Determine the depth of the photic zone (the depth of at which 99% of surface irr

Question

Determine the depth of the photic zone (the depth of at which 99% of surface irradiance is attenuated). Below 1% surface irradiance, respiratory requirements exceed photosynthetic gains. Is there enough irradiance in the metalimnion to support photosynthetic organisms?

Light Values from 0-15 meters in depth.

The metalimnion is from 13-16 meters.

Not sure how to go about this question. Thanks for the help!

408 257 166 129 89 44.4 33.4 16.5 14.7 17.1 9.9 8.6 5.8 5.5 4.1 3.3 Wood Lake: Depth vs. Irradiance Irradiance (uE/cm-2 s-1) 0 100 200 300 400 500 12 16

Explanation / Answer

Last 3 values of irradiance (such as 5.5, 4.1 and 3.3 uE/cm2/sec) in between 13-16 meters of the metalimnion from above graph.

At 14 meters of the depth 99% irradiance will be inhibited, since at surface it is 408, of which 99% is 403.92.

If you substract 403.92 from 408, it gives 4.08 uE/cm2/sec, that is shown at 14 meters depth point from your data sheet.

Based on above calculation only 3.3 uE/cm2/sec is in below 1% irradiation which is present at the depth of 15 meters (metalimnion). But 13 and 14 meter of metalimnion are slightly above 1% of irradiance could support photosynthetic organisms for minor extant.

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