Apparent dryland salinity on the uplands of southeastern Australia

510 Pages·2016·19.64 MB·English

by  Glen Bann

Apparent dryland salinity on the uplands
of southeastern Australia:
quantification of biotic and abiotic
indicators, causes, mechanisms,
processes and effects

by

Glen Bann

Submitted in fulfilment of the requirements for the degree of
Doctor of Philosophy
of the Australian National University
December 2014

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Candidate's Declaration

This thesis contains no material which has been accepted for the award of any other degree or diploma
in any university. To the best of the author’s knowledge, it contains no material previously published or
written by another person, except where due reference is made in the text.

Glen R. Bann Date:

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ACKNOWLEDGEMENTS and THANK-YOUS
Due to the multidisciplinary nature of the research, many people assisted...
Richard Arculus for supporting my scholarship application and continued encouragement, David Hilhorst
for guided tours around the dryland salinity sites near Boorowa; Brian Cumberland for initial site
suggestions and ideas; Kevin Baker and Peter Brown for providing information and ongoing access to my
sites; Don Stazic for attaining difficult to get government reports; Dean (Carrot) Wheeler and Ken
England for expert training in fox detection pre thesis times; David Tongway for initial soily discussions, a
training day in the field for his LFA procedure and ideas as to how to construct the respirometers; Nico
Marcar for initial discussions re salinity and plants; Theo Evans for termite discussions and insect/spider
identification; Brian Tunstall for a number of initial useful discussions that helped congeal observations
and ongoing advice and encouragement; Geoff Baker for worm identification and ecology discussions;
Ann Cowling, Emlyn Williams and Colin Matheson for statistical analyses assistance; Rex Wagner for a
couple of interesting and useful discussions on the bigger picture; Nik Henry and John Spring for the loan
of the EM38 and EM31 respectively; Rachel Nanson for editing many early papers and help in the field;
Gerald Nanson for useful discussions and encouragement; Bill Semple for editing early papers and plant
identification assistance; John (and Susan) Rowntree for assistance, support and encouragement; Mauro
Davanzo for cutting up the hundreds of log discs, on two occasions; ACT Forests and ACT Urban Services
for providing the pine and red gum logs for the log discs; Adam Smiarowski and Jim Macnae for
producing the EM inversion analyses; Richard Hobbs for an early discussion; John Williams for attending
an exclusive extended seminar and providing useful feedback; Marcus Hardie for providing an
interesting route of Tasmanian salinity sites; Clive Malcolm for providing an enlightening salinity route
through the WA Wheatbelt; Willem Vervoort for a number of useful discussions regarding soils and the
EM; Clive Hilliker for producing countless conference posters over the years, many at the last minute;
Sarah O’Callaghan for efficient attention to equipment and administration requests; Lorna Fitzsimmons
for the soil and water analyses; Cathy Grey and Amy Chen for administration assistance, Karl Nissen and
Steve Leahy for prompt IT assistance during IT panic attacks; Steve Dovers for a topup scholarship and
editing some papers, Barbara Triggs for scat identification, Dad and brother Chris for their support; my
first supervisor, John Field, especially for attaining topup funds and keeping my office for the duration,
second supervisor, Ian White, and to assist with thesis restructuring and completion, final supervisor,
David Freudenberger.
And last but not least, my gorgeous and ever so tolerant wife, Kiki - and not so tolerant but just as
loveable, son Banjo “Have you finished your fesis yet Dad? Can we please go and play now?”
I would also like to thank the CRC Landscape Environments and Mineral Exploration for stipend and
working funds, the Southern Tablelands Farm Forestry Network for two top-up scholarships, and the
Fenner School of Environment and Society, for the extended use of my office and funds.

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Apparent dryland salinity on the uplands of southeastern Australia: quantification of
biotic and abiotic indicators, causes, mechanisms, processes and effects.
Secondary dryland salinity in Australia has been a major environmental concern for a number of
decades, yet aspects remain controversial. These include the processes which induce salinised
soils, the environmental impacts of salinity, and the way in which it is mapped and managed.
Dryland salinity has been almost universally attributed to rising saline groundwater caused by
excess water accumulation in the landscape following European settlement and tree clearing.
However, there is a body of evidence that instead suggests increased soil salinisation in SE
Australia is attributable to localized surface water problems associated with soil and vegetation
degradation.
The ‘Rising Groundwater Model’ has been widely accepted as the paradigm for understanding,
mapping and monitoring dryland salinity. However, little quantitative research has been
undertaken to understand the mechanisms and processes that cause secondary dryland salinity
in the uplands of south eastern Australia. Further, there is little research that demonstrates
adverse impacts of secondary salinity on terrestrial endemic biota even though it is listed as a
threatening process to biodiversity. This research tested the applicability of an alternative
‘Surface Water Model’ to explain outbreaks of salinity or soil surface degradation in this region.
This research investigated the effects of the joint phenomenon of soil and vegetation
degradation and elevated salinity levels on soil biotic and abiotic parameters. Field research
was conducted at ten box/gum grassy woodland sites in the agricultural zone of the Southern
Tablelands of NSW. A holistic suite of metrics, including soil physical, chemical, hydrological
and biological attributes, were assessed in the field and laboratory; geophysical surveys
(EM31/EM38) and various fauna and flora surveys were performed.
Results indicated that degraded soil surfaces were generally small in area and localized. These
surfaces had highly variable soil EC levels (often very low), and were associated with in situ
synergistic factors related to in situ soil and vegetation degradation. Some surfaces had
accumulated NaCl, but many also had other, both toxic and low cation and anion levels
particularly reduced levels of Ca, Fe, N, SOM and SOC. Extreme pH levels and other soil
physical, chemical and biological impacts were also common. It is concluded that elevated soil
salinity levels are a symptom of soil and vegetation degradation, not the cause. It was found that
the predominant water movement in these landscapes occurred as overland runoff and surficial
lateral interflow above the clay-dominant B horizon. There was no biological, pedological,
geophysical or hydrological evidence of groundwater being a major factor for elevated soil
surface salinity levels.
Evidence suggests that these degraded ecosystems are relatively stable but urgently require
nutrient/SOM input. Many endemic fauna and flora species flourish at highly degraded and
salinised sites; tolerating elevated and fluctuating salinity levels, at all life cycle stages, which
may effectively increase the gamma biodiversity in these grassy woodlands. No evidence was
found to suggest that biodiversity is suffering from rising saline groundwater or elevated soil
salinity levels per se, or that elevated salinity levels favour exotic species. It is therefore
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problematical to directly link soil salinity per se with ecological stress, as many other synergistic
factors are involved and are more significant for degraded soils.
Management decisions based on reducing the soil surface evaporation potential on site is the
most coherent approach. Management activities should focus on stock grazing exclusion, soil
amelioration and revegetation activities using endemic species, rather than focusing on excess
deep landscape water management with hybrids and exotic plants. The present use of AEM for
mapping dryland salinity in upland environments is therefore questionable.

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THESIS CONTENTS

CHAPTER 1. INTRODUCTION 1.

1:1 Overview: Dryland salinity; causes and consequent loss of biodiversity
1.1.1 Secondary dryland salinity in Australia
1.1.2 Dryland salinity and terrestrial biodiversity
1.2 Thesis focus
1:3 Problems and paradigms
1:4 Thesis Questions
1:5 Research Aims and Hypotheses
1:6 Research Outcomes and Implications
1.7 Research steps
1.8 Thesis structure

CHAPTER 2. LITERATURE REVIEW 9.
2.1. Problem definition: Secondary soil salinity in Australia
2.2. History and sources of dryland salinity in Australia
2.2.1. Salt origin
2.2.2. Primary and secondary salinity
2.3. Causes of dryland salinity in Australia
2.3.1. Model 1: The ‘Rising Groundwater Model’
2.3.2. Model 2: ‘Transient Salinity’ or the ‘Surface Water Model’
2.3.4. The Groundwater Associated Salinity (GAS) and Non-groundwater Associated
Salinity (NAS) models.
2.4. Dryland salinity and geology
2.5. Groundwater Flow Systems
2.6. Saline and Sodic soils
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2.7. Thesis questions and hypotheses
2.8. Dryland salinity and biodiversity
2.8.1. Terrestrial biodiversity
2.8.2. Implications and problems identified
2.8.2. Dryland salinity, degradation and biota.
2.8.3. Salinity and plants
2.9. Confounding factors to salinity impacts
2.9.1. Drought and climate
2.9.2. Dieback
2.9.3. Stock grazing and salinity
2.10. Ecosystem functioning
2.11. Thesis questions and hypotheses
2.12. Current management practices
2.13. Thesis questions and hypotheses
2.14. Summary

CHAPTER 3. STUDY REGION and RESEARCH SITES 59.
3.1. Study area
3.1.1. Regional geology
3.1.2. Soils
3.1.3. Salinity on the Southern Tablelands
3.1.4. Climate
3.1.5. Yellow Box/Red Gum Grassy Woodlands
3.1.6. Travelling Stock Reserves
3.1.7. Crown Land, Nature Parks and cemeteries
3.1.8. Private Land
3.2. Sites
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3.2.1. Site selection criteria
3.2.2. Site locations
3.1.3. Catchments
3.2.4. Site geology
3.2.5. Scalds

CHAPTER 4. METHODS 79.
4.1 Sampling design and data collection
4.2 Transects
4.3 Sampling within transects
4.4 Quantitative and qualitative indicators
4.5 Methods summarised
4.6 Data analyses
4.7 Methodology and results presentation
4.8 LFA Patch Type introduction

CHAPTER 5: ELECTRICAL CONDUCTIVITY, pH, CATIONS & ANIONS 90.
5.1. Introduction.
5.2. Electrical Conductivity Measurements
5.2.1. EC methodology
5.2.2. EC Results
5.3. EC and Patch Type
5.3.1. EC and Patch Type Results
5.4. EC Vertical variation
5.5. EC Temporal variation
5.6. EC association with degradation:
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5.7. Scalds
5.8. Soil pH
5.8.1. Methodology
5.8.2. Results
5.9. pH & EC
5.10. pH & Patch Type
5.11. Association of pH with degradation
5.12. Hydrochloric acid and pH
5.13. Cations and Anions
5.13.1. Soil subsample method
5.13.2. Cation Results
5.13.3. EC and cation results
5.13.4. Patch Type and cation results
5.13.5. Anion results
5.13.6. EC and Anions
5.13.7. Anions and Patch Type
5.13.8. Correlations of pH with the soil subsamples
5.13.9. Summary: Soil cations and anions
5.14. Discussion pH
5.15. CEC, ESP and SAR
5.16.1. Introduction and methodologies
5.16.2. CEC, ESP and SAR results
5.16. Summary

CHAPTER 6. ELECTROMAGNETIC INDUCTION 140.
6.1. Introduction
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6.2. Electromagnetic Induction (EM)
6.2.1. Methodology
6.3. Results
6.3.1. Apparent electrical conductivity (ECa)
6.3.2. Association between EC and ECa
(1:5)
6.3.3. ECa and Patch Type
6.3.4. Associations with degradation
6.4. EM depth weighted ratios
6.4.1. Depth weighted ratio results
6.4.2. Differences between scalds and non-scalds
6.5. Discussion
6.5.1. EM Depth Ratios
6.5.2. Electromagnetic Induction
6.6. Summary

CHAPTER 7: LANDSCAPE HYDROLOGY 175.
7.1. Landscape Hydrology
7.1.1. Surface water
7.1.2. Infiltration (sorptivity)
7.1.3. Soil Moisture
7.1.4. Subsurface water
7.2. Methods
7.2.1. Surface water
7.2.2. Infiltration
7.2.3. Soil Moisture
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