THIS IS ONE QUESTION WITH SUB-PARTS Primary productivity in the ocean can be mea
ID: 51046 • Letter: T
Question
THIS IS ONE QUESTION WITH SUB-PARTS
Primary productivity in the ocean can be measured with the “light-dark bottle method.” Seawater is collected from a given depth along with its natural plankton content. The dissolved oxygen content is measured, and then the water is split into two sets of bottles – one transparent (“light”), so that light can penetrate it, and the other opaque (dark), so that light cannot penetrate. After a specific interval (e.g., 3 hours) the bottles are retrieved, and the dissolved oxygen content in each sample is re-measured. This enables the rate of photosynthesis to be determined in two forms: gross primary productivity (total amount of oxygen produced through photosynthesis) and net primary productivity (amount of oxygen produced through photosynthesis minus the amount of oxygen consumed through respiration). The figure to the right shows such an experiment, in which the light and dark represent bottles at 10-meter depth intervals after 3 hours of submergence. The value in each bottle is the change in dissolved oxygen concentration from the initial concentration (initial minus final). Use these values as a proxy for primary productivity and respiration during the time interval.
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A) Which bottles (light or dark) tend to have an increase in concentrations of dissolved oxygen at shallower depths after three hours? Why?
Which bottles (light or dark) tend to have a reduced concentration of dissolved oxygen after three hours? Why?
The light bottles reflect the net primary productivity that has occurred at the various depths during the 3 hours. Calculate the total gross primary productivity at the 7 depths for the 3 hours (Hint: Consider what processes are occurring in each bottle).
10m:
20m:
30m:
40m:
50m:
60m:
70m:
In this example, zooplankton were not filtered from the seawater samples before re-submergence. How would the removal of zooplankton have affected the net primary productivity calculations (i.e., would they be higher/lower)? Why?
How can you explain the fact that positive gross primary productivity can take place at greater depths than positive net productivity?
3.7 D 30 1.3 0.4 50 -0.3 1.3 60 1.3 H 1.3 70 1-1 .3Explanation / Answer
Answer:
Increase in the dissolved oxygen can be seen in 10m,20, and 30m depth, higher primary production takes place in these depths due to penetration of the sun light.
Low concentrations of the dissolved oxygen can be seen in 60m and 70m due less penetration of the sunlight leading to low primary production.
Gross primary productivity (GPP)= NPP (net primary productivity) + R (respiration)
If the zooplankton were not filtered from the seawater samples before re-submergence, there may be chance of the grazing of the phytoplankton by zooplankton leading to reduction in the gross primary production, finally net primary production may lower.
Gross primary production will be higher at upper depths and low at bottom depths, when we caliculate net primary production,NPP = (GPP - R).
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