Further evidence of elemental composition as an indicator of the bioavailability of humic substances to bacteria

Batch culture experiments examined the ability of an isolated bacterial com munity to utilize four humic substances with similar molecular size but var iable elemental composition. Univariate and multivariate linear regression analysis of the results provided evidence of a significant positive relatio nship between the N:C ratio and bacterial concentrations. In contrast, neit her H:C nor O:C ratios were significant predictors of humic substances bioa vailability, and their inclusion in the multivariate model provided no furt her explanatory power compared with the univariate model using N: C as the single independent variable. These findings suggest that N:C ratios provide the best indicator of bioavailability for complex, recalcitrant carbon moi eties typical of many aquatic systems.