Comparison of Planktonic Microbial Communities among Nine North American Streams

The ecological significance of microbial communities in aquatic systems has been documented to varying degrees in marine and lentic systems; however much less is known about their relative abundance and distribution among streams with different environmental conditions. In this study, the relative abundance and distribution of different bacterial taxa, virus-like-particles (VLP) and protozoa in planktonic communities from nine streams in different regions of the USA were examined. There were clear differences in the abundance and distribution of the microorganisms examined among sites within a stream and among the streams. Also, there were strong relationships between the abundance of some of the microbiological variables measured and the environmental conditions of the streams. Most of the bacterial taxa examined were correlated with chlorophyll-a concentrations, while no significant relationships were observed between VLP numbers and any of the environmental or microbiological variables measured in the streams. In contrast, protozoa numbers were correlated with nitrate and dissolved organic carbon (DOC) concentrations. Our results suggest that differences in environmental conditions influence microbial numbers and distribution among the streams examined.