Gwydir River Selected AreaMER Project

Newsletter 2December 2019

In this issue:

Core monitoring activities July - December 2019o Hydrologyo Water quality and Foodwebso Birdso Vegetationo Turtles

Contingency monitoring activities July - December 2019o Water quality in pool refugiao Water quality Incident responseo Fire response

HYDROLOGY

Recent flows through the lower Gwydir system have been restricted to regulated deliveries of high security water, stock and domestic water, and water for the environment. Over the last three months several environmental flow events have been delivered into the Gwydir, Mehi and Carole Creek systems to re-connect previously isolated waterholes. These occurred on the 15-25 October and 9-22 December 2019. Another flow is scheduled for early in the New Year, with the purpose of maintaining and providing access to refuge habitat, increase connectivity through these channels and improve water quality in pools.

The October flow consisted of 5,000ML of environmental water from Copeton Dam which reached Tyreel and Combardello weirs and Carole Creek near Garah in early November. This was shortly followed by a WaterNSW delivery of stock and domestic water that extended water further down the Mehi, Gwydir and Carole systems.

The December release was 2,000ML delivered out of Tareelaroi weir down the Gwydir, Mehi and Carole Creeks. As of 20 December, the water had reached Tyreel weir on the Gwydir, Moree town on the Mehi, and Midkin on Carole creek.

Photo 1: Refuge pool upstream of Boolooroo Weir on the Gwydir River before (top), during (middle) and after (bottom) the October flow event.

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Gwydir River Selected AreaMER Project

Newsletter 2December 2019

WATER QUALITY AND FOODWEBS

The MER team monitored water quality before, during and after the October environmental flow event (Photo 2). Water quality parameters in most of the channels and waterholes remained good with oxygen levels in the acceptable range for aquatic animals (>4mg/L).

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Gwydir River Selected AreaMER Project

Newsletter 2December 2019

Photo 2. Taking water quality samples at Combardello weirpool during the flow event in October.

However, in the Mehi River, an initial slug of poor quality water occurred (black water, Photo 3). At some points, dissolved oxygen concentrations were as low as 0.5mg/L, especially around Combardello weir. This caused a number of fish deaths (200-300 fish) along this reach of the Mehi River. The water quality of Gingham Waterhole was also poor as it dried down, with very high levels of dissolved oxygen (from high algal growth), and high salinity and turbidity. This deterioration of water quality is not unusual for a waterhole in dry times with very low water levels.

Photo 3. Blackwater within the Mehi River in October 2019.

As part of ongoing water quality monitoring in refuge pools of the Gwydir, Mehi and Carole channels, continuously logging dissolved oxygen and temperature sensors have been deployed at various sites within each channel (Photo 4). This will allow us to monitor the changing conditions in these pools to inform ongoing environmental water delivery (Figure 1). If you see these loggers please do not touch them!

Photo 4. Buoy with dissolved oxygen/temperature probe suspended under it.

Figure 1. Water temperature in one of the monitored pools in the Mehi River. Surface temperature (orange) showed marked daily fluctuations, while at the bottom of the pool (blue) temperature is more consistent over time.

Micro and macroinvertebrates were also sampled within the refuge pool sites in December (Photo 5) as part of a research project into foodweb concentration and contraction during pool drydown. This was the first sampling time for this project and these data

contribute to establishing the pre-drydown resource base available to aquatic fauna such as fish and turtles.

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Gwydir River Selected AreaMER Project

Newsletter 2December 2019

Photo 5. A water flea (Macrothricidae) under microscopic magnification. The pink dye (Rose Bengal stain) makes them visible against the organic matter and sediment in the sample.

BIRDS

Spring Waterbird diversity surveys were undertaken in November by UNE/2rog, DPIE EES and NPWS staff. Surveys were hampered by the extreme fire danger, which protracted the survey of all sites. Most sites were dry and hence waterbird numbers were generally low, except in the Mallowa and at Whittakers Lagoon, where better numbers were seen due to recent watering of these areas.

VEGETATION

Spring vegetation surveys were undertaken in late November at sites within the lower Gwydir, Gingham and Mallowa systems. Most sites were dry except for several sites in the eastern Mallowa that had been recently inundated. Vegetation cover was generally low across most of the Gingham sites, with many sites being recently impacted by a fire that occurred in September. On a positive note, there was evidence of vegetative regrowth across many fire effected sites (Photo 6).

Sites in the Gwydir wetlands showed greater vegetation cover, through most of it was very dry (Photo 7).

Photo 6. Post fire regrowth in the Gingham watercourse.

Photo 7. Vegetation site in the Old Dromana area of the lower Gwydir wetlands.

TURTLES

Annette Deppe, a Masters student at UNE, is investigating the movement of turtles in the Gwydir Wetlands. She has been catching, measuring and tracking turtles in Gingham Waterhole in the Gingham system for the last few months (Photo 8), which is nearly dry. She has trackers on 24 turtles in total – 9 Eastern longneck and 15 Murray River turtles. Her data suggests a very different response from the two species, with all Murray River turtles remaining in the receding pool within the Waterhole. In contrast, many of the Eastern longneck turtles have walked from the waterhole, taking refuge in leaf litter under logs in the surrounding

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Gwydir River Selected AreaMER Project

Newsletter 2December 2019

woodlands. One turtle has even walked over 2km from the waterhole!

Photo 8. Surveying turtles in Gingham Waterhole

FIRE RESPONSE

As noted above, a fire burned around 1400ha of the Gingham watercourse within the Gwydir SCA in September 2019. This event offers an opportunity for the MER project to investigate vegetation response post-fire and how water for the environment influences this. Planning is underway to undertake surveys to compare burnt and unburnt sites for vegetation cover and diversity in water couch/sedgeland and Coolibah woodland communities (Photo 9). We are also planning to conduct mesocosm experiments to look at differences in invertebrate seedbank response to inundation from fire-affected soil samples. This will inform how the productivity of these areas has changed, and how this may change over time as the system recovers from the fire.

Photo 9. Surveying vegetation at a sedgeland plot that was recently effected by fire in the Gwydir SCA.

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