IMPACT OF STORM-FLOW ON ELECTRON-TRANSPORT SYSTEM ACTIVITY IN RIVER BIOFILMS

1. The effect of storm-flow on light- and dark-grown biofilms from a North Wales river was monitored using electron transport system (ETS) activity and epifluorescence cell counts. 2. Artificial substrata were colonized in the river, exposed to ambient-flow (60 cm s-1) or storm-flow (235 an s-1 with suspended sediment addition) for 12 h in a laboratory flow tank, and returned to the river to monitor the recovery period. 3. Total cell densities decreased in both the light- and dark-grown biofilms as a result of storm-flow. In addition, storm-flow ETS activity per cell increased significantly in the light-grown samples (2.7 times) but did not increase significantly in the dark-grown samples (1.6 times). 5. Within 48 h, storm-flow total cell densities and ETS activity levels had returned to ambient-flow levels in both light- and dark-grown biofilms. 6. Within each light regime, despite their different histories, both ambient and storm-flow samples responded the same to daily changes in the river environment, including a second disruption by natural causes, for the remainder of the 24-day experiment.