Primary production in lakes Huron and Michigan: in vitro and in situ comparisons |
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Authors: | Fahnenstiel Gary L; Carrick Hunter J |
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Institution: | Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration 2205 Commonwealth Blvd, Ann Arbor, MI 48105, USA |
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Abstract: | Oxygen- and carbon-14-based primary production estimates from916 h in vitro incubations were compared in lakes Huronand Michigan. For surface mixing layer compansons, gross O2/14Cphotosynthetic quotients (gross PQ) averaged 2.2, and net O2/14Cphotosynthetic quotients (net PQ) averaged 1.4. The mean grossPQ is consistent with a theoretical P0 based on the CO2 andNO3 assimilation ratio. However, within the deep chlorophylllayer, gross PQ and net PQ averaged 4.9 and 2.8 respectively.These higher values were likely due to excess NO3 reductionat the expense of CO2 uptake. Thus, during short experimentsunder low light conditions, oxygen evolution and CO2 uptakemay not be tightly coupled. In vitro and in situ O2 productionestimates were compared in four diurnal (dawn to dusk) experimentsin Lake Huron. In situ production estimates were determinedby measuring water-mass oxygen changes and oxygen transfer acrossthe air-water interface. In situ production estimates were approximatelytwice in vitro production estimates for both surface mixinglayer and deep chlorophyll layer comparisons. The differencebetween estimates was attributable to containment effects manifestin 1316 h bottle incubations. Short-term (12 h)in vitro production was also compared to diurnal in vitro production.Rates of short-term production were {small tilde}1.6 times higherthan rates of diurnal production, suggesting that short-termin vitro production experiments may provide reasonable estimatesof in situ primary production. |
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