The application of radioactive tracers to the study of lake metabolism

TitleThe application of radioactive tracers to the study of lake metabolism
Publication TypeThesis
Year of Publication1958
AuthorsSaunders GW
DegreeDoctor of Philosophy
Number of Pages102 pp.
UniversityUniversity of Michigan
CityAnn Arbor, MI

1. Synthetic experiments on the utilization of radioactively labeled glucose, glycine, glutamic acid, starch, and two protein fractions by the biotic community in a small eutrophic lake were conducted. 2. A fractionation technique for differentiating algal and bacterial bioactivity was developed. The algae and some bacteria were removed by filtration through a 13 micron pore size sintered glass filter. The radioactivity in the bacteria of the filtrate was determined. By prorating bacterial metabolism on the basis of cell counts and assumed uniform bioactivity, the total bacterial metabolism in a lake sample was estimated. Algal metabolism was determined by subtracting total bacterial metaboism from total community metabolism. The standard error for such determinations was +- 8.4%. 3. The fractionation technique requires that only an insignificant number of bacteria are attached to the algal forms and that size selection of bacteria does not occur. When bacterial attachment occurs the error introduced cannot be determined. The error introduced by size selection may be roughly corrected. In most cases this correction is not necessary and for the example given it was 16%. 4. In 1956 Oscillatoria tenuis constituted at least 90% of the algal biovolume. The fractionation technique was validated by plotting the metabolism of glucose and glycine versus the biovolume of this alga. The regression was tested by the Kendall rank correlation coefficient. Glycine satisfied the 0.02 significance level; glucose the 0.10 significance level. 5. Autoradiography was used to verify the utilization of various organic compounds by the algal species present in the 1957 samples. The algae were not able to utilize starch or the protein fractions. Only certain species were able to take up the organic monomers. 6. It was demonstrated that tracer-fractionation methodology could be used in time sequence studies to follow the metabolism of organic substances in the total community or in two fractions of the community. This has potential significance in determining turnover times for both the organic metabolites and the metabolically active biomass of the aquatic organisms. The community turnover time for starch during the summer of 1957 was from 10-24 hours. 7. It was shown that algal glucose-glycine heterotrophy could amount to 15-300% of photosynthesis. 8. A synthesis of tracer-fractionation methodology with the concepts of bioactivity and productivity was discussed within the framework of a simplified tripartite trophic level system of trophic dynamics. Both quantitative determination of bioactivity and evaluation of causal relations were theoretically developed.