Dealing with salinity in Wheatbelt Valleys - Department of Water

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SALINITY IMPACTS ON BIODIVERSITY Wetland Communities Terrestrial Communities Flora Keighery, Halse and McKenzie Flora The impacts are greatest low in the landscape in and Of the 4,000 species present in the Wheatbelt, over 1,500 occur low in the landscape, in riverine valleys, freshwater or primarily saline lands. Of these taxa an estimated 450 are endemic to the Wheatbelt. These taxa are in danger of extinction over the next 100 years as a consequence of rising saline groundwaters. Several hundred other species found only in lowland woodland, Mallee and Melaleuca shrubland sites, will be under threat in the longer term. Another 400-500 lowland taxa are centred on the Wheatbelt although not confined to it. These taxa are also under immediate threat of major genetic erosion from salinisation and hydrological changes. Areas affected by secondary salinisation show significant declines in vascular plant biodiversity and loss of structural diversity. Rich complex communities are replaced by a few succulent shrubs and weeds. Outside of the Wheatbelt hydrological changes threaten the diverse floras of naturally saline landscapes and areas of species rich heathland and ephemeral wetlands of the northern sandplains and Swan Coastal Plain. The karst communities, both subterranean and surface heaths, of the northern Swan Coastal Plain are threatened by flooding and perhaps increased impact of diseases from Phytophthora species. Fauna Approximately 25% (31 of 125 species) of its small ground-dwelling vertebrates (mammals, reptiles and frogs) have distributions centred on the Wheatbelt or are endemic to it. At least 40% (210 of 500+ species) of the region's terrestrial invertebrates have distributions centred on the Wheatbelt or are endemic to it. A significant decline in the biodiversity of terrestrial invertebrates is apparent at secondarily saline quadrats (even partially affected), which have an average of 30% fewer species than their nonsalinised counterparts. This loss is actually higher as localised specialists are replaced by “weedy” around all wetland types. However as the terrestrial and wetland plant communities intergrade specific comment is made under Flora in the section above. Fauna Birds Of the 61 more common waterbird species in the south-west, only 16 prefer strongly saline (more than 20,000 mg/L) or hypersaline (more than 50,000 mg/L) conditions. Data from a 1981-85 survey of the south-west showed that an average of five waterbird species used hypersaline wetlands, compared with 20 in saline wetlands and 40 in fresh wetlands containing live trees and shrubs. Death of shrubs and trees in many wheatbelt wetlands due to salinity has caused a 50% decrease in the number of waterbird species using them. If the trend of increasing salinity continues, only 16 species, plus three or four species that use freshwater dams, will persist in the Wheatbelt out of an original waterbird fauna of more than 60 species. Invertebrates In a preliminary analysis of the first 700 species recorded, 253 species (45%) were restricted to fresh water with salinity less than 3,000 mg/L. However, 35 of the species occur on granite rock outcrops where salinity is unlikely to occur, leaving 218 species (39% of the fauna) that are vulnerable to increasing salinity. If all wetlands in the Wheatbelt became saline (more than 10,000 mg/L), most of these 218 species will disappear from the Wheatbelt, despite the fauna being more saline tolerant than in eastern Australia. Species richness declines with salinity and the average number of invertebrate species present in fresh wetlands is about 50, in wetlands with salinity 20,000 mg/L about 25, in wetlands with salinity 50,000 mg/L about 12 and in wetlands with salinity greater than 100,000 mg/L about four. As a rule of thumb, doubling salinity halves the number of aquatic invertebrate species. generalist species. Caveats that must be attached to the above statements at this stage of the work are that probably not all wetlands will become saline, some species will persist in dams, and many – 5 –
Keighery, Halse and McKenzie species have ranges that extend outside the Wheatbelt. Summary The areas most immediately threatened by salinisation are the valley floors of the Wheatbelt. These areas affected by secondary salination show major declines in vascular plant and animal biodiversity. Rich complex communities are replaced by a few succulents and weeds. Similarly, major declines in diversity occur in animal communities where specialists are lost and/or replaced by generalist species. Although dryland salinity is an Australian wide problem, information about the impact of hydrological change on biodiversity in Western Australia is more substantial than that of eastern Australia. For example, the Murray Darling Commission report on Salinity (Murray-Darling Basin Ministerial Council 1999) noted: “No assessment has been made of the impact of dryland salinity on the biodiversity of the Murray- Darling Basin.” The challenge is what are we going to do with this new information? How to integrate these data into managing this changing landscape. SALINITY IMPACTS ON WHEATBELT VALLEYS We have already seen that the valley systems of the Wheatbelt contain a large component of the communities and species of the region threatened by salinisation. Since these areas are low in the landscape this is not surprising. In the final section on impacts we will consider the plant communities under threat from salinisation. These communities are the most readily understood and visible “management unit.” They are the units for which all managers of lands can observe the visible signs of salinisation and can undertake intervention activities to maintain and monitor the results. Non Saline Valley Floor Communities A considerable diversity of tall woodlands of Wandoo (E. wandoo), Inland Wandoo (E. capillosa), Salmon Gum (E. salmonophloia), Red Morrell (E. longicornis), Black Morrell (E. melanoxylon) and Gimlet (E. salubris) once dominated the better drained heavy soils of the valley floors and slopes throughout the Wheatbelt. These woodlands generally extend into – 6 – the adjacent pastoral regions. However, we know that the woodland understory varies across their range with rainfall and soil. These woodlands are now greatly fragmented but remain evocative of the area and are of considerable significance to our local and national heritage. The Wheatbelt will lose much of its local landscape character if they are lost. In the south-east Wheatbelt there are woodlands of different composition, especially by dominant species (for example, Eucalyptus ovularis, E. myriadena and E. flocktoniae). In this area variable Mallee communities (Eucalyptus platypus, E. celastroides, E. calycogona, E. cooperana, E. forrestiana and E. kessellii) largely replace these woodlands on clays and calcareous clays and are being impacted by rising saline groundwaters. There are also a number of possibly naturally rare woodlands, such as Lowland Brown Mallet (E. astringens) and Black Wandoo (E. melanophitra) that are also at risk. Freshwater wetlands: (Creeks, Rivers, Lakes, Ephemeral wetlands) Rivers in the incised western Wheatbelt are fringed by Flooded Gum (Eucalyptus rudis) communities and these are already greatly impacted by salinisation. Inland of these rivers, Flat Topped Yate woodlands (E. occidentalis) and its related Mallee form (E. sporadica) are dominant around small freshwater swamps and are also being impacted by salinisation and more frequent flooding. The communities of lakes and ephemeral wetlands of the Wheatbelt contain an enormous diversity of plant communities depending on soil type and inundation, ranging from woodlands of Melaleuca species, through shrublands, heaths and sedgelands to aquatic herblands and are all under great threat. As an example Gibson and Keighery (2000) documented over 25 distinct wetland plant communities in the Muir – Unicup Recovery Catchment. Rising groundwaters and drought are also causing stress of several of the major trees species of the western Wheatbelt such as Flooded Gum, Yate and Wandoo leading to increased insect and fungal attack. Naturally Saline Habitats These areas contain a diversity of Mallet (Eucalyptus spathulata), Mallee (including the oil Mallees, E. suggrandis and E. vergrandis), Woodland (Casuarina obesa, Eucalyptus salicola, E. sargentii and
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Foreword Dealing with Salinity in W
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1Day one: Monday 30th July. Field t
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Papers Dealing with Salinity in Whe
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Ali and Coles biggest challenges fa
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Ali and Coles erosion, maintenance
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Ali and Coles expected under these
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Ali and Coles Coles, N.A. & Ali, M.
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Commander, Schoknecht, Verboom and
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Page 131 and 132: Pannell Pannell, D.J. (2001). Dryla
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Porter, Bartle and Cooper support i
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Porter, Bartle and Cooper that is a
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CASE STUDY - TOOLIBIN LAKE AND CATC
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• The distribution, storage and m
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Secondly, there is a set of practic
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within three categories: relationsh
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CONCLUSIONS Actions to protect and
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FIELD TOUR LOCATIONS FIELD TOUR NOT
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COLES FARM “Avon River Basin Over
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Conference Outcomes Dealing with Sa
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with Salinity in Wheatbelt Valleys:
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with Salinity in Wheatbelt Valleys
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Photo Gallery 2 Dealing with Salini
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APPENDIX 1 BACKGROUND HYDROLOGY AND
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WHEATBELT HYDROLOGY Flow in the Yil
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Flow (ML) STREAM SALINITY Salt Rive
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APPENDIX 2 WATER MANAGEMENT OPTIONS
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APPENDIX 3 MANAGING WATER AND SALIN
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SUMMARY- TIMELINE OF RECENT SIGNIFI
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RECENT HISTORY OF WATER AND SALINIT
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Figure 1. Hydrological cross-sectio
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Depth (m) 316 315 314 313 312 311 M
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FURTHER INVESTIGATIONS AND MANAGEME
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Dealing with salinity in Wheatbelt Valleys - Department of Water

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