Response of epixylic biofilm metabolism to water level variability in a regulated floodplain river

Managed flow releases can influence biomass and productivity of littoral biofilms in regulated lowland rivers by varying the frequency and duration of inundation and desiccation. I examined the effects of inchannel water level variability on the productivity of littoral biofilms growing on woody substrata in the highly regulated Murrumbidgee River, southeastern Australia. Wooden blocks of river red gum (Eucalyptus camaldulensis) were placed at a subsurface depth and used to experimentally simulate 3 regimes of water level variability common to the Murrumbidgee River: 1) low inundation/emersion frequency (permanent inundation), 2) high inundation/emersion frequency (5 d inundated, 9 d emersed), or 3) intermediate inundation/emersion frequency (11 d inundated, 21 d emersed). Maximum net primary productivity of biofilm was achieved after 29 d of permanent inundation. After 75 d, a heterotrophic biofilm developed on blocks exposed to the high frequency of inundation and emersion, whereas an autotrophic biofilm developed on blocks exposed to the intermediate frequency of inundation and emersion. In regulated lowland rivers, water level variations from managed-flow releases of intermediate frequency and duration have the potential to provide maximum rates of biofilm productivity on woody substrata.