Effects of experimental hydropeaking on periphyton nutritional quality in an Alpine stream

Hydropeaking has been shown to limit secondary production, most notably by causing catastrophic drift in downstream consumer communities. We hypothesized that rivers undergoing hydropeaking may also have suppressed periphyton biomass and especially nutritional quality (i.e. essential fatty acids) which may result in a secondary limitation on aquatic consumers. We further hypothesized that woody substrates, due to its effect on local hydraulic conditions, may react differently to hydropeaking than other hard substrates. We simulated daily 5-hour hydropeaks for 5 days in an in situ, open air, experimental flume system fed by a 2nd order stream in the Italian Alps. Hydropeaking resulted in decreased periphyton biomass on tile substrates, but there was no corresponding decrease in periphyton growing on wood. Essential polyunsaturated fatty acids and ω3:ω6 ratios decreased on both substrates, but there was less loss on wood. This suggests that hydropeaking may also limit production via depressing primary biomass and nutritional quality, and that the availability of wood substrates in the channel may mitigate this effect