Relation of environmental factors to density of epilithic lotic bacteria in 2 ecoregions

Abstract

AbstractAlthough heterotrophic bacteria are important components of stream ecosystems, little is known about the factors that contribute to their abundance. We used data from 69 streams to examine both the direct and indirect effects of algal biomass (chlorophyll a), dissolved organic C (DOC), NO3−, soluble reactive P (SRP), and NH4+ on bacterial density. All potential relationships were simultaneously evaluated using path analysis. Streams in 2 ecoregions (unglaciated and glaciated) were used to determine if important factors varied between ecoregions. The results indicated that algal biomass was the best predictor of bacterial density in both ecoregions. Furthermore, inorganic nutrients appeared to mainly affect bacteria indirectly through their influence on algal biomass. However, a quantitative relationship between algae and bacteria was not observed when algal biomass was <5 μg chlorophyll a/cm2. The lack of relationship between algae and bacteria at low algal biomass may help to explain why some stu...