Department for Environment and Natural Resources— emergency actions (2008–10)
As part of the DENR’s Murray Futures Long-term Plan, several remediation measures were carried out within the icon site during the drought. These measures were designed to reduce the impacts of continued low or non-existent flows and to prevent continued ecological degradation.
Acid sulfate soil remediation
The primary threat during the drought condition within the Lower Lakes was the presence and potential for exposure of acid sulfate soils as a result of declining water levels. A series of emergency measures were put in place to prevent, mitigate and control soil acidification including:
• the Goolwa Channel Water Level Management Project which included the installation of temporary flow regulators at Clayton Bay, and Currency Creek in order to retain fresh water, maintain soil saturation and prevent further soil and water acidification
• construction of a bund at the Narrung Narrows between Lake Alexandrina and Lake Albert to allow the Lakes to be managed independently of each other. Pumping was undertaken to maintain water levels in Lake Albert above the predicted acidification trigger point
Bioremediation and revegetation
Several thousand hectares of exposed lakebed sediments were aerial, machine and hand seeded in order to stabilize soils and prevent soil erosion. In addition to addressing soil erosion, the seeding was part of a trial to understand how plants grow in acid sulfate soils and to assess whether the techniques used mitigates acid sulfate soils by promoting bioremediation.
The threat of local extinction of threatened fish species from the Lower Lakes has led to specific conservation measures. Yarra pygmy perch (Nannoperca obscura) are also being bred in captivity at Cleland Wildlife Park. Environmental water was delivered to Boggy Creek on Hindmarsh Island to conserve a population of Murray hardyhead (Craterocephalus fluviatilis), while a captive breeding population was also established. Environmental water has also been delivered to Turvey’s Drain near Milang, to conserve southern pygmy perch (Nannoperca australis) and Murray hardyhead. Extensive ex-situ conservation measures have also been undertaken by releasing and breeding native fish within spring fed dams within the catchments near the CLLMM region. These populations will then be translocated back to the CLLMM when suitable conditions have re-established.
Monitoring of diadromous fish populations (including congolli), common Galaxias (Galaxias maculatus), lampreys (Geotria australis & Mordacia mordax) and short-finned eels (Anguilla australis)) in the Lower Lakes and Coorong estuary through The Living Murray program over the last four years by SARDI Aquatic Sciences has detected catastrophic declines in populations and recruitment due to a lack of flows over the barrages and a loss of connectivity between Lake Alexandrina and the Murray Mouth/Coorong region (Jennings et al. 2009).
Prior to the drought, the last barrage fishway releases occurred in 2006–07. As congolli only live for only 4-5 years, there was a real concern that this species would be lost from the Murray–Darling Basin, as the lack of connectivity between freshwater and marine environments prevented recruitment of the species. Acoustic tagging of adult females in Lake Alexandrina and specifically the Goolwa weir-pool detected fish travelling large distances over winter between barrages trying to find a passage out of the lake and into the Coorong and ocean environments to breed.
As a result of the alarming data collected through the barrage fish assemblage monitoring program and congolli tagging and tracking, a water bid to operate the Goolwa barrage vertical slot fishway was submitted to TLM for 5.5 GL to be split between winter and summer 2010–11 by Department for Water. While the bid was ultimately approved, water levels on the freshwater side of Goolwa barrage in winter 2010 (critical migration time for adult females) were still too low to operate the fishway, therefore fresh and estuarine environments were still separated.
In a joint State government agency initiative led by DENR, the boat-lock at Goolwa Barrage was then utilised in a successful trial to provide passage for fish. The trial took place in August 2010; when the upstream gate was partially opened, nearly 800 adult congolli and various other species of fish swam into the lock. After the water equalised, the downstream gate was partially opened, allowing the adult female congolli to exit into the estuarine environment. SARDI Aquatic Sciences trapped and released around 1,700 adult females utilising the lock during the trial, indicating the boat lock was an effective method of providing fish passage during periods of low lake levels (Figure ).
Conditions in spring 2010 allowed for all fishways to be operational since the 14 September 2010. Monitoring by SARDI Aquatic Sciences has determined juvenile congolli and common galaxias utilising fishways (in particular Hunters Creek) to gain access into Lake Alexandrina. This indicates that spawning and recruitment has occurred in the estuary, and that this is likely due to the Goolwa lock intervention (B. Zampatti, personal communication, 31 January 2011).