Colonisation and temporal dynamics of macrophytes in artificial stream channels with contrasting flow regimes

Abstract

Colonisation and temporal dynamics of macrophytes were followed over 2 years in 12 artificial channels to determine the effect of contrasting hydrological regimes. The channels had similar baseflow and four different frequencies of flow pulses (six times the baseflow). causing an eight fold increase in current velocity. It took 30 weeks for the initial 1% macrophyte cover to establish in the channels and 83 weeks for 90 % cover to establish. The relatively long colonisation time indicates that the artificial channels were not affected by adjacent vegetation that could grow into the channels, or propagules in the sediment. Propagules were only supplied from upstream reaches. Species composition changed over time. Veronica anagallis-aquatica and Lagarosiphon major were the primary colonists, Potamogeton crispus and Myriophyllum propinquum the secondary colonists, and the tertiary colonists were dominated by amphibious species (V anagallis-aquatica, Rorippa nasturtium-aquaticum, Mimulus guttatus). Colonisation of the channels was not affected by local current velocity within the baseflow range (0-0.12 m s -1 ) and plants were not washed out at any velocities up to 0.74 m s -1 at high flows. Flow regime did not show any effect on colonisation or growth of the macrophytes suggesting that high flow conditions did not result in removal of vegetation by increased current velocity. This supports previous studies, which have suggested that removal of vegetation during high flow may be more related to bed sediment destabilisation.