Use the following information to answer the next 3 questions. To measure primary

Question

Use the following information to answer the next 3 questions. To measure primary production of algae in a stream, you place two sealed chambers in the stream, each enclosing the sediments as well as the water above them. One chamber is covered with black tape (blocking all light) while the other is transparent to light. You measure dissolved oxygen (DO) before and after a 24-hour incubation. DO in the light chamber increased by 1.5 g/m2 while DO in the dark chamber decreased by 2.0 g/m2. (Hint: You have all the information you need to answer the following 3 questions—you do not need initial and final DO values. Think carefully about what is actually being measured in each of the two chambers!)

Q2.30. What is the estimated ecosystem respiration (Re) for the stream? g O2 m-2 day-1

Q2.31. What is the stream's esitmated NEP (net ecosystem production)? g O2 m-2 day-1

Q2.32. Based on these data, what is the stream's estimated gross primary production (GPP)? g O2 m-2 day-1

Q2.33. The position of Earth's continents has shifted dramatically over its history. Imagine that all of Earth's land mass was bunched together with approximately equal areas above and below the Equator. Assume that seasonal patterns of growth and respiration are otherwise similar, with the Northern Hemisphere's summer occurring June-August and the Southern Hemisphere's summer occurring December-February. How will this new configuration affect seasonal swings in average global CO2?

Seasonal swings would be larger, but CO2 would still peak in late April.

Seasonal swings would be similar, but CO2 would now peak in late August.

Seasonal swings would be larger, but CO2 would now peak in late August.

Seasonal swings would be much smaller, perhaps even undetectable.

Explanation / Answer

Q2.30

2.0g O2 m-2 day-1. Respiration occur only in the dark chamber  and respiration rate is the decrease in DO over time. It can be measured by O2 consumption in the absence of photosynthesis

Q2.31   

1.5 g O2 m-2 day-1. Photosynthesis takes place in the presence of light, which can support the growth of algae.

Q2.32

Gross productivity = Net productivity + respiration = 1.5+2

Gross productivity = 3.5 g O2 m-2 day-1

Gross productivity is the entire photosynthetic production of all organic compound in the specific ecosystem.   

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