A student measures net primary productivity (NPP) in an aquatic ecosystem using the light/dark bottle method. Two sealed bottles of pond water are incubated for 24 hours: one in light (allows photosynthesis and respiration) and one in dark (only respiration). Initial dissolved O2 is also measured. Results: initial 8.0 mg/L; light bottle 11.5 mg/L; dark bottle 6.0 mg/L.
What is the gross primary productivity (GPP) in mg O2/L per 24 h?
- Acheck_circle
5.5
- B
11.5
- C
3.5
- D
2.0
Explanation
GPP = O2 produced by photosynthesis = light bottle final - dark bottle final = 11.5 - 6.0 = 5.5 mg/L. (Equivalently, NPP + respiration = (11.5 - 8.0) + (8.0 - 6.0) = 3.5 + 2.0 = 5.5.)