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    • News: 2011-2012

The Commonwealth Environmental Water Office engaged Charles Sturt University to monitor the ecological response to environmental water delivered to the Edward-Wakool river system during the 2011-12 water year.

This is the first of two reports published on this monitoring. The second and final report is expected in late 2012.

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• Monitoring of ecosystem responses to the delivery of environmental water in the Edward-Wakool river system 2011-12 - Report 1 (PDF - 1,830 KB) | Monitoring of ecosystem responses to the delivery of environmental water in the Edward-Wakool river system 2011-12 - Report 1(Word - 1,890 KB)

Executive Summary

The Edward-Wakool river system, a major anabranch and floodplain of the Murray River, is a complex system of interconnected regulated streams, ephemeral creeks, flood runners and wetlands intersected by a network of irrigation channels. It has a history of regulated flows for irrigation, stock and domestic supply. This system has a high native species richness and diversity, including threatened and endangered fishes, frogs, mammals, and riparian plants.

Environmental water use options for the Edward-Wakool river system are outlined in Hale and SKM (2011). Water use options for the Edward-Wakool river system include: providing base flows to Jimaringle and Cockrans Creeks to maintain in stream water quality; augmenting natural flows to improve connectivity between the river channel and floodplains within Werai Forest; and providing pulse flows in the Edward-Wakool rivers to promote ecosystem function for in-channel flora and fauna.

In 2011-12 Commonwealth environmental water was delivered to the Edward-Wakool river system on three occasions. The overarching purpose of the delivery of Commonwealth environmental water was to provide pulse flows in the Edward-Wakool rivers to promote ecosystem function for in-channel flora and fauna. However each of the individual watering events also had specific targeted objectives. The three environmental watering actions were:

• November 2011 environmental watering in Colligen Creek
• February 2012 environmental watering in Colligen Creek and the Wakool River
• April to May 2012 environmental watering via irrigation escapes to the Edwards, Yallakool and Wakool Rivers.

Preliminary results of the monitoring of ecosystem responses to environmental watering in the Edward-Wakool system in 2011-2012 are presented in this report. A final report will be available later in 2012.

Delivery of environmental water in November 2011

In November 2011 5.5 gigalitres (GL) of Commonwealth environmental water was delivered to Colligen Creek in conjunction with 1.7 GL of water supplied by the New South Wales Government. The environmental water was used to gradually raise flows commencing on 19/11/2011 and then lower flows over 20 days.

The primary objective for the November 2011 environmental watering was to encourage movement of large bodied native fish such as Murray cod, silver perch and golden perch to initiate spawning and recruitment of these species. The watering event was also expected to maintain and enhance instream habitat (Commonwealth Environmental Water 2012a).

Delivery of environmental water in February 2012

In February 2012 7.5 GL of Commonwealth environmental water was delivered to Colligen Creek and the Wakool River in conjunction with 6.9 GL of water supplied by the New South Wales Government. The environmental watering in Colligen Creek commenced on 7/2/2012 to build on a natural high-flow event due to rainfall in the Murray catchment. The flow was maintained for five days before receding to baseflows by 1/3/2012. The delivery of environmental water to the Wakool River from the Wakool escape (providing water from the Mulwala Canal) commenced on 14/2/2012 but was reduced on 1/3/2012 and suspended on 6/3/2012 due to rainfall in the upper catchment.

The objective of the February 2012 watering action in Colligen Creek and the Wakool River was to improve the condition of the river and riparian ecosystems. The action was expected to enable the transfer of carbon, sediment, nutrients and biota, providing benefits to river channel food chains and the riverine ecosystem, and provide opportunities for small-bodied fish, such as Murray-Darling Rainbow fish and carp-gudgeon, to access important breeding and feeding habitat (Commonwealth Environmental Water, 2012b).

Delivery of environmental water in April to May 2012

During April and early May 2012 42 GL of Commonwealth environmental water was delivered into the Edward-Wakool system in conjunction with 2 GL of water provided by the New South Wales Government. Releases were made from the Edward, Yallakool and Wakool Escapes (from the Mulwala Canal). The environmental water was in addition to unregulated flows that had been delivered into the system via the escapes.

The objective of the April to May 2012 environmental watering action in the Edward-Wakool system was to provide and maintain refuge habitats for remnant fish populations, particularly Murray cod, (Commonwealth Environment Water, 2012c). The Commonwealth environmental water contributed to watering efforts of the Murray-Darling Basin Authority to prevent environmental damage in the area and ensure native fish such as the Murray cod have the best possible conditions.

Monitoring of responses to environmental watering

Monitoring of ecosystem responses to environmental watering was undertaken in four rivers in the Edward-Wakool system; Colligen Creek from the northern part of the system, Wakool River and Yallakool Creek from the southern part of the system, and Little Merran Creek from the western part of the system.

Parameters assessed were water quality, organic carbon, leaf-litter breakdown rates, biofilms, phytoplankton, zooplankton, macroinvertebrates, frogs and fish. For the majority of the parameters, sampling was undertaken monthly between August 2011 and early May 2012. Sampling was undertaken fortnightly for fish larvae between September 2011 and April 2012. Additional sampling of water chemistry was undertaken during the blackwater event in autumn 2012.

Hypotheses

This preliminary report focuses on responses to the November 2011 environmental watering in Colligen Creek by comparing results from samples collected before the environmental watering in November 2011 to those collected in December 2011, immediately after the watering event. The following hypotheses were examined:

• There will be a short-term increase in dissolved organic carbon and particulate organic carbon levels following the in-channel environmental watering in Colligen Creek in November 2011, but the environmental watering is not expected to trigger a blackwater event in this system.
• Following the environmental watering in Colligen Creek in November 2011, there will be a change in the community composition of algal biofilms, with an increase in early successional algal taxa in this river.
• Increased flow variability in Colligen Creek following environmental watering in November 2011 will ensure biofilm organic biomass in Colligen Creek remains below nuisance levels. Biofilm organic biomass is expected to be highest in Yallakool Creek that had a constant discharge over this period.
• Increased flow variability in Colligen Creek following environmental watering in November 2011 will maintain macroinvertebrate biodiversity via the provision of additional habitat and food resources made available with bank inundation (organic matter) and potential increases in algal primary production.
• Increased flow variability in Colligen Creek following environmental watering in November 2011 will maintain macroinvertebrate biodiversity via disturbance which eliminates competitive exclusion in the community by continually allowing less competitive species opportunities to colonise.
• Increases in river flow should select for invertebrate biological traits such as smaller body size, firmer attachment to substrate, and a streamlined body form, whereas decreases in flow should favour invertebrates with larger body size, increased swimming abilities, and spherical shape.
• Spawning of some native fish species, as measured by the abundance of larvae, will increase following the environmental watering in Colligen Creek in November 2011.

Preliminary findings from the delivery of environmental water to Colligen Creek in November 2011

Preliminary results of the monitoring and evaluation are presented in this report. It will focus primarily on short-term responses to the November 2011 environmental watering in Colligen Creek by comparing results from samples collected in November 2011 before the environmental watering to those collected in December 2011, immediately after the environmental watering.

• The primary objective for the November 2011 environmental watering was to initiate spawning and recruitment of large bodied native fish. There were consistent numbers of Murray cod larvae present at all reaches, but no evidence of immediate increases in spawning of this species in response to the environmental watering in Colligen Creek. Despite evidence of silver perch and golden perch adults occurring in the system, we did not detect these species spawning in response to the environmental watering with the sampling methodology employed in this project. Therefore no conclusion can be made regarding the effect of the environmental watering on spawning of these species.
• There was an increase in the abundance of carp gudgeon larvae in Colligen Creek following the November environmental watering. This response may be attributed to the environmental watering because at the same time there was little or no increase in the abundance of carp gudgeon larvae in the Wakool River, Little Merran Creek or Yallakool Creek. All fish larvae sampled in Colligen Creek following the environmental watering were native species. Larvae and juveniles of seven species of fish were sampled, with the dominant species in all rivers being Carp gudgeon spp., Australian smelt, and Murray cod.
• The November 2011 environmental watering had no adverse impacts on water quality in Colligen Creek. Dissolved oxygen concentrations measured in situ in all river reaches were above the 4mg/L (milligrams per litre) threshold of concern for aquatic health and were similar in all four rivers between September 2011 and February 2012. There was no evidence of blackwater associated with the November 2011 environmental watering in Colligen Creek, as dissolved organic matter profiles for the four rivers during November and December 2011 were very similar.
• There was a positive response of phytoplankton biomass (water column chlorophyll-a concentrations) to the November environmental watering in Colligen creek. Chlorophyll-a concentrations in water from Colligen Creek remained relatively constant after the environmental watering, whereas over the same period chlorophyll-a levels reduced in Yallakool Creek, Wakool River and Little Merran Creek that did not receive environmental water.
• There was no apparent response of leaf-litter breakdown rates to the November 2011 environmental watering, as breakdown rates were similar among the four rivers. This suggests that leaf-litter breakdown rates may not be a sensitive short-term response indicator of environmental watering. These results may change after examining samples from January to March 2012, as increasing summer temperatures potentially increases biological activity (microbial degradation and invertebrate feeding) and therefore breakdown rates.
• There was no change in organic biomass of one month old biofilms in Colligen Creek after the November environmental watering, although there was a build up of inorganic sediment on the bioflms over this period. Further analysis will test whether the environmental watering resulted in a change in the community composition of algal biofilms.
• There was a positive response of biofilm algal biomass (chlorophyll-a) to the November environmental watering in Colligen creek. Chlorophyll-a concentrations of one month old biofilms from Colligen Creek remained relatively constant in November and December 2011, whereas over the same period chlorophyll-a levels of one month old biofilms increased in the Wakool River and increased substantially in Yallakool Creek, as the constant discharge in these systems created conditions beneficial for rapid algal growth. The chlorophyll-a levels in Yallakool Creek in December did not approach nuisance levels outlined by Quinn (1991), but there is the potential for this to occur under prolonged low flows and increasing summer temperatures. Analysis of samples from January to April 2012 will determine whether environmental watering in Colligen Creek limited algal biomass in biofilms in that system compared to the other rivers.
• There was a seasonal increase in the abundance of zooplankton from November to December 2011 in all four rivers. This parameter did not appear to respond to environmental watering, as patterns of abundance in Colligen Creek were comparable to the rivers not receiving environmental water.
• There was an increase in the diversity of zooplankton in Colligen Creek following the November 2011 environmental watering, largely due to increases in a small number of rarely sampled taxon. This suggests that environmental watering may promote diversity in this group. The robustness of this pattern will be assessed following the processing of the remaining samples and analysis of the entire dataset.
• Preliminary findings suggest macroinvertebrate abundances decreased in Colligen Creek immediately after the environmental watering relative to the other three rivers. Macroinvertebrate family richness was higher in Colligen Creek prior to the environmental watering than in the other three rivers, but was similar to the other rivers after the environmental watering. This pattern may be related to the initial disturbance caused by the environmental watering. These preliminary findings may change once more data is processed.

Preliminary findings from the delivery of environmental water between February and May 2012

Although this report focuses on short-term responses to the November 2011 environmental watering in Colligen Creek, preliminary results for January to May 2012 are available for water quality, dissolved organic matter characterisation, and frogs. The final report on this project (available later in 2012) will include a detailed assessment of ecosystem responses over this period.

• Dissolved oxygen concentrations measured in situ on each sample date reveal that Colligen Creek had higher dissolved oxygen levels than all of the other rivers following the February 2012 environmental watering in Colligen Creek. There was no evidence of blackwater associated with the environmental watering, as the dissolved organic matter profiles for the four rivers during February were very similar.
• During the blackwater event in April 2012, Colligen Creek, Yallakool Creek and Wakool River (rivers that received environmental water as dilution flows via irrigation escapes) had higher dissolved oxygen levels than Little Merran Creek that did not receive the dilution flows. Dissolved oxygen data from continuous loggers (to be presented in the final report) will provide more detail related to the environmental watering and natural pulses. Weekly water samples collected during the natural flow events in March 2012 illustrate the progression of the associated blackwater event through all sites, with Little Merran Creek being the only system continuing to be affected in early April and all sites returning to normal levels by May 2012.

There was no immediate response of frogs to the environmental watering in Colligen Creek in February 2011. The abundance of frogs in Colligen Creek did not change in response to the February environmental watering or during the unregulated high flows in March. In contrast the abundance of frogs increased in March and April in Yallakool, Wakool and Little Merran Creeks with the most notable increase occurring in Yallakool Creek. The frog community in Colligen Creek was different to that in the other three rivers. It is not clear whether this was influenced by the environmental watering in Colligen Creek or reflects specific geomorphic features of the study reach. In future studies a more comprehensive understanding of frog responses to environmental watering would be gained by increasing the number of sample reaches within each river in order to capture the full extent of geomorphic diversity within each river.

Publishing information

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.