National Wetlands Update September 2012
Issue No. 21, September 2012
From dry to DAAMMP - restoring an ephemeral system
Deborah Bogenhuber, The Murray-Darling Freshwater Research Centre, Mildura
In-channel survey site after flood recession with
groundcover of amphibious species including
Limosella australis and Callitriche sonderi.
The Great Darling Anabranch, in south-west New South Wales, is an ancestral path of the Lower Darling River, approximately 480 kilometres long. It is a naturally ephemeral system, but was managed as a permanent water storage supply for landholders until early this century. Water was maintained behind the various block banks/regulators with little to no end of system flow into the Murray River.
Collaboration between landholders, managers, government and scientists over many years resulted in the construction of a pipeline in 2007, to secure water supply and return the Darling Anabranch to an ephemeral system. The Darling Anabranch Adaptive Management Monitoring Program (DAAMMP) was established to monitor ecological responses to the changed hydrology. Monitoring began in 2010, funded by the New South Wales Office of Environment and Heritage, and the program is expected to continue until 2020.
The DAAMMP includes annual condition monitoring of understorey vegetation communities and riparian tree health, and intervention monitoring of fish, frog and waterbird communities during managed and natural flows. In September 2010, an environmental flow was released down the Anabranch, which was superseded by an overbank flood by mid-October. The Anabranch flowed its full length for the first time in over 10 years.
At the time of the 2011 survey, many of the monitored sites had recently exposed damp sediments, following flood recession. These conditions are required for the germination and recruitment of many common 'damp-loving' plant species along the Darling Anabranch. Therefore the understorey landscape underwent a significant shift from being dominated by terrestrial, dry-loving species in 2010, to one dominated by amphibious and damp-loving species in 2011.
However, hydrological differences occurred along the Darling Anabranch, and persisted at the time of monitoring. This resulted in different plant communities being recorded in different parts of the system. Sites that experienced a 'natural' flood recession differed from sites that did not (due to regulation by man-made structures) in the following ways:
- higher species and functional group diversity at all elevations
- lower proportion of exotic species
- high abundances of amphibious and 'damp-loving' species.
Diverse understorey community with amphibious
and damp-loving species. (D. Boganhuber)
Of interest was the lack of submerged and to some extent amphibious emergent species recorded throughout the system. As further data is collected, it is anticipated that this will be combined with historical research, seed bank trials and understorey surveys in more stable backwater habitats to investigate the question: Were aquatic vegetation communities in inundated zones ever a major component of the vegetation community along the Darling Anabranch?
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