Execise 8: Light transparency and turbidity

Topics: Light, Lake, Water Pages: 2 (520 words) Published: February 26, 2014
Abstract
Clarity refers to how deep the light penetrated the water and turbidity is the measure of the light scattering property of water. In this experiment, Secchi disk was used to directly measure the amount of penetrated sunlight and indirect amount of the suspended materials in the seawater. The study site was at the littoral zone of the ocean. The coordinates recorded for the study site were found to be N 160 23’ 56.0” E 1190 54’ 06.5” and N 160 24’ 02.5” E 1190 53’ 59.5”. When the rope was lowered down until the disk was no longer visible, the depth measurement was 9.6858 meters for the first site and 7 meters for the second site and when it was pulled up and reappeared, the depth measured was 9.3048 and 6.3048 meters respectively. The average of the two depths resulted to 9.4953 and 6.6524 which represents the transparency reading or also known as the Secchi depth. Therefore, the clarity of water is concluded to be proportional to the depth of the water and amount of creatures dwelling in that certain area.

Introduction
The term water clarity refers to the transparency or clearness of water. The visibility of seawater depends primarily on the reflectance, contrast, color of water, sea state, incident illumination and optical image. The more materials are suspended in the water, the less transparent it becomes.

Turbidity is used to describe the cloudiness or “lack of transparency” of water (Wilson, 2013). It is a physical characteristic where the light is scattered and absorbed by particles and molecules rather than being straightly transmitted through a water sample. According to Shoulejkin, there are four factors that affect the transmission of light in the sea: (1) selective absorption of light by water, (2) scattering of light by tiny suspended particles such as small bubbles of air or gas, (3) selective reflections of light by other particles such as fine dust or plankton and (4) an admixture of the reflected light of the sky.

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