Response of Stream Biofilms to Pulsed Versus Steady-State Phosphorus Additions

Our current understanding of how algal-dominate biofilms in streams respond to phosphorus (P) enrichment is largely based on the assumption that streams have a constant P supply. However, in reality natural streams experience large swings in P concentrations due to runoff and in-stream biotic and abiotic uptake. The purpose of this study was to compare the effects of a steady-state P release versus successive pulse events on algae-dominated biofilms colonizing artificial streams. One treatment (n=4) was maintained at a constant 12 µg P/L, another was subjected to weekly 8-hour pulses at 252 µg P/L (n=4) and a third treatment was maintained below P detection limits (n=4). Both the steady-state and the pulse treatments received an equivalent amount of P by the end of the experiment. We found that an overplus storage of polyphosphate (polyP) occurred in response to P pulses. Furthermore, this internal P storage mechanism supported primary productivity during later P stress. This experiment could demonstrate how the effects of temporal P pulses have been previously underestimated which may have largescale implications for nutrient assessments in oligotrophic environments.