Aquatic ecosystems - Light climate

11 important questions on Aquatic ecosystems - Light climate

What does turbidity in a water system mean?

The reduction in light strength when it penetrates in the water column. The opposite of turbidity is transparency

What effect does low transparency of the water have on its quality?

The quality decreases. It can be caused by suspended sediment, either by wind or biota.

What are inherent optical characteristics of water?

The result of absorption and scattering. They form the light attenuation.

Scattering is caused by suspended particles, especially clay.
Organic and inorganic suspended matter ccontribute most to light absorption.
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What determines the absoption in water?

Dissolved substances, the colour of the light and suspended particles like algae, detritus, sand and clay.

What is the law of Lambert-Beer

Iz=I0 x e^-Ez
Iz: light intensity at water depth z
I0: light intentsity at the water surfacce
E: etinction coefficient/vertical light attenuation coefficient (based on wavelengths used by photosynthesis: PAR (photosynthetically active radiation))

What is scattering dependant on?

Suspended particles. Scattering enlarges the travel distance and therefor the change to be absorped.

What is the Secchi depth?

Secchi depth is operationally defined as the depth at which a white disc is indistinguishable from the surrounding water, or the black and white quadrants of a black and white disc are indistinguishable from one another when the disc is lowered into a water.

The secchi depth is approximately inversely proportional to the vertical light attenuation coefficient: in a turbid lake the etinction coefficient is large and the Secchi depth is small

Why is the under water light climate important?

A decrease in water transparency has a big effect on water quality
-less suitable for drinking or swimming
-hosts problematic algae
-lower species diversity

How can we calculate the amount of absorbed light in a water column?

Iz = Io x e^-Ez

How can the water turbidity be measured?

1) Measuring light at 2 water depths and applying Lambert-Beer's law.
2) The Secchi depth

Which fraction of substances contibutes the moest to the total vertical light attenuation here?

Phytoplankton.

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