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Heterotrophic Utilization of Organic Carbon in Aquatic Environments¹

ABSTRACT

Field and laboratory investigations were performed to determine the contribution of dissolved organic carbon (DOC) to the eutrophication process and its effect on heterotrophic bacterial activity. Organic carbon concentrations of selected waters and waste waters from northern Idaho were determined by a modified persulfate wet combustion method. Electrolytic respirometry was employed to assess heterotrophic respiration responses to DOC in natural and enriched water samples. Concentration ranges of dissolved organic carbon furnished by sewage and glucose supplemented with micronutrients were incorporated into natural water samples taken from two experimental reservoirs. The heterotrophic bacterial response to simulated DOC enrichment was measured in terms of oxygen uptake and CO₂ evolution, substrate utilization, and biomass production. Oxygen uptake was found to be the most sensitive parameter for response measurement. Results indicated growth factors or vitamin limitations occurred in some aquatic samples. Significant responses to heterogenous carbon substrates were detected at substrate concentrations commonly occurring in pristine, low DOC waters. A direct linear relationship existed between heterotrophic activity and the concentration of available DOC. Assuming no deficiency in other essential nutrients, the DOC concentration was shown to regulate the rate and net response of heterotrophic bacterial growth and activity in aquatic environments. DOC levels were found to reflect net trophic conditions unique to individual sampling locations, thereby lending itself to assays for eutrophication assessment and pollution.

Key Words: eutrophication • bacteria • simulated organic enrichment • sewage • respiration • biomass response

¹ Contribution from the Dep. of Bacteriol. and Biochem., Univ. of Idaho and the Idaho Agric. Exp. Stn., Moscow, ID 83843. Approved by the Director of the Idaho Agric. Exp. Stn. as Res. Pap. no. 77510.

² The senior author is now Assistant Professor, Univ. of Tennessee, Knoxville, TN 37916. Second author is Professor and Head, Dep. of Bacteriology, Univ. of Idaho.

Received for publication October 12, 1977.