Question

state any two factors on which the extent of absorption of light depends

Answer 1

Perhaps the most fundamental set of properties of lakes relates to the interactions of light, temperature and wind mixing. The absorption andattenuation of light by the water column are major factors controlling temperature and potentialphotosynthesis. Photosynthesis provides the food that supports much of the food web. It also provides much of the dissolved oxygen in the water. Solar radiation is the major source of heat to the water column and is a major factor determining wind patterns in the lake basin and water movements.

Light intensity at the lake surface varies seasonally and with cloud cover and decreases with depth down the water column. The deeper into the water column that light can penetrate, the deeper photosynthesis can occur. Photosynthetic organisms include algae suspended in the water (phytoplankton), algae attached to surfaces (periphyton), and vascular aquatic plants (macrophytes).

The rate at which light decreases with depth depends upon the amount of light-absorbing dissolved substances (mostly organic carbon compounds washed in from decomposing vegetation in the watershed) and the amount of absorption and scattering caused by suspended materials (soil particles from the watershed, algae and detritus).

The percentage of the surface light absorbed or scattered in a 1 meter long vertical column of water, is called the vertical extinction coefficient. This parameter is symbolized by "k".

In lakes with low k-values, light penetrates deeper than in those with high k-values. Figure 2 shows the light attenuation profiles from two lakes with attenuation coefficients of 0.2/m and 0.9/m.

Answer 2

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