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Murrumbidgee blackwater monitoring

Blackwater management using environmental water allowance – November 2010 to March 2011

Publisher: NSW Department of Primary Industries, Office of Water

Murrumbidgee Blackwater Monitoring

Published: September 2013

ISBN 978 1 74256 551 4

More information

Lorraine Hardwick, NSW Office of Water, Wagga Wagga Gordon Honeyman, NSW Office of Water Hay, John Temple, NSW Office of Water, Leeton

www.water.nsw.gov.au

Acknowledgments

David Ryan, Simon Mitrovic, Lee Bowling Jobtrack 11869

© State of New South Wales through the Department of Trade and Investment, Regional Infrastructure and Services 2012. You may copy, distribute and otherwise freely deal with this publication for any purpose, provided that you attribute the NSW Department of Primary Industries as the owner.

Disclaimer: The information contained in this publication is based on knowledge and understanding at the time of writing (November 2012. However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of the Department of Primary Industries or the user’s independent adviser..

http://www.water.nsw.gov.au/


1 NSW Office of Water, September 2013

Contents Introduction .................................................................................................................................................. 3

Methods ........................................................................................................................................................ 4

Site Selection........................................................................................................................................... 4

Hydrology ................................................................................................................................................. 4

Time series data collection .................................................................................................................... 4

Point data collection ............................................................................................................................... 5

Results .......................................................................................................................................................... 6

Hydrology ................................................................................................................................................. 6

Dissolved oxygen .................................................................................................................................... 8

Nutrients and water quality .................................................................................................................. 12

Water quality in the River ................................................................................................................ 12

Effect of inflows of blackwater into the river ................................................................................. 16

Discussion .................................................................................................................................................. 18

Bibliography ............................................................................................................................................... 20

Appendices ................................................................................................................................................ 22

Figures Figure 1. Murrumbidgee blackwater monitoring sites................................................................................... 4

Figure 2. Lower Murrumbidgee Flows September 2010 to May 2011 ......................................................... 7

Figure 3. State Water releases to achieve initial dilution ............................................................................. 7

Figure 4. Cumulative dilution releases, volumes and impact on flow at Maude weir ................................... 8

Figure 5. Lower Murrumbidgee blackwater event ........................................................................................ 9

Figure 6. Maude weir loggers, 1 and 4 metres depth dissolved oxygen and flow ....................................... 9

Figure 7. Redbank weir loggers, 1 and 6 metres depth dissolved oxygen and flow .................................. 10

Figure 8. Balranald weir loggers, 1 and 3 metres depth dissolved oxygen and flow ................................. 10

Figure 9. Dissolved oxygen, lower Murrumbidgee River, January - April 2011 ......................................... 11

Figure 10. Blackwater at Bourpie ............................................................................................................... 11

Figure 11. Dissolved oxygen (mg/L), lower Murrumbidgee River, November 2010 to April 2011 ............. 12

Figure 12. Electrical conductivity (μS/cm) .................................................................................................. 12

Figure 13. Turbidity (NTU) .......................................................................................................................... 13

Figure 14. Colour (true colour units) ........................................................................................................... 14

Figure 15. Dissolved organic carbon (mg/L) .............................................................................................. 14

Figure 16. Total nitrogen (mg/L) ................................................................................................................. 15



Figure 17. Total phosphorus (mg/L) ........................................................................................................... 15

Figure 18. Effect of Bourpie Creek inflows on Murrumbidgee River water quality during blackwater event ..................................................................................................................... 17

Figure 19. Floodwater returning from the Lowbidgee floodplain into the Murrumbidgee River near Balranald ......................................................................................................................... 18

Tables Table 1. Temperature (Onetemp - Hobo) loggers depth (cm) …………………………………………………4

Table 2. Dissolved oxygen logger (D-Opto) depth 1 metre from surface and one metre from bottom ……4

Table 3. Dilution releases (ML) for lower Murrumbidgee river, January-February 2011 …………………...6

Table 4. Travel times between weirs ………………………………………………………….………………….6

Table 5. Relationships between water quality parameters …………………………………………………...16

Table 6. Reports of fish deaths ……….…………………………………………………………………………16



Introduction Blackwater events are a feature of forested arid zone rivers, such as those in the Murray Darling Basin. High variability in flows, with occasional floodplain inundation, mean that flood pulses may episodically return large flows to the river from the floodplain (Junk et al. 1989). Australian river red gum (Eucalyptus camaldulensis ) floodplains produce large quantities of highly refractive leaf and tree litter, which accumulates during dry periods (Baldwin 1999). Flooding creates pools and runners across the floodplain where high rates of microbially mediated decomposition during summer (Burns and Ryder 2001; Burford et al. 2008; Hladyz et al. 2011)) creates low dissolved oxygen (hypoxia) conditions. In addition, leaching of tannins and polyphenols from the red gum material results in coloured water – or blackwater - high in dissolved carbon (Howitt et al. 2007; Whitworth et al. 2012) and associated nutrients (Scholz et al. 2002). Hypoxic blackwater commonly affects aquatic biota by reducing available dissolved oxygen, particularly during summer, when temperatures are high and microbial decomposition of the organic carbon is greatest (Hladyz et al. 2011). In many other parts of the world,in particular colder regions, high levels of dissolved organic carbon (DOC) are normal features of blackwater rivers and not associated with severe oxygen depletion. (Meyer 1999; Whitworth et al. 2012). Microbial decomposition of DOC occurs more slowly than DO replenishment rates

While blackwater events occurred naturally in the past, regulation of Australian lowland floodplain river systems has increased their intensity while decreasing their frequency (Boulton and Lloyd 1992; Bunn et al. 2006). Blackwater events are now more likely to lead to lower levels of oxygen in rivers and more devastating fish kills and ecosystem collapse.

The Murrumbidgee River experienced drought conditions between 2000 and 2010, with flows well below long term averages. Floodplain inundation was minimal during these years, with any available water being diverted for essential human services and irrigation. Over that 10 year period, litter fall accumulated naturally and may have been exacerbated by red gum logging on some parts of the floodplain. This resulted in high levels of available detritus on parts of the lower Murrumbidgee floodplain.

During spring 2010, there were several large flow events that led to the end of the drought in the Murrumbidgee valley (Figure 1). During December, the largest of these spilled substantially onto the Murrumbidgee floodplain with widespread inundation. As irrigation demand was high at the time, the water operators - State Water, made significant diversions from the in-channel tail of the flood peak, leaving low flows below major irrigation diversions at Gogeldrie weir. Due to flat topography and differential flow rates in the river and floodplain, large returns of floodplain water were expected to continue for up to three months, while river channel flows were minimal. This widespread flooding of the Lowbidgee floodplain which had experienced little recent inundation, combined with extensive litter accumulation from red gum forests and logging debris, led to large amounts of blackwater being generated on and entering the river from the floodplain. With high rates of flow recession in the river due to irrigation diversions and hot weather, this return water was likely to place a high oxygen demand within the low river flows. These conditions would be expected to result in a large blackwater event leading to fish kills and ecosystem collapse (Whitworth et al. 2012).

The reach of river downstream of Redbank weir to the Murray River confluence has, in the past, supported Murray Cod, silver and golden perch, bony bream and many species of smaller native fish (Gilligan 2005). Recent surveys indicate that many of these populations may be locally extinct (Gilligan 2005). Anecdotal evidence indicated that the 2010-2011 blackwater event had an extremely detrimental effect on fish populations in the lower Murrumbidgee River, with fish deaths reported at Hay on 25 December 2010 and January 7 2011 and at Balranald on 27 and 29 December 2010 and 2 January 2011.

The flow studied here was the third such event since September 2010, with recession from the first flow event creating the first blackwater event from the mid Murrumbidgee and the Lowbidgee floodplain. The Murrumbidgee Environmental Water Advisory Group (EWAG)



agreed to the release of an Environmental Water Allocation (EWA) to dilute blackwater returning into the river downstream of the Lowbidgee floodplain in January 2011. This new approach to blackwater management and monitoring was important to develop knowledge for better predictive ability in developing mitigation strategies in the future and also to reduce the effect of a third blackwater event on fish and invertebrate communities.

This report documents some of the changes in water quality observed as a result of the EWA allowance releases.

Methods Site Selection Four sites (Murrumbidgee River at Maude and Redbank weir pools, downstream of the Bourpie escape and at Balranald weir pool) were chosen for logger installation. Timeseries temperature (Oneset Hobo light and pendent loggers) and Dissolved Oxygen (D-Opto loggers) data were collected at these sites between 21 January and 21 April 2011 (Figure 1).

In addition there were 11 field monitoring sites at which fortnightly, weekly or biweekly multiprobe WQ measurements and organic carbon, total nutrients and colour samples (point data) were collected (Figure 1, Appendix 1).

Hydrology Mean daily flow data was sourced from NSW Office of Water Hydsys database. Details of environmental releases and estimated flow travel times were provided by State Water. Dilution calculations were performed by aligning releases to Maude weir – the upstream point of the lower Murrumbidgee floodplain, using State Water release data and estimated travel times.

Time series data collection Thermistor chains with 5 Hobo pendant loggers were positioned with loggers set at depths through the water column (Table 1). Logging occurred at 30 minute intervals. Two pre-calibrated D-Opto dissolved oxygen loggers were positioned on the chain to measure dissolved oxygen at one metre depth and one metre above the bottom and were moved as weir depths changed (Table 2).

Table 1. Temperature (Onetemp - Hobo) loggers depth (cm)

Maude Weir Redbank Weir Bourpie Escape Balranald Weir

15 15 15 15

90 90 90 90

200 200 200 200

300 300 300 300

500 600 400 400

Table 2. Dissolved oxygen logger (D-Opto) depth 1 metre from surface and one metre from bottom

Maude Weir Redbank Weir Bourpie Escape Balranald Weir

100 cm 100 cm 100 cm 100 cm

400 cm 500 cm 300 cm 300 cm



Figure 1. Murrumbidgee blackwater monitoring sites

Point data collection Fortnightly, weekly or biweekly samples were taken at each of the monitoring sites at each visit (with data collected prior to the project also integrated) using a precalibrated multiprobe water quality instrument (Hydrolab Surveyor 4A and MS5 minisonde) collecting:

• electrical conductivity (μS/cm), temperature (oC), dissolved oxygen (mg/L and % saturation), and pH.

• turbidity (NTU) was measured using a calibrated HACH turbidity field nephelometer. Water samples were collected according to APHA – AWWA- WEF methods (1992), as follows: For separate Total Organic Carbon (TOC) and Dissolved Organic Carbon (DOC) collection:

• TOC samples were collected with the total nutrients sample into polypropylene bottles as below.

• DOC water samples were filtered through 0.45 micron cellulose acetate filters into 50 ml polypropylene sample containers prewashed using milliQ ultrapure water and frozen immediately.

Blanks were taken during each sampling run to check for accuracy of methods. Total phosphorus and total nitrogen were collected into prewashed 250 ml sample bottles and frozen immediately for transfer to the laboratory. Samples for colour were collected into prewashed 250 ml sample bottles and chilled. All analyses were performed according to APHA – AWWA – WEF methods in a NATA registered laboratory.



Results Hydrology Dilution flows of 17,215 ML from environmental water allowance (EWA) were released during January and February 2011 (Table 3). These flows comprised credits for previous under release (quantity of unreleased environmental water accumulated as a result of dam management), EWA1 and EWA2 as described (NSW Government 2003). Releases were made locally from Hay and Maude weir and Tombullen reservoir with progressive replacement from the major storages further upstream (Vincent Kelly, State Water pers.comm.)

Table 3. Dilution releases (ML) for lower Murrumbidgee river, January-February 2011 (State Water release records)

Credit for previous under release

EWA1 EWA2 CEWH Environmental release total

January 2011 3771 4835 8606

February 2011 4994 3515 15612 24121

March 2011 42139 42139

Releases of Commonwealth Government (CEWH) environmental allowances as an inter-valley transfer into the Murray River increased dilution rates beyond 2 February. A further intervalley transfer was released in early March to dilute flows following recession of a natural fresh event.

Flow hydrographs for the period (Figure 2-4) illustrate the original flood pulse being investigated and subsequent recession at Maude and Redbank weirs including the following releases from Maude that increased river flows downstream. Earlier floods in September and October were monitored for flow and water quality. The EWA flow intervention was monitored more intensively to investigate the impact of dilution flows on blackwater recession back into the river. These releases kept flows through Redbank weir above 3,500 ML/day and Balranald weir above 6,000 ML/day until April 2011. EWA releases from Tombullen, Hay and Maude storages combined at various times to add to the total releases, complicated by travel times (Table 4).

Table 4. Travel times between weirs (source State Water – flow calculations spreadsheet)

Upstream site Downstream site Travel time (days)

Tombullen regulator Darlington Point ½ (approx).

Darlington Point Hay weir 5

Hay weir Maude weir 1

Maude weir Redbank weir 2

Redbank weir Balranald weir 3



Figure 2. Lower Murrumbidgee Flows September 2010 to May 2011

Figure 3. State Water releases to achieve initial dilution

Drawdown releases from nearby weirs (Figure 3), combined with actual river flows allowed dilution flows to reach the affected area much more quickly, raising cumulative river flows downstream of Maude weir from 1,616 ML/day on 3 February to 15,850 ML/day on 20 February. Short term releases indicated a rapid rise from 1616 ML/day to 7,734 ML/day on 7 Feburary (Figure 4).

Period of project

Redbank gauge not operational



Figure 4. Cumulative dilution releases, volumes and impact on flow at Maude weir

Dissolved oxygen Results indicated that the release of environmental flows in the Murrumbidgee River were able to dilute water of extremely low dissolved oxygen (DO), increasing DO concentrations. Low dissolved oxygen levels at Balranald weir before the EWA release were disrupted by increased flows, lags between peak flows and increases in DO were evident at all weirs. (Note: Figure 8 - bottom logger resting in sediment was fouled in early February and therefore gave inaccurate zero readings for that period).



Figure 5. Lower Murrumbidgee blackwater event

Dissolved oxygen levels at Maude weir (Figure 6) were always above lethal levels for instream aquatic communities from 22 January (greater than 4.5 mg/L). However, there is evidence that DO had been lower prior to commencement of monitoring with previous fish kill events and with Redbank weir exhibiting increasing DO from 22 January to around 5 mg/L (Figure 7).

Figure 6. Maude weir loggers, 1 and 4 metres depth dissolved oxygen and flow



Rapid increases in flow in early February led to rise in DO of around2 mg/L. However this rise wasn’t sustained and dipped again in mid February, perhaps in response to water flowing back into the river from the floodplain upstream following the flood peak.

Figure 7. Redbank weir loggers, 1 and 6 metres depth dissolved oxygen and flow

Figure 8. Balranald weir loggers, 1 and 3 metres depth dissolved oxygen and flow

The single Bourpie dissolved oxygen logger was installed later than the others due to flooding restricting access to the site, with no flow data available as it was an ungauged site.

Dilution flow



At commencement of monitoring, Balranald Weir DO levels were below lethal levels, dropping to 0 mg/L at night (Figure 8). Dissolved oxygen levels increased as environmental flows were released from Maude and Hay weirs, then further upstream (Figure 3).

Figure 9. Dissolved oxygen, lower Murrumbidgee River, January - April 2011

These environmental releases lifted DO at Bourpie to around 4 mg/L, which continued until late March when the top logger became unstable (Figure 9). Continued DO improvement occurred until late April when the project was completed. These releases were effective at raising DO at Redbank and Balranald to sublethal levels for fish and other aquatic fauna. Further upstream, dissolved oxygen levels were high enough to sustain aquatic life (Figures 6,7), although there is evidence that DO at Redbank weir had been low prior to 21st January.

Dissolved oxygen fell to critical levels at Balranald to less the 0.5 mg/L during mid January before high intensity monitoring commenced (Figure 11). Subsequent dilution flows led to strong upward trends in DO in the lower river, while inflow from the Bourpie regulator continued to be less than 3 mg/L.

Figure 10. Blackwater at Bourpie

Point sampling (Figure 11) illustrated the impact of blackwater returns to the river downstream of Redbank weir, leading to extremely low dissolved oxygen levels measured at Balranald weir



during January 2011. Continued low DO in Bourpie Creek upstream of the regulator continued through until April with dilution flows raising instream DO from early February in an increasing trajectory (Figure 18).

Figure 11. Dissolved oxygen (mg/L), lower Murrumbidgee River, November 2010 to April 2011

Nutrients and water quality Water quality in the River

Figure 12. Electrical conductivity (μS/cm)



Rises and falls in electrical conductivity illustrate rising limb of flood events (Figure 2), where dilution occurs, followed by recession flows where water with high solutes enters the river, leading to falls in electrical conductivitywas evident at the upstream sites in January (Figure 12). Later events and continued flow back into the river complicated patterns of dilution. Electrical conductivity was well below the ANZECC trigger values for lowland rivers of between 125-2200 µS/cm.

Figure 13. Turbidity (NTU)

Turbidity levels indicated a relationship to river flows from further upstream but in May appeared to be related to local inflows from the floodplain (Figure 13). Sources of turbidity in the Murrumbidgee are known to primarily originate from river banks and gullies in the middle reaches of the catchment (Wilkinson and Kennedy 2005). Normally high flows are related to high levels of turbidity as erosion is increased with runoff. ANZECC trigger values for aquatic ecosystems for lowland rivers of 6-50NTU were exceeded most of the time during and following the flow event.



Figure 14. Colour (true colour units)

Figure 15. Dissolved organic carbon (mg/L)

Dilution flows led to concurrent dilution in colour and DOC (Figures 14, 15) at more upstream sites. Once the dilution flows ceased, both colour and DOC increased again and slowly trended downwards as inflows of blackwater decreased. Maude and redbank weir, being further upstream, were less affected by blackwater recessions from the Lowbidgee floodplain.



Figure 16. Total nitrogen (mg/L)

All total nitrogen data were less than the ANZECC trigger values for aquatic ecosystems of 0.5 mg/L, whereas all total phosphorus were greater than the value of 0.05 mg/L. Both trended with blackwater recessions back into the river from the Lowbidgee floodplain.

Figure 17. Total phosphorus (mg/L)



Relationships between water quality parameters followed predictable eutrophic models (Connell 1981). There were statistically significant positive or negative relationships between most parameters other than for turbidity and strong negative associations between DO% and DOC/TOC. Other strong associations were between DO%, colour and pH (indicating the presence of tannins and tannic acid in blackwater).

Table 5. Relationships between water quality parameters, showing positive and negative Pearson's R values and red text denoting relationships with p<0.05

R values DOC TOC DO% EC pH TN TP Turbidity

True Colour

DOC 1.0

TOC 0.97 1.0

DO % -0.92 -0.90 1.0

EC 0.70 0.68 -0.68 1.0

pH -0.69 -0.69 0.81 -0.40 1.0

TN 0.69 0.72 -0.64 0.36 -0.65 1.0

TP 0.69 0.69 -0.63 0.49 -0.41 0.68 1.0

Turbidity -0.33 -0.36 0.33 -0.22 0.16 0.02 -0.04 1.0

True Colour

0.93

0.94 -0.84 0.61 -0.70 0.68 0.68 -0.32 1.0

Fish deaths were recorded in the river from upstream of Hay to the Murray confluence, related to several flow events. The most severe, reported near the end of December and early January, occurred as a result of blackwater flowing back into the river from the mid Murrumbidgee floodplain upstream of Hay. Later blackwater flows below the Lowbidgee floodplain caused further fish deaths (Table 6).

Table 6. Reports of fish deaths (excerpt from NSW DPI - Fisheries)

Date Waterway Location Comments

22 Nov 10 Yanga Ck Reports of dead fish

25 Dec 10 – 7 Jan 11

Murrumbidgee River Burrabogie to Hay Golf Course

1000’s of dead fish – predominantly murray cod(Maccullochella peelii peelii), also golden perch (Macquaria ambigua) & European carp (Cyprinus carpio)– 10cm to 1m.

29 Dec 10 Murrumbidgee River Upstream of Murray confluence & Balranald

Blackwater also in lower 2km of Murrumbidgee River. Dead fish and crayfish(Euastacus armatus) out of water in the Bidgee u/s and d/s of Balranald (Paul Childs DECCW)

2 Jan 11 Murrumbidgee River Balranald Blackwater coming off Yanga floodplain. 100’s of dead fish. Mainly cod(Maccullochella peelii peelii), 1 bony bream(Nematalosa erebi), 2 golden perch(Macquaria ambigua), shrimp.

19 Jan 11 Murrumbidgee Steam Pump Swamp to Murray confluence

100’s of Golden Perch(Macquaria ambigua), carp(Cyprinus carpio), Bony bream(Nematalosa erebi), cod (Maccullochella peelii peelii), over 200km of river. Cod reported to have died around New Year.

Effect of inflows of blackwater into the river Bourpie Creek regulator has the ability to drain large parts of the north Redbank floodplain. During the 2010-2011 floods, much of the returning floodwater ran directly over the natural levee into the river. However large flows entered via the Bourpie creek regulator just upstream of



Balranald. Water sampling indicated diverging relationships for EC, total phosphorus and nitrogen; and similar trending relationships for turbidity, colour and DOC for floodplain compared to river water. These results indicate increasing evaporation and concentration of EC on the floodplain, similar levels of phosphorus in river and floodplain water and increasing mobilisation of nitrogen on the floodplain. DOC and colour results indicate dynamic respiration activity over time, with turbidity decreasing with flow.

Figure 18. Effect of Bourpie Creek inflows on Murrumbidgee River water quality during blackwater event



Discussion Dilution of blackwater returning to the Murrumbidgee from the Lowbidgee floodplain using better quality water from upstream has proven a successful approach, as long as implementation occurs before hypoxia falls below lethal levels. However, during the 2010 and early 2011 flood events hypoxic events occurred several times before dilution effort and monitoring were initiated. Levels of dissolved oxygen recorded at Balranald weir during this event were well below the ANZECC Guidelines for recreational waters (> 6.5mg/L) (ANZECC 2000). Unfortunately, fish kills in the Murrumbidgee River had occurred before dilution flows were available (Table 5).

Dissolved oxygen (DO) levels of between 0 and 2 mg/L are known to be lethal to aquatic organisms and levels lower than 1.5 mg/L are known to kill fish in warm waters (Townsend and Edwards 2003). However this effect is complex and related to lability and concentrations of organic carbon and variable rates of microbial degradation (which are also associated with temperature). Small fish species have been observed surviving low DO (0.4-6.8 mg/L) and high DOC (16-50 mg/L) conditions in southern Australian intermittent streams (McMaster and Bond 2008) and floodplain fish may exhibit adaptations to hypoxia (Townsend and Edwards 2003). These low levels of DO were experienced in the lower Murrumbidgee as highly tannic water returned from the upstream floodplain during October and December 2010. The January 2011 event mirrored the earlier events, with low DO and accompanying high levels of dissolved organic carbon (DOC), electrical conductivity and nutrients in return flows from the floodplain. Fish kills recorded during the summer of 2010-2011 were mirrored in the Murray River, with significant impacts on both fish populations and crustaceans such as Murray crayfish (Euastacus armatus),shrimps and yabbies (King et al. 2012). It is likely that the loss of these major food sources for fish would affect recolonisation processes following such blackwater events.

Generally carbon in streams originates via several pathways: forested floodplains, agricultural floodplains and flushing from upstream (Whitworth et al. 2012). During earlier flood events, upstream factors probably contributed to the hypoxic events in the lower Murrumbidgee River witnessed in November and December (Table 5).

Figure 19. Floodwater returning from the Lowbidgee floodplain into the Murrumbidgee River near Balranald

Dissolved oxygen measured Maude weirs during December indicated upstream involvement in hypoxic conditions (Figure 11). However, in the January 2011 event, DOC remained relatively low throughout the monitoring period at the upstream sites, indicating that blackwater was originating locally from the Lowbidgee floodplain.

Inputs from Bourpie Creek, exhibiting high DOC, nutrients and colour, with associated low turbidity and DO, provided an illustration of this local floodplain runoff and its effect on river water quality. At this time, water was returning directly from the floodplain back into the river (Figures 18, 19). The floodplain on both sides of the river comprises extensive red gum forest and woodlands, implicating local flood mediated degradation of floodplain vegetation as a major cause of this particular hypoxic event.



Dissolved organic carbon is released from both red gum litter and floodplain vegetation. While more DOC is released from red gum leaves than from bark and twigs (O’Connell et al. 2000), breakdown of red gum leaves on dry floodplains has been shown to be quite rapid, with a half life between 5 ½ months in autumn to 12 months in winter conditions (Glazebrook and Robertson 1999). However peak litterfall for river red gums shows marked seasonality, peaking during summer with minimum abscission during winter (Briggs and Maher 1983; Hladyz et al. 2011). Summer floods would be expected to utilise recently fallen leaf material, with rapid exponential decomposition in warm water of submerged leaves. Decomposition rates leading to 20% loss in mass have been measured over periods of several days (Briggs and Maher 1983) Recent studies in the nearby Edward-Wakool system also illustrated the strong impact of seasonality in development of hypoxic events, with peak litter fall and high water temperatures both contributing to blackwater impact (Howitt et al. 2007).

In addition to peak leaf fall and decomposition on the Lowbidgee floodplain in December 2010 and January 2011, logging activity during the intervening drought left litter and sawdust scattered on the floodplain. Piles of sawdust remain on the floodplain, but during the flood event, boulder sized concretions were dislodged off these piles and were evident in floating debris returning to the river. The documented effects of drought on increasing blackwater risks were therefore potentially exacerbated by floodplain vegetation management (King et.al 2012).

Floodplain primary production also plays a part, with high levels of vegetative production during spring and summer contributing to organic material load (Robertson et al. 2001). The combination of season, preceding drought, river regulation, extent of inundation and floodplain logging all played a part in both the earlier and monitored hypoxic events in the lower Murrumbidgee River (Whitworth et al. 2012).

During the monitored January event, the volume and severity of blackwater entering the river was unable to be measured. Water was entering the river from multiple flood runners over the natural levee (Figure 19), making dilution calculations impossible. It is clear that dilution was an effective measure to improve DO levels from lethal levels (Figures 8 and 9), but lack of data to enable more comprehensive analysis and modelling remained a constraint to better predictive ability.

This monitoring project was performed as a rapid response to the release and use of environmental water allowance (EWA) and Federal Government environmental allocations for blackwater dilution purposes. Advance planning wasn’t possible. As such it provides an opportunity to reflect on information requirements for blackwater monitoring generally, the level of resourcing required and constraints to measuring improvement. It provides an adaptive management opportunity for future similar management and monitoring programs. Recommendations given can be used in more generic ways to guide event based monitoring.

Recommendations to improve prediction and management of hypoxic events in the lower Murrumbidgee River include:

• development of a monitoring plan ahead of expected hypoxic events, factored into budgets and work plans of monitoring staff

• better hydrological knowledge of Lowbidgee floodplain returns – with a combination of time series flow data at points along the river, better ratings data from escapes and adequate gaugings at major floodplain escapes during events

• more comprehensive dissolved oxygen time series monitoring • comprehensive dissolved organic carbon monitoring before, during and following events • increased use of existing blackwater models to enable better validation and enhance

prediction. Further management and research options are provided by King et al. 2012 and Whitworth et al. 2013.



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Appendices Appendix 1. Site Details for Blackwater study

Site Name Number Zone Eastings Northings Logger WQ

Murrumbidgee River @ downstream Hay weir

410002 or hayds

55 302013.2 6178584.7 Hydrolab only 30 cm depth

Fortnightly

Murrumbidgee River @ Maude Weir Buoy

41010362 55 55

252463.2 252613.2

6181734.8 6181784.8

Hydrolab profile, Onetemp temperature and D-Opto DO loggers

Validation of thermistor chain at intervals

Murrumbidgee River @ Maude Storage gauge

4100941 55 252463.2 252613.2

6181734.8 6181784.8

Hydrolab Biweekly.

Murrumbidgee River @ Maude Bridge (d/s weir)

Maudds or 410040

55 252011.8 6181578.8 Hydrolab only 30 cm depth

Biweekly

Murrumbidgee River @ Redbank Weir Buoy

41010361 54 756021.2 6192778.0 Hydrolab profile, Onetemp temperature and D-Opto DO loggers

Validation at thermistor Chain at intervals

Murrumbdigee River @ Redbank Storage gauge

41010966 54 756021.2 6192778.0 Hydrolab only – 30 cm depth

Biweekly

Murrumbidgee River d/s Redbank Weir

redds 54 756021.2 6192778.0 Yes – hydrolab and samples

Biweekly

Murrumbidgee River @ Balranald Bridge

410003 54 734921 6163178 Hydrolab and samples

Biweekly

Murrumbidgee River @ Balranald Weir storage gauge

41010901 54 728721.1 6161978 Hydrolab and samples

Biweekly

Murrumbidgee River @ Balranald Weir Buoy

41010417 728597 6161305 Hydrolab profile, Onetemp temperature and D-Opto DO loggers

Validation at thermistor chain at intervals

Bourpie Creek Escape

41015747 54 739147.8 6151602.2 Hydrolab and samples

Biweekly

Murrumbidgee River u/s Bourpie Creek Escape

41010067 54 739147.8 6151602.2 Hydrolab profile, Onetemp temperature and D-Opto DO loggers

Biweekly Validation at thermistor chain at intervals

Murrumbidgee River d/s Bourpie Escape

41015746 54 739147.8 6151602.2 Hydrolab and samples

Biweekly

Yanga Creek u/s Yanga Creek regulator

Sampled by NPWS

54 736755.2 6162520.3 Hydrolab and samples

Biweekly (NPWS staff)?

Murrumbidgee blackwater monitoring · 2015-03-06 · Murrumbidgee blackwater monitoring 3 NSW...

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