An investigation and evaluation of photosynthetic and respiratory measurements as determined from pCO2 changes of incubated culture and lake water samples

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Davies, John Mark
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A new method for measuring net community primary productivity and dark respiration was examined using steady state cultures and tested under field conditions. The method is based on measuring changes of pCO$\sb2$ in the headspace of a sealed incubation bottle by gas chromatography over the course of an incubation. At the end of the incubation the sample is acidified and the total DIC in the bottle is determined. Using the defined relationships between pCO$\sb2,$ DIC, and alkalinity (Park 1969) DIC is calculated for each sampling time with the assumption that alkalinity change is not significant. Nitrogen-limited, phosphorous-limited, and nitrogen and phosphorous limited cultures of Chlamydomonas reinhardtii were grown in chemostats, and subsamples were incubated using the pCO$\sb2$ method. Principal component analysis was used to evaluate expected rates of photosynthesis based on changes in particulate carbon with pCO$\sb2$ measured rates. Field measurements were conducted at the Experimental Lakes Area (ELA), Northwestern Ontario. Photosynthesis-irradiance curves were generated for all but two dates. (Abstract shortened by UMI.)