Downstream of Lock 1, the Lower Lakes, Murray Estuary and Coorong.

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Downstream of Lock 1, the Lower Lakes, Murray Estuary and Coorong.

A Literature Review.

Susan Gehrig and Jason Nicol 27 May 2010

SARDI Publication Number RD xx/xxxx

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the Lower Lakes, Murray Estuary and Coorong. A literature review. South Australian Research and Development Institute (Aquatic Sciences), Adelaide, 64pp. SARDI Publication Number RDxx/xxxx.

South Australian Research and Development Institute SARDI Aquatic Sciences

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The authors warrant that they have taken all reasonable care in producing this report. The report has been through the SARDI Aquatic Sciences internal review process, and has been formally approved for release by the Chief Scientist. Although all reasonable efforts have been made to ensure quality, SARDI Aquatic Sciences does not warrant that the information in this report is free from errors or omissions. SARDI Aquatic Sciences does not accept any liability for the contents of this report or for any consequences arising from its use or any reliance placed upon it.

This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the author.

Printed in Adelaide April 2010

SARDI Aquatic Sciences Publication Number RDxx/xxxx SARDI Research Report Series Number xx

Authors: S. Gehrig and J. Nicol

Reviewers: Chris Bice and Katherine Cheshire Approved by: Q. Ye

Signed:

Date: 27 May 2010

Distribution: DEH, MDBA, SAMDBNRM Board, DWLBC, and SARDI Aquatic Sciences Library Circulation: Public Domain

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List of Figures

Figure 1: The River Murray from Morgan to the mouth including the Lower Lakes and

Coorong Lagoons...13

Figure 2: Plant functional groups in relation to depth and duration of flooding...18

Figure 3: Water levels in the Lower Lakes (m AHD) from 1978 to 2008 (DWLBC 2010). ...23

Figure 4: Annual discharge from the barrages from 1975 to 2006 (Bice 2010)...24

List of Tables

Table 1: Functional classification of plant species based on water regime preferences, modified from Brock and Casanova (1997). ...17

Table 2: Functional classification based on salinity tolerance...21

Table 3: Species present (and functional group) in the 2005 (Nicol et al. 2006; Weedon et al. 2006), 2006 (Marsland and Nicol 2007) and 2007 (Marsland and Nicol 2008) River Murray Wetlands Baseline Surveys not recorded in the Lock 1 Wetlands draw down monitoring (Nicol 2010) (*denotes exotic species, #denotes listed as rare in South Australia). ...31

Table 4: Species present (and functional group) in the 2004 (Holt et al. 2005) and 2005 (Nicol et al. 2006) River Murray Wetlands baseline surveys that were not recorded in the 2008-09 Living Vegetation Murray condition monitoring surveys for the Lower Lakes (Marsland and Nicol 2009) (*denotes exotic species). ...34

List of Appendices

Appendix 1: Plant species list (Womersley 1975; Paton 1982; Pressey 1986; Thompson 1986; Geddes 1987; Renfrey et al. 1989; Brandle et al. 2002; Seaman 2003; Holt et al. 2005; Nicol et al. 2006; Weedon et al. 2006; Marsland and Nicol 2007; Marsland and Nicol 2008; Marsland and Nicol 2009; Stewart et al. 2009; Marsland et al. 2010; Nicol 2010; Nicol and Marsland 2010) of the River Murray downstream of Lock 1, the Lower Lakes, Murray Estuary and Coorong with functional classification (sensu Brock and Casanova 1997), salinity tolerance or salinity tolerance group (if known) and regions where species were recorded (*denotes exotic species, # denotes listed as rare in South Australia)...48 Appendix 2: List of dominant plant communities in a. the gorge, b. lower swamps, c. Lower Lakes, d. Murray Estuary and e. Coorong Lagoons (Brandle et al. 2002; Holt et al. 2005; Nicol et

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al. 2006; Marsland and Nicol 2007; Marsland and Nicol 2008; Stewart et al. 2009; Marsland et al.

2010). ...55

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Acknowledgements

The authors thank Amy George, Hafiz Stewart, Chris Bice and Katherine Cheshire for comments on early drafts of this review. This review was funded by the Department for Environment and Heritage, through the Murray Futures (Lower Lakes) Program.

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Executive Summary

This literature review summarises the available information on the aquatic and littoral vegetation communities of the Murray River downstream of Lock 1, Lakes Alexandrina and Albert, Murray Estuary and Coorong. The purpose of the review is to provide background information for:

 identification of key drivers that influence the aquatic and littoral vegetation of the system,

 determining key knowledge gaps,

 a series of risk assessments that will investigate the potential impacts of proposed management scenarios for acid sulfate soil mitigation in the Lower Lakes,

 the potential recovery of the system when freshwater flows return,

 and long-term planning,

The study region has been split into five biogeographic regions that historically had significantly different aquatic and littoral plant communities:

 the gorge (Lock 1 to Mannum),

 lower swamps (Mannum to Wellington),

 Lower Lakes (Lakes Alexandrina and Albert),

 Murray Estuary (Goolwa to Tauwitchere)

 Coorong Lagoons

The two main factors that determine the aquatic and littoral plant community in the study area are water regime (especially water depth) and salinity. Upstream of the barrages water regime is probably the most important factor (although salinity is important at a local scale) and downstream of the barrages salinity is the most important factor (although water level is important in the South Lagoon of the Coorong).

The study area has undergone significant changes since European settlement. Prior to large- scale water abstraction and river regulation there were spring floods with low water levels in summer and autumn upstream of Wellington, the Lower Lakes were predominantly fresh and Murray Estuary (which extended to Point Sturt) and Coorong had a variable salinity regime that was dependent on river flow. Large-scale abstraction for irrigated agriculture commenced in the early 1900s, which resulted in reduced river flows and saline incursions extending upstream of Point Sturt. The construction of the barrages in 1940 returned the Lower Lakes to freshwater ecosystem but disconnected the Murray Estuary and Coorong from Lake Alexandrina. This has resulted in predominantly static water levels between Goolwa and Lock 1, a variable salinity

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regime in the Murray Estuary and North Lagoon of the Coorong and the South Lagoon being predominantly hypersaline. Subsequently, the vegetation communities of each biographic region are typically characterised by species that are adapted to the prevailing environmental conditions in each region.

Despite being highly modified, a total of 353 taxa (including 132 exotics and four listed as rare in South Australia) have been recorded from the study region since 1975. The study area is important (it is an aquatic system in an otherwise dry environment) and contributes to regional and state biodiversity because a completely different suite of species is often present compared to the adjacent highland.

The River Murray downstream of Lock 1, Lower Lakes, Murray Estuary and Coorong has undergone further changes in recent years due to the combination of drought and water abstraction. Reduced inflows into the system have resulted in a series of issues, including, the longest closure of the barrages on record, the near closure of the Murray Mouth in the early 2000s which consequently requires dredging to remain open. Further compounding these effects are low flows over Lock 1 since 2007, which have resulted in a drop in water levels in the Lower Lakes and Murray downstream of Lock 1, which are currently below sea level. As a result the vegetation of the system has undergone significant changes. Ruppia megacarpa, which was common in Murray estuary and North Lagoon, has not been observed since the mid 1990s.

Ruppia tuberosa, a highly salt tolerant species that was common in the South Lagoon early this century, has declined in abundance in the South Lagoon but colonised the North Lagoon.

Fringing wetlands in the Lower Lakes and floodplain wetlands upstream of Wellington that were historically permanent have dried completely, which has resulted in the loss of large areas of submergent (e.g. Vallisneria spiralis, Potamogeton crispus) and (in some cases) amphibious species (e.g. Myriophyllum spp.) from these habitats. Species lost from the permanent wetlands have not colonised the remnant inundated habitats (the main channel and Lower Lakes). Fringing communities have also undergone significant changes with the less desiccation tolerant species (e. g Typha spp. Schoenoplectus validus) declining in abundance; however, the more desiccation (e.g.

Phragmites australis) and salt (e.g. Halosarcia pergranulata, Sarcocornia quinqueflora) tolerant fringing species have remained but are disconnected from the remnant inundated habitats.

Nevertheless, the system has showed that it is resilient and currently has capacity for recovery.

Water level rises as part of Goolwa Channel water level management plan have resulted in recolonisation of submergents and growth of fringing species in Goolwa Channel. How long the system can remain resilient is unknown.

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1. Introduction

This literature review summarises the available information on the aquatic and littoral vegetation communities of the River Murray downstream of Lock 1, Lakes Alexandrina and Albert, Murray Estuary and Coorong. The purpose of the review is to provide background information for:

 identification of key drivers that influence the aquatic and littoral vegetation of the system,

 determining key knowledge gaps,

 a series of risk assessments that will investigate the potential impacts of proposed management scenarios for acid sulfate soil mitigation in the Lower Lakes,

 the potential recovery of the system when freshwater flows return,

 and long-term planning,

The information available regarding the aquatic and littoral vegetation of the study region has been collected sporadically and there is only one long term data set; Ruppia tuberosa monitoring in the South Lagoon of the Coorong that was first undertaken in 1999 (Paton 2000) and is ongoing.

The majority of the information available is from targeted, short-term studies (usually 2-3 years);

therefore, medium to long-term changes through time can only be compared on a qualitative basis. Nevertheless, there is a considerable amount of peer reviewed and grey literature available regarding the vegetation of the study region dating back to the mid 1970s and documented oral history accounts of the region dating back to the late 1800s (Sim and Muller 2004).

The earliest available published information was a catalogue of the submergent plants and algae of the Coorong Lagoons (Womersley 1975). In the late 1970s Brock (1979; 1981b; 1981a;

1982a; 1982b) investigated the ecology and physiology of Ruppia spp. the dominant submergent species in the Coorong. There were further studies of the submergent plants in the Coorong in the 1980s (Geddes and Butler 1984; Geddes 1987; Geddes and Hall 1990) and 1990s (Edyvane et al. 1996) and recent long-term monitoring in the South Lagoon (Paton 1996; Paton 2000; Paton 2001; Paton and Bolton 2001; Paton 2005a; Paton 2005b; Paton and Rogers 2008).

The aquatic and littoral vegetation upstream of the barrages has not been studied to the same extent as the Coorong. Qualitative one-off surveys as part of large scale biological surveys were undertaken in the mid 1980s (Pressey 1986; Thompson 1986), mid 1990s (Nichols 1998), early this century (Stewart et al. 2009) and the South Australian Murray-Darling Basin Natural Resources Management Board commissioned wetland baseline surveys in 2004 (Holt et al. 2005), 2005 (Nicol et al. 2006), 2006 (Marsland and Nicol 2007) and 2007 (Marsland and Nicol 2008).

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The aforementioned studies were one-off surveys with the aim to record species present;

however, they provide an excellent baseline with which to compare recent changes. In addition, a vegetation condition monitoring program was established in the Lower Lakes in 2008 to report on Living Murray targets (Marsland and Nicol 2009; Nicol and Marsland 2010) and monitoring was undertaken in 2008-09 in wetlands downstream of Lock 1 to investigate the impacts of low water levels (Nicol 2010), which are used to assess the current condition of the plant communities.

Many of the dominant species in the study area are cosmopolitan and information regarding the physiological tolerances and water regime preferences of individual species usually comes from peer reviewed scientific papers; however, quantitative information regarding the salinity tolerances is only available for 69 species. Furthermore, much of this information has been collected from outside of the study area and has been supplemented by expert opinion and observations.

1.1. Study Region

This review will focus on the aquatic and littoral (fringing) vegetation of the River Murray and associated wetlands (connected at historical pool level) downstream of Lock 1 (gorge and lower swamps), Lakes Alexandrina and Albert, the Murray Estuary (Goolwa to Tauwitchere) and the Coorong lagoons (Figure 1). The River Murray below Lock 1 was included in this review due to its hydrological connectivity with the Lower Lakes (upstream of the Clayton regulator). Water levels in the Lower Lakes are dependent on flows over Lock 1 and wind driven water level fluctuations (seiches) in the lakes affect water levels in the main channel and wetlands as far upstream as Lock 1. The Coorong and Murray Estuary, whilst disconnected from Lake Alexandrina by the barrages, rely on flows from the lakes to maintain a variable salinity regime.

The River Murray in South Australia has been traditionally split into five biogeographical units based primarily on geomorphology (Pressey 1986; Thompson 1986). The valley section (NSW/SA border to Lock 3) is characterised by a broad floodplain with numerous permanent and temporary wetlands (Holt et al. 2005). Downstream of Lock 3 the river enters a narrow, deep limestone trench, with steep cliffs on either side of the river (gorge section, Lock 3 to Mannum) (Pressey 1986; Thompson 1986; Jensen et al. 1996). Between Mannum and Wellington (the lower swamps), the river still flows through a narrow gorge; however, the floodplain has been extensively modified and largely converted to dairy swamps (the remnant wetlands are generally areas where levees could not be constructed) (Pressey 1986; Thompson 1986). Downstream of Wellington the river flows into a broad, shallow terminal freshwater lake

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system (Lakes Alexandrina and Albert, the Lower Lakes) (Pressey 1986; Thompson 1986; Jensen et al. 1996; Phillips and Muller 2006) (Figure 1). The Murray Estuary stretches from Goolwa to Tauwitchere (Figure 1) and is separated from Lake Alexandrina by a series of five barrages that prevent saline water from entering the lake (Phillips and Muller 2006). South east of the Murray Estuary lies the Coorong (North and South Lagoons), a shallow elongate coastal lagoon system separated from the Southern Ocean by the Younghusband Peninsula (Geddes and Brock 1977;

Geddes and Butler 1984; Geddes 1987; Department for Environmnetnand Heritage 2000;

Phillips and Muller 2006) (Figure 1).

Despite the interactions and common factors that influence the plant community, there is considerable evidence that the plant communities in each region are distinct and will be treated separately throughout this review. For example, Nicol et al. (2006) reported that the wetland and floodplain plant communities were significantly different between the gorge, lower swamps and Lower Lakes wetlands. Likewise the plant community of the Coorong and Murray Estuary is very different from the community upstream of the barrages due to large differences in salinity upstream and downstream of the barrages.

1.1.1 Gorge (Lock 1 to Mannum)

Downstream of Lock 1 the River Murray flows predominately in a southerly direction constrained within a limestone gorge with steep cliffs on both sides of the river (Pressey 1986;

Thompson 1986; Holt et al. 2005) (Figure 1). The floodplain is generally less than 500 m wide and permanent wetlands have developed on the floodplain as a result of stable water levels due to river regulation (Pressey 1986; Thompson 1986).

The primary factor that influences the aquatic and littoral vegetation between Lock 1 and Mannum is water regime, especially water level, which is primarily controlled by flows over Lock 1 and barrage operations. In addition, wind speed and direction can influence water levels on daily or even hourly time scales. Strong southerly winds can push water from the Lower Lakes up the main channel of the Murray River causing water levels to rise and strong northerly winds have the opposite effect. These short-term, wind driven water level fluctuations (seiches) have resulted in the fringes of permanent wetlands and the river channel being subjected to wetting and drying, which has probably increased the area of the littoral zone compared to wetlands with static water levels. Salinity also has an impact, especially in recent times, in dry wetlands where there is evidence of saline groundwater intrusions (J. Nicol pers. obs.).

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1.1.2 Lower Swamps (Mannum to Wellington)

Similar to the gorge section, the River Murray between Mannum and Wellington flows in a southerly direction constrained within a limestone gorge (Pressey 1986; Thompson 1986; Holt et al. 2005) (Figure 1). However, in contrast to the gorge region, the floodplain has been extensively modified for irrigated agriculture (Pressey 1986; Thompson 1986; Jensen et al. 1996).

Levee banks were constructed along the either side of the River Murray, irrigation channels dug and the floodplain levelled to flood irrigate pasture for dairy production. Jensen et al. (1996) reported that 93% of the floodplain between Mannum and Wellington was converted to dairy swamp with the remnant wetlands in areas where levees could not be constructed. However, in recent years, several dairy swamps have had grazing removed and rehabilitation/restoration is currently being undertaken (e.g. Piawalla Swamp).

The primary factor that influences the aquatic and littoral vegetation in the lower swamps is also water regime, especially water level, which is controlled by the same factors that influence water regime in the gorge region (flows over Lock 1, barrage operations and seiching). However, adjacent land use, historical land use, restoration activities, levee bank construction, salinity and invasive species are also important factors that influence the lower swamps plant community.

1.1.3 Lower Lakes (Lakes Alexandrina and Albert and the Lower Finniss River and Currency Creek)

Lakes Alexandrina and Albert are large shallow freshwater lakes situated at the terminus of the Murray-Darling Basin (Figure 1). Surface water predominantly feeds into Lake Alexandrina from the River Murray near the township of Wellington with minor inflows from tributaries (the Bremer, Angas and Finniss Rivers and Currency and Tookayerta Creeks) that drain the Eastern Mount Lofty Ranges (EMLR) along the south western edge of the Lake Alexandrina (Phillips and Muller 2006) (Figure 1). Groundwater discharge and rainfall also contribute significant inflows (Phillips and Muller 2006). Lake Albert then primarily receives water from Lake Alexandrina via a narrow channel (Narrung Narrows) connecting the two systems near Pt Malcolm (Figure 1); however, there is also bidirectional exchange between the lakes depending on wind direction. Water from Lake Alexandrina is similarly supplemented by rainfall and groundwater discharge in Lake Albert (Phillips and Muller 2006). Lake Albert represents the final, local terminus of the River Murray, since it has no current or historical through flow connection with the Coorong. Only water from Lake Alexandrina drains into the Murray Estuary, Southern Ocean or the Coorong via a series of channels (Phillips and Muller 2006) (Figure 1).

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The primary factor that influences the plant community in the Lower Lakes is water regime particularly water level, which is influenced by inflows (predominantly the River Murray but inflows from the eastern Mt Lofty Ranges can be significant at times) and barrage operations.

Since the construction of the Clayton regulator in 2009, which impounds flows from the Finniss River, Currency Creek and Tookayerta Creek (Figure 1), water levels between Clayton and Goolwa are higher than the remainder of Lake Alexandrina. Similarly the bank that was constructed across the Narrung Narrows in 2008 and subsequent pumping from Lake Alexandrina has meant that the water level in Lake Albert is higher than Lake Alexandrina.

Nevertheless the seasonal water level fluctuations (winter/spring high water levels and summer/autumn low water levels) that occurred throughout the Lower Lakes still occur as do short-term wind driven water level fluctuations (Noye and Walsh 1976). Salinity is also an important factor, especially in Lake Albert wetlands and in areas adjacent to the barrages and Coorong in Lake Alexandrina.

1.1.4 Murray Estuary (Goolwa to Tauwitchere)

The Murray Estuary (via the Murray Mouth) is the only site where material (primarily sediment, nutrients and salt) can move from the Murray-Darling Basin into the Southern Ocean (Phillips and Muller 2006). The Murray Estuary is located between the Goolwa and Tauwitchere Barrages (Figure 1), which historically was considered part of the Coorong; however, for the purposes of this review it has been designated a separate region because it represent the extent of tidal influence and the area most affected by controlled barrage releases (Webster 2005a; Webster 2005b; Webster 2007).

The primary factor influencing the vegetation of the Murray Estuary is salinity, which is dependent upon River Murray inflows and tidal incursion. Due to limited freshwater inflows to the Murray Estuary through the Murray Barrages over the past 10-15 years, increased sedimentation has resulted in the need for constant dredging of the Murray Mouth (since late 2002) to maintain a connection between the Coorong and Southern Ocean (Geddes 2005a;

Phillips and Muller 2006; Brookes et al. 2009).

1.1.5 Coorong Lagoons

The Coorong is a shallow, elongate coastal lagoon confined by the coastal dune barrier of the Younghusband Peninsula (Figure 1). The Coorong stretches for 140 km in a south-east, north- west direction (Geddes and Butler 1984; Geddes 1987; Geddes and Hall 1990; Seaman 2003) and is comprised of two main lagoons (the North and South Lagoons) of similar size almost separated by a spit of land (Hells Gate) (Lothian and Williams 1988) (Figure 1).

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Salinity is the primary factor that influences the plant community in the Coorong (Womersley 1975; Noye and Walsh 1976; Geddes and Brock 1977; Gilbertson and Foale 1977; Geddes 1987;

Geddes and Hall 1990; Webster 2005a; Webster 2005b; Brookes et al. 2009; Lester and Fairweather 2009). Salinity in the Coorong is spatially and temporally variable. Salinity ranges from fresh near the barrages when large quantities of water are being released from Lake Alexandrina, through brackish to the salinity of seawater (35‰ TDS) near the Murray Mouth (when the Barrages are closed), grading to hypersaline (>35-115‰ TDS) in the southern end of the North Lagoon and the South Lagoon (e.g. Paton 1982; Geddes 1987; Lothian and Williams 1988; Seaman 2003; Phillips and Muller 2006; Paton and Rogers 2008). Water level is also an important factor in the South Lagoon where water levels fluctuate seasonally from winter/spring highs to late summer/autumn lows (Geddes 1987; Seaman 2003) and over shorter temporal scales due to the speed and direction of the wind (Noye and Walsh 1976).

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Figure 1: The River Murray from Morgan to the mouth including the Lower Lakes and Coorong Lagoons.

South Australia

Queensland

New South Wales

Victoria

Morgan

Meningie

Lake Albert

Wellington Lake

Alexandrina Mannum

Blanchetown (Lock 1)

Narrung Gorge Section

(Blanchetown to Mannum)

Lower Swamps (Mannum to Wellington)

South Lagoon Hell’s Gate North Lagoon Milang

Clayton (Regulator)

Goolwa (Barrage)

Lower Finniss River Lower Currency

Creek

Murray Mouth

Mundoo Barrage

Tauwitchere Barrage Ewe Island

Barrage

Murray Bridge

Murray Estuary Goolwa Channel (Clayton Regulator to Goolwa

Barrage)

Younghusband Peninsula

South Australia

Queensland

New South Wales

Victoria

Morgan

Meningie

Lake Albert

Wellington Lake

Alexandrina Mannum

Blanchetown (Lock 1)

Narrung Gorge Section

(Blanchetown to Mannum)

Lower Swamps (Mannum to Wellington)

South Lagoon Hell’s Gate North Lagoon Milang

Clayton (Regulator)

Goolwa (Barrage)

Lower Finniss River Lower Currency

Creek

Murray Mouth

Mundoo Barrage

Tauwitchere Barrage Ewe Island

Barrage

Murray Bridge

Murray Estuary Goolwa Channel (Clayton Regulator to Goolwa

Barrage)

Younghusband Peninsula

N

0 10 km

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1.1.6 Changes to the Natural Flow Regime

The River Murray downstream of Lock 1, Lower Lakes, Murray Estuary and Coorong have undergone significant changes since European settlement (Sim and Muller 2004; Phillips and Muller 2006; Fluin et al. 2007; Dick et al. 2010). Prior to the construction of the barrages, main channel locks and weirs and headwater storages the River Murray downstream of Lock 1 would have had a variable flow regime with spring floods and low water levels in autumn (Walker 1985;

Walker 1986; Walker et al. 1992; Walker and Thoms 1993; Davies et al. 1994; Maheshwari et al.

1995; Walker et al. 1995; Puckridge et al. 1998; Puckridge et al. 2000). Downstream of Wellington the water levels were more stable because of the large area of the lakes and permanent inflows from the River Murray, which resulted in the lakes being predominantly fresh with occasional saline incursions only as far upstream as Point Sturt, during periods of low flow (Sim and Muller 2004; Fluin et al. 2007). The Murray Estuary and Coorong were truly estuarine systems with a variable salinity regime along the entire length of the Coorong (Fluin et al. 2007; Dick et al. 2010).

Early last century abstraction of water for irrigation commenced and the construction of Hume Dam was completed, which resulted in more frequent saline incursions that reached much further upstream (Sim and Muller 2004; Fluin et al. 2007). The saline incursions prompted the construction of the barrages, which were completed in 1940 and returned the Lower Lakes to a freshwater system (Sim and Muller 2004; Fluin et al. 2007). The construction of the barrages, coupled with regulation further upstream meant that the water level between the barrages and Lock 1 was generally static, except during periods of high flow (Walker 1985; Walker 1986;

Walker et al. 1992; Walker and Thoms 1993; Davies et al. 1994; Maheshwari et al. 1995; Walker et al. 1995; Puckridge et al. 1998; Puckridge et al. 2000). The Murray Estuary and Coorong were disconnected from the lakes and the salinity gradient in the Coorong changed. The salinity in the Coorong ranged from fresh to marine in the Murray Estuary (depending on barrage outflows), brackish to hypermarine in the North Lagoon and hypermarine the South Lagoon (Geddes and Hall 1990; Dick et al. 2010).

Following construction of the Barrages and Lock 1, the conditions in the River Murray downstream of Lock 1, the Lower Lakes, Murray Estuary and Coorong were dependent on flow over Lock 1 and barrage operations. During the 1940s there were several years of drought and was considered a dry decade, in the 1950s there were several large floods, the 1960s were generally dry, there were several large floods in the 1970s, in the 1980s there was a severe drought that resulted in the closure of the Murray Mouth (Geddes and Butler 1984), in the 1990s there were several large floods (the last one in 1996) and early this century has been the driest period on record in the Murray-Darling Basin (DWLBC 2010). Climatic factors, and the high

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level of abstraction have determined flow over Lock 1, which has determined the water levels in the Lower Lakes and inturn barrage outflows and the salinity in the Murray Estuary and Coorong.

1.2. Vegetation of the River Murray Downstream of Lock 1, Lower Lakes, Murray Estuary and Coorong

A total of 353 taxa (including 132 exotics and four listed as rare in South Australia) have been recorded from the study region since 1975 (list compiled from the following studies: Womersley 1975; Paton 1982; Pressey 1986; Thompson 1986; Geddes 1987; Renfrey et al. 1989; Brandle et al.

2002; Seaman 2003; Holt et al. 2005; Nicol et al. 2006; Weedon et al. 2006; Marsland and Nicol 2007; Marsland and Nicol 2008; Marsland and Nicol 2009; Stewart et al. 2009; Marsland et al.

2010; Nicol 2010; Nicol and Marsland 2010) (Appendix 1).

The River Murray (and associated wetlands and floodplain), Lower Lakes, Murray Estuary and Coorong is an aquatic ecosystem in an otherwise dry environment and many of the recorded 353 plant taxa do not occur above the 1956 flood level. Therefore, the region covered in the review (albeit highly modified) contributes significantly to regional and state biodiversity because a completely different suite of species is often present compared to the surrounding land (sensu Pollock et al. 1998). In addition, the Lower Lakes is the common boundary of South Australia’s three wettest bioregions; the Mt Lofty Ranges, South East and Murray and elements of the wetland flora for each region is represented in the Lower Lakes.

1.2.1 Functional Groups

Due to the large number of species and communities present, species were classified into functional groups (based on water regime preferences) outlined in Table 1. The position each group occupies in relation to flooding depth and duration is outlined in Figure 2. The functional classification was based on the classification framework devised by Brock and Casanova (1997), which was based on species from wetlands in the New England Tablelands region of New South Wales and modified to suit the River Murray downstream of Lock 1, the Lower Lakes, Murray Estuary and Coorong.

The use of a functional group approach to assess change through time and potential impacts of management strategies has several advantages compared to a species or community based approach:

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 species with similar water regimes preferences are grouped together, which simplifies systems with high species richness (especially where there are large numbers of species with similar water regime preferences),

 predictions about the response of the plant community are made based on processes and does not require prior biological knowledge of the system,

 is transferrable between systems,

 robust and testable models that predict the response of a system to an intervention or natural event can be constructed, which can in turn be used as hypotheses for monitoring programs.

However there are limitations of the approach, which include:

 loss of information on species or communities (especially if there are species or communities of conservation significance or there is a pest plant problem),

 uncertainty regarding which species should be classified into which functional group,

 important factors (e.g. salinity) are often not taken into consideration (additional factors can be included; however, this can often complicate the functional classification and in systems where there is low species richness the number of groups may be greater than the number of species).

In this review changes in ecological condition through time for each biogeographical region will be reviewed using species, community and functional approaches. The functional approach is explored because the conceptual models used in the environmental impact assessment and risk assessment will use functional groups to predict responses and impacts.

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Table 1: Functional classification of plant species based on water regime preferences, modified from Brock and Casanova (1997).

Functional Group Water Regime Preference Examples Terrestrial dry Will not tolerate inundation and tolerates low soil

moisture for extended periods.

Atriplex vesicaria, Rhagodia spinescens, Enchylaena tomentosa Terrestrial damp

Will tolerate inundation for short periods (<2 weeks) but require high soil moisture throughout their life cycle.

Centaurea calcitrapa, Chenopodium album, Fumaria bastardii Floodplain

Temporary inundation, plants germinate on newly exposed soil after flooding but not in response to rainfall.

Epaltes australis, Centipeda minima, Lachnagrostis filiformis Amphibious

fluctuation tolerators-emergent

Fluctuating water levels, plants do not respond morphologically to flooding and drying and will tolerate short-term complete submergence (<2 weeks).

Cyperus gymnocaulos, Juncus kraussii, Schoenoplectus pungens Amphibious

fluctuation tolerators-woody

Fluctuating water levels, plants do not respond morphologically to flooding and drying and are large perennial woody species.

Eucalyptus camaldulensis, Melaleuca halmaturorum, Muehlenbeckia florulenta Amphibious

fluctuation tolerators-low growing

Fluctuating water levels, plants do not respond morphologically to flooding and drying and are generally small herbaceous species.

Limosella australis, Crassula helmsii, Brachycome basaltica

Amphibious fluctuation responders-plastic

Fluctuating water levels, plants respond morphologically to flooding and drying (e.g.

increasing above to below ground biomass ratios when flooded).

Persicaria lapathifolium, Ludwigia peploides, Myriophyllum spp.

Floating

Static or fluctuating water levels, responds to fluctuating water levels by having some or all organs floating on the water surface. Most species require permanent water to survive.

Azolla spp., Lemna spp., Spirodella punctata

Submergent r- selected

Temporary wetlands that hold water for longer than 4 months.

Ruppia tuberosa, Ruppia polycarpa, Lamprothamnium papulosum Emergent Static shallow water <1 m or permanently saturated

soil.

Typha spp., Phragmites australis, Schoenoplectus validus Submergent k-

selected Permanent water.

Vallisneria americana, Potamogeton crispus, Ruppia megacarpa

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Figure 2: Plant functional groups in relation to depth and duration of flooding.

The “terrestrial dry” functional group is intolerant of flooding and taxa will persist in environments with low soil moisture (Table 1) (Brock and Casanova 1997). Taxa from this functional group often invade wetlands that have been drawn down for an extended period or floodplains where there has been a lack of flooding but are generally restricted to highlands that never flood (Brock and Casanova 1997).

Taxa in the “terrestrial damp” group will tolerate inundation for short periods and require high soil moisture to complete their life cycle (Table 1) (Brock and Casanova 1997). Taxa from this functional group are often winter annuals, perennial species that grow around the edges of permanent water bodies where there is high soil moisture or species that colonise wetlands shortly after they are drawn down and riparian zones and floodplains shortly after flood waters recede (Brock and Casanova 1997).

Taxa in the “floodplain” functional group exhibit most of the traits of terrestrial species; they are generally intolerant of long-term inundation but are restricted to areas that flood periodically

Increasing Depth

Increasing Duration

Terrestrial dry

Terrestrial damp

Submergent k-selected

Submergent r-selected E

Floodplain

Amphibious fluctuation Tolerator-emergent Amphibious fluctuation

Tolerator- woody

Amphibious fluctuation Tolerator-low growing

Amphibious fluctuation Tolerator-plastic

Floating

Increasing Depth

Increasing Duration

Terrestrial dry

Terrestrial damp

Floodplain

Amphibious fluctuation Amphibious fluctuation

Amphibious fluctuation

Floating

Increasing Depth

Increasing Duration

Terrestrial dry

Terrestrial damp

Submergent k-selected

Floodplain

Amphibious fluctuation Tolerator-emergent Amphibious fluctuation

Tolerator- woody

Amphibious fluctuation Tolerator-low growing

Amphibious fluctuation Tolerator-plastic

Floating

Increasing Depth

Increasing Duration

Terrestrial dry

Terrestrial damp

Floodplain

Amphibious fluctuation Amphibious fluctuation

Amphibious fluctuation

Floating

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(they are absent from the highlands) because they only germinate after flood waters recede or wetlands are drawn down, not in response to rainfall (Table 1) (Nicol 2004). Taxa from this functional group colonise floodplains and riparian zones after flood waters have receded and when wetlands are drawn down (Nicol 2004). Floodplain species often have flexible life history strategies, they grow whilst soil moisture is high and flower and set seed (after which most species die) in response to low soil moisture (Nicol 2004).

The “amphibious fluctuation tolerator-emergent” group consists mainly of emergent sedges and rushes that prefer high soil moisture or shallow water but require their photosynthetic parts to be emergent, although many will often tolerate short-term submergence (Table 1) (Brock and Casanova 1997). Taxa from this group are often found on the edges of permanent water bodies, in seasonal and temporary wetlands, in riparian zones and areas that frequently wet and dry.

Species in the ”amphibious fluctuation tolerator-woody” group have similar water regime preferences to the amphibious fluctuation tolerator-emergent group (Figure 2) and consist of woody perennial species (Table 1) (Brock and Casanova 1997). Plants generally require high soil moisture in the root zone but there are several species (e.g. Eucalyptus largiflorens) that are tolerant of desiccation for extended periods (Roberts and Marston 2000). Species in this functional group are generally found on the edges of permanent water bodies, in seasonal and temporary wetlands, in riparian zones and areas that frequently wet and dry.

The “amphibious fluctuation tolerator-low growing” group have similar water regime preferences to the amphibious fluctuation tolerator-emergent and amphibious fluctuation tolerator-woody group (Figure 2); however, some species can grow totally submerged except during flowering (when there is a requirement for a dry phase) (Table 1) (Brock and Casanova 1997). Species in the this functional group are generally found on the edges of permanent water bodies, in seasonal and temporary wetlands, in riparian zones and areas that frequently wet and dry but species are usually less desiccation tolerant than species in the other amphibious tolerator groups (Figure 2).

The “amphibious fluctuation responder-plastic” group occupies a similar zone to the amphibious fluctuation tolerator-low growing group; except that they have a physical response to water level changes such as rapid shoot elongation or a change in leaf type (Brock and Casanova 1997). They can persist on damp and drying ground because of their morphological flexibility but can flower even if the site does not dry out. They occupy a slightly deeper/wet for longer area than the amphibious fluctuation tolerator-low growing group (Figure 2).

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Species in the “floating” functional group float on the top of the water (often unattached to the sediment) with the majority of species requiring the presence of free water of some depth year round; although, some species can survive and complete their life cycle stranded on mud (Table 1) (Brock and Casanova 1997). Taxa in this group are usually found in permanent waterbodies, often forming large floating mats upstream of barriers (e.g. weirs), in lentic water bodies and slackwaters.

“Submergent r-selected” species colonise recently flooded areas (Table 1) and show many of the attributes of Grime’s (1979) r-selected (ruderal) species, which are adapted to periodic disturbances. Many require drying to stimulate germination; they frequently complete their life cycle quickly and die off naturally. They persist via a dormant, long-lived bank of seeds, spores or asexual propagules (e.g. Ruppia tuberosa and Ruppia polycarpa turions in the soil) (Brock 1982b).

They prefer habitats that are annually flooded to a depth of more than 10cm but can persist as dormant propagules for a number of years (temporary or ephemeral wetlands).

The “emergent” group consists of taxa that require permanent shallow water or a permanently saturated root zone, but require emergent leaves or stems (Table 1). They are often found on the edges of permanent waterbodies and in permanent water up to 2 m deep (depending on species) or in areas where there are shallow water tables (Roberts and Marston 2000).

“Submergent k-selected” species require permanent water greater than 10 cm deep for more than a year to either germinate or reach sufficient biomass to start reproducing (Table 1) (Roberts and Marston 2000). Species in this group show many of the attributes of Grime’s (1979) k-selected (competitor) species that are adapted to stable environments and are only found in permanent water bodies. The depth of colonisation of submergent k-selected species is dependant on photosynthetic efficiency and water clarity (sensu Spence 1982)

Whilst water regime is the primary driver of plant community composition (e.g. Brownlow 1997;

Nielsen and Chick 1997; Begg et al. 1998; Blanch et al. 1999b; Blanch et al. 1999a; Blanch et al.

2000; Casanova and Brock 2000; Capon 2003; Nicol et al. 2003; Capon 2007; Deegan et al. 2007;

Boers and Zedler 2008), especially upstream of the barrages, salinity is also an important driver particularly in the region (Geddes and Butler 1984; Geddes 1987; Geddes and Hall 1990;

Brookes et al. 2009; Lester and Fairweather 2009). Therefore, each taxon and community was assigned a salinity tolerance group based on values reported in the literature (if available) or field or observations (Table 2).

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Table 2: Functional classification based on salinity tolerance.

Salinity Tolerance Group EC (Salinity) Range Examples High >50,000 EC (>31,250 mgl^-1)

Halosarcia pergranulata, Sarcocornia quinqueflora,

Ruppia tuberosa, Melaleuca halmaturorum Moderate 10,000-50,000 EC (6,250-31,250 mgl^-1)

Phragmites australis, Eucalyptus camaldulensis,

Lepilaena australis, Juncus kraussii

Low <10,000 EC (<6,250 mgl^-1)

Potamogeton crispus, Schoenoplectus validus,

Salix babylonica, Azolla filiculoides

The values for salinity tolerance are (where possible) absolute salinity tolerances of adult plants determined under laboratory or greenhouse conditions. If this information is unavailable inferences of the salinity tolerance of species have been made from field observations (e.g.

coexistence with species of high salinity tolerance, present in areas of salt scald or high salinity water). In addition, salinity tolerance values did not take into consideration the salinity thresholds of juveniles (e.g. Marcar et al. 2000; Naidoo and Kift 2006), germination and recruitment (e.g. Ungar 2001; Malcolm et al. 2003; Greenwood and MacFarlane 2006; Robinson et al. 2006; Song et al. 2008; Wetson et al. 2008; Elsey-Quirk et al. 2009), key life history stages (e.g. flowering and seed set) (e.g. Short and Colmer 1999; Salter et al. 2010), interactions between salinity and other environmental factors (e.g. Clarke and Hannon 1970; Davis 1978; Stephens 1990; Naidoo and Kift 2006; Raulings et al. 2007; Salter et al. 2007; Colmer and Flowers 2008;

Flowers and Colmer 2008; Salter et al. 2008; Song et al. 2009) and competition (e.g. Greenwood and MacFarlane 2009).

2. Recent Ecological Condition (2004-2007)

The plant communities present at the regional scale prior to 2007 were primarily the result of water regime (upstream of the barrages) (Holt et al. 2005; Nicol et al. 2006; Weedon et al. 2006;

Marsland and Nicol 2007; Marsland and Nicol 2008; Marsland et al. 2010) and salinity (downstream of the barrages) (e.g. Geddes and Brock 1977; Paton 1982; Geddes and Butler 1984; Geddes 1987; Geddes and Hall 1990; Paton and Rogers 2008) (Appendix 2), which is driven by River Murray flows. However, local land use (e.g. urbanisation, grazing) and wave action are also important at the wetland or reach scale (e.g. Holt et al. 2005; Nicol et al. 2006;

Weedon et al. 2006; Marsland and Nicol 2007; Marsland and Nicol 2008; Marsland et al. 2010).

The Murray-Darling Basin had been in extended drought during 2004-2007 with no overbank flows (the last large overbank flow was in 1996 and there was an in channel flow in 2000) with one small in-channel flow in 2005 (DWLBC 2010). During this time water levels upstream of the barrages fluctuated between 0.8 m AHD in spring and 0.5 m AHD in autumn (Figure 3).

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Prior to 2004 water levels generally fluctuated between 0.9 m AHD in spring 0.5 m AHD in autumn with water levels falling to 0.4 m AHD in autumn 2003 (Figure 3). In addition, flows over the barrages have been limited with small releases in September-October 2003 (Geddes 2005a) and August 2004 (Geddes 2005b) (Figure 4). The resultant low flows caused the near closure of the Murray Mouth, which has been kept open by dredging since late 2002 (Phillips and Muller 2006). This has resulted in marine (or greater) salinities in the Murray Estuary and a salinity gradient ranging from marine adjacent to Tauwitchere Barrage to hypermarine in the South Lagoon of the Coorong (Phillips and Muller 2006). The salinity in the North and South Lagoons of the Coorong has been steadily increasing through time due to the continual input of salt from the Southern Ocean via the open Murray Mouth, lack of tidal flushing south of Tauwitchere Barrage and lack of flows from the River Murray that will flush salt out of the system into the Southern Ocean (Brookes et al. 2009).

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Historical Lake Alexandrina Water Level

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Year

Water Level (m AHD) _

Figure 3: Water levels in the Lower Lakes (m AHD) from 1978 to 2008 (DWLBC 2010).

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1975-76 1976-77

1977-78 1978-79

1979-80 1980-81

1981-82 1982-83

1983-84 1984-85

1985-86 1986-87

1987-88 1988-89

1989-90 1990-91

1991-92 1992-93

1993-94 1994-95

1995-96 1996-97

1997-98 1998-99

1999-00 2000-01

2001-02 2002-03

2003-04 2004-05

2005-06 2006-07

2007-08 2008-09

0 5000 10000 15000 20000

mean annual end of system discharge - post regulation mean annual end of system discharge - pre regulation

Annual discharge GL

Figure 4: Annual discharge from the barrages from 1975 to 2006 (Bice 2010).

2.1. Gorge (Lock 1 to Mannum)

The aquatic and littoral plant communities between Mannum and Lock 1 between 2004 and 2007 were typical of areas with limited water level fluctuations (Walker 1985; Walker 1986;

Walker et al. 1992; Walker and Thoms 1993; Walker et al. 1994; Blanch et al. 1999b; Blanch et al.

2000) (Appendix 2a).

The shallow (<1 m depth) permanently inundated areas of wetlands connected at pool level were dominated by submergent k-selected species such as Vallisneria spiralis, Ceratophyllum demersum Potamogeton crispus and Potamogeton tricarinatus, desiccation intolerant Amphibious fluctuation responder-plastic species such as Myriophyllum verrucosum and Myriophyllum papulosum and floating species such as Azolla filiculoides (Appendix 2a). The areas deeper than 1 m were generally devoid of vegetation with the exception of Floating species (Holt et al. 2005; Nicol et al. 2006; Weedon et al. 2006; Marsland and Nicol 2007; Marsland and Nicol 2008).

The wetland fringing vegetation was often dominated by dense; almost monospecific stands of Emergent species such as Typha spp., Phragmites australis and Schoenoplectus validus; however, there

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were areas with diverse Floodplain, Amphibious and Emergent herb, sedge and rush communities that included, Juncus usitatus, Cyperus gymnocaulos, Limosella australis, Bolboschoenus caldwellii, Mimulus repens, Lycopus australis, Berula erecta, Epaltes australis, Sporobolus mitchellii, Ludwigia peploides, Persicaria lapathifolium, Lachnagrostis filiformis and Stemodia florulenta (Holt et al. 2005; Nicol et al. 2006; Weedon et al. 2006; Marsland and Nicol 2007; Marsland and Nicol 2008) (Appendix 2a). The overstorey (if present) was Eucalyptus camaldulensis, with Myoporum montanum, Acacia stenophylla (open woodland) and Muehlenbeckia florulenta (often forming dense closed shrublands).

The condition of Eucalyptus camaldulensis trees was generally good to excellent; although, the proportion of trees in moderate to poor condition was generally higher in wetlands closer to Lock 1 (Holt et al. 2005; Nicol et al. 2006; Weedon et al. 2006; Marsland and Nicol 2007;

Marsland and Nicol 2008).

The main channel was generally devoid of submergent species except for small patches on shallow bars and benches (Marsland et al. 2010). In contrast the fringing vegetation was dominated by dense stands of the Emergents Typha spp. Phragmites australis and Schoenoplectus validus, often with Eucalyptus camaldulensis and Acacia stenophylla overstorey. Salix spp. (willows) formed dense; almost monospecific stands in some areas especially between Mannum and Purnong (Marsland et al. 2010).

2.2. Lower Swamps (Mannum to Wellington)

Similar to the gorge section the aquatic and littoral plant communities between Mannum and Wellington between 2004 and 2007 were typical of areas with limited water level fluctuations (Walker 1985; Walker 1986; Walker et al. 1992; Walker and Thoms 1993; Walker et al. 1994;

Blanch et al. 1999b; Blanch et al. 2000) (Appendix 2b).

Wetlands in the Lower Swamps are generally shallower that those in the gorge section and generally do not have large beds of Submergent species (Appendix 2b) or areas of open water (with the exception of Reedy Creek and Rocky Gully, which were dominated by open water and floating species and Ruppia megacarpa and Potamogeton crispus respectively) (Holt et al. 2005; Nicol et al. 2006). Lower Swamps wetlands are generally dominated by extensive stands of emergent species such as Typha spp. and Phragmites australis with high abundances of agricultural weeds and pasture species such as Medicago spp., Trifolium spp., Lolium spp. and Melilotus spp. in the littoral zone (Holt et al. 2005; Nicol et al. 2006) (Appendix 2b). Nevertheless there are small areas of diverse Floodplain, Amphibious and Emergent herb, sedge and rush communities with similar species compositions to gorge wetlands (Holt et al. 2005; Nicol et al. 2006) (Appendix 2b). The over storey was generally Eucalyptus camaldulensis, Acacia stenophylla (open woodlands or scattered

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trees) or Muehlenbeckia florulenta (scattered shrubs or closed shrublands) and the majority of Eucalyptus camaldulensis trees were in either good or excellent condition (Holt et al. 2005; Nicol et al. 2006) (Appendix 2b).

Similar to the gorge section the main channel was generally devoid of Submergent species except for small patches on shallow bars and benches. The fringing vegetation between Mannum and Wellington is predominantly Salix spp. with small scattered patches of Phragmites australis and Typha spp. (Marsland et al. 2010).

2.3. Lower Lakes (Lakes Alexandrina and Albert and the Lower Finniss River and Currency Creek)

The vegetation in the Lower Lakes was also typical of systems with limted water level fluctuations (Walker 1985; Walker 1986; Walker et al. 1992; Walker and Thoms 1993; Walker et al. 1994; Blanch et al. 1999b; Blanch et al. 2000) (Appendix 2c); however, salinity (sensu King et al.

1990) and wave action (sensu Wilson and Keddy 1985; Foote and Kadlec 1988; Coops and Van der Velde 1996; Hudon et al. 2000; Doyle 2001; Hawes et al. 2003; Riis and Hawes 2003) were also important factors that determined the abundance and distribution of plants.

The open water areas of Lakes Alexandrina and Albert were generally devoid of plants probably due to wave action and depth (most areas that were shallow and could support submergent or amphibious species were subjected to wave action and there was insufficient light penetration in areas that are deeper than 1 m to support submergent and amphibious species). Submergent and amphibious species were generally restricted to fringing wetlands, sheltered bays, Goolwa Channel and the lower reaches of Currency Creek and the Finniss River. The areas with the greatest abundances of Submergent and Amphibious species were the wetlands and sheltered areas along the western shoreline of Lake Alexandrina and Goolwa Channel (Holt et al. 2005;

Nicol et al. 2006). For example, extensive beds of Vallisneria spiralis were present at Milang Shores, Dunns Lagoon, Clayton Bay and in the channels on Hindmarsh Island (Holt et al. 2005) and Myriophyllum spp. was abundant near the Hindmarsh Island bridge (J. Nicol pers. obs.), in Clayton Bay, Dunns Lagoon (Holt et al. 2005) and Hunters Creek (Nicol et al. 2006). The plant communities present in wetlands along the eastern shoreline of Lake Alexandrina and around the edges of Lake Albert suggested that salinity plays a role in structuring the community. Ruppia spp. and Lepilaena cylindrocarpa were the dominant Submergent species in wetlands along the eastern shoreline of Lake Alexandrina and around Lake Albert (Holt et al. 2005; Nicol et al.

2006).

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The fringing vegetation of the Lower Lakes was dominated by dense stands of Typha spp. and Phragmites australis, particularly the western shoreline of Lake Alexandrina, Goolwa Channel and lower reaches of Currency Creek and Finniss River (Seaman 2003). Nevertheless, there were areas of samphire vegetation (Sarcocornia quinqueflora, Suaeda australis, Juncus kraussii, Halosarcia pergranulata) and dense Muehlenbeckia florulenta shrublands predominantly around the edges of wetlands along the eastern shore of Lake Alexandrina, adjacent to the barrages and around Lake Albert (Seaman 2003; Holt et al. 2005; Nicol et al. 2006) (Appendix 2c).

Melaleuca halmaturorum is the dominant tree in the Lower Lakes and forms dense closed woodlands (Holliday 2004). Melaleuca halmaturorum woodlands are scattered around the edges of the Lower Lakes with the largest woodlands located at the mouth of Hunters Creek, on the northern shore of Hindmarsh Island, on Goat and Goose Islands near Clayton, in Salt Lagoon on the south-eastern shore of Lake Alexandrina and Kennedy Bay on the southern shore of Lake Albert. Age class information is only available for the stand at the mouth of Hunters Creek, which are predominantly older trees (>28 years) and there was no evidence of recruitment in the previous 10 years (all juveniles were planted by the local landcare group) (Nicol et al. 2006).

2.4. Murray Estuary (Goolwa to Tauwitchere)

The temporally variable salinity regime (low salinities during barrage outflows and marine salinities when the barrages are closed) that historically characterised the Murray Estuary (Geddes and Hall 1990) have not been present since the mid 1990s due to closure of the barrages and dredging of the Murray Mouth (Geddes 2005a; Geddes 2005b). The salinity in the Murray Estuary from 2004 to 2007 was marine for the most part with very little temporal variation (Brookes et al. 2009).

Historically, Ruppia megacarpa was the dominant submergent species in the Murray Estuary (and North Lagoon of the Coorong) because it is adapted to variable salinities ranging from fresh to 46‰ TDS (Brock 1982a; Brock 1982b). From the 1980s to the mid 1990s extensive beds of Ruppia megacarpa were present throughout the Murray Estuary (Geddes and Butler 1984; Geddes 1987; Edyvane et al. 1996). However, after the near closure of the Murray Mouth in 2001 the Murray Estuary was completely devoid of submergent species and has remained devoid of submergents to the present day, even after the controlled barrage releases in September-October 2004 and August 2005 (Geddes 2005a; Geddes 2005b; Nicol 2007). In addition, Nicol (2007) reported that there was no viable Ruppia megacarpa seed bank in the Murray Estuary. The

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population dynamics of Ruppia megacarpa in the Murray Estuary from the mid 1970s to 2005 are summarised in Nicol (2005)

There is little information regarding the littoral vegetation of the Murray Estuary, there are extensive areas of sandy beaches and samphire shrublands (Halosarcia pergranulata, Suaeda australis, Sarcocornia quinqueflora) (Phillips and Muller 2006; Stewart et al. 2009) (Appendix 2d). In addition there are localised areas of emergent freshwater species (Typha spp., Phragmites australis) in areas where fresh groundwater discharges along the shoreline (Phillips and Muller 2006) (Appendix 2d).

2.5. Coorong Lagoons

A salinity gradient (salinity increases south-easterly along the length of the Coorong), ranging from marine close to Tauwitchere Barrage to hypermarine throughout most of the North Lagoon and all of the South Lagoon existed from 2004 to 2007. The increasing salinities were due lack of freshwater inflows (Figure 4) and inputs of salt from the Southern Ocean and evapoconcentration along the length of the Coorong lagoons in areas where tidal flushing is absent (Webster 2005b).

Historically Ruppia megacarpa was the dominant submergent species in the North Lagoon and Ruppia tuberosa in the South Lagoon (Womersley 1975; Geddes and Brock 1977; Geddes and Butler 1984; Geddes 1987; Geddes and Hall 1990). Ruppia megacarpa has not been observed in the North Lagoon since the early 1990s (Geddes and Hall 1990; Edyvane et al. 1996). Ruppia tuberosa has a higher salinity tolerance than Ruppia megacarpa and was common in the South Lagoon until the 2000s (Womersley 1975; Geddes and Brock 1977; Geddes and Butler 1984;

Geddes 1987; Geddes and Hall 1990; Leary 1993; Paton 2000; Paton 2001; Paton et al. 2001;

Nicol 2005; Phillips and Muller 2006). Since the early 2000s the abundance of Ruppia tuberosa has declined and by 2007 was absent from the southern half of the South Lagoon and had began to colonise the southern end of the North Lagoon (Paton 2005a; Paton 2005b; Paton and Rogers 2008; Brookes et al. 2009). The population dynamics of Ruppia megacarpa and Ruppia tuberosa in the North and South Lagoons of the Coorong from the mid 1970s to 2005 are summarised in Nicol (2005).

Similar to the Murray Estuary there is little information regarding the littoral vegetation of the Coorong; however, there are extensive areas of sandy beaches and samphire shrublands (Halosarcia pergranulata, Suaeda australis, Sarcocornia quinqueflora) (Phillips and Muller 2006; Stewart et al. 2009) (Appendix 2e). In addition, there are localised areas of emergent freshwater species

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(Typha spp., Phragmites australis) where fresh groundwater discharges along the shoreline (Phillips and Muller 2006) (Appendix 2e).

3. Current Ecological Condition (post 2007)

Since 2007 flows over Lock 1 have not been sufficient to maintain pool level upstream of the barrages and water levels have been steadily falling to unprecedented lows (Figure 3). This has resulted in exposure and desiccation of large areas of lakebed, all of the fringing freshwater wetlands in the Lower Lakes, large areas of riverbank and all of the formerly permanent freshwater wetlands between Wellington and Lock 1. Exposure and subsequent oxidization of sediments that have not been exposed, in some cases, for thousands of years have resulted in the development of extensive areas of acid sulfate soils between the barrages and Lock 1 (Merry et al.

2003; Lamontagne et al. 2004; Fitzpatrick et al. 2009a; Fitzpatrick et al. 2009b). In attempts to prevent the formation or mitigate acid sulfate soils; a bank was constructed at the Narrung Narrows and a regulator constructed at Clayton (Figure 1). Water was pumped from Lake Alexandrina into Lake Albert at Narrung and the Goolwa Channel at Clayton to maintain higher water levels in Lake Albert and Goolwa Channel. In addition, flows from the Finniss River and Tookayerta and Currency Creeks will be impounded by the Clayton regulator and prevented from flowing into Lake Alexandrina to maintain water levels after pumping has ceased. The aforementioned structures have disconnected Lake Albert and Goolwa Channel from Lake Alexandrina and water levels are now held at higher levels in the aforementioned waterbodies.

The absence of flows over the barrages (Figure 4) and continued dredging to keep the Murray Mouth open has resulted in almost constant marine salinities in the Murray Estuary and further salt inputs into the North and South Lagoons of the Coorong (Brookes et al. 2009).

3.1. Gorge (Lock 1 to Mannum)

Nicol (2010) undertook understorey vegetation and Eucalyptus camaldulensis condition surveys in six gorge wetlands between Mannum and Lock 1 (Mannum Swamps, Lake Carlet, Caurnamont, Wongulla Lagoon, Devon Downs North and Noonawirra) in spring 2008 and autumn 2009.

The current condition of vegetation in the gorge section was determined by comparing information from Nicol (2010) and the River Murray Wetlands baseline surveys (Holt et al. 2005;

Nicol et al. 2006; Weedon et al. 2006; Marsland and Nicol 2007; Marsland and Nicol 2008).

The major change in the plant community since 2007 between Lock 1 and Mannum is the complete disappearance of submergent and floating species from wetlands due to desiccation of floodplain wetlands. Extensive beds of Vallisneria spiralis, Potamogeton crispus, Potamogeton

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tricarinatus, Azolla filiculoides and the amphibious fluctuation responder-plastic species Myriophyllum verrucosum that were present in wetlands throughout the gorge section (Holt et al. 2005; Nicol et al.

2006; Weedon et al. 2006; Marsland and Nicol 2007; Marsland and Nicol 2008) (Appendix 2a) have completely disappeared and there has been no observed colonisation of these species (except Azolla filiculoides) in the main channel (Table 3) (Marsland et al. 2010; Nicol 2010). In addition to the loss of submergents, the amphibious and floodplain herb and grass communities that were present in the littoral zone (Holt et al. 2005; Nicol et al. 2006; Weedon et al. 2006;

Marsland and Nicol 2007; Marsland and Nicol 2008), were not observed by Nicol (2010) in spring 2008 or autumn 2009 (Table 3).

The large stands of Phragmites australis that were present prior to 2007 along the banks of the River Murray and around the edges of wetlands (Holt et al. 2005; Nicol et al. 2006; Weedon et al.

2006; Marsland and Nicol 2007; Marsland and Nicol 2008; Marsland et al. 2010) (Appendix 2a) still remained and appeared to be in good condition and growing (Marsland et al. 2010; Nicol 2010). The Typha spp. and Schoenoplectus validus stands, whilst live plants were present, showed reduced extent and appeared to be in poor condition (Marsland et al. 2010; Nicol 2010).

Terrestrial dry species such as Atriplex spp., Enchylaena tomentosa, Teucrium racemosum and Einadia nutans, which were historically only present on the floodplain above historical pool level (Holt et al. 2005; Nicol et al. 2006; Weedon et al 2006; Marsland and Nicol 2007; Marsland and Nicol 2008) had colonised the dry wetland beds (Nicol 2010). However, large numbers of healthy Eucalyptus camaldulensis saplings were also present on the dry wetland bed that had recruited as a result of low water levels (Nicol 2010).

Eucalyptus camaldulensis condition, despite the low water levels, was predominantly good to excellent in the surveyed wetlands prior to 2007 (Weedon et al. 2006; Marsland and Nicol 2007;

Marsland and Nicol 2008) and in 2008-09; however, canopy density was generally lower in autumn 2009 than in spring 2008 (Nicol 2010). It is unknown whether this result was a seasonal pattern or the early stages of a decline in condition (Nicol 2010).