Monitoring of ecosystem responses to the delivery of environmental water in the Murrumbidgee system - Report 1
Commonwealth Environmental Water engaged Charles Sturt University in June 2011 to monitor the ecological response to the environmental water release that took place in June 2011. This is the first of two reports published on this monitoring.
In June 2011 nearly 110 gigalitres of Commonwealth environmental water was provided to a watering action managed by New South Wales, which totalled 161 gigalitres (including 23 gigalitres The Living Murray; 21 gigalitres of New South Wales Environmental Water Allowance and 8 gigalitres of private donations) targeting the mid-Murrumbidgee wetlands.
The environmental water was released from Burrinjuck and Blowering Dams with the environmental flow reaching a maximum daily discharge of 24908 ML/day in the Murrumbidgee River downstream of Burrinjuck Dam on 17th June 2011 and 9492 ML/day in the Tumut River downstream of Blowering Dam on 16th June 2011.
Monitoring of in-channel parameters (biofilms and macroinvertebrates) was undertaken at three reaches in the Murrumbidgee River downstream of Burrinjuck Dam and four reaches in the Tumut River downstream of Blowering Dam. Sampling was also undertaken in the Goobarragandra River, an unregulated tributary of the Tumut River that will serve as a reference site. Sampling was undertaken on four occasions between June and September 2011; one prior to the first flow pulse, and three sample dates after the environmental flow. The final monitoring of in-channel parameters will be undertaken in early October.
Aquatic vegetation, water quality, frogs, fish and waterbirds were monitored in mid-Murrumbidgee wetlands on three occasions between June (pre-watering) to August (post watering). The monitoring focused on 12 wetlands between Wagga Wagga and Carrathool. Nine of the 12 wetlands were inundated as part of the environmental flow release in June 2011. Two types of control wetlands have been included in the monitoring: (1) Control 1 wetland was inundated in December 2010 from the river but was not inundated by the environmental watering event in June 2011; and (2) Control 2 wetlands were not inundated via the Murrumbidgee River in December 2010 or June 2011 but are subject to relatively frequent low level inundation via rainfall run-off and as managed flows through the Murrumbidgee Irrigation Area. Monitoring of the ecosystem responses in the wetlands will continue until February 2012.
The ecosystem responses to date have been as expected, with a stronger ecological response likely to be detected in spring 2011 and summer 2012.
- Water quality was good at all of the inundated wetlands with no evidence of low dissolved oxygen or high salinity at any of the wetlands that received environmental water in June 2011.
- Aquatic vegetation cover remains low but there is evidence of germination by an increasing number of aquatic and semi-aquatic species which suggests that at least some species are beginning to recover following drought.
- Waterbirds were abundant with 26 species recorded. Dabbling ducks and fish-eating waterbirds such as little pied and little black cormorants were dominant. There is not yet any evidence of breeding activity, but this is not unexpected given the time of year and further surveys will be conducted in October.
- Fish communities were surveyed at seven wetlands in August. In contrast to earlier studies, two native fish, carp gudgeon and Australian smelt, dominated fish communities and juvenile carp gudgeon were observed at a number of wetlands.
- Frog species, particularly the winter and early spring active frog species including spotted marsh frog and plains froglet, have commenced breeding and egg masses were observed during August surveys although it is still too early to expect large numbers of tadpoles to be present. The spring and summer active species (Southern bell frog, Barking marsh frog and Peron‟s tree frog) are not yet active but are expected to commence breeding by October when further surveys are planned.
- Water rats were recorded at two of the wetlands that were inundated; this is the first time that this cryptic species has been recorded in the mid-Murrumbidgee wetlands between Narrandera and Hay.
- Biofilm response to the environmental flow suggest a short term benefit to in-channel communities. Immediately following the environmental watering event there was a significant reduction in the biomass of nuisance biofilm at some of the monitoring sites, most likely due to scouring of biofilms from increased water velocity. However, by 30th July (approximately 5 weeks after the recession of the environmental flow) when the dam operations returned to normal regulated practices, the biofilm biomass had increased to levels higher than observed prior to the environmental flow at most sites.
To provide maximum benefits of environmental flows to in-channel communities, multiple flow pulses may need to be delivered over a period of months to avoid long periods of relatively constant discharge.
Aquatic vegetation recovery has to date been slow since the improved water availability in 2010. Low seed-bank viability and fluctuating water levels may have contributed to reduced germination of aquatic vegetation. Follow-up flooding over multiple years may be required to re-establish aquatic vegetation communities and seed-banks.
Frog, fish and water bird responses recorded to date are typical of late winter. Top-up flows may be required later in summer to ensure successful breeding by summer active frog species such as the Southern bell frog or if bird breeding occurs. The need for top-up flows will be established during later monitoring in October and December 2011.
This report was funded and published by the Department of Sustainability, Environment, Water, Population and Communities.
The views and opinions expressed in this publication are those of the authors and do not necessarily reflect those of the Australian Government or the Minister for Sustainability, Environment, Water, Population and Communities.
While reasonable efforts have been made to ensure that the contents of this publication are factually correct, the Commonwealth does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication.
- Monitoring of ecosystem responses to the delivery of environmental water in the Murrumbidgee system - Report 2