Changes in riparian vegetation communities resulting from weir pool manipulation at the Lindsay-Mulcra-Wallpolla icon Site, 2020-2022 (#207)
Gary J Palmer
1
,
Susan Gehrig
2
- Ecology Australia, Thomastown, VIC, Australia
- Flora Flow and Floodplains, Mildura, VIC, Australia
- The Murray River is highly regulated by infrastructure that creates weir pools. Changes to flow regimes created by this infrastructure include reductions in flow regime variability, decreased flood frequency and seasonal redistribution of flows. Manipulation of weir pool levels within the main river channel and associated creek channels has the potential to effect understorey composition and recruitment.
- Ecology Australia was engaged by the Mallee Catchment Management Authority (CMA) to monitor six sites within the Lindsay-Mulcra-Wallpolla floodplains each spring and autumn during 2020-2021, 2021-2022 and 2023-2024. Field surveys were conducted on the Victorian floodplains adjacent to weir pools 7 and 8, where water levels are manipulated, and weir pool 9, where water level variability is considerably lower, acting as a control. Ten transects assessing species composition were conducted at each site at fixed elevations. Additionally, a seedbank study was conducted using soil samples taken at staged elevations to provide further quantitative data on species composition and recruitment.
- The vegetation composition on the floodplain adjacent to weir 9 appears to be distinctive from that at weirs 7 and 8. Species associated with Weir 9 tend to require year-round presence of water, indicative of generally stable water levels within Weir 9. Results suggest that greater fluctuation in water levels at weirs 7 and 8 is promoting a different composition of floodplain vegetation to that found at weir 9. Species richness and abundance across all years and weirs has been variable. The soil seedbank study found weir 8 to have the greatest species richness and abundance (although no significant difference was found between the 3 sites).
- Results can inform weir pool manipulation and adaptive management to help achieve long-term watering plan targets. Appropriate environmental watering regimes will help to restore vegetation communities, that in turn will contribute to ecosystem functioning as a source of nutrients and organic matter.