A framework for values-based condition assessment in the
Lowbidgee
Prepared by:
NSW Office of Environment and Heritage
1
Table of Contents
1
Introduction ___________________________________________________________ 7
2
2.1
2.2
2.3
The Murrumbidgee and its aquatic ecosystems _____________________________ 9
Murrumbidgee catchment _________________________________________________ 9
The Lowbidgee ________________________________________________________ 11
Aquatic ecosystems of the Lowbidgee ______________________________________ 12
3
3.1
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.3
Ecosystem values and related services ___________________________________ 15
Criteria for identifying HEVAE _____________________________________________ 15
Ecosystem values of the Lowbidgee floodplain ________________________________ 15
Vital Habitat ________________________________________________________ 15
Representativeness _________________________________________________ 16
Distinctiveness _____________________________________________________ 16
Diversity __________________________________________________________ 16
Ecosystem services _____________________________________________________ 16
Critical ecological components relating to values of HEVAE ________________________ 17
3.4
Threatened fauna species ________________________________________________ 17
3.4.1
Indicator species: southern bell frog _____________________________________ 18
3.5
Waterbirds ____________________________________________________________ 19
3.5.1
Indicator cohort: egrets _______________________________________________ 24
3.5.2
Indicator cohort: ibis’ _________________________________________________ 25
3.6
Fish _________________________________________________________________ 26
3.6.1
Indicator species: Unspecked hardyhead _________________________________ 28
3.6.2
Indicator species: Murray cod __________________________________________ 29
3.7
Invertebrates __________________________________________________________ 29
3.7.1
Indicator species: Yabby ______________________________________________ 30
3.8
Important vegetation communities _________________________________________ 31
3.8.1
River red gum forest and woodland _____________________________________ 33
3.8.2
Black box woodland _________________________________________________ 38
3.8.3
Lignum ___________________________________________________________ 38
3.8.4
Tall spike rush ______________________________________________________ 40
3.9
Key values and components for HEVAE in the Lower Murrumbidgee ______________ 41
4
4.1
4.1.1
4.1.2
4.2
4.2.1
4.3
4.3.1
Critical processes relating to values of HEVAE _____________________________ 44
Hydrological process ____________________________________________________ 44
Natural overbank flows _______________________________________________ 47
Artificial Watering ___________________________________________________ 50
Geomorphic processes __________________________________________________ 52
Sedimentation ______________________________________________________ 52
Other ecosystem processes ______________________________________________ 55
Nutrient cycling and trophic dynamics ___________________________________ 55
5
5.1
5.2
5.3
5.4
Critical ecological threats relating to the values of HEVAE ___________________ 56
Alteration to the natural flow regimes _______________________________________ 56
Habitat loss and fragmentation ____________________________________________ 57
Introduced and problematic species ________________________________________ 58
Climate change ________________________________________________________ 59
2
5.5
5.6
Other issues___________________________________________________________ 60
Summary _____________________________________________________________ 61
6
Ecological conceptual models ___________________________________________ 65
7
7.1
7.2
7.3
7.4
Management triggers for key ecological components _______________________ 73
Definition of limits of acceptable change and thresholds of potential concern ________ 73
Thresholds of potential concern ___________________________________________ 74
Limits of Acceptable Change ______________________________________________ 77
Selected indicators _____________________________________________________ 78
8
Condition assessment methodology _____________________________________ 82
9
9.1
9.1.1
9.1.2
9.1.3
9.1.4
9.1.5
9.2
9.2.1
9.2.2
9.2.3
9.2.4
9.3
9.3.1
9.3.2
9.3.3
9.3.4
9.3.5
9.4
9.4.1
9.4.2
9.4.3
9.4.4
Results ______________________________________________________________ 87
2008 Wetland Indicators _________________________________________________ 88
Southern bell frog indicators ___________________________________________ 88
River red gum indicators ______________________________________________ 90
Waterbird indicators _________________________________________________ 93
Vegetation indicators ________________________________________________ 97
Fish indicators ______________________________________________________ 99
2008 River reach indicators ______________________________________________ 101
River red gum indicators _____________________________________________ 101
Waterbird indicators ________________________________________________ 104
Vegetation indicators _______________________________________________ 108
Fish indicators _____________________________________________________ 110
2010 Wetland indicators ________________________________________________ 112
Southern bell frog indicators __________________________________________ 112
River red gum indicators _____________________________________________ 114
Waterbird indicators ________________________________________________ 117
Vegetation indicators _______________________________________________ 121
Fish indicators _____________________________________________________ 124
2010 River reach indicators ______________________________________________ 126
River red gum indicators _____________________________________________ 126
Waterbird indicators ________________________________________________ 130
Vegetation indicators _______________________________________________ 134
Fish indicators _____________________________________________________ 137
10
Conclusions _________________________________________________________ 139
11
References __________________________________________________________ 140
Figures
Figure 1.Murrumbidgee catchment and Lowbidgee floodplain. _______________________________ 9
Figure 2.Australian National Aquatic Ecosystem Structure; regionalisations, classes and systems within
the classification scheme. The Lowbidgee floodplain includes lacustrine, palustrine and riverine aquatic
ecosystems. _______________________________________________________________________ 13
3
Figure 3.Aquatic ecosystems of the Lowbidgee; these include the 60 reporting locations identified in
the LYNC DSS, 10 additional wetlands located in the southern and western regions of the Lowbidgee
and three river reaches. ______________________________________________________________ 14
Figure 4.Southern bell frog. Photograph: Sascha Healy (OEH)________________________________ 19
Figure 5.A) great egret. B) intermediate egret. C) little egret. Photograph: Chris Herbert (Hunter Birds
Observers Club). ____________________________________________________________________ 25
Figure 6.A) glossy ibis. B) Australian white ibis. C) straw-necked ibis. Photographs: Chris Herbert
(Hunter Bird Observers Club) and Kerrylee Rogers (OEH) ____________________________________ 25
Figure 7.Schematic shows the importance of floodplain wetland as fish feeding, spawning and nursery
habitat. Adapted from Mussared (1997). ________________________________________________ 26
Figure 8.Unspecked hardy head. Photograph: Gunther Schmida. _____________________________ 28
Figure 9.Murray cod. Photograph: Gunther Schmida. ______________________________________ 29
Figure 10.Western yabby: Photograph: Gunther Schmida. __________________________________ 30
Figure 11.2008 Vegetation map for Yanga National Park, nature Reserve and State Conservation Area.
Source: Bowen and Simpson (2010) ____________________________________________________ 32
Figure 12.River red gum forest adjacent to Piggery Lake. Photograph: Kerrylee Rogers DECCW ____ 33
Figure 13.River red gum forest with dense tall spike rush understorey located at Little Piggery.
Photograph: Kerrylee Rogers OEH ______________________________________________________ 34
Figure 14.Condition of river red gum in 2005 based on aerial photography. Source: McCosker (2008).37
Figure 15.Black box woodland at Fingerboards. Photograph: Kerrylee Rogers, OEH. _____________ 38
Figure 16.Black box woodland with dense lignum understorey on Uara Creek. Photograph: Kerrylee
Rogers, OEH _______________________________________________________________________ 39
Figure 17.Lignum swamps are important waterbird breeding habitat in Lowbidgee floodplain. Strawnecked ibis rookery at Telegraph Bank. Photo: James Maguire, 2005 _________________________ 40
Figure 18.Tall spike rush swamp (foreground) and river red gum forest with tall spike rush understorey
(background) at Mercedes Swamp. Photograph: Kerrylee Rogers, OEH. _______________________ 41
Figure 19.Relationships between hydrological processes and other floodplain ecosystem processes
under a natural flood regime__________________________________________________________ 45
Figure 20.Monthly flow distribution comparison before (solid line with circles) and after (dashed line
with triangles) 1970. Source: Wen et al. (2009a). _________________________________________ 49
Figure 21.Water diverted to Yanga from the Murrumbidgee. The values were “best guess” by
Department of Water and Energy staff. There is not volumetric allocation for LFCID and the District is
dependent on unregulated flow for diversion (produced from DWE operational data). ___________ 51
Figure 22.Irrigation water distribution pattern in the Lowbidgee (based on Clarkson 2000). The
majority of diversions are through Yanga Regulator. The distribution of water within Yanga is primarily
overland flow, following natural flood runners. The diversion from Nimmie-Caira Flood and Irrigation
District (via Maude) fills Tala Lake (major irrigation storage, part of which is in Yanga National Park)
via Talpee Creek. ___________________________________________________________________ 51
Figure 23.Sediment erosion and deposition processes in the river-floodplain system. The boxes contain
storage locations with example sediments and erosion processes. Arrows represent the links between
the various storage sites largely driven by water movement and gravity. ______________________ 53
Figure 24.Murrumbidgee Catchment shows the three geomorphic regions. (reprinted from Olley and
Scott 2002). _______________________________________________________________________ 54
Figure 25.Linkages between climate change and ecosystem responses. _______________________ 60
Figure 26.Conceptual ecological model of threats/stressors/risks in HEVAE of the Lowbidgee. _____ 64
4
Figure 27.Integrated conceptual ecological model detailing the critical components, processes and
threats relating to the values of the HEVAE of the Lowbidgee. Model adapted from Spencer et al.
(unpublished). _____________________________________________________________________ 67
Figure 28.Vegetation conceptual ecological sub-model detailing critical components, processes and
threats for vegetation of the HEVAE of the Lowbidgee. Model adapted from Spencer et al.
(unpublished). _____________________________________________________________________ 68
Figure 29.Waterbird conceptual ecological sub-model detailing critical components, processes and
threats for waterbirds frequenting the HEVAE of the Lowbidgee. Model adapted from Spencer et al.
(unpublished). _____________________________________________________________________ 69
Figure 30.Fish conceptual ecological sub-model detailing critical components, processes and threats
for fish frequenting the HEVAE of the Lowbidgee. Model adapted from Spencer et al. (unpublished). 70
Figure 31.Invertebrates conceptual ecological sub-model detailing critical components, processes and
threats for invertebrates occurring in the HEVAE of the Lowbidgee. ___________________________ 71
Figure 32.Frogs conceptual ecological sub-model detailing critical components, processes and threats
for frogs occurring in the HEVAE of the Lowbidgee. ________________________________________ 72
Figure 33.Relationship between a limit of acceptable change and threshold of potential concern for a
wetland value with respect to management targets, a healthy wetland value (i.e. value = 1) of the loss
of a wetland value (i.e. value = 0). _____________________________________________________ 74
Tables
Table 1. Landuse within the Murrumbidgee River catchment. _______________________________ 10
Table 2. Ecosystem values and related services that form the foci of management actions in the
Lowbidgee floodplain. _______________________________________________________________ 16
Table 3. Selected ecological components that relate to the values of the Lowbidgee floodplain, as
identified using the HEVAE criterion.____________________________________________________ 17
Table 4. Endangered and vulnerable fauna found within Yanga National Park and its vicinity. Source:
Wen et al. (2009b) __________________________________________________________________ 18
Table 5. List of migratory birds protected under international treaties _________________________ 20
Table 6. Major bird surveys in Lowbidgee region __________________________________________ 20
Table 7. Waterbirds species recorded in Yanga and surrounding floodplain _____________________ 23
Table 8. Fishes species in the Lowbidgee region including the Murrumbidgee channel. ___________ 27
Table 9. Extent of vegetation communities of the Lowbidgee floodplain in 2008. Source: Bowen and
Simpson (2010) ____________________________________________________________________ 31
Table 10. River red gum condition and stem density at Yanga National Park. Source: Bowen and
Simpson (2010). ____________________________________________________________________ 35
Table 11. Eucalyptus communities within Yanga National Park. Source: McCosker (2008), Benson et al.
(2006). 36
Table 12. Key values and related components for each aquatic ecosystem in the Lowbidgee. Source:
Bowen and Spencer (2011). ___________________________________________________________ 42
Table 13. Hydrological processes in the Lowbidgee. _______________________________________ 45
5
Table 14. Major developments on the Murrumbidgee River (1855-1982). Source: Kingsford and
Thomas (2001), Pressey et al. (1984), Wen et al. (2009b). ___________________________________ 48
Table 15. Changes in selected hydrological indicators in Murrumbidgee at downstream of Redbank
Weir. Source: Wen et al. (2009a). ______________________________________________________ 49
Table 16. Summary of actual &likely threats to the eological character of the Lowbidgee floodplain 61
Table 17. Thresholds of potential concern for critical components and indicators that relate to values
of HEVAE in the Lowbidgee.___________________________________________________________ 75
Table 18. Limits of Acceptable Concern as they relate to key values of the Lowbidgee Floodplain ___ 77
Table 19. Condition assessment indicators and data sources used to obtain condition for wetland
storages and river reaches. ___________________________________________________________ 79
Table 20. Condition assessment indicators and the rankings applied to water storages and tiver
reaches in the Lowbidgee. ____________________________________________________________ 82
6
1 Introduction
The purpose of this condition assessment framework has been twofold; to develop
an assessment framework that incorporates values associated with different
ecosystem types; and to test the utility of the assessment framework given data
availability. Consideration was given to the inclusion of different types of
hydrological and ecological information, and the number and types of aquatic
ecosystems contributing to the assessment.
The Lowbidgee is uniquely suited to the testing of an Ecological Condition
Assessment framework. The river channel and associated floodplain support a range
of aquatic ecosystem types, including riverine, lacustrine, and palustrine ecosystems
ranging in ecological character across an extensive inundation gradient. Further, the
Lowbidgee Floodplain has been extensively studied over the past few years, being a
focal point of the science program of the NSW Governments Rivers Environmental
Restoration Program (RERP), and the CSIRO-led Hyper-drought program. Recent
condition information has been collected by the Catchment Action NSW program
“Testing our assumptions about wetland resilience - monitoring the response of
iconic wetlands to rewetting following historic drought”, and a condition assessment
of the river in-stream condition is scheduled for early 2011 under the Sustainable
Rivers Audit.
The Lowbidgee is therefore rich in aquatic ecological communities and information
relevant to ecological condition assessment. A hydrological model of the Lowbidgee
floodplain has recently been completed by the NSW Office of Water, reporting on
hydrological conditions for each of 60 key wetlands across the Lowbidgee floodplain
within the Integrated Quality and Quantity Model (IQQM) hydrological modelling
environment. The inundation history of the floodplain over the past two decades has
been documented by the OEH Rivers and Wetlands Unit. Detailed vegetation surveys
have been conducted in time-series including benchmark data for 2008. On-ground
surveys conducted under the Catchment Action Program (CAP) in the past 6 months
have included surveys of frog, fish and bird responses to re-wetting.
Few wetlands have this level of resources available for an ecological assessment, and
it is not practical to expect that this information-rich environment can be extended
to aquatic ecosystems across the nation. However, the Lowbidgee provides a good
opportunity to test the sensitivity of condition assessments to types of data
available. This framework and sensitivity analysis will enable the Commonwealth of
Australia to assess the implications of conducting condition assessments in data poor
environments and will facilitate the targeting of data acquisition toward the most
sensitive and cost-effective indicators of ecosystem health.
The purpose of this report is to inform the ecological context of the assessment of
the Lowbidgee floodplain and associated ecosystems (an identified national High
Ecological Value Aquatic Ecosystem – HEVAE) and to identify indicators and
methodologies for monitoring assessment and reporting. Specifically this report
describes the:
7
 Suite of aquatic ecosystems comprising the Lowbidgee floodplain (Chapter 2)
 Key values of each aquatic ecosystem in the Lowbidgee (Chapter 3)
 Critical components that support these key values (Chapter 4)
 Critical processes that support these key values (Chapter 5)
 Driver, threats, pressures and stressors to each critical component (Chapter 6),
and in so doing a conceptual model was developed (Chapter 7)
 Thresholds of potential concern relating to key values of HEVAE in the Lowbidgee
(Chapter 8)
 Identified indicators, including indicators of connectivity, and methodology for
monitoring, assessment and reporting in relation to key values, components,
processes, drivers and threats (Chapter 9)
8
2 The Murrumbidgee and its aquatic ecosystems
2.1 Murrumbidgee catchment
The Murrumbidgee catchment is the fourth largest in the Murray-Darling Basin and
drains an area exceeding 84 000 km2 (Figure 1). The catchment consists of 6749 km
of streams including about 1500 km of the Murrumbidgee River, which is regarded
as the main channel. The headwaters of the Murrumbidgee catchment are located
1600 m above sea level in the Fiery Range in the Kosciuszko National park. The
Murrumbidgee flows into the Murray River at Boundary Bend, which has an
elevation of 60 m above sea level.
Figure 1. Murrumbidgee catchment and Lowbidgee floodplain.
The climate of the Murrumbidgee is diverse, ranging from cooler high alpine in the
east to the hot plains of the west. Its annual rainfall varies from more than 1500 mm
in the high country to less than 400 mm on the western plains, while evaporation
averages about 1000 mm in the high country to 1800 mm on the western plains. The
runoff coefficient for the 28 000 km2 catchment above Wagga Wagga is 24% and this
runoff makes up the majority of the river flow. Below Wagga Wagga, the runoff
coefficient is less than 2% (Khan et al. 2004).
The Murrumbidgee catchment support a population of approximately 545 000
people and has an annual growth rate of 1.5%. The catchment includes the
Australian capital, Canberra, with a population exceeding 314 000; and NSW’s largest
9
inland city, Wagga Wagga, with a population of approximately 57 000 people
(Murrumbidgee Catchment Management Authority 2008).
Approximately 15% or the Murrumbidgee catchment area is managed publicly
(National Parks and Wildlife service estate, State Forests and Crown Lands).
Agricultural production is worth in excess of $1.9 billion annually and includes fruit
and vegetable, grape and rice production; dryland agricultural industries of livestock
and cropping; and softwood plantations (Murrumbidgee Catchment Management
Authority 2008) (Table 1).
Table 1. Landuse within the Murrumbidgee River catchment.
Landuse
ACT
Cropping
Cropping and grazing
Flood irrigation
Forestry and forest reserves
Grazing native/improved pastures
Horticulture
Limited grazing
Nature conservation & recreation
Urban
Vacant
Water storage/lakes
Total
Source: DECC
10
Area (ha)
235 743
25 042
2 467 162
439 350
247 025
3 992 705
13 877
367 496
344 345
1353
22 807
23 356
8 147 261
Percentage
2.89
0.31
30.28
5.39
3.03
49.01
0.17
4.51
3.82
0.02
0.28
0.29
100
2.2 The Lowbidgee
The Lowbidgee is situated on the Murrumbidgee River floodplain between Maude
and Balranald, just upstream of the confluence with the Murray River. The
Lowbidgee wetland complex includes three distinct areas: the Nimmie-Caira system;
the Fiddlers-Uara Creek system, and the Redbank system. Each is characterised by
different topography, flooding behaviour and ecological communities.
The Lowbidgee Floodplain is the largest area of floodplain wetland remaining in the
Murrumbidgee Valley, and includes the second largest river red gum forest in
Australia, as well as significant black box, lignum and reed-bed communities
(Eastburn 2003, cited in Sinclair Knight Mertz 2011). The wetlands also include
15 000 ha of common reed Phragmites australis, cumbungi Typha spp., rushes
Eleocharis spp. and Juncus spp. (Macgrath 1992). The Lowbidgee has been identified
as a nationally important wetland (Environment Australia 2001), in part because it
covers a large area (217 000 ha) and is strategically placed for the provision of
ecosystem services to the Murray-Darling river system, but also because it is
regionally significant for waterbirds, both as a drought refuge and as breeding
habitat.
Under natural conditions the Lowbidgee wetlands experienced regular inundation by
floodwaters from the Murrumbidgee River, driven by reliable winter and spring
rainfall and snow melt (Kingsford and Thomas 2004). Channel capacity within the
Lowbidgee floodplain was low and comprised a complex system of interconnected
creeks flowing east to west including Fiddlers, Uara, Caira, Nimmie, Pollen,
Waugorah, Talpee, Monkem, Kietta, Yanga, and Paika Creeks (Kingsford and Thomas
2004). Flooding occurred on average every two to three years, although there were
years where the river achieved bankfull conditions without overflowing onto the
floodplain (Eastburn 2003, cited in Sinclair Knight Mertz 2011). Flood events were
also known to ‘cluster’, whereby the system would experience two or three floods in
quick succession followed by a drier period (Eastburn 2003, cited in Sinclair Knight
Mertz 2011).
The Lowbidgee, in particular the Nimmie-Caira system, is one of the most significant
wetland habitats for water birds in eastern Australia. Sixty species of waterbirds
have been recorded on the Lowbidgee floodplain and 41 of these are known to
breed in the Lowbidgee wetland (Kingsford and Thomas 2001). The area contains
nationally important breeding colonies of Australian white ibis Threskiornis molucca,
glossy ibis Threskiornis falcinellus, straw-necked ibis Threskiornis spinicollis, royal
spoonbill Platalea regia, great egret Ardea alba, and intermediate egret Ardea
intermedia. Annual bird surveys conducted by the New South Wales National Parks
and Wildlife Service (NPWS) monitor the 13 rookeries in the Lowbidgee system. The
most significant of these occur at Avalon Swamp, Telephone Bank, Eulimbah and
Suicide Bank, although all may be utilised during optimum conditions in the
September to November breeding season. A total of 58, 000 ML of water is required
in the Nimmie-Caira system to provide stable water in rookeries during the bird
breeding season (Kneebone et al. 2000). The minimum required duration of flooding
11
to support successful breeding for most waterbirds is approximately 5-7 months
(Scott 1997). The wetlands also provide important habitat for fish, frogs (including
the endangered southern bell frog) and macroinvertebrates.
Studies have shown that inland wetlands are most productive when flooding follows
a period of complete drying. Under natural conditions the entire Lowbidgee system
was ephemeral, with the channel, riparian zone and floodplain each linked in a
wetting and drying regime that supported a diverse ‘boom and bust’ ecology typical
of inland river systems in Australia. Accordingly, under natural conditions water
levels in the Lowbidgee would have been highly variable.
The extent of the Lowbidgee wetlands has significantly decreased in recent decades
due to flow regime changes in the regulated Murrumbidgee River and conversion of
wetland floodplain into irrigated cropland. Conversion of wetland into cropland
within the former Yanga Station and in the wider Lowbidgee floodplain has seen
construction of extensive channels and embankments throughout the wetlands, and
of large supplementary licence water storage bays. This threatens the health of the
remaining wetlands, such as the Yanga Nature Reserve, which are adversely affected
by the change in the distribution of flows and reduced flood volumes. The current
extended drought has exacerbated the effects of river regulation placing greater
environmental stress on water dependent ecosystems. River red gum communities
in particular, are showing significant signs of stress (Wen et al. 2009a).
2.3 Aquatic ecosystems of the Lowbidgee
The draft Australian National Aquatic Ecosystem Classification Scheme (Auricht
2010) consists of three levels that attempt to capture the broad spatial patterns and
ecological diversity of aquatic ecosystems and habitat types (Figure 2). The according
to this scheme, the aquatic ecosystems of the Lowbidgee are regarded as lacustrine,
palustrine and riverine.
12
Figure 2. Australian National Aquatic Ecosystem Structure; regionalisations, classes and
systems within the classification scheme. The Lowbidgee floodplain includes lacustrine,
palustrine and riverine aquatic ecosystems.
The Lowbidgee-Yanga and Nimmie-Caira (LYNC) Decision Support System (DSS),
commonly referred to as LYNC (Sinclair Knight Mertz 2011), identifies 60 reporting
locations that may be considered as individual wetlands (Figure 3). These reporting
locations include both lacustrine and palustrine aquatic ecosystems.
Consultation with the project team and strategic advisory group established that 10
additional wetlands to the south and west of the existing reporting locations
identified in the LYNC DSS could also be incorporated within the project (Figure 4).
However, the project team and strategic advisory group also recognised that
ecological information pertaining to these wetlands would be lacking and dataset
availability would be poor.
While wetland definitions, including the ANAE Classification Scheme, commonly
incorporate river reaches and riverine aquatic ecosystems, these were not
incorporated into the LYNC DSS, despite their ecological value as aquatic ecosystems.
The integrated ecological condition assessment framework will be applied to the 60
identified wetlands, 10 additional wetlands in the southern and western regions of
the Lowbidgee and three river reaches on the Lowbidgee; Balranald – Redbank,
Redbank – Maude and above Maude (Figure 3).
13
Figure 3. Aquatic ecosystems of the Lowbidgee; these include the 60 reporting locations
identified in the LYNC DSS, 10 additional wetlands located in the southern and western
regions of the Lowbidgee and three river reaches.
14
3 Ecosystem values and related services
3.1 Criteria for identifying HEVAE
The HEVAE draft guidelines(Aquatic Ecosystems Task Group 2011) outlines six
criteria to be used in regard to identifying HEVAE.
1. Diversity – the asset exhibits exceptional diversity of species or habitats, and/or
geomorphological features/processes.
2. Distinctiveness – the asset is a rare/threatened or unusual aquatic ecosystem;
and/or the asset supports rare/threatened species/communities; and/or the
asset exhibits rare or unusual geomorphological or hydrological
features/processes and/or environmental conditions, and is likely to support
unusual assemblages of species adapted to these conditions
3. Vital habitat – an asset provides vital habitat for flora and fauna if it supports
unusually large numbers of a particular natural species; and/or maintenance of
populations of specific species at critical life cycle stages; and or key/significant
refugia at times of stress.
4. Evolutionary history – exhibits features or processes and/or supports species or
communities which are important in demonstrating key features of the evolution
of Australia’s landscape, riverscape or biota, especially in a world context.
5. Naturalness – the ecological character of the aquatic ecosystem is not adversely
affected by modern activity.
6. Representativeness – the asset is an outstanding example of an aquatic
ecosystem class to which it has been assigned, within a drainage division.
3.2 Ecosystem values of the Lowbidgee floodplain
These criteria have been used to identify the key ecological values contributing to
the conservation significance of the Lowbidgee floodplain.
3.2.1 Vital Habitat
The Lowbidgee Floodplain is one of a small number of large wetland complexes that
regularly supports colonially nesting waterbird breeding events in the order of tens
of thousands of breeding pairs. Though the range and site fidelity of colonially
nesting waterbirds is poorly understood, it is reasonable to suppose that the
Lowbidgee Floodplain provides an important role in the preservation of waterbird
populations at the scale of the Murray-Darling Basin. The Lowbidgee Floodplain
supported the largest colonial nesting event recorded in the regulated rivers of the
northern basin during the peak of the Millennium Drought 2003-2007 (the 2005
event at Telegraph Bank which was estimated to include approximately 30 000
breeding pairs of waterbirds).
15
3.2.2 Representativeness
The Lowbidgee Floodplain contains the second largest contiguous stand of river red
gum in Australia, and is an outstanding example of the class vegetation functional
group EIW - Eucalyptus communities of inland watercourses and inner floodplains
(NSW Vegetation Classification and Assessment from Benson et al. 2006). The total
area of river red gum forest in the north and south Redbank system amounts to
approximately 45 000 ha (the largest is Barmah-Millewa with 61 000 ha). This
compares with the next-largest stand of 38 400 ha of river red gum forest and
woodland in the Macquarie Marshes.
3.2.3 Distinctiveness
The wetlands of the Lowbidgee floodplain support several threatened species. The
waterholes of the Lowbidgee provides the most important drought refuge for the
southern bell frog, and the management of these refuges during drought is critical to
the survival of this once wide-spread species.
3.2.4 Diversity
The Lowbidgee floodplain supports a diversity of wetland habitats including river red
gum forest and woodland, lignum shrubland, spike-rush, black box woodland and
ephemeral lakes. These habitats in turn support a diverse array of species, and the
successful conservation of aquatic biota in the Lowbidgee is contingent upon the
maintenance of the heterogeneity of wetland habitats in the landscape.
3.3 Ecosystem services
Table 2 links the core values of the Lowbidgee floodplain, established using the
criteria for identifying HEVAE, to specific ecosystem services. These ecosystem
services form the foci of management actions on the Lowbidgee floodplain.
Table 2. Ecosystem values and related services that form the foci of management actions in
the Lowbidgee floodplain.
HEVAE Criterion/Value
Vital Habitat
Representativeness
Distinctiveness
Diversity
Services
Supports 50 000+ breeding pairs of waterbirds in favourable
hydrological conditions
Supports second largest stand of RRG forest and woodland
in Australia at 45 000 ha
Supports the threatened species, such as southern bell frog,
and is especially important as critical drought refuge
Supports extensive area and diversity of wetland habitat
including spike-rush, river red gum forest and woodland,
black box woodland, lignum shrubland
Supports diversity of wetland fauna including waterbirds,
fish, amphibians and invertebrates
16
Critical ecological components relating to values of
HEVAE
Ecosystems consist of various non-living, abiotic, and living, biotic components.
Ecosystem components are defined as the physical, chemical and biological parts of
an aquatic ecosystem (see glossary). For this study, components have been selected
on the basis of having the greatest influence on the value of the aquatic ecosystems
of the Lowbidgee floodplain (Table 3). These components may be regarded as
central to maintaining the ecosystem services that form the foci of management
actions on the Lowbidgee floodplain.
Table 3. Selected ecological components that relate to the values of the Lowbidgee
floodplain, as identified using the HEVAE criterion.
Selected component
Vital
habitat
Threatened fauna species
(e.g. southern bell frog)
Waterbirds
(e.g. egrets, ibis)
Fish (e.g. unspecked
hardyhead, Murray cod)
Invertebrates
(e.g. yabby)
River red gum forest
Value
RepresentDistinctativeness
iveness
X
X
Diversity
X
X
X
X
X
X
X
River red gum woodland
Black box woodland
X
X
X
X
X
Lignum
X
Tall spike rush
X
3.4 Threatened fauna species
The Yanga Ecological Character Description (Wen et al. 2009b) identified 21
endangered and vulnerable fauna that have been recorded within Yanga National
Park and its vicinity (Table 4). Endangered fauna include three birds, one amphibian,
and one reptile; and vulnerable fauna include 14 birds and two mammals.
17
Table 4. Endangered and vulnerable fauna found within Yanga National Park and its vicinity.
Source: Wen et al. (2009b)
Class
Family
Amphibian Hylidae
Aves
Acanthizidae
Accipitridae
Anatidae
Anseranatidae
Ardeidae
Burhinidae
Cacatuidae
Climacteridae
Eupetidae
Meliphagidae
Petroicidae
Pomatostomidae
Psittacidae
Rostratulidae
Strigidae
Mammalia Dasyuridae
Vespertilionidae
Reptilia
Elapidae
Actinopter Percichthyidae
ygii
Scientific name
Common name
Litoria raniformis
Pyrrholaemus
brunneus
Lophoictinia isura
Oxyura australis
Stictonetta naevosa
Anseranas
semipalmata
Botaurus poiciloptilus
Burhinus grallarius
Cacatua leadbeateri
Southern bell frog
Redthroat
Legal
status
E
V
Square-tailed kite
Blue-billed duck
Freckled duck
Magpie goose
V
V
V
V
Australasian bittern
Bush stone-curlew
Major Mitchell's
cockatoo
Brown treecreeper
Chestnut quail-thrush
V
E
V
Painted honeyeater
Hooded robin
V
V
Grey-crowned babbler
V
Regent parrot (eastern
subsp.)
Superb parrot
Painted snipe
E
Barking owl
Spotted-tailed quoll
Large-footed bat
Bardick
Murray-cod
V
V
V
E
V
(EPBCA
1999)
Climacteris picumnus
Cinclosoma
castanotus
Grantiella picta
Melanodryas
cucullata
Pomatostomus
temporalis temporalis
Polytelis anthopeplus
monarchoides
Polytelis swainsonii
Rostratula
benghalensis australis
Ninox connivens
Dasyurus maculatus
Myotis Macropus
Echiopsis curta
Maccullochella peelii
peelii
V
V
V
E
3.4.1 Indicator species: southern bell frog
The southern bell frog (Figure 4) has been selected as an indicator species for
threatened species and thereby acts as an indicator of the value of the Lowbidgee
floodplain in providing vital habitat to threatened species.
18
Figure 4. Southern bell frog. Photograph: Sascha Healy (OEH)
The southern bell frog was once widespread and abundant throughout southeastern
Australia (Wassens et al. 2008b). Over the last three decades, its population and
distribution has reduced to a critical level (Lunney et al. 2000) and for this reason it is
listed as endangered on the schedule of the NSW Threatened Species Conservation
Act (1995).
In the Lowbidgee, the southern bell frog occupies two different habitats, river red
gum forests and black box/lignum woodland (Wassens et al. 2008b). In river red gum
swamps (e.g. Yanga), the southern bell frog is associated with emergent
macrophytes such as tall spike rush (Eleocharis sphacelata) and water primrose
(Ludwigia peploides). In contrast, the black box/lignum wetlands within NimmieCaira system contain abundant floating and submerged macrophytes such as nardoo
(Marsilea drummondii) and common milfoil (Myriophyllum variifolium) (Wassens et
al. 2008a). As there is no long-term monitoring data, it is not clear exactly when
southern bell frog populations began to decline within the Lowbidgee. However, like
many amphibians, the southern bell frog is thought to be particularly vulnerable to
habitat loss and fragmentation (Wassens et al. 2008b).
3.5 Waterbirds
In the past the Lowbidgee has regularly supported more than 50 000 waterbirds and
sometimes more than 100 000 waterbirds, including some of the largest breeding
19
colonies of straw-necked ibis in Australia (Department of Water Resources 1994;
Kingsford and Thomas 2001; Wetlandcare Australia 2008).
The Lachlan/Murrumbidgee confluence was identified as an important migratory
waterbird habitat in NSW (Watkins 1993) and has been included in the Wildlife
conservation plan for migratory shorebirds (Department of Environment and
Heritage 2006). The Lowbidgee region has provided habitat for 11 migratory species
scheduled within international agreements for migratory birds (JAMBA, CAMBA and
ROKAMBA, Table 5).
Table 5. List of migratory birds protected under international treaties
Family
Apodidae
Ardeidae
Common Name
Fork-tailed Swift *
Great Egret
Cattle Egret
Accipitridae
White-bellied Sea Eagle
Threskiornithidae Glossy Ibis
Rostratulidae
Painted Snipe
Scolopacidae
Black-tailed Godwit
Sharp-tailed Sandpiper
*
Latham's Snipe *
Greenshank *
Marsh Sandpiper *
Scientific Name
Apus pacificus
Ardea alba
Ardea ibis
Haliaeetus leucogaster
Plegadis falcinellus
Rostratula benghalensis
Limosa limosa
Calidris acuminate
Gallinago hardwickii
Tringa nebularia
Tringa stagnatilis
Legal Status
C, J, K
C, J
C, J
C
C
C
C, J, K
C, J, K
J
C, J, K
C, J, K
C = CAMBA, J = JAMBA, K = ROKAMBA
* Listed in Australian National Conservation Plan for Migratory Shorebirds.
A number of bird surveys have been undertaken in the Lowbidgee region (Bales
2002; Kingsford and Porter 2006; Magrath 1992; Maher 1990; Maher 2006; Pressey
et al. 1984; Spencer and Allman 2008). A summary of these surveys are presented in
Table 6.
Table 6. Major bird surveys in Lowbidgee region
Year
Location
1982
Lowbidgee/
Lachlan
confluence
Lowbidgee/
Lachlan
confluence
Lower Lachlan &
Murrumbidgee
valley
1989/90
1990/91
1998/99
Redbank District
Total Waterbird Reference
Species Species
114
42
Pressey et
al., 1984
164
142
61
Maher,
1990
?
Magrath,
1992
44
Bales, 1999
20
Comments
Severe drought in 198283
Major flood during 1989
resulting breeding
events
This survey was
specifically for
waterbirds. Major flood
occurred during
sampling period
Recorded 15 species
1983-2008
Lowbidgee
floodplain
2005/2006 Yanga National
Park
2008-2010
Lowbidgee
54
36
Kingsford
& Thomas,
2001
Maher,
2006
46 (18
Spencer &
breeding) Wassens,
2010
that had not recorded in
previous surveys
Total species detected
in the annual aerial
survey
Following the release of
large volume of EWA.
12 colonial nesting
species were recorded
breeding
RERP ecological
investigation. Wetland
availability and
waterbird abundance
and diversity low in
2008-2009 season and
higher in 2009-2010
season
Pressey et al. (1984) identified 114 bird species. They noted that the range of birds
observed were generally similar to those that had been recorded by a number of
observers in 1923, 1940 and 1961. However, they also noted that a number of
ground living birds, notably the plains wanderer (Pedionomus torquatus), southern
stone-curlew (Burhinus grallarius), Australian bustard (Ardeotis australis) and the
brolga (Grus rubicunda), had either declined or become locally extinct. They
attributed this to the effect of feral animals or grazing practices. They also indicated
the number of wetland species observed may have been depressed by the dry
conditions, and the number of honeyeater species by the lack of flowering trees, at
the time of the survey.
Maher (1990) recorded a total of 164 species of bird during his survey. These
consisted of 61 species which were classified as waterbirds and 103 which were land
birds. Sixteen of the waterbirds were colonial nesting species. Results were
presented for the habitat preference of the birds. River Red Gum forested wetlands,
in conjunction with adjacent reed or rush dominated swamps, were identified as the
most important habitat for waterbird breeding. Of 42 species found in the River Red
Gum forest 30 were confirmed as breeding and this habitat was the main breeding
habitat for 11 of the colonial nesting bird species. The presence of the reed/rush
habitat within a reasonable proximity to the colonial nesting sites was considered
important in providing feeding grounds.
Maher (1990) found the highest number of waterbirds in shallow marsh/reed/rush
habitats. A total of 53 waterbird species were observed of which 17 were confirmed
as breeding. The second most popular habitat for waterbirds was found to be
lignum/nitre goosefoot dominated swamps where 50 species were observed, 21 of
which were breeding. The lowest number of waterbirds, 36 of which 10 were
breeding, was observed in black box swamps. Open water was an important
breeding ground for a small number of species, in particular gull-billed terns
21
(Gelochelidon nilotica) and silver gulls (Chroicocephalus novaehollandiae), but was
more important as a major feeding area particularly as floodwaters receded. Flooded
cropland was considered to provide an important feeding ground but provided little
benefit for breeding purposes.
Magrath (1992) undertook a study specifically of waterbirds of the lower Lachlan and
Murrumbidgee valley. This study included three wetland areas within Yanga National
Park, namely Redbank Swamp (including the Mercedes and Pococks Swamp in Table
13), Tarwillie Swamp, and Egret Swamp. Redbank Swamp, a river red gum dominated
swamp, was found to support sizeable populations of a number of waterbirds
including three egret and two cormorant species and rufous night heron (Nycticorax
caledonicus). It was suggested that the swamp was inundated annually and could
support colonies in most years. Tarwillie Swamp was found to have supported one of
the largest great egret colonies recorded in Australia. Large colonies of egrets and
cormorants were observed on Egret Swamp.
A total of 64 waterbird species from 14 families were recorded by these surveys
discussed above (Table 7).
22
Table 7. Waterbirds species recorded in Yanga and surrounding floodplain
Family
Common Name
Scientific Name
Accipitridae
Swamp Harrier
Circus approximans
White-bellied Sea Eagle
Haliaeetus leucogaster
Whistling Kite
Haliastur sphenurus
Chestnut Teal
Anas castanea
Grey Teal
Anas gracilis
Australasian Shoveler
Anas rhynchotis
Pacific Black Duck
Anas superciliosa
Hardhead
Aythya australis
Musk Duck
Biziura lobata
Australian Wood Duck
Chenonetta jubata
Black Swan
Cygnus atratus
Plumed Whistling Duck
Dendrocygna eytoni
Pink-eared Duck
Malacorhynchus membranaceus
Blue-billed Duck
Oxyura australis
Freckled Duck
Stictonetta naevosa
Australian Shelduck
Tadorna tadornoides
Anhingidae
Darter
Anhinga melanogaster
Ardeidae
Great Egret
Ardea alba
Little Egret
Ardea garzetta
Cattle Egret
Ardea ibis
Intermediate Egret
Ardea intermedia
White-faced Heron
Ardea novaehollandiae
Pacific Heron
Ardea pacifica
Australasian Bittern
Botaurus poiciloptilus
Little Bittern
Ixobrychus minutus
Rufous Night Heron
Nycticorax caledonicus
Black-fronted Plover
Charadrius melanops
Red-fneed Dotterel
Erthrogonys cintus
Masked Lapwing
Vanellus miles
Banded Lapwing
Vanellus tricolor
Caspian Tern
Hydroprogne caspia
Silver Gull
Larus novaehollandiae
Whiskered Tern
Sterna hybrida
Gull-billed Tern
Sterna nilotica
Pelecanidae
Australian Pelican
Pelecanus conspicillatus
Phalacrocoracidae
Great Cormorant
Phalacrocorax carbo
Little Pied Cormorant
Phalacrocorax melanoleucos
Little Black Cormorant
Phalacrocorax sulcirostris
Anatidae
Charadriidae
Laridae
23
Pied Cormorant
Phalacrocorax varius
Great-crested Grebe
Hoary-headed Grebe
Podiceps cristatus
Poliocephalus poliocephalus
Australasian Grebe
Tachybaptus novaehollandiae
Eurasian Coot
Fulica atra
Dusky Moorhen
Gallinula tenebrosa
Black-tailed Native-hen
Gallinula ventralis
Purple Swamphen
Porphyrio porphyrio
Australian Crake
Porzana fluminea
Baillon’s Crake
Porzana pusilla
Spotless Crake
Porzana tabuensis
Buff-Banded Rail
Rallus philippensis
Banded Stilt
Cladorhynchus leucocephalus
Black-winged Stilt
Himantopus himantopus
Red-Necked Avocet
Recurvirostris novaehollandiae
Rostratulidae
Painted Snipe
Rostratula benghalensis
Scolopacidae
Sharp-tailed Sandpiper
Calidris acuminate
Latham's Snipe
Gallinago hardwickii
Black-tailed Godwit
Limosa limosa
Greenshank
Tringa nebularia
Marsh Sandpiper
Tringa stagnatilis
Yellow-billed Spoonbill
Platalea flavipes
Royal Spoonbill
Platalea regia
Glossy Ibis
Plegadis falcinellus
Australian White (Sacred) ibis
Threskiornis aethiopica
Straw-necked Ibis
Threskiornis spinicollis
Podicipedidae
Rallidae
Recurvirostridae
Threskiornithidae
Data sources: Pressey et al. (1984); Maher (1990, 2006); Magrath (1992); Bale (1999); Kingsford and
Thomas (2001); Spencer and Allman (2008).
3.5.1 Indicator cohort: egrets
Egrets, including the great egret (Ardea alba), eastern great egret (Ardea modesta),
intermediate egret (Ardea intermedia) and the little egret (Egretta garzetta) (Figure
5), have been selected as indicators of the provision of vital habitat for waterbirds
and as an indicator of the diversity of fauna occurring within HEVAE in the
Lowbidgee. Vital habitat and diversity are identified as values for the HEVAE within
the Lowbidgee. Egrets have specifically been selected as they are largely regarded as
tree-nesting waterbirds and therefore act as an indicator of the provision of forest
and woodland habitat that is vital for breeding of tree-nesting waterbirds.
24
Figure 5. A) great egret. B) intermediate egret. C) little egret. Photograph: Chris Herbert
(Hunter Birds Observers Club).
Egrets can be observed in a range of aquatic habitats; however they do exhibit a
preference for breeding in fringing or flooded trees, with a specific preference for
river red gum. Ideally flooding should occur in spring for a duration of at least 6
months, however flooding of up to 12 months will promote breeding success (Rogers
2010). In the 2009-2010 breeding season, an egret and cormorant rookery
established in the Top Narockwell wetland storage.
3.5.2 Indicator cohort: ibis’
Ibis’, including the glossy ibis (Plegadis falcinellus), Australian white ibis (Threskiornis
molucca) and straw-necked ibis (Threskiornis spinicollis) (Figure 6) have been
selected as indicators of the provision of vital habitat for waterbirds and as an
indicator of the diversity of fauna occurring within HEVAE in the Lowbidgee. Vital
habitat and diversity are identified as values for the HEVAE within the Lowbidgee.
Ibis’ have specifically been selected as they are largely regarded as lignum-nesting
waterbirds and therefore act as an indicator of the provision of lignum habitat that is
vital for breeding of lignum-nesting waterbirds.
Figure 6. A) glossy ibis. B) Australian white ibis. C) straw-necked ibis. Photographs: Chris
Herbert (Hunter Bird Observers Club) and Kerrylee Rogers (OEH)
Ibis occur in a range of inland permanent and ephemeral wetlands settings. However
they do exhibit a preference for breeding in wetlands that are vegetated with reeds,
25
rushes, lignum, and cumbungi that are at or near water level. In the Lowbidgee, ibis’
typically establish nests in lignum by constructing a platform of sticks above the
water level (Rogers 2010).
3.6 Fish
Under flood conditions the Lowbidgee is hydrologically connected to the
Murrumbidgee River during overbank flow and flooding. Under these conditions, the
Lowbidgee floodplain and river reaches provides diverse habitats for fish including
low-flow and wetland specialists, main channel generalists and wetland
opportunists, main channel specialists and flood spawners (Figure 7).
Figure 7. Schematic shows the importance of floodplain wetland as fish feeding, spawning
and nursery habitat. Adapted from Mussared (1997).
Fish use floodplain habitats for a variety of reasons, including shelter, feeding,
spawning and recruitment (Junk et al. 1989). These habitats provide shelter during
flood events, away from the fast flows of the main channel. The slow water velocity
and high productivity of floodplain habitats makes them important feeding and
nursery areas. Spawning in floodplain habitats can provide larvae and juveniles with
safer conditions (e.g. protection from predation) and more food than the main
waterway channel. Many southeastern fish (see Table 18 in Section 5.3.3), such as
silver perch (Bidyanus bidyanus), golden perch (Macquaria ambigua), and bony
herring (Nematalosa ereb), spawn and shelter in floodplain habitats. The Murray
hardyhead (Craterocephalus fluviatilis), an endangered species in the Murray-Darling
Basin, lives along the edges of slow-flowing lowland rivers and in lakes, billabongs
and backwaters. Although these species use floodplain habitats, there has been little
research on the importance of these habitats for fish. Fish movement during flooding
is generally unknown, and the dependence on the floodplain has not been
thoroughly researched.
26
As the floodplain becomes more and more isolated from the Murrumbidgee River
due to catchment-scale regulation and reach-scale development, the Yanga National
Park and Lowbidgee floodplain is losing this service. For example, according to the
latest fish survey, the exotic European carp dominated the majority of sampled
habitats (Spencer and Wassens 2010).
Some research has been undertaken on fish in the lower Murrumbidgee. Maher
(1990) predominantly reported on birds of the Lachlan-Murrumbidgee confluence,
however the study did refer to observed fish. These were European Carp (Cyprinus
carpio), Bony Bream (Nematalosa eribi) and the Mosquito Fish (Gambusia affinis).
The carp were said to be abundant in all swamps, particularly those used as water
storages and in the Lachlan/Murrumbidgee Rivers. Bony Bream were observed in
large numbers in Tala Creek during a period of rising floodwater. Mosquito Fish were
observed to be common in shallow floodwater (Maher 1990).
A number of fish surveys have been done undertaken in the Murrumbidgee
catchment by NSW Fisheries (Baumgartner 2004; Gilligan 2005). These studies
focused on the instream habitats and did not consider fish use of the floodplain.
Bales (2002) sampled a range of fish habitats in Yanga including small and large
irrigation channels, lakes and deep waters, and shallow wetlands. Eight species was
recorded, however, the fish community was dominated by introduced species,
notably European Carp in all habitats. In addition, two hardy freshwater species,
Yabby (Cherax destructor) and Long-necked Turtle (Chelodina longicollis), were also
abundant in these habitats except the lakes.
As part of the RERP ecological investigation in the Lowbidgee, Spencer and Wassens
(2010) sampled 11 sites on the Lowbidgee during the 2008-2009 breeding season
and 14 sites during the 2009-2010 season. Over the 2008-2010 study period 13 fish
species were detected in the surveyed wetlands, including four alien species:
European carp, goldfish, gambusia and redfin perch Perca fluviatilis. Carp gundgeons
were the most abundant fish; however the bony bream comprised most of the
native fish biomass. Golden perch and unspecked hardyheads were the least
common native fish species.
Table 8 lists all fish species known to occur in the Lowbidgee wetlands and river
reaches.
Table 8. Fishes species in the Lowbidgee region including the Murrumbidgee channel.
Family
Clupeidae
Galaxiidae
Retropinnidae
Plotosidae
Atherinidae
Melanotaeniidae
Scientific name
Nematalosa erebi
Galaxias brevipinnis ^
Retropinna semoni
Tandanus tandanus +
Craterocephalus fluviatilis +
Craterocephalus stercusmuscarum fulvus
Melanotaenia fluviatilis +
27
Common name
Bony Breem
Climbing Galaxias
Australian Smelt
Freshwater Catfish
Murray Hardyhead
Un-specked Hardyhead
Murray-Darling
Rainbowfish
Percichthyidae
Terapontidae
Eleotridae
Cyprinidae
Cobitidae
Poecilidae
Percidae
Macquaria ambigua ambigua
Maccullochella peelii peelii +
Bidyanus bidyanus
Leiopotherapon unicolor
Philypnodon grandiceps
Hypseleotris spp
Cyprinus carpio *
Carassius auratus *
Misgurnus anguillicaudatus *
Gambusia holbrooki*
Perca fluviatilis *
Golden Perch
Murray Cod
Silver Perch
Spangled Perch
Flat-headed Gudgeon
Western carp Gudgeon
Carp
Goldfish
Oriental Weatherloach
Eastern Gambusia
Redfin Perch
* Exotic species, + Likely to be locally extinct., ^ trans-located native species.
Data source: Bale, 1999; Baumgartner, 2004; Gilligan, 2005; Spencer and Allman, 2008.
3.6.1 Indicator species: Unspecked hardyhead
Unspecked hardyhead (Figure 8) have been selected as an indicator of the provision
of vital habitat for fish regarded as low-flow and wetland opportunists and as an
indicator of the diversity of fauna occurring within HEVAE in the Lowbidgee. Vital
habitat and diversity are identified as values for the HEVAE within the Lowbidgee.
Unspecked hardyhead have been selected as they represent the group of fish that
may readily use floodplain wetland habitats when conditions are suitable.
Figure 8. Unspecked hardy head. Photograph: Gunther Schmida.
Unspecked hardyheads are regarded as wetland specialists as they tend to spawn
and recruit in anabranches, billabongs and floodplain wetlands, although they may
also spawn in riverine settings (Ralph et al. 2010). They are typically found around
the margins of slow-flowing rivers, back-waters and billabongs in shallow vegetated
areas with sandy or muddy substrates (Allen et al. 2003). Increased abundance of
unspecked hardy head was evident in a 2009-2010 survey compared to a similar
28
2008-2009 survey (Spencer and Wassens 2010), perhaps in response to greater
inflows and greater connectivity.
3.6.2 Indicator species: Murray cod
Murray cod (Figure 9) have been selected as an indicator of the provision of vital
habitat for fish regarded as main channel specialists and as an indicator of the
diversity of fauna occurring within HEVAE in the Lowbidgee. Vital habitat and
diversity are identified as values for the HEVAE within the Lowbidgee. Murray cod
have been selected as they represent the group of fish that prefer habitats that
largely occur in main channels.
Figure 9. Murray cod. Photograph: Gunther Schmida.
The Murray cod is a large-long-lived fish that is regarded as a main channel specialist
as it tends to spawn and recruit during high or low flows in the main channel.
Spawning typically occurs from spring to summer and requires a minimum water
temperature of 15oC (Ralph et al. 2010). While they do not require floods to
stimulate spawning, large floods may enhance recruitment due to an increase in
food availability (King et al. 2003).
3.7 Invertebrates
Invertebrates are animals without backbones and may be grouped as
microinvertebrates of less than 1 mm length (e.g. protozoa, rotifers and
microcrustaceans) and macroinvertebrates of greater than 1 mm length. These
invertebrates play an essential role within aquatic food webs by breaking down
29
organic matter, transforming nutrients, feeding on fungi and algae and ultimately
providing a major food source to higher order animals such as fish, amphibian,
reptiles and waterbirds (Young 2001).
Invertebrates have been surveyed in the Lowbidgee as part of the Office of Waters’
Integrated monitoring of Environmental Flows (IMEF) and Office of Environment and
Heritages’ Sustainable Rivers Audit (SRA). The SRA for 2004-2007 indicated the the
Murrumbidgee Valley macroinvertebrate community was in poor condition. Lowland
macroinvertebrate communites, which would include the Lowbidgee, were in better
condition than communities in the Slopes, Upland and Montane regions. Four
common families in the lowland regions include damselflies (Corduliidae), pond
snails (Lymnaeidae), pill clams, (Sphaeriidae) and isopods (Phraetoicidae) (Davies et
al. 2008).
3.7.1 Indicator species: Yabby
Yabbies (Figure 10) have been selected as an indicator of the provision of vital
habitat for invertebrates and as an indicator of the diversity of fauna occurring
within HEVAE in the Lowbidgee. Vital habitat and diversity are identified as values for
the HEVAE within the Lowbidgee. Yabbies have been selected as they are high
trophic order invertebrates and may act as indicator of the health of invertebrate
communities at lower tropic orders. In addition, yabbies are an important food
source for some waterbirds and collapse of yabby populations may provide an
indication of high order ecosystem collapse.
Figure 10.
Western yabby: Photograph: Gunther Schmida.
Yabbies occupy a range of habitats, but are regarded to be most abundant in
floodplain habitats such as billabongs, swamps, intermittently flowing creeks,
irrigation channels and reservoirs (Walker 1983). Yabbies are regarded as resilient
30
and are able to aestivate for several years in drought conditions. Flooding is not
regarded as a breeding stimulus (Jones 2010), yet breeding does not occur when
aestivating. Ideal flood conditions occur in spring and summer when water
temperatures exceed 15oC (Jones 2010).
3.8 Important vegetation communities
The distribution of different vegetation communities across landscapes is influenced
by various factors such as climate, position in the landscape; biological interactions
and site history (e.g. bush fires, floods, human activities such as land clearing and
logging). For the purpose of this study, river red gum forest, river red gum woodland,
black box woodland, lignum and tall spike rush are regarded as integral components
that relate to the values of the HEVAE of the Lowbidgee (Figure 11, Table 9).
Table 9. Extent of vegetation communities of the Lowbidgee floodplain in 2008. Source:
Bowen and Simpson (2010)
Vegetation
Community
River red gum
forests and
woodlands
River red - black box
woodland
Black box
woodlands
Lignum and/or nitre
goosefoot
shrublands
Spikerush
dominated
sedgeland
Waterbody
NSW Vegetation Classification and Assessment Plant
Community
VCA ID 2: River red gum sedge dominated very tall open forest
in frequently flooded sites along major rivers and floodplains in
south western NSW
VCA ID 7: River red gum Warrego grass herbaceous riparian tall
open forest mainly in the Riverina bioregion
VCA ID 9: River red gum wallaby grass tall woodland on the
outer river red gum zone mainly in the Riverina bioregion
VCA ID 10: River red gum – black box woodland of the semi
arid (warm) climatic zone (mainly Riverina and MDD)
VCA ID 13: Black box - lignum woodland of the inner
floodplains in the semi arid (warm) climate zone mainly
Riverina and MDD
VCA ID 15: Black box open woodland with chenopod
understorey mainly on the outer floodplains in south western
NSW (mainly Riverina and MDD)
VCA ID 16: Black box grassy open woodland of rarely flooded
depressions in south western NSW (mainly Riverina and MDD)
VCA ID 17: Lignum shrubland of the semi arid (warm) plains
(mainly Riverina and MDD)
Area
(ha)
27 306
VCA ID 12: Shallow marsh of regularly flooded depressions on
floodplains mainly in the semi-arid(warm) climatic zone mainly
Riverina and Murray Darling Depression Bioregions (MDD)
VCA ID 238: Permanent and semi-permanent freshwater lakes
of the inland slopes and plains
304
Total
407
19 299
40 105
2 195
89 616
31
Figure 11.
2008 Vegetation map for Yanga National Park, nature Reserve and State
Conservation Area. Source: Bowen and Simpson (2010)
32
Historical time series vegetation mapping of Yanga National Park has been
undertaken by the former DECCW (now OEH) as part of the Rivers and
Environmental restoration program for the years of 1965, 1973, 1997 and 2005
(McCosker 2008). This mapping was updated in 2008 and expanded to the
Lowbidgee floodplain as part of RERP (Bowen and Simpson 2010) (Figure 11, Table
9). Mapping of the Lowbidgee floodplain in 2008 indicates that the Lowbidgee
floodplain is dominated by river red gum and black box communities (Redbank
system) and by lignum shrublands and chenopod shrublands (Nimmie-Caira system)
(Bowen and Simpson 2010). McCosker (2008) established that the boundaries of
major plant communities have remained relatively unchanged in the Lowbidgee
from the 1960s. However, the canopy cover and condition for each community has
declined, with the exception of small areas receiving regular controlled flooding
(irrigation), which are regarded to be in good condition. This assessment was reconfirmed by the mapping of Bowen and Simpson (2010).
3.8.1 River red gum forest and woodland
River red gum forest/woodland occurs along rivers, creeks, levees and adjacent flats,
channeled plains and other areas subject to frequent or periodic flooding (Figure 12,
13). It is usually on heavy grey, brown and red clays (Porteners 1993).
Figure 12.
DECCW
River red gum forest adjacent to Piggery Lake. Photograph: Kerrylee Rogers
33
Figure 13.
River red gum forest with dense tall spike rush understorey located at Little
Piggery. Photograph: Kerrylee Rogers OEH
In Yanga National Park, four sub-classes of river red gum forest/woodland were
identified by McCosker (2008); river red gum tall gallery forest, river red gum forest
with dense tall spike rush understorey, river red gum woodland with grassy
understorey, river red gum forest with shrubby lignum understorey (Table 11). River
red gum communities exhibiting structural characteristics of a forest (i.e. crown
cover >30% and regarded as mid-dense to dense, based on Specht 1970) were
generally regarded to be in good to fair condition, while river red gum woodlands
(i.e. crown cover <30% and regarded as sparse to very sparse, based on Specht 1970)
were regarded as being in poor condition in 2005 (McCosker 2008) (Table 11). A
similar assessment in 2008 indicated that almost 75% of river red gum communities
in Yanga National Park were in poor condition or declining condition (Table 10).
However, many of these communities were formerly managed for timber production
by artificially inundating higher ground using levee banks. This is a management
practice that has not been maintained since Yanga was purchased by DECCW and
gazetted a National Park in 2005 (Bowen and Simpson 2010).
The majority of river red gum communities are severely stressed except the small
areas of riparian forest lining the Murrumbidgee and Pee Vee Creek, which deliver
irrigation water to Lake Tala, and other patches which have been regularly irrigated.
The stands of river red gum in good condition are general located along the flood
way from Yanga Regulator to upstream of Piggery Lake. Downstream of Piggery Lake
to the upstream of Yanga Lake, the communities are either severely stressed or dead
(Figure 14).
34
Table 10. River red gum condition and stem density at Yanga National Park. Source: Bowen
and Simpson (2010).
River red gum
stem density
<200
200-400
400-800
>800
Total
Good
3089
10
0
0
3099 (15%)
River red gum condition
Intermediate Intermediate/Poor
1339
3695
917
778
108
376
0
154
2364 (11.5%)
5003 (24.5%)
35
Poor
6679
243
46
2959
9927 (49%)
Table 11. Eucalyptus communities within Yanga National Park. Source: McCosker (2008), Benson et al. (2006).
River red gum community
sub-class
River red gum tall gallery
forest; lines main channel of
Murrumbidgee and levees
River red gum forest with
dense understorey dominated
by tall spike rush
River red gum woodland with
grassy understorey
River red gum forest with
shrubby lignum understorey
Black box – lignum woodland
Characteristic species
Structure
Condition
Eucalyptus camaldulensis subsp. camaldulensis; Eleocharis
acuta-Centipeda cunninghamii-Ranunculus inundatusPseudoraphis spinescens
Eucalyptus camaldulensis subsp. camaldulensis; Eleocharis
acuta, Paspalidium jubiflorum; Wahlenbergia fluminalis;
Senecio quadridentatus; Carex tereticaulis
Eucalyptus camaldulensis subsp. camaldulensis;
Austrodanthonia caespitosa; Juncus flavidus; Carex inversa
Eucalyptus camaldulensis subsp. camaldulensis; Acacia
stenophylla; Muehlenbeckia florulenta; Paspalidium
jubiflorum; Cyperus gymnocaulos; Einadia nutans subsp.
nutans
Eucalyptus largiflorens; Muehlenbeckia florulenta;
Chenopodium nitrariaceum; Einadia nutans subsp. nutans;
Paspalidium jubiflorum; Sclerolaena muricata var. muricata;
Austrodanthonia caespitosa
Open forest
Good to fair
Open forest
Poor to very poor.
Small stands in
good condition
Poor, very poor,
dead tree stands
Poor, very poor,
dead tree stands
Black box open woodland with
chenopod understorey
36
Woodland
Open forest/
woodland
Area
(ha)
1 083
4 622
3 689
11 926
Woodland
open
woodland
Poor to very poor
3 020
Open
woodland,
woodland
Poor, very poor,
dead tree stands
9 044
Figure 14.
Condition of river red gum in 2005 based on aerial photography. Source:
McCosker (2008).
37
3.8.2 Black box woodland
Black box woodland typically occurs on the less frequently flooded areas of the
floodplain above the level of the adjacent river red gum forest. The understorey of
the black box woodlands is variable and may include nitre goosefoot (Chenopodium
nitrariaceum), thorny saltbush (Rhagodia spinescens), old man saltbush (Atriplex
nummularia) and lignum (Muehlenbeckia florulenta) (Figure 15).
Figure 15.
Black box woodland at Fingerboards. Photograph: Kerrylee Rogers, OEH.
The extent of black box woodland remains constant at about 12 000 ha since 1965
(McCosker 2008) ( Table 11). However, the condition of black box in most areas
displayed symptoms of stress with bare branches (dieback) and epicormic shoots
were evident. Patches of dead mature cooba in black box woodland is not
uncommon throughout Yanga.
3.8.3 Lignum
Lignum forms a shrubland adjacent to major creeks and rivers and in low-lying
swampy areas on heavy grey cracking clays (Porteners, 1993). It can withstand
infrequent but prolonged flooding and can form dense almost impenetrable stands
(Cunningham et al. 1981; Porteners 1993). It commonly occurs on channelled plains
and depressions with impeded drainage and is often associated with river red gum
and black box as an understorey (Figure 16).
38
Figure 16.
Black box woodland with dense lignum understorey on Uara Creek.
Photograph: Kerrylee Rogers, OEH
Lignum swamps that have been subject to regular inundation become dense and tall
and are favoured breeding sites for many waterbird species, such as ibis (Figure 17).
These types of lignum swamp are quite rare and the lignum swamps around the
Lowbidgee floodplains were identified in 1990 as supporting the best stands in NSW
and possibly eastern Australia (Maher 1990). Nitre goosefoot (Chenopodium
nitrariaceum) occurs as a co-dominant with lignum in some locations with an
inconsistent ground cover, depending on flooding history. There are currently
around 7,000 ha lignum/nitre goosefoot shrubland in Yanga. The condition has
deteriorated over the 40 years of sampling period (1965 – 2005) (McCosker 2008).
39
Figure 17.
Lignum swamps are important waterbird breeding habitat in Lowbidgee
floodplain. Straw-necked ibis rookery at Telegraph Bank. Photo: James Maguire, 2005
3.8.4 Tall spike rush
This general term covers many shallow low-lying areas, scattered throughout the
better-watered parts of the floodplain. Under natural flow regime, these areas are
subjected to irregular but frequent (once 2-3 years) inundation (Maher 1990), but
regularly refilled by diversions via the Yanga regulator and Waugorah regulator after
the regions was gazetted as the Lowbidgee Flood Control and Irrigation District in
1944. They are generally small (size ranges from less than one to hundreds of
hectares), and have different geomorphic history.
40
Figure 18.
Tall spike rush swamp (foreground) and river red gum forest with tall spike
rush understorey (background) at Mercedes Swamp. Photograph: Kerrylee Rogers, OEH.
In the Lowbidgee, these areas are generally dominated by common spike-rush
(Eleocharis acuta), and occasionally co-habiting with Tall Spike-Rush (E. sphacelata)
in standing water or recently wet areas (Figure 18). Associated water plants include
common nardoo (Marsilea drummondii), smooth nardoo (Marsilea mutica), watermilfoils (Myriophyllum spp.), wavy marshwort (Nymphoides crenata), water couch
(Paspalum distichium), Common Joyweed (Alternanthera nodiflora) and Buttercups
(Ranunculus spp.), Lagoon Saltbush (Atriplex suberecta), and Black Rolypoly
(Sclerolaena muricata subsp. muricata) grow in wetland margins. Common Reed
(Phragmites australis) is regenerating in places, particularly where it is being
protected from grazing by fallen logs and windrows left by logging operations.
3.9 Key values and components for HEVAE in the Lower
Murrumbidgee
Table 12 details the key values and related components for each aquatic ecosystem
in the Lowbidgee.
41
Table 12. Key values and related components for each aquatic ecosystem in the Lowbidgee. Source: Bowen and Spencer (2011).
Aquatic ecosystem name
Avalon North
Avalon Swamp
Eulimbah Bank Rookery
Eulimbah Dam
Lees Bank
Littlewood Swamp
Nap Nap Creek
Nap Nap Swamp
Nimmie Creek
Nolans Chance
Pollen Dam Rookery
Suicide Bank
Talpee Creek
Telephone Bank
Warwaegae
Redbank South
Bull Swamp
Pococks
River Narockwell
The Avenue
McCabes Gap
Top Narockwell
Tarwille
Tarwillie Holding
South Avenue
Piggery Bridge
Piggery Bridge South
Distinctiveness
Vital habitat
Southern bell frog
(maintenance &
recruitment)
Birds (Egrets /
ibis)^
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Unspecked
hardyhead
Murray cod
Representativeness
Yabby
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
River red gum
woodland
(maintenance &
recruitment)
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
42
River red gum forest
(maintenance &
recruitment)
Diversity
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Black box
woodland
Lignum
Tall spike rush
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Piggery Lakes
Narkungerie Swamp
Tarwille Swamp South
Narkungerie Swamp South
Breer Swamp
Shaws Swamp
X
X
X
X
X
X
X
X
X
X
Tala Swamp
Loosesmalls
South Tala
Jardines
Yanga Lake
Uara
Fingerboards
Yanga Nature Reserve
Indeena Athen Narwi
Narwille Paika
Paika
Springbank
Glen Avon Auley Riv
X
X
X
X
X
X
X
X
Devils Creek
River Smyths
Pee Vee
Primary Plain
Creek Breer
Woolshed Creek
Tala Lake
Hickeys
Waugorah Lake
North Stallion
Hill (Hoblers)
Juanbung Lake Marim
Redbank Swamp
Tori Lake Marimley
Jindeena Lake Marim
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
43
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
4 Critical processes relating to values of HEVAE
Ecosystem processes are the physical, chemical and biological actions or events that
link organisms and their environment. They include decomposition, production,
nutrient cycling, and fluxes of nutrients and energy (Millennium Ecosystem
Assessment 2005) as well as the overarching drivers imposed by geomorphology,
climate and hydrology. Rather than describing all ecosystem processes (and it is an
impractical task), this chapter will be focus on those critical processes that most
strongly influence the values of the Lowbidgee HEVAE, such as hydrology and
geomorphology.
4.1 Hydrological process
The ‘‘flood pulse’’, a term used for the floodwater input to floodplains, is commonly
perceived as the main factor that controls the existence and productivity of
floodplain ecosystems of major world rivers (Junk et al. 1989; Lewis et al. 2000). The
flood pulse is event based and may be described in terms of flood volume, flood
duration, flood timing, rate of flow delivery and recession, flood extent, water depth,
time since last flood and antecedent conditions. The flood pulse contrasts with the
flood regime, which is described as the long-term statistical pattern of floods, and
may be described in terms of flood frequency, seasonality, duration and antecedent
conditions.
Groundwater is an essentially component of hydrological processes. Groundwater
conditions, such as depth, may significantly influence the effects of the flood pulse
and regime on critical components and ecosystem function. In addition, both surface
water and groundwater quality may also influence the effectiveness of the flood
pulse and flood regime in maintaining ecosystem function.
In the Lowbidgee, where evaporation greatly exceeds rainfall, floodwater is vital to
sustain functioning ecosystems in the floodplain, and the flood regime is the
governing process for other critical processes (Figure 19). Key hydrological drivers in
the Lowbidgee floodplain include:
 Total flow volume
 Flood frequency
 Flood duration
 Flood extent
 Timing (seasonality)
 Rate of flow delivery and recession
 Antecedent conditions
 Water depth
 Groundwater
 Time since last flood
 Evapo-transpiration
 Water quality
In the Lowbidgee, the natural inundation regime is primarily governed by the river
flow in the Murrumbidgee. However, the construction of Redbank and Maude Weirs
44
in 1939 and the subsequent introduction of “Lowbidgee Flood Control and Irrigation
District” in the 1940s greatly modified the distribution and retention of water within
the floodplain resulting in smaller inundated areas with longer residence times
(Table 13).
River hydrograph
Upward limb
Flood season
Downward Limb
Dry season
Bank full level
Floodplain forest
and woodlands
1. Water and associates material
(dispores, sediment, nutrient)
inputs
2. Terrestrial fauna escape or
drowned or preyed
3. Nutrient release from live
understorey vegetation, litter and
topsoil
4. Primary production booms
5. Recharging aquifers
Connected to river and floodplain
Lakes and wetlands 1. Nutrient, sediment and organic
2.
3.
4.
5.
6.
matter input
Seed/egg bank emerge
Rapid growth of aquatic plants
and invertebrates
Fishes enter, spawn, and rapidly
grow on floodplain
Number of waterbirds increase as
food sources increase
Large flood events initiate
colonial waterbird breeding
1. Water flows back to river
2. Coarse materials (litter),
dissolved nutrient (DOC, N,
P), and salts export to river
3. Fish and other aquatic
fauna move to river
4. Sediment exports to river
as bank and soil erosion
5. Maintain high productivity
6. Recharging aquifers
1. Formation of variety of sites with different sediment types
(e.g. fine and coarse, organic debris) providing varied niches
for regeneration
2. Regeneration of tree (e.g. River red gum)
3. Water tables recede
4. Seedling establishment
5. Encroachment and colonisation of terrestrial grass species
6. Establishment of terrestrial fauna population
7. Accumulation of organic matter as litter, animal waste, and
topsoil
Connected to river and
floodplain
Isolated ephemeral/permanent aquatic habitats
1. Organic matter exports
Fishes move to river
2. Peak phytoplankton growth
3. Plankton, aquatic plant
invertebrate drift to river
4. Abundance of waterbird
reaches maximum
5. Colonial waterbird
breeding completed.
6. Fledged young feed in
surrounding floodplain
Connected to floodplain
Rivers and
anabranches
1. Fish and plant propagules enter floodplain.
2. Nutrient, organic matter (fine/coarse/large wood debris) and other
matters (e.g. salt) enter river
3. Fish and invertebrates move from floodplain to river
4. Small numbers of waterbirds roost and feed along channel edge.
1. Water level decreases due to evaporation and groundwater
infiltration
2. Nutrient, salinity, turbidity increase
3. Concentration of organisms
4. Dying and avian predation of the stranded fish
5. Increase in algal abundance and drift in species composition
6. Predation and competition among biota increase
7. Rezoning of vegetation community
8. Aquatic invertebrates either find refuge or go on persistent
stages (egg bank)
9. Waterbirds disperse to other wetlands; other areas with
greater prey resources
10. Limited waterbird breeding. Rookeries usually small and
confined to permanent waterholes
11. Consolidation of sediment
Confined to channels
1. Main material inputs from upstream
2. May connect to the floodplain through subsurface flow.
Figure 19.
Relationships between hydrological processes and other floodplain
ecosystem processes under a natural flood regime
Table 13. Hydrological processes in the Lowbidgee.
Process
Description
Overbank
flows
Overbank flow is an infrequent, high-flow event that breaches riverbanks. Overbank flow
occur when river discharge reaches 7,500 ML/day, 9,500 ML/day and 20,000 ML/day at
Balranald, Redbank and Maude Weir, respectively. The Lowbidgee was flooded naturally
in 15-20% of the years before European settlement (Pressey et al. 1984). As the
hydrological records Redbank and Maude Weir began at late 1930s, the pattern of
natural overbank flow cannot be re-structured without complicated modeling.
Nevertheless, the investigation of available river discharge record (1937-2007) at
Redbank Weir reveals that while the median duration of floods (defined as the
consecutive days of overbank flow) has not changed significantly, the frequency of
overbank flow at Redbank Weir has been halved from 18.5% (1937-1970) to less than 9%
(1970-2007) (Wen et al. 2009a). Furthermore, Yanga National Park has not experienced
natural overbank flow since 1997 (Wen et al. 2009a).
45
Process
Description
Artificial
watering
(including
environmental
water
allocation)
To compensate the reduction in natural overbank flows due to upstream water
extraction that resulted in decrease in agricultural productivity, Maude and Redbank
Weirs were constructed primary for diverting water (termed “surplus flow”) to
Lowbidgee Flood Control and Irrigation District. “Surplus flows” to Yanga are primarily via
Yanga Regulator, and the delivery of water follows the natural network of waterways
with relatively minor assistance or guidance from constructed channels or levees. The
volume of diversion depends on available flow in the Murrumbidgee and climatic
conditions with a median of 38.7 GL/yr (Figure 30), and the timing of diversion generally
follows the demand for agriculture (autumn/winter).
Rainfall and
Rainfall in Lowbidgee is highly erratic with slightly more rainy days and higher rainfall in
evaporation
winter (See Figure 4 in section 2.2). Evaporation is high ranging from 190 to 200 cm per
year.
Groundwater There is no detailed study investigating the interactions between surface and ground
exchange
water. A study conducted for the river reach between Hay and Maude estimated high
transmission loss (0.5% per km) (WRC, 1982) suggesting high rate of groundwater
recharge. However, the recorded river discharges at Maude and Balranald suggest a
much lower loss at this reach. The top soil (to 1 m) at Yanga National Park has low
saturated hydraulic conductivity (less than 2 mm/hour) except the higher ground less
flooded areas (EA Systems 2008).
Overbank
Overbank flow is an infrequent, high-flow event that breaches riverbanks. Overbank flow
flows
occur when river discharge reaches 7,500 ML/day, 9,500 ML/day and 20,000 ML/day at
downstream of Balranald, Redbank and Maude Weir, respectively. The Lowbidgee was
flooded naturally in 15-20% of the years before European settlement (Pressey et al.
1984). As the hydrological records at downstream of Redbank and Maude Weir began at
late 1930s, the pattern of natural overbank flow cannot be re-structured without
complicated modeling. Nevertheless, the investigation of available river discharge record
(1937-2007) downstream of Redbank Weir reveals that while the median duration of
floods (defined as the consecutive days of overbank flow) has not changed significantly,
the frequency of overbank flow at Redbank Weir has been halved from 18.5% (19371970) to less than 9% (1970-2007) (Wen et al. 2009a). Furthermore, Yanga National Park
has not experienced natural overbank flow since 1997 (Wen et al. 2009a).
Artificial
To compensate the reduction in natural overbank flows that resulted in decrease in
watering
productivity, Maude and Redbank Weirs were constructed in 1939 (completed in 1940)
(including
primary for diverting water (termed “surplus flow”) to Lowbidgee Flood Control and
environmental Irrigation District. “Surplus flows” to Yanga are primarily via Yanga Regulator, and the
water
delivery of water follows the natural network of waterways with relatively minor
allocation)
assistance or guidance from constructed channels or levees. The volume of diversion
depends on available flow in the Murrumbidgee and climatic conditions with a median of
38.7 GL/yr (Figure 31), and the timing of diversion generally follows the demand for
agriculture (autumn/winter).
Rainfall and
Rainfall in Lowbidgee is highly erratic with slightly more rainy days and higher rainfall in
evaporation
winter (See Figure 5 in section 2.2). Evaporation is high ranging from 190 to 200 cm per
year.
Groundwater There is no detailed study investigating the interactions between surface and ground
exchange
water. A study conducted for the river reach between Hay and Maude estimated high
transmission loss (0.5% per km) (NSW Water Resources Commission 1982) suggesting
high rate of groundwater recharge. However, the recorded river discharges at Maude
and Balranald suggest a much lower loss at this reach. The top soil (to 1 m) at Yanga
National Park has low saturated hydraulic conductivity (less than 2 mm/hour) except the
higher ground less flooded areas (EA Systems 2008).
46
4.1.1 Natural overbank flows
The Lowbidgee experiences natural flooding during high flows. Kingsford and Thomas
(2001) provided a detailed description of how overbank flows disperse in Lowbidgee
Floodplain, as cited below.
Overbank flows are distributed throughout the floodplain by a series of distributaries
(Fiddlers, Uara, Caira, Nimmie, Pollen, Waugorah, Talpee, Monkem, Kietta, Yanga,
Paika and other unnamed small creeks), which form a highly complex interconnected
network of braided creeks on the Lowbidgee floodplain. Most of these convey water
to the south but some small creeks also take water to the north where the Lachlan
River terminates in the Great Cumbungi Swamp. Flows from the Lachlan River rarely
reach the Murrumbidgee River except in major floods. Flows leave the
Murrumbidgee River first at Fiddlers Creek (previously known as Gum Creek). This
creek system is shallow and provided water to the south. The floodplain of this creek
system includes Yanga Nature Reserve (1,772 ha), an area recognised for its stands
of Black Box woodland. Anastomosing channels of Fiddlers Creek eventually form the
Uara Creek that forms a channel and conveys water to Yanga Lake and the
Murrumbidgee River near the town of Balranald. The next creeks to leave the
Murrumbidgee River are the Caira and Nimmie Creeks that also convey water to the
southwest. Neither has well defined channels from the river. The river used to flow
over the banks to these systems of anastomosing channels. Water from the Caira
Creek flowed south before bifurcating to the north to form Pollen Creek and to the
south to continue as Caira Creek. Nimmie Creek water joined up with Pollen Creek
but also flowed to the northwest to inundate areas near the river. Between Nimmie
Creek and Waugorah Creek, conveying water to the south, smaller channels take
water to the floodplain. Waugorah Creek flows southwest to fill channels and
floodplains and links up with Monkem and Talpee Creeks that similarly flow to the
south to join up with the main channel of the Murrumbidgee River. The
Murrumbidgee River also has many small channels that convey water to the south.
North and west of the Murrumbidgee River, the Redbank system is a large floodplain
dissected by channels with no defined distributary creeks. This area is primarily
reliant on overbank flows caused by a constriction in the main channel capacity of
the river.
Flood regimes and patterns in the Lowbidgee floodplain have changed dramatically due
to upstream development and management of the Lowbidgee Scheme (Table 14) (Eddy
1992; Kingsford 2003; Page et al. 2005). Kingsford (2003) summarised the development
of the area since European settlement and distinguished three major periods; before
1912, 1939-1980, and after 1980 when most of the development was completed. As
flow records are available only after 1936 for both Maude and Redbank stations, the
natural flow regime (i.e. before 1912) for the Lowbidgee Floodplain cannot be
restructured without complicated modelling. However, comparison of river discharges
before (1937-1970) and after 1970 (1971-2007) at downstream Redbank (Figure 21)
indicates that the frequency of over-bank flow decreased more than 50% from about
18.5% to less than 9%. The year 1970 (rather than 1980 as in Kingsford’s study) was
chosen as benchmark because a study indicates that the reduction of river discharge at
Hay became significant only after late 1960s (Wen et al. 2009a). The dramatic decrease
47
in frequency of over-bank flows may be the single most important factor contributing to
the continuous deterioration of River Red Gum condition in Yanga National Park.
There have been dramatic changes in hydrology downstream of Redbank Weir since
1970 (Figure 20, Table 15). The annual median flow decreased more than 60% from
2,727.0 ML day-1 to 1,048.5 ML day-1 (Table 15); and the reduction was evidenced for
every month (Figure 20). The biggest reduction (up to 90%) is in November, when the
natural spring peak flow occurs. The altered and reduced peak occurs in September,
when the demand for irrigation is at its lowest level.
Table 14. Major developments on the Murrumbidgee River (1855-1982). Source: Kingsford and
Thomas (2001), Pressey et al. (1984), Wen et al. (2009b).
Period
Development
Brief description
18551902
1880Present
Deepening of Yanco Creek Open to increase water
diversions from Murrumbidgee
River pumps were used to take water from the
Murrumbidgee for irrigation, town water supply,
domestic and livestock use
Burrinjuck Dam stage 1
In the period of 1979-1990, average 301.6 GL
was taken annually for irrigation, 36.0 GL for
other uses
Total capacity of 951.9GL
1907 1927
19121927
19141957
1928
19361940
19371940
1956 –
1962
19581968
1965 1968
1982
Murrumbidgee Irrigation Area (MIA) developed
Receives up to 780 GL per year diverted from
Murrumbidgee River; Licensed irrigation area
about 150,000 ha
Burrinjuck Dam stage 2, capacity increased by 400 Total capacity of Burrinjuck Dam is 1026 GL; first
GL
supply water to MIA in 1912. From 1979-1990,
annual mean division is 1,143.5GL.
Yanco weir constructed
Capacity of diverting 700 ML/day to irrigation
areas and properties along Yanco Creek
Maude Weir constructed
Diverts water to Lowbidgee Irrigation Area.
Mean annual diversion (1970-1982) is 100.4 GL.
Redbank Weir constructed
Diverts water from the Murrumbidgee to
Lowbidgee Irrigation Area. Mean annual
diversion (1970-1982) is 77.7 GL.
Main expansion of Coleambally Irrigation Area
Received up to 600 GL per year from
Murrumbidgee River. Licensed irrigation area
approximately 80,000 ha.
Snowy –Tumut Hydro-electricity Scheme
Diverts up to 600 GL per year from Snowy River
to Tumut River
Blowering Dam built
Capacity 1626.0 GL, storing water diverted from
Snowy River system and regulate flow in Tumut
River
Hay Weir constructed
Capacity 13.5 GL. Mean annual division (19791990) is 7.7 GL.
Both the 30-day maximum and minimum flows decreased; and the duration and
frequency of extreme low flows increased 33.3% and 300%, respectively. One direct
impact of the decreased flow is the reduction of floodplain inundation, which depends
on the over bank flows. The frequency of bankfull river discharge declined by 53.0%
48
from 18.5% to 8.7% (Table 15), which may be the single most important factor
contributing to the continuous deterioration of River Red Gum condition in Yanga
National Park.
Table 15. Changes in selected hydrological indicators in Murrumbidgee at downstream of
Redbank Weir. Source: Wen et al. (2009a).
Indicator *
1936-1970
1971-2007
Change (%)
Annual median flow (ML/day)
2727.0
1048.5
-61.6
30-day maximum flow (ML/day)
10368.0
7430.4
-28.3
30-day minimum flow (ML/day)
691.2
259.2
-62.5
Extremely low flow duration (days/year)
7.5
10.0
33.3
Extremely low flow frequency
1.0
4.0
300.0
Change rate (cubic meter per second per day)
1.6
0.6
-62.5
Frequency of bankfull flows (%)
18.5
8.7
-53.0
^
*
Median values except for overbank flow frequency.
^ Flows fall below the 10% percentile during the corresponding period.
Mean monthly flow (GL/day)
Monthly flow distribution at downstream of
Redbank Weir
250
200
Before
After
150
100
50
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 20.
Monthly flow distribution comparison before (solid line with circles) and after
(dashed line with triangles) 1970. Source: Wen et al. (2009a).
49
4.1.2 Artificial Watering
Following the completion of Redbank and Maude Weirs, “surplus river flows” were
diverted to the Lowbidgee through three pathways (Figure 23): a) Yanga Regulator,
where the majority of diversions to Yanga take place; b) Waugorah Regulator; and c) the
Nimmie-Caira Flood and Irrigation District. The historical records of diversion to Yanga
through Yanga and Waugorah Regulators (Figure 19) were estimated by eye, thus only
provided a “best guess” for water supply to the floodplain.
Over years, a complex bank system has been developed in the Lowbidgee floodplain to
maximise the value of diverted water for livestock. For example, Piggery Lake was
artificially divided into three sections with different water levels separated by banks and
broad spillways. Other significant alterations include banking up water in Lake Tala with
a weir, diverting water to Yanga Lake by blocking the effluent channel, and stopping
southern flow from Tala Lake by Woolshed regulator.
As there is no volumetric allocation for the Lowbidgee Flood Control and Irrigation
District (LFCID), the district is dependent on unregulated flows in the Murrumbidgee for
water diversion. There is a marked seasonal pattern in the operation of Redbank Weir,
most diversions being made in the late winter and early spring months reflecting the
crop water requirements. Large variations occur from year to year (Figure 21) as the
operations depend on natural flooding, the available water and to less degree local
rainfall.
In 2007, a gauge was installed for the Yanga Regulator to record the environmental flow
allocations into Yanga as part of RERP subprogram II. The gauge will improve the
accountability of environmental water usages.
160
Annual diversions to Yanga
140
120
80
60
40
20
Water Year
50
06/07
05/06
04/05
03/04
02/03
01/02
00/01
99/00
98/99
97/98
96/97
95/96
94/95
93/94
92/93
91/92
90/91
89/90
88/89
87/88
86/87
85/86
84/85
83/84
82/83
0
81/82
GL
100
Figure 21.
Water diverted to Yanga from the Murrumbidgee. The values were “best guess”
by Department of Water and Energy staff. There is not volumetric allocation for LFCID and the
District is dependent on unregulated flow for diversion (produced from DWE operational data).
Figure 22.
Irrigation water distribution pattern in the Lowbidgee (based on Clarkson 2000).
The majority of diversions are through Yanga Regulator. The distribution of water within Yanga is
primarily overland flow, following natural flood runners. The diversion from Nimmie-Caira Flood
and Irrigation District (via Maude) fills Tala Lake (major irrigation storage, part of which is in
Yanga National Park) via Talpee Creek.
51
4.2 Geomorphic processes
Geomorphic processes significantly influence floodplain ecology and critical components
in the Lowbidgee. Sediment erosion and deposition and episodic avulsion are dominant
geomorphologic processes within lowland floodplains. These processes are largely
driven by:
 Channel shape, size and features
 Floodplain topography, area and width
 Connectivity; and
 Soil type
4.2.1 Sedimentation
Sediments are mineral or organic particles that are transported by flowing water. These
typically include fine silts, coarser sands, gravels, and larger cobbles that are
progressively eroded and transported by flowing water. During flooding events,
sediments enter and deposit on the floodplain and create a variety of geomorphic
features (Figure 24), which provide principal nursery sites for colonisation by riparian
plants.
The different sediments provide different physical properties, including the capacity to
retain water, which is essential to sustain vegetation in semi-arid regions. Fine
sediments drain more slowly and have increased "capillarity", the capacity to ‘wick’
water upwards to create a moist zone above the water table (the capillary fringe). This
unsaturated zone is especially important for providing water to floodplain plants and
the extent of the capillary fringe varies substantially with sediment texture (particle
size), ranging from being only a few centimetres above coarse gravel to more than a
metre above silty-sand. Therefore, as well as being critical for the formation of new
nursery sites, alluvial sediments are also critical for the retention and provision of
moisture during dry periods.
Geomorphic features formed from valley sediments are diverse, but some are common
to all river systems. Their development can be associated with general links between
sediment storage sites and erosion processes that occur within floodplain and channel
areas, as shown in Figure 23 and described below.
52
Figure 23.
Sediment erosion and deposition processes in the river-floodplain system. The
boxes contain storage locations with example sediments and erosion processes. Arrows
represent the links between the various storage sites largely driven by water movement and
gravity.
Gradually, accumulated rock and soil (colluviums) and mass-movement deposits are
generally located at the valley margins. These sediments are put in motion by sheets of
running water (sheet erosion). Depending on the local topography, the sediments move
slowly over gradual slopes (soil creep), and rapidly over steep terrain (debris
slides/flows), and are carried to the floodplain, channel margin, or stream channel.
Deposits on the floodplain (overbank deposits) have various forms such as vertical buildup (vertical accretion) and local, fan-shaped slopes (splays). This area may be eroded by
slides cutting into banks (slide-scarp erosion), gradual slides of a wider expanse of land
(slide sheet erosion), or debris slides/flows that move sediments to the channel margin
during floods. Point and marginal bars (lateral accretion deposits) are formed in the
channel margin. These sediments enter the channel by erosion of gully walls or stream
banks. The sediments may accumulate in the channel (channel fills), be deposited and
resuspended (transitory channel deposits), or form sand bars and islands when the
deposit is not so transitory (lag deposits). Sediments may be taken up again by erosion
53
of the stream bed or island banks and redeposited in the channel margin or in the
floodplain as overbank deposits.
The Murrumbidgee catchment can be divided into three distinct regions (Figure 24): the
upper, middle and Lowbidgee (Page 1994 in Olley and Scott 2002). The hilly upper
region is the principal area from which dissolved solids and sediments are derived.
However, the two large dams, Blowering and Burrinjuck, effectively cut off the upper
catchment from the middle and lower river, and trap most of the sediment (Murray et
al. 1992; Olley and Scott 2002). The middle catchment is featured by undulating terrain
dissected by numerous gully networks (Olley and Wasson 2003). Most of the major
tributaries join the Murrumbidgee in this region (Olley and Scott 2002). This is the major
source of fine-grained sediment transported to the Lowbidgee (Olive et al. 1994). There
is essentially no input (runoff, therefore suspended solid) from the catchment
downstream of Wagga Wagga (Murray et al. 1992). Bank erosion is the main process
contributing to in-stream turbidity in this region. While 15% of bank length was
considered as unstable between Berembed Weir and Hay, it was estimated that 8% of
bank length was classified as unstable downstream of Hay (Department of Land and
Water Conservation 1995). Bed mobilization in this reach is of little significance except
at weirs where downstream scouring occurs over short distances (Department of Land
and Water Conservation 1995).
Figure 24.
Murrumbidgee Catchment shows the three geomorphic regions. (reprinted from
Olley and Scott 2002).
Along the river reach from Hay to Balranald, bank erosion occurs as a result of meander
movement. On the recession of a flow event, bank slumping contributes a major
proportion of sediment in the River.
54
River regulation, such as the construction of dams and weirs, and the operation of these
infrastructure, has an inevitable impact on sedimentation patterns and thus on the
water retention capacity of the floodplain. All but the finest sediments settle out in the
slow-moving reservoirs and weir-pools and consequently, the released water is typically
depleted of sediments and sometimes referred to as ‘hungry water’. Without sediment
transport, the riparian zones and floodplains downstream of major dams and weirs lack
areas of sediment deposition and new nursery sites become deficient. Further, the
sediment-depleted outflow water has substantial capacity to erode and remove the
sediments that were present. Over time there is the progressive depletion of alluvial
sediments with corresponding loss in suitability for floodplain vegetation and reduction
in primary productivity as well.
Few data exist to quantify sediment dynamics within the Lowbidgee floodplains, partly
due to episodicity of transport events, and more importantly, the lack of long-term
monitoring data. However, a palaeoecological study by Gell and Little (2006), which took
cores at the Balranald Weir and Waugorah Lagoon, estimated that the sedimentation
rate was as high as 8.8 mm y-1 at weir pools contrasting to around 1 mm y-1 (low) to 20
mm y-1 (relatively high) in the floodplain swamps.
4.3 Other ecosystem processes
In addition to climatic, geomorphic and hydrological processes, a range of other
geomorphic processes may influence the components related to the values of HEVAE on
the Lowbidgee. These were identified to include:
 Nutrient and carbon cycling and trophic dynamics
 Competition
 Reproduction
 Predation
4.3.1 Nutrient cycling and trophic dynamics
Although a multitude of concepts, principles, and methodologies exist to assist in
understanding the biological interactions in floodplain wetlands, the level of knowledge
is still relatively rudimentary: very little quantitative information is available on primary
productivity, and even less on secondary production. This is particularly true for Yanga
National Park: the effects of primary productivity, herbivory, competition and predation
on Yanga National Park biota are largely unknown although these processes have an
important role in structuring the biological community in aquatic and forest ecosystems.
Two projects conducted as part of the former DECCW (now OEH) will greatly increase
the knowledge and understanding of food web structure and trophic dynamics in Yanga:
 Trophic Dynamics and Ecosystem Function of the lower Lachlan and Murrumbidgee
by Rivers and Wetlands Unit in DECC; and
 Examination of organic matter dynamics and secondary production in floodplain
wetlands of the Lowbidgee River by Murray-Darling Freshwater Research Centre
55
5 Critical ecological threats relating to the values of
HEVAE
The aim of this section is to identify the threats to the health of HEVAE in the Lower
Murrumbidgee. Threats may be related to alterations to the geomorphic, climatic and
hydrological processes influencing the health of HEVAE in the Lowbidgee, or they may
be related to land use and management practices within the Lowbidgee floodplain.
Special consideration is given to the threats posed by:
 Alterations to the natural flow regime
 Habitat loss, fragmentation and loss of connectivity
 Introduced and problematic species
 Climate change
5.1 Alteration to the natural flow regimes
Alteration to natural flow regimes refers to reducing or increasing flows, altering
seasonality of flows, changing the frequency, duration, magnitude, timing, predictability
and variability of flow events, altering surface and subsurface water levels and changing
the rate of rise or fall of water levels (National Research Council 1992). In the Lowbidgee
downstream major irrigation areas, the alteration is realised principally as reduction in
river flows (Page et al. 2005; Wen et al. 2009a). In the Lowbidgee, like elsewhere in the
Murray-Darling Basin, natural flow regimes have been interrupted through three
hydrological processes related to water resource development: river regulation (dam
and weir), water diversion (includes groundwater pumping), and alteration of flows
within floodplains with levees and structures (such as bank enforcement).
Alteration to the natural flow regimes of rivers and streams and their floodplains and
wetlands is listed as a “Key Threatening Process” on Schedule 3 of the Threatened
Species Conservation Act 1995. A direct and most significant consequence of alteration
to the natural flow regimes to the Lowbidgee floodplain is the dramatic reduction in
frequency and duration of over-bank flows, which in turn is recognised as a major factor
contributing to loss of biological diversity and ecological function (Briggs et al. 1997;
Gilligan 2005; Kingsford and Thomas 2004; Sherman et al. 1998; Wen et al. 2009a).
Impacts associated with reduced flooding relevant to the Lowbidgee include:
 Loss of lateral connectivity with the Murrumbidgee;
 Loss of persistent soil moisture levels;
 loss of ecological function;
 Increase fire risk; and
 Ultimately lead to degradation of floodplain habitat.
56
5.2 Habitat loss and fragmentation
Together with reduction of flooding, the floodplain development, which includes the
construction and enforcement of bank, levee and regulators, clearing of Lignum, and
creation of water storages, accelerated the loss and fragmentation of floodplain habitats
in the Lowbidgee floodplains. While the development of floodplain for agricultural
production in Yanga National Park was ceased in 2005, the existing infrastructure in
Nimmie-Caira has management implications for Yanga. For example, the blockages
along the Fiddlers Creek deny water entering the Yanga Natural Reserve.
Using historical floodplain map and more recent satellite imagery, Kingsford and
Thomas (2001) investigated the floodplain loss in Lowbidgee from the turning of twenty
century. They found that 127 688 ha (58%) of wetland have been lost to developed land
in the Lowbidgee Region. In Yanga, the figure was 37 253 ha (41%).
In the developed area of the Lowbidgee floodplain, particularly in the Nimmie-Caria
Flood Control and Irrigation District, a water delivery and retaining network, which has
about 2 100 km of banks and 394 km of constructed channels (Kingsford and Thomas
2001), has been developed since the completion of Redbank and Maude Weir. The main
purpose of the network is to deliver water efficiently and quickly. However, besides
distributing floodwater, the natural floodway network, including streams and flood
runners, also provides hydrological continuity for nutrients and aquatic animals, such as
fish, amphibians and waterbirds. Consequently, the development and operation of the
modified network has increased habitat isolation through denying water reach some
floodplain areas and prolonging inundation of targeted areas. For example, the
Southern Caira Channel was built to bypass the floodway and allow more efficient
transmission to irrigated areas downstream and key habitat areas (Department of Land
and Water Conservation 1997). In the mean time, the channel bank also alienated the
southern part of the floodplain from flood flows because it was constructed above the
estimated 1956 flood level (one in 100 years) at the site and did not allow passage of
floodwater so the levee needed to be breached during floods (Department of Water
Resources 1994).
The diversion of water from Redbank and Maude weirs is generally beneficial for the
flora and fauna on the Lowbidgee floodplain as it compensates the reduction of overbank flow due to upstream water extraction. For example, bank construction and water
storages have enhanced waterbird breeding, particularly Ibis, in the Telephone and
Eulimbah Swamps (Maher 1990). However, water storages, which have artificially
enhanced wet periods (more than two years), may have lower quality as waterbird
(Maher 1990) and fish habitat. Furthermore, the prolonged inundation is in favour of
the spread of Cumbungi (Typha domingensis) (Department of Land and Water
Conservation 1997; Eddy 1992; Kingsford and Thomas 2001; Maher 1990; Pressey et al.
1984). In more permanent water habitats, Cumbungi tends to dominate over Lignum,
and becomes a main cause of decline in Lignum areas in the Lowbidgee (Department of
Land and Water Conservation 2000). In April 1997 the Nimmie-Caira floodway system
57
was infested with approximately 3,530 hectares of Cumbungi, representing some 15% of
the total floodway vegetation (Department of Land and Water Conservation 1997).
The development plan for the Lowbidgee floodplain (Department of Water Resources
1989, 1994) emphasised the conservation need of identified special habitat areas or
rookeries (e.g. Avalon Swamp, Nap Nap Swamp, Telephone banks Rookery, etc.), while
development was permitted elsewhere on the floodplain. Consequently, a constricted
distribution of floodways (through enforcement of natural levees) and isolated rookeries
(targeted artificial watering) would be maintained reflecting the narrow definition of
ecosystem function applied.
5.3 Introduced and problematic species
The NSW Wildlife Atlas recorded 58 introduced plant species in Yanga National Park, of
which the majority are small ground plants, and some of these are widespread and
abundant, such as Paterson’s curse (Echium plantagineum), horehound (Marrubium
vulgare), onion weed (Romulea rosea var. australis) and spear thistle (Cirsium vulgare
(Savi) Ten.). The widespread of introduced small ground plant (some are valued as stock
feed (e.g. medics Medicago spp.) reflects the agricultural history of the site. The
prolonged dry period in water plant dominated areas (i.e. shallow temporary swamps)
and lake beds increases the risk of exotic plant invasion.
Cumbungi infestation of Lignum swamps and permanent water ways is common at
Lowbidgee, especially at Nimmie-Caria Flood Control and Irrigation District due to
artificially enhanced inundation period.
A number of surveys found that introduced fish species, in particular European carp
(Cyprinus carpio) and golden fish (Carassius auratus) and eastern gambusia (Gambusia
holbrooki), dominate water ways (including the Murrumbidgee channel) and wetlands
(Bales 2002; Baumgartner 2004; Spencer and Allman 2008; Wassens et al. 2008a).
Introduced fish species pose a threat to native fish species as predators, competitors,
disease carriers and through modification of habitat (NSW Fisheries Scientific
Committee 2008) and are thought to be a significant contributor to reductions in native
fish species abundance in the Murrumbidgee Catchment (Gilligan 2005). The predation
by European Carp may also contribute to the decline in Southern Bell Frog population in
Lowbidgee (Wassens et al. 2008a). The introduction of fish to fresh waters within a river
catchment outside their natural range has been listed as a Key Threatening Process in
Schedule 6 of the Fisheries Management Act 1994 (NSW Fisheries Scientific Committee
2008).
Other introduced animals of concern include feral pig (Sus scrofa), cat (Felis catus), and
European red fox (Vulpes vulpes). These animals predate on small native animals (e.g.
lizards, frogs and ground-nesting birds). They are all listed as 'key threatening processes'
58
in NSW by the NSW Scientific Committee because of their impacts on native animals
(Department of Environment and Climate Change 2008).
5.4 Climate change
Increased greenhouse gas emissions during the 20th and 21st century’s are projected to
alter the global climate, influencing temperature and rainfall globally and affecting
water availability and water security within the Murrumbidgee catchment. Global
Circulation Models (GCM) simulate climate systems and are used to project future
climate change scenarios. Decoupling the influence of natural climate variability and
climate change resulting from human activity is difficult, as GCMs aim to model climate
systems rather than sources of climate change. For this reason, we have adopted the
climate change definition used in the Intergovernmental Panel on Climate Change (IPCC)
fourth assessment report which states:
“Climate change refers to a change in the state of the climate that can be
identified (e.g. using statistical tests) by changes in the mean and/or the
variability of its properties, and that persists for an extended period, typically
decades or longer. It refers to any changes in climate over time, whether due to
natural variability or as a result of human activity.”
Bernstein et al. (2007), p. 30
A recent study of climate change in Australia (CSIRO and BOM 2007) has projected
significant warming of the Australian climate in the 21st century. The best estimate of
warming for inland areas is around 1 to 1.2°C by 2030 and 1.8 to 3.4°C by 2070. While
precipitation is not directly influenced by greenhouse gas emissions, increased
atmospheric temperatures will alter circulation (wind) patterns and consequently affect
rainfall. Due to great natural variability in rainfall over Australia, GCMs are particularly
sensitive to small changes in circulation and rainfall changes can vary significantly
between models. Best estimates of annual precipitation change indicate decreases of
between 2% to 5% by 2030 and between -30% and +20% (+5%) in central (southern)
areas by 2070, with large seasonal changes.
Changes in global climate - warming temperatures, rising sea level and variations in
rainfall and storm patterns could have tremendous human and ecological impacts
(Figure 25).
The resilience of many ecosystems is likely to be exceeded this century by an
unprecedented combination of climate change, associated disturbances (e.g., flooding,
drought, wildfire, insects, ocean acidification), and other global change drivers (e.g.,
land use change, pollution, overexploitation of resources) (IPCC 2007).
59
Figure 25.
Linkages between climate change and ecosystem responses.
Solid arrows indicate very likely impacts and dashed arrow indicates likely impacts according to IPCC (2007).
5.5 Other issues
Land management practices in the Lowbidgee, including grazing, clearing, logging and
burning, are likely to have significant and long lasting impacts on the ecological
character of the HEVAE on the Lowbidgee. Grazing by both livestock and other
native/introduced animal has been observed to have a significant impact on the
condition of vegetation communities in the Lowbidgee (Beadle 1948; Benson et al.
2006; Cunningham et al. 1981; Pressey et al. 1984; Scott 1992). Grazing has direct
impacts on vegetation community structure by altering the relative abundance of
floodplain plants. For example, more tolerant species such as Paspalum distichum
(water couch), are likely to become more abundant as a result of intensive grazing.
Intensive grazing may prevent the regeneration of river red gum (Jacobs 1955). Other
impacts associated with grazing include puddling, trampling, reducing plant biomass,
and altering nutrient cycling.
Clearing, in particular the clearing of lignum community, has occurred in the Lowbidgee
for decades, and 60% of the estimated 40 000 ha of lignum in the Lowbidgee was
cleared by 1988 (Cross et al. 1991 cited in Kingsford and Thomas 2001).
The river red gum forests of the Lowbidgee have been logged to varying degrees over
the past 150 years, and some areas have been extensively logged until very recently
(Maher 1990). The large-scale logging could change the landscape from scattered,
mature tree stands with patches of younger trees to dense even-aged re-growth,
consequently, loss value as fauna habitats. For instance, apart from the general faunal
60
values, tree holes of river red gum are particularly important for breeding and sheltering
of a range of species (e.g. grey teal Anas gracilis, bats).
Small-scale burning has occurred in Yanga to control the growth of common reed
(Phragmites australis). Burning would have impact on floodplain flora and fauna;
however, the impact is likely to be localized and temporary. Burning in patches may
even enhance the ecological values by diversifying the vegetation structure and
breaking-down soil organic matter, consequently accelerating nutrient cycle.
5.6 Summary
Threats are summarised in Table 16 using the threat classification hierarchy developed
by the International Union for the Conservation of Nature and the Conservation
Measures Partnership (International Union for the Conservation of Nature 2006), and
detailed in the following sections.
Based on Table 16, a conceptual model (Figure 26) was developed specifically for risk
management for HEVAE in the Lowbidgee floodplain. Agriculture was not included as a
threat in Figure 26, while climate change and mitigation and adaptation strategy should
be addressed at global, national and regional scales, therefore not included in the
model. The model illustrates the ecological linkages among the major threats
(distinguished as external pressures and system-wide stressors), effects and ecological
characters. The cause and effect relationships explain the important consequences of
system-wide stressors on the major ecological attributes of the Lowbidgee. These
stressors, which include flood reduction, loss and shift of natural discharge variability,
floodplain loss and fragmentation, are further discussed.
Table 16. Summary of actual &likely threats to the eological character of the Lowbidgee floodplain
Threat Theme
(threat class: level 1)
Natural System Modifications
Threat Activity
(threat class: level 2)
Dams and Water
Diversion
Habitat Shifting and
Alteration
Threat Agent
(threat class: level 3)
Upstream surface water
extraction
Structures including floodgate,
culvert, levee, road crossing, etc
Irrigation salinity
Loss of open water
Timeframe
Likelihood*
Immediate-medium
H
Immediate-medium
M
Medium
Immediate-medium
L
H
Medium-long
Immediate-medium
Immediate-medium
H
L
M
Arson
Immediate-medium
L
Clearing
Immediate-medium
L
Habitat change
Sheet Erosion
Fire and Fire Suppression Natural fire
Agriculture
Agriculture
Annual non-timber crops Irrigated pastures and cropping Immediate-medium
M
Livestock/Native Animal Grazing
Grazing
M
61
Immediate-medium
Fishing and Harvesting
Aquatic Resources
Recreation
Immediate-medium
L
Biological Resource Use
Hunting of waterbirds
Climate Change and Severe
Weather
Drought
Storms and Flooding
Strong wind
Temperature Extremes
Illegal take
Recreation
Drought
Flood
Wind erosion
Water temperature change
Immediate-medium
Immediate-medium
Medium to Long
Immediate
Immediate
Medium to Long
L
L
H
L
M
M
Ecosystem/Community Stresses Ecosystem Degradation Deterioration of vegetation
health
Encroachment of chenopod into
sedge
Human Intrusions and
Inappropriate
Allocation of environmental
Disturbance
conservation measures water
Recreational Activities Hunting
Ecotourism
Medium to Long
H
Medium to Long
H
Immediate-medium
M
Immediate-medium
Medium
L
L
Invasive and Other Problematic Invasive Exotic Species
Species and Genes
European Carp Cyprinus carpio
Feral Pig Sus scrofa
Immediate-medium
Immediate-medium
H
M
Red Deer Cervus elaphus
Immediate-medium
L
Feral Cat- Felis catus
Immediate-medium
M
Rabbit - Oryctolagus cuniculus
Immediate-medium
L
Pollution
Other Problematic
Species and Genes
Agricultural Effluents
Other sources
Natural System Modifications
Dams and Water
Diversion
Habitat Shifting and
Alteration
European Red Fox- Vulpes vulpes Immediate-medium
M
Lippia
Immediate-medium
M
Other plants
Immediate-medium
L
Toxic algae
Immediate-medium
H
Herbicides
Immediate
L
Nutrients
Immediate
M
Sediments
Immediate-medium
L
Toxins
Immediate
L
Acid sulphate soils
Medium
L
Nutrients
Immediate-medium
L
Pesticides
Immediate
L
Upstream surface water
extraction
Structures including floodgate,
culvert, levee, road crossing, etc
Irrigation salinity
Loss of open water
Immediate-medium
H
Immediate-medium
M
Medium
Immediate-medium
L
H
Medium-long
Immediate-medium
Immediate-medium
H
L
M
Arson
Immediate-medium
L
Clearing
Immediate-medium
L
Habitat change
Sheet Erosion
Fire and Fire Suppression Natural fire
Agriculture
Agriculture
62
Annual non-timber crops Irrigated pastures and cropping Immediate-medium
M
Livestock/Native Animal Grazing
Grazing
Fishing and Harvesting Recreation
Aquatic Resources
Immediate-medium
M
Immediate-medium
L
Biological Resource Use
Hunting of waterbirds
Climate Change and Severe
Weather
Drought
Storms and Flooding
Strong wind
Temperature Extremes
Immediate-medium
Immediate-medium
Medium to Long
Immediate
Immediate
Medium to Long
L
L
H
L
M
M
Ecosystem/Community Stresses Ecosystem Degradation Deterioration of vegetation
health
Encroachment of chenopod into
sedge
Human Intrusions and
Inappropriate
Allocation of environmental
Disturbance
conservation measures water
Recreational Activities Hunting
Ecotourism
Medium to Long
H
Medium to Long
H
Immediate-medium
M
Immediate-medium
Medium
L
L
Invasive and Other Problematic Invasive Exotic Species
Species and Genes
European Carp Cyprinus carpio
Feral Pig Sus scrofa
Immediate-medium
Immediate-medium
H
M
Red Deer Cervus elaphus
Immediate-medium
L
Feral Cat- Felis catus
Immediate-medium
M
Rabbit - Oryctolagus cuniculus
Immediate-medium
L
Pollution
Other Problematic
Species and Genes
Agricultural Effluents
Other sources
Illegal take
Recreation
Drought
Flood
Wind erosion
Water temperature change
European Red Fox- Vulpes vulpes Immediate-medium
M
Lippia
Immediate-medium
M
Other plants
Immediate-medium
L
Toxic algae
Immediate-medium
H
Herbicides
Immediate
L
Nutrients
Immediate
M
Sediments
Immediate-medium
L
Toxins
Immediate
L
Acid sulphate soils
Medium
L
Nutrients
Immediate-medium
L
Pesticides
Immediate
L
Threats hierarchy adopted from IUCN, 2006.
* L/M/H: low, medium and high.
63
Figure 26.
Conceptual ecological model of threats/stressors/risks in HEVAE of the Lowbidgee.
64
6 Ecological conceptual models
An ecological conceptual model is a schematic, organisational or mathematical
representation of a natural phenomenon. Ecological conceptual models are
abstractions or simplifications of the reality and portray the dominant components,
key processes and threats. Typically, models define relationships among states
(components of the ecosystem) and transitions (processes that change the states).
These relationships are the basis on which to predict changes in the ecological
character over time depending upon trajectories of, or perturbations to, key
processes. Ecological conceptual models are excellent tools for generating questions
about the system behaviours and guiding decision making for planning and
management. In addition, models also document and record major assumptions and
current understanding of the system.
Wetland ecosystems are dynamic in space and time, with the components and
processes being primarily determined by the hydrogeologic settings, which is in turn
determined by the climate and geomorphology. Climate, through precipitation,
evaporation and transpiration, influences surface and groundwater flows and the
hydrology and hydrological variability of wetlands. Geomorphology determines the
size, shape and location of wetlands within the landscape, and the water sources,
physico-chemical properties and soils as well. The natural drivers are strongly
affected by human activities on the landscape, such as land use and water diversion.
The hydrogeologic setting of the landscape is the primary variable driving wetland
form and function. Hydrogeologic setting is defined by topography, soils, subsurface
geology, and climate, and drives groundwater and surface water movement
patterns. The formation, distribution, and biogeochemistry of individual wetlands
are based on the interaction between these groundwater/surface water movement
patterns and climate.
An ecological conceptual model of the Lowbidgee floodplains that describes the key
ecological components, processes, drivers and threats was developed to provide a
framework for understanding the specific responses of components for which HEVAE
in the Lowbidgee are valued (Figure 27). The ecological conceptual model informs
the framework for IECA of HEVAE on the Lowbidgee. The objectives in developing
the ecological conceptual model for the Lower Murrumbidgee were to:
 Identify existing data and knowledge about the key processes, interactions,
drivers and threats that will inform the condition assessment
 Create an ecological conceptual model that captures the ecological values,
components, processes, drivers and threats within the Lowbidgee floodplain.
The developed ecological conceptual model was designed to follow similar models
developed for the Gwydir Decision Support System (Powell et al. 2008) and has a top
to bottom layout. Key processes and threats that drive ecological change are
positioned at the top of the model. Key aspects of these processes were identified
from the review of critical processes and ecological threats relating to the values of
65
the HEVAE. Beneath these processes critical components relating to the values of
HEVAE are positioned.
Additional sub-models have been developed that relate to the critical components
relating to the values of the HEVAE. These include a vegetation sub-model (Figure
28), waterbird sub-model (Figure 29), native-fish sub-model (Figure 30),
invertebrates sub-model (Figure 31) and a frog sub-model (Figure 32).
66
Figure 27.
Integrated conceptual ecological model detailing the critical components, processes and threats relating to the values of the HEVAE of the
Lowbidgee. Model adapted from Spencer et al. (unpublished).
67
Figure 28.
Vegetation conceptual ecological sub-model detailing critical components, processes and threats for vegetation of the HEVAE of the
Lowbidgee. Model adapted from Spencer et al. (unpublished).
68
Figure 29.
Waterbird conceptual ecological sub-model detailing critical components, processes and threats for waterbirds frequenting the HEVAE of the
Lowbidgee. Model adapted from Spencer et al. (unpublished).
69
Figure 30.
Fish conceptual ecological sub-model detailing critical components, processes and threats for fish frequenting the HEVAE of the Lowbidgee.
Model adapted from Spencer et al. (unpublished).
70
Figure 31.
Invertebrates conceptual ecological sub-model detailing critical components, processes and threats for invertebrates occurring in the HEVAE
of the Lowbidgee.
71
Figure 32.
Lowbidgee.
Frogs conceptual ecological sub-model detailing critical components, processes and threats for frogs occurring in the HEVAE of the
72
7 Management triggers for key ecological
components
The concept of applying triggers for management action to key ecological
components and processes is a useful tool for management and ensures there is
little of no loss of ecological character of HEVAE. Management triggers may be
applied to the long-term or operational objectives and once these limits are
exceeded there will be a need for immediate remedial action.
Limits of acceptable change (LACs) have been widely used to identify and set limits
within which change may be tolerated, particularly within the context of wetlands of
international importance (Ramsar Convention 2005). However, a range of other
management triggers, such as Thresholds of Potential Concern (TPC) and Critical
ecological thresholds, may be applied to aid management of HEVAE. In the context
of this assessment, LACs and TPCs have been developed for key components and
processes that relate to the values of the HEVAE of the Lowbidgee.
7.1 Definition of limits of acceptable change and thresholds
of potential concern
LACs and TPCs differ in purpose (Figure 33). The LAC establishes that the ecological
character of the wetland has changed in relation to a key wetland value. The
purpose of the LAC is to trigger the notification of this changing ecological character
to a high management level (e.g. State, National or International) so that additional
higher-level management intervention may occur. The LAC is essentially a social
construct, and is best defined by local asset managers with delegated authority for
the management of the wetland values. These managers are in the best position to
identify the values identified for the wetland by the community and their agency,
and the points at which change to these values has become unacceptable to the
community charging them with responsibility for asset management. In some cases
the LAC might relate to a biological threshold, but may not in all cases. For example,
identification of the exceedance of a biologically defined critical threshold cannot be
identified for a stand of river red gum that is undergoing incremental decline;
however a LAC still needs to be established.
The purpose of the TPC is to trigger management intervention at a more local scale,
within existing management regimes and using locally available levers. For example,
a TPC might flag the need to water a particular asset within the wetland using
available water, while crossing an LAC would indicate that the water planning regime
is failing the wetland. The TPC implies movement beyond a threshold or a change
from one condition or risk state to another. For example, the TPC for maximum
inter-flood dry-period may be crossed for a vegetation class, or vegetation may
transition from one class to another on a part of the floodplain. Such changes will
occur incrementally across the floodplain. This contrasts with the LAC, which might
define the proportion of the asset for which such a change might be acceptable (e.g.,
30% of the total extent of the asset transitioning from one state to another).
73
TPCs may not always be a measure of the component relating to the values of the
HEVAE, but should relate to the value within the conceptual models developed
relating the wetland value to pressures and stressors. For example, the value of a
viable southern bell frog population will be influenced by a range of threat variables,
such as carp numbers within floodplain waterholes, the health of aquatic vegetation
within the wetland, connectivity between southern bell frog habitats across the
floodplain, duration of flooding, interflood period, and the timing of flooding. The
TPC reports on trends in these indicators and whether they have crossed thresholds
of concern, but does not draw any direct or predictive relationship with the LACwhich might in this case be the loss of bell frog from the Lowbidgee, or reduction in
numbers to a key refuge. However, TPCs should prompt management intervention,
such as the construction of carp exclusion structures, the watering of specific
waterholes, or the exclusion of grazing to protect or restore wetland aquatic
vegetation. It is envisaged, therefore that there would be many more TPC’s than
LAC’s covering a greater range of indicators, and that these would be quantitatively
defined where possible, and biologically or geomorphologically meaningful (in the
sense that thresholds are, where possible, not arbitrary but defined by physical
thresholds of resilience).
Limit of
Acceptable
Change
Threshold
of Potential
Concern
Management
Target
1
0
Figure 33.
Relationship between a limit of acceptable change and threshold of potential
concern for a wetland value with respect to management targets, a healthy wetland value (i.e.
value = 1) of the loss of a wetland value (i.e. value = 0).
7.2 Thresholds of potential concern
TPCs have been developed in consultation with asset managers and reflect the point
at which management actions would be implemented (Table 17).
74
Table 17. Thresholds of potential concern for critical components and indicators that relate to
values of HEVAE in the Lowbidgee.
Value
Selected Threat/condition
TPC
component/i
indicator
ndicator
Vital habitat
Threatened Sites with
Found in less than10 sites
Distinctiveness species
Frogs/tadpoles
across the Lowbidgee
Diversity
- Southern
bell frog Carp numbers
Carp in most sampled SBF
sites
Loss of Aquatic
vegetation
Notable thinning of
submerged vegetation at SBF
locations
Feral animals
Increase in populations of
foxes and pigs in the vicinity
of SBF refuges
Representative River Red
Loss of Flooding
-ness
Gum forest/ Frequency
Diversity
woodland
Maximum recommended
inter-flood period exceeded
in RRG forest or woodland
storage
Decline in crown Change in crown condition
condition
category across storage
Too frequent
flooding
Exceeding maximum
recommended flooding
duration/frequency in forest
or woodland storage
Clearance
Loss of RRG forest or
woodland to land clearance
75
Goal
Found in 40
sites across the
Lowbidgee
Carp in less
than 10% of
sampled sites
All sites
containing
submerged
aquatic veg
Elimination of
foxes and pigs
from the
Lowbidgee
Optimal interflood period in
all RRG
storages
Good or
moderate
crown
condition in all
storages
Optimal interflood period
and duration in
all RRG
storages
No loss of RRG
forest or
woodland to
land clearance
Value
Vital habitat
Diversity
Selected Threat/condition
TPC
component/i
indicator
ndicator
Waterbirds Loss of rookery
Clearing of lignum shrubland
- Ibis
sites
anywhere on the floodplain
- egrets
Decline in condition class of
RRG or Lignum in more than
20% of rookery storages
Diversity
Black box
woodland
Lignum
shrubland
Tall spike
rush
Vital habitat
Diversity
Fish
- unspecked
hardy head,
- Murray cod
Vital habitat
Diversity
Invertebrates
- Yabby
Goal
Restoration of
lignum
shrubland
All RRG and
Lignum in
known
rookeries in
good condition
class
Alteration to
Rookery sites not flooded for All rookery
hydrology
sufficient depth/duration
sites flooded to
during suitable climatic
suitable
conditions
depth/duration
in moderate
and wet years
Numbers of
Less than 30 000 pairs in
More than 50
waterbirds
conditions suitable for major 000 breeding
event
pairs in
conditions
suitable for a
major event
Less than 30 000 breeding
More than 30
pairs in 5 consecutive years 000 breeding
pairs one year
in 3
Hydrology of
Exceedance of
Optimal interBlack Box
maximum/minimum inter- flood period
Woodland, lignum flood period in storage
shrubland, spike
rush
Clearance of Black Any loss to clearance of Black Restoration
Box Woodland,
Box Woodland, lignum
lignum shrubland, shrubland, spike rush
spike rush
Data insufficient Data insufficient at this time No net loss in
at this time
unspecked
hardyhead and
Murray cod
abundance
Data insufficient Data insufficient at this time No net loss in
at this time
yabby
abundance
76
7.3 Limits of Acceptable Change
Table 18 (below) links these core values of the Lowbidgee floodplain to specific
ecosystem components and processes that form the foci of management actions.
Limits of Acceptable Change are suggested which relate back to the significance of
the Lowbidgee with respect to the HEVAE criteria
Table 18. Limits of Acceptable Concern as they relate to key values of the Lowbidgee
Floodplain
HEVAE
Criterion/Value
Component or Process
Limit of Acceptable Change
Vital Habitat
50 000+ breeding pairs of
waterbirds in favourable
hydrological conditions
Less than 30 000 breeding
pairs in three consecutive
events of suitable climatic
conditions, co-incident with
loss of suitable hydrological
and/or vegetated habitat
Representativeness Second largest stand of RRG
forest and woodland in
Australia at 45 000 ha
Loss of 7000 ha of RRG, ie
loss of status as second
largest stand.
Distinctiveness
Stronghold of the Southern
Bell Frog, especially critical
drought refuge
Reduction in distribution of
mature frogs and tadpoles to
5 waterholes, threatening
population viability
Diversity
Supports extensive area and
diversity of wetland habitat
including spike-rush, river red
gum forest and woodland,
blackbox woodland, lignum
shrubland
Reduction in extent of spikerush by 20% (measured postflood against previous postflood benchmarks).
Reduction in RRG as above.
Reduction in blackbox
woodland and lignum
shrubland by 20%.
77
7.4 Selected indicators
Condition indicators were selected for a number of reasons:
 Indicators directly related to the established TPCs and LACs, selected
components and values (Table 19)
 Data sets were available to compile information about indicators (see
methodology for further detail).
Selected indicators and their relationship to the values and selected components of
the HEVAE of the Lowbidgee are provided in Table 19.
78
Table 19. Condition assessment indicators and data sources used to obtain condition for wetland storages and river reaches.
Value
Vital habitat
Distinctiveness
Diversity
Component
Indicator
Southern bell frog Southern bell frog presence/absence
Representativeness River red gum
Diversity
Vital habitat
Diversity
Waterbirds
Source
2008
2010
Carp presence/absence
2008
2010
Aquatic vegetation cover
2008
2010
Feral animal population density
2008
2010
Area flooded
2008
2010
Change in river red gum area
2008
2010
Maximum inter-flood period for river red gum forest 2008
2010
Maximum inter-flood period for river red gum
2008
woodland
2010
River red gum crown condition
2008
2010
Change in river red gum condition
2008
2010
Maximum flood duration for river red gum
2008
2010
Unmanaged clearance of river red gum
2008
2010
Loss of river red gum area
2008
2010
79
Spencer and Wassens (2009)
Thomas et al. (2011)
Spencer and Wassens (2009)
Thomas et al. (2011)
Spencer and Wassens (2009)
Thomas et al. (2011)
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011), Thomas et al. 2011
Bowen and Simpson (2010)
No data
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
Bowen and Simpson (2010)
No data
McCosker (2008), Bowen and Simpson (2010)
No data
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
James MaGuire, pers comm.
James MaGuire, pers comm.
McCosker (2008), Bowen and Simpson (2010)
No data
Loss of lignum area
Change in river red gum condition
Flood conditions to support egret breeding
Flood conditions to support ibis breeding
Degree of waterbird breeding under suitable
hydrological conditions
Degree of waterbird breeding in previous 5 years
Area flooded
Diversity
Vegetation
Maximum inter-flood period for lignum
Ideal flood frequency for tall spike rush
Change in black box woodland area
Change in lignum area
Change in tall spike rush area
Vital habitat
Diversity
Fish
Fish kill associated with black water
Golden perch presence/absence
80
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
2008
2010
McCosker (2008), Bowen and Simpson (2010)
No data
McCosker (2008), Bowen and Simpson (2010)
No data
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
Not suitable breeding conditions
James MaGuire, pers comm.
Kingsford et al. (2008)
James MaGuire, pers comm.
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011), Thomas et al. 2011
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
Sinclair Knight Mertz (2011)
McCosker (2008), Bowen and Simpson (2010)
No data
McCosker (2008), Bowen and Simpson (2010)
No data
McCosker (2008), Bowen and Simpson (2010)
No data
No data
Observations
Spencer and Wassens (2009)
Thomas et al. (2011)
Carp presence/absence
Vital habitat
Diversity
Yabby
2008
2010
2008
2010
No indicators, data insufficient
81
Spencer and Wassens (2009)
Thomas et al. (2011)
No data
No data
8 Condition assessment methodology
Condition assessment was trialled for the inundations seasons of 2008-09 and 201011. These periods were selected on the basis of maximising data availability.
To undertake the conditions assessment data sets from which information relevant
to each indicator could be retrieved were compiled. The source material used for
each indicator is provided in table 20.
For each indicator a ranking system was developed whereby wetland storages and
river reaches were assigned a rank based on the quality of an indicator or the degree
of impact posed by a threat. Typically green indicated good quality or low impact
posed by a threat, orange indicated moderate quality or moderate threat and red
indicated poor quality or high impact posed by a threat.
Table 20. Condition assessment indicators and the rankings applied to water storages and
tiver reaches in the Lowbidgee.
Southern bell frog indicators
Indicator: Southern bell frog presence/absence
R
Southern bell frog absent
O
G
ND
Southern bell frog present
No data
Indicator: Carp presence/absence
R
Carp present
O
G
ND
Carp absent
No data
Indicator: Aquatic vegetation cover
R
Aquatic vegetation absent
O
Aquatic vegetation cover 0-10 %
G
Aquatic vegetation > 10%
ND
No data
Indicator: Fox and pig populations
R
Fox/pig populations increasing near SBF site between 2007/2008 and 2010/2011
O
Fox/pig populations stable near SBF sites between 2007/2008 and 2010/2011
G
Fox/pig population decreasing near SBF sites between 2007/2008 and 2010/2011
ND
No data
Indicator: Area flooded
R
No flooding
O
<50% flooded
G
>50% flooded
ND
No data
82
River red gum indicators
Indicator: Change in river red gum area
R
Decline in area of river red gum
O
No change in area of river red gum
G
Increase in area of river red gum
x
Large areas of river red gum absent
ND
No data
Indicator: Maximum inter-flood period for river red gum forest
R
Inter-flood period > 36 mo
O
Inter-flood period = 36 mo
G
Inter-flood period <36 mo
ND
No data
Indicator: Maximum inter-flood period for river red gum woodland
R
Inter-flood period > 48 mo
O
Inter-flood period = 48 mo
G
Inter-flood period < 48 mo
ND
No data
Indicator: River red gum crown condition
R
Crown condition poor-very poor-most trees dead
O
Crown condition moderate
G
Crown condition good-excellent
ND
No data
Indicator: Change in river red gum condition
R
Crown condition declining
O
Crown condition constant or increasing
G
Crown condition good-excellent
ND
No data
Indicator: Maximum flood duration for river red gum
R
>3 continuous years of flooding
O
2-3 continuous years of flooding
G
<2 years continuous flooding
ND
No data
Indicator: Unmanaged clearance of river red gum
R
Land cleared
O
G
ND
Land uncleared
No data
83
Waterbird indicators
Indicator: clearing or loss of river red gum
R
Decline in area of river red gum
O
No change in area of river red gum
G
Increase in area of river red gum
Large areas of river red gum absent
ND
No data
Indicator: clearing or loss of lignum
R
Decline in area of lignum
O
No change in area of lignum
G
Increase in area of lignum
Large areas of lignum absent
ND
No data
Indicator: Change in river red gum condition
R
Crown condition declining in rookery storage
O
Crown condition constant or increasing in rookery storage
G
Crown condition good-excellent in rookery storage
X
Significant waterbird rookery absent
ND
No data
Indicator: Flood conditions to support egret breeding
R
Flooding < 6 mo
O
G
ND
Flooding = 6-12 mo
No data
Indicator: Flood conditions to support ibis breeding
R
Flooding < 6 mo
O
Flooding 6-9 mo
G
Flooding = 9-12 mo
ND
No data
Indicator: Waterbird breeding under suitable hydrological conditions
R
No breeding
O
<30 000 breeding pairs within all storages
G
>30 000 breeding pairs within all storages
X
Significant waterbird rookery absent
ND
No data
Indicator: Waterbird breeding events in past 5 years
R
No breeding
O
<30 000 breeding pairs within all storages
G
>30 000 breeding pairs within all storages
X
Significant waterbird rookery absent
ND
No data
Indicator: Area flooded
R
No flooding
O
50% flooded
G
>50% flooded
ND
No data
84
Vegetation indicators
Indicator: Maximum inter-flood period for lignum
R
Inter-flood period >10 years
O
G
Inter-flood period < 10 years
x
Large areas of lignum rush absent
ND
No data
Indicator: Ideal flood frequency for tall spike rush
R
No annual flooding in past 5 years
O
Almost annual flooding (≥3 floods in 5 years)
G
Annual flooding in past 5 years
x
Large areas of tall spike rush absent
ND
No data
Indicator: Change in black box woodland area (2005-08)
R
Decline in area of black box woodland
O
No change in area of black box woodland
G
Increase in area of black box woodland
x
Large areas of black box absent
ND
No data
Indicator: Change in lignum area (2005-08)
R
Decline in area of lignum
O
No change in area of lignum
G
Increase in area of lignum
x
Large areas of lignum absent
ND
No data
Indicator: Change in tall spike rush area (2005-08)
R
Decline in area of tall spike rush
O
No change in area of tall spike rush
G
Increase in area of tall spike rush
x
Large areas of tall spike rush absent
ND
No data
85
Fish indicators
Indicator: Fish kill associated with black water event
Large scale fish kill
Moderate-small fish kill
No large scale fish kill
No data
Indicator: golden perch presence/absence
Golden perch absent at site with suitable conditions
Golden perch present at site with suitable conditions
No data
Indicator: Carp presence/absence
R
Carp present
O
G
ND
Carp absent
No data
Using a database, a ranking of red, orange, green or no data was assigned to each
wetland storage and river reach for each indicator. The information within the
database was spatially referenced within ARC GIS by joining information within the
database to the wetland storages and river reaches spatial layers. Report cards, or
maps, were prepared for each indicator identifying the value assigned to each
wetland storage or river reach for each indicator.
86
9 Results
Report cards for each indicator are provided below. Results are presented for
condition at floodplain wetland component condition in 2008 (section 9.1), river
reach component condition in 2008 (section 9.2), and for floodplain wetland
component condition in 2010 (section 9.3), and river reach component condition in
2010 (section 9.4).
87
9.1 2008 Wetland Indicators
9.1.1 Southern bell frog indicators
88
89
9.1.2 River red gum indicators
90
91
92
9.1.3 Waterbird indicators
93
94
95
96
9.1.4 Vegetation indicators
97
98
9.1.5 Fish indicators
99
100
9.2 2008 River reach indicators
9.2.1 River red gum indicators
101
102
103
9.2.2 Waterbird indicators
104
105
106
107
9.2.3 Vegetation indicators
108
109
9.2.4 Fish indicators
110
111
9.3 2010 Wetland indicators
9.3.1 Southern bell frog indicators
112
113
9.3.2 River red gum indicators
114
115
116
9.3.3 Waterbird indicators
117
118
119
120
9.3.4 Vegetation indicators
121
122
123
9.3.5 Fish indicators
124
125
9.4 2010 River reach indicators
9.4.1 River red gum indicators
126
127
128
129
9.4.2 Waterbird indicators
130
131
132
133
9.4.3 Vegetation indicators
134
135
136
9.4.4 Fish indicators
137
138
10 Conclusions
The approach taken to condition assessment in this report is linked directly to values
identified by water and wetland managers in the Lowbidgee as contributing to the
high ecological value of the site. We identified links between values and threats for
each of these values using conceptual models representing best available science, a
process supported by detailed ecological investigations into the Lowbidgee wetland
conducted under the Rivers Environmental Restoration Program (2007-2010). Using
these values and associated indicators, we developed limits of acceptable change
and thresholds of potential concern in collaboration with the relevant water and
wetland managers from the NSW Office of Environment and Heritage and the NSW
Office of Water, and produced report cards documenting where thresholds of
concern had been exceeded for each of the indicators identified for the wetland
values.
The approach was useful in provide a geographic representation highlighting
variability in condition between storages at a scale appropriate to focussing
management interventions. The approach did not seek to aggregatre indices to
create summary trend indices, or aggregate across storages. This was in response to
feedback from managers that they felt comfortable with the degree of disaggretation, and that combining scores would obscure the links between indicators
and threats, and thereby the clarity required for targeted invervention. For this
reason the project approach is not compatible with approaches to assessment which
seek to integrate scores across ecosystem types or spatial scales.
The work demonstrated the response of the wetland to good inflows in the 2009/10
watering season. These historically large inflows led to an improvement in idicies
associated with flooding, though there were some negative outcomes, most notably
the spread of carp through bell-frog storages, and the fish kills along the main
channel associated with a black-water event. Some consideration will need to be
given in futher re-flooding events to the exclusion of carp from the floodplain, and
the control of de-oxygenated water re-entering rivering ecosystems from the
floodplain after extensive drought.
The trail demonstrated the importance of detailed inundation mapping conducted
annually for major wetland systems. The extent of inundation and time since
previous inundation were critically important indicators for a range of biota and
were the basis for many condition estimates. One significant information gap was
the absence of 2010 vegetation condition mapping. These data exist for 2008 but the
replication of this work for 2010 would require an investment of approximately $200
000. At present there are no immediate plans to re-fly the lower Murrumbidgee with
aerial photography of sufficient resolution to replicate the 2008 mapping exercise. A
rolling program of image collection and mapping for the major wetland systems in
the Murray Darling Basin would be a key component of any wetland condition
assessment program reporting on the values identified in this report.
139
This condition assessment appends Rogers et al. (2011), and together these
documents detail the process of indicator selection for condition assessment of high
ecological value aquatic ecosystems in the Lowbidgee. The Lowbidgee provides a
good opportunity to test the sensitivity of condition assessments to types of data
available and it is anticipated that sensitivity analysis will be undertaken in the
future. Sensitivity analysis will enable the Commonwealth of Australia to assess the
implications of conducting condition assessments in data poor environments and will
facilitate the targeting of data acquisition toward the most sensitive and costeffective indicators of ecosystem health.
Acknowledgements
We wish to thank the many water and wetland managers who contributed their
time to discussions of key values and indicators of the Lowbidgee floodplain and
riverine ecosystems, including James Maguire (OEH), Paul Childs (OEH), Lorrain
Hardwick (NSW Office of Water), Bruce Whitehill (NSW Office of Water), and Mike
Maher (OEH). We are indebted to input and ideas from Matt Colloff (CSIRO), Ian
Overton (CSIRO) and Tanya Doody (CSIRO).
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