?

There is less directy light, so more atmopshere is going thru an angle

How is light seen below a lake’s surface?

light loses intensity (quickly) with increasing depth

What is Beer’s Law?

A beam of monochromatic light passing through a given distance of a solution is absorbed exponentially according to concentration of solute

• why it is easier to tan when swimming than when outside

• beer law what makes spectrophotometry possible (how much shit in the way)

What is Beer-Bouguer’s Law?

light absorbed exponentially with distance

• combines two laws

Three terms give you the total coefficient of Absorbtion

How much light rlly goes thru?

It depends on things such as water, dissolved solids, undissolved solides, and absorbtion, transmittance, attenuation, and scattering

TLDR:

• Red penetrates farther than expected

• Clear lakes transmit green and yellow well

• Orange goes farthest in stained water

Explain what the fuckkk is going on in this graph

Lines are the wavelengths of light

• 720nm being red

• 620nm being orange

• Bottom wavelengths are blue, indigo, and violets

• At 5m of depth, all red is gone

Everything eventually turns blue as you increase in depth

What are the wavelengths of visible light?

ROY G. BIV

Explain the graph of vertical penetration and bodies of water

Depths of 0-2 meters have water color of brown dookie color

• light gets lost at 5ft of water due to turbudity

• Take note of Lake Itasca, Minnesota

• Lake Tahoe has some light at aorund 20% light at 6m depth

Which lake is the clearest and which is the least clear?

At around 4m of depths, there’s a thermocline present where it disbands from not being a linear relationship

• lake Erie: Least clear lake

• Lake Huron: Most clear lake

Explain the transmission curves occuring in the graph

The graph illustrates a shift increasing transmittance (lsomething coming thru) of long waves as absorption of coefficient increases

• 0.25 on graph is absorption of coefficient

What is the secchi disk?

Flat disk is lowered, measure where you can’t see it anymore

• measures water transparency

• can be inconsistasnt since everyone has diff eyesight and reflectance of water can vary

• ex) Crater Lake so clear that secchi disk can be seen at 40m depth

  • most lakes less than 1m due to biotic and abiotic factors

What is the euphotic/photic zone?

Region where at least 99% of surface light has disappeared

How do you find the bottom of the photic zone?

Vertical Absorption Coefficient:

• 1.7 divided by Z_SD

Multiply 3 times the Z_SD

What are the effects of ice and snow cover?

• Clear ice transmits light better than water beneath it

With snow, albedo increases by an incredible amount

• In a lake with low amounts of oxygen, can lead to winterkill

What is black ice/ congelation ice?

Congelation ice forms when there is no wind and a lake freezes fast

• lake looks so clear

Why do lakes and any natural system usually not meet the Beer-Bouguer law?

they are not homogenous

• there’s biotic interactions such as

  • cyanobacteria

  • sulfur using bacteria

  • eukaryoptic algae

• temeprature and density effects

Wtf is happening here

Linear line present in the solid line is due to bacteria being absorbed in

• at 100m of depth is where purple sulfur forms (where the linear line forms)

What is seen in the graph where optical density is shown?

• At between 4-5m of depth, there is a lot of light being transmitted

• between the depths of 7-10m, the lake is clear

• remember: OD is how much light material (lake) is absorbed

  • Low OD: No light goes thru

  • High OD: light absorbed and scattered a lot

How are colors usually seen in a lake?

Ultraoligotrophic- bluest water

• like Lake Tahoe and Crater lake

Usually from one of two sources

• Inorganic edaphic materials

• Biotic sources

  • Usually bacteria or algae

What is the science behind red and pink colored lakes?

Pink or red lakes form due to excessive salt and salt loving bacteria being present

What is the Forel-Ule scale?

Color matching board that matches the color of the water with what’s on the board

• Classifies the color/type of lake based on the color of the water

Light penetration and aquatic plant zonation

Aquatic plants usually make water more clear and increase photosynthetic ability.

• Usually disappears before the 1% zone

  • Many other factors influence distribution

What can you interpret from this table?

Deepest plant growth usually means that the secchi disk depth will also be high in value, meaning clear water

Light and aquatic animals

• blue is a rare color within nature due light absorption

  • Many surface dwelling species in the neuston have blue carotenoproteins or white sheens to protect themselves from UV radiation