Batch culture experiments examined the ability of an isolated bacterial community to utilize four humic substances with similar molecular size but variable elemental composition. Univariate and multivariate linear regression analysis of the results provided evidence of a significant positive relationship between the N:C ratio and bacterial concentrations. In contrast, neither H:C nor O:C ratios were significant predictors of humic substances bioavailability, and their inclusion in the multivariate model provided no further 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 moieties typical of many aquatic systems.

This study assessed the effects of substratum roughness, using two grades of silicon carbide sandpaper coupons, and river flow rate on the colonisation dynamics of bacteria, heterotrophic flagellates and algae over a 16 week incubation period in the River Conder, UK. In the short-term i.e. up to 2 weeks, a combination of substratum roughness and high river flow significantly increased bacterial biomass on the coupons, but did not affect any of the numbers cm -2 of other organisms. In the long-term i.e. up to 16 weeks, neither parameter appeared to affect the development and maintenance of the mature biofilms. Evidence of a diverse protozoan community within the biofilms was recorded, thereby highlighting the need to consider the effect of these primary consumers on biofilm dynamics in future studies.

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