Pre-Recorded Oral Presentation as part of National Virtual Conference AFSS Conference 2020

Using experiments to quantify the effect of inundation duration and timing on herbaceous plants to inform flow management in regulated rivers (#108)

Christopher Jones 1 , Joe Greet 2 , Lyndsey Vivian 1 , Vanja Kitanovic 2 , Alanna Main 2 , Scott McKendrick 2
  1. Arthur Rylah Institute for Environmental Research, Heidelberg, VIC, Australia
  2. The University of Melbourne, Burnley, VIC, Australia

Aims: Regulated river flow regimes often differ significantly from natural regimes, with decreased natural flow peaks and increased summer flow. While temperate seasonal flows in winter and spring are thought to benefit riparian plants, we aimed to quantify the impacts of seasonal (winter/spring) and unseasonal (summer) flows on riparian plants.

Methods: We conducted a series of nursery experiments using outdoor tanks to investigate the survival and growth responses of various herbaceous plant species to different periods of inundation in different seasons. Three experiments were conducted: (Exp 1) late winter/early spring; (Exp 2) mid-spring; and (Exp 3) late summer/early autumn. We also examined the effects of shading (Exp 1 and Exp 3) and increased water temperature (Exp 2), on plant responses.

Results: In all experiments, longer durations of inundation had greater negative impacts on survival and/or growth all species than shorter durations. Inundation in winter/spring killed only three of 324 plants, following the longest inundation duration of 35 days. Seedlings had very similar survival to more mature plants. Inundation in mid-spring killed some terrestrial plants in as little as 9-18 days but did not kill many riparian species even after 44 days. Artificially warming tank water to summer temperatures in mid-spring killed some species faster. Summer inundation killed nearly all terrestrial plants in two weeks. While many riparian species survived mid-spring and summer inundation, plant growth (height and biomass) declined due to inundation. Shading when inundated increased mortality rates in summer but had minor impacts on inundated plant growth.

Conclusions: This set of experiments demonstrates the significant impacts of plant inundation over timeframes experienced in rivers through natural and regulated flows. Flows in warmer months have far more damaging impacts on plants and need to be carefully managed to avoid negative ecosystem impacts. Strategic timing of regulated flows can be used to manipulate plant composition towards riparian species dominance.