This report describes in detail the current field method employed to identify, assess and
map the extents of dryland salinity in Victoria.
Salinity has long been recognised as a feature of the Victorian landscape. Where
hydrological balances have or had been maintained by retention of deep-rooted vegetation
and natural water flow into sinks such as salt lakes continued unchanged, the distribution
of salt in the landscape did not change significantly; apart from seasonal ebbs and flows.
However, a significant increase in soil salinity levels (thought to result from changes in land
use following European settlement), became evident in the 1940s. By the 1950s soil salinity
was acknowledged as a major environmental problem that had significant impacts upon
both natural and built assets. Through the 1970s and 1980s above average rainfall led to a
significant rise in groundwater levels and an increase in the extent of salt affected soil.
In order to manage an environmental threat such as soil salinity, it is necessary to
understand the extent and severity of the problem, and then provide ongoing feedback to
intervention programs by monitoring change over time. Early efforts to identify the size of
the problem and combat it were piecemeal and fragmented and it was not until the late
1980s that a nationally coordinated approach led to the development of a set of criteria for
identifying and assessing dryland soil salinity in Victoria. A Victorian field guide (Spotting
Soil Salinity) was also produced to assist in mapping the extent of the problem and since the
late 1980s almost all soil salinity mapping in Victoria has used both these standards and the
field guide. The mapping standards were formally documented in 1996 (Allen 1996).
Changes in community values and technology have altered the way salinity is viewed and
the way it is mapped since the field mapping method was last documented in 1996. Both land
managers and the broader community have come to take a broader view of salinity, and as
well as viewing salinity as a threat to agricultural productivity and built infrastructure, the
value of naturally saline areas for the unique ecosystems they support is now recognised.
The advent of Global Positioning System (GPS) technology has revolutionised the way field
data can be mapped. GPS technology is now commonly used for a variety of applications,
and provides an integral tool for further dryland salinity mapping projects in Victoria. In
addition, there have been advances in the way sites are attributed to take better advantage
of the GIS environment in which the data is stored.
Field data collected using the method described in this report is added to the soil salinity
layer in the Corporate Spatial Data Library (CSDL). This dataset forms the primary source for
almost all dryland salinity monitoring and reporting in Victoria. As such it represents a
valuable public resource as land salinity has been accepted as one of the Matters for Targets
indicators within the National Framework for Natural Resource Management Standards.
Additionally, the extent and severity of land salinity has been listed by the Victorian
government as one of the Victorian Catchment indicators. Its status will be reported in a
statewide Catchment Condition Report in 2007 and a State of Environment Report for Victoria
and a second National Land and Water Audit are both due in 2008. Method for field assessme nt of dry land salinity in Victoria using
Dryland salinity is a major soil and water problem in Victoria and refers to the
build-up of salt in the soil and groundwater in non-irrigated areas. Early mapping
targeted secondary (human induced) salinity, but over time a number of primary
(natural) sites have been mapped as their environmental value was recognised. To date,
over 260 000 ha of land has been mapped and this estimate includes both primary and
secondary salinity located across non-irrigated areas of Victoria and impacts upon
both natural and built assets. Victorian government estimates put the direct cost of
salinity in irrigated and dryland areas at $50 million annually and the Victorian
Auditor General calculated that $1.8 billion of private and public funds had been spent on
salinity management over the period 1990-2001 (Auditor General Victoria 2001).
In order to manage an environmental threat such as soil salinity, it is first necessary
to understand the extent and severity of the problem, and then provide ongoing
feedback to intervention programs by monitoring change over time. In addition, the
Victorian government is committed to a number of salinity monitoring requirements,
particularly in the Murray Darling Basin, where end of valley targets (for salt-loads)
have been set for northern catchments. Land salinity has been accepted as one of the
Matters for Targets indicators within the National Framework for Natural Resource
Management Standards. The extent and severity of land salinity has been listed by the
Victorian government as one of the Victorian Catchment indicators. Its status will be
reported in a statewide Catchment Condition Report in 2007. A State of Environment
Report for Victoria and a second National Land and Water Audit are both due in 2008
To provide feedback to landholders, land managers and federal and state
government funding bodies, all dryland salinity mapping conducted across Victoria
was compiled onto a single database in the early 1990s. This database records the
extent of all recorded salt affected sites in Victoria at a scale of 1:25 000 (Allan 1994). A
number of other attributes, including severity, have been recorded at many of the sites.
This database is currently held on the Corporate Spatial Data Library (CSDL) in a
Geographic Information System (GIS) environment and is managed by the Department
of Primary Industries (DPI) for the Department of Sustainability and Environment
(DSE). It forms the primary source for almost all dryland salinity monitoring and
reporting in Victoria (Figure 1). The extent and severity of soil salinity in irrigated
areas has primarily been mapped via ground-based electromagnetic (EM38) surveys 1
rather than using the method described in this report which is based on an
assessment of vegetation and other physical indicators . This information is held on
a separate database.
1The EM38 surveys were conducted as part of a whole farm planning exercise for farmers in the irrigation
district where the high value of the land and the farming enterprises justified the extra time and cost. 1
This report details the current field method employed to identify and assess
dryland salinity in Victoria. It represents an updated version of the method
documented by Allan (1996) and is heavily based on that text. There are a number
of significant differences between the current
method and that described by Allan (1996), primarily in the attributes recorded
for each site and the technology and method used to map the spatial extents of the
saline areas. However, much of the original approach remains and to save frequent
repetition, the 1996 report is not always cited. Nevertheless the authors would like to
acknowledge a debt to previous contributors and their documentation.
1.1 History of dryland salinity assessment
Salinity has long been recognised as a feature of the Victorian landscape.
Robertson (1898) referred to the appearance of saline springs on the Dundas
Tablelands in Western Victoria in 1853
shortly after European settlement of the district commenced. While hydrological
balances were maintained by retention of deep-rooted vegetation and natural water
flow into sinks such as salt lakes continued unchanged, the distribution of salt in the
landscape was unlikely to change significantly over long periods-apart from
seasonal ebbs and flows. However, a significant increase in soil salinity levels
(thought to result from changes in land use following European settlement), became
evident in the 1940s. The 1950s saw dryland salinity acknowledged as a major
environmental problem in Victoria and government agencies began to assess the
size of the problem and monitor its progress. Cope(1958), estimated that over 5000 ha of land was affected by dryland salinity. Through the 1970s and 1980s above average
rainfall led to a significant rise in groundwater levels and an increase in the extent of
salt affected soil. By the late 1970s, the Soil Conservation Authority (1978) estimated
that 85 000 ha was affected by dryland salinity.
In the early 1900s it was recognised that certain plants were useful indicators for
identifying both saline and alkaline soils. A body of research based on the
interaction between vegetation and the chemical and physical characteristics of soil
was developed in the USA (United States Salinity Laboratory Staff 1954). The first
salinity surveys in Victoria were confined to specific regions and assessment criteria
varied from region to region. Over time it was recognised that a piecemeal or
uncoordinated approach to identifying the extent and severity of soil salinity would
not be in the best interests of the community. As a consequence, a project was funded
under the National Soil Conservation Project to develop a standard method for
identifying, assessing and recording dryland salinity in Victoria (Matters 1987).
Following this initiative, a statewide project was established in 1989 to compile all
existing data on secondary discharge sites and to coordinate the collection of further
data by Department of Conservation and Natural Resource (CNR) regional staff
(Allan 1994). In addition, a strategy involving a network of monitoring sites was
designed to identify how soil salinity changed over time. This work is continued
through the Salinity Discharge Monitoring and Salinity GIS Project funded by the
Department of Sustainability and Environment (DSE) and undertaken by the
Department of Primary Industries (DPI), Bendigo (Clark 2005).
Much of the field data was collected in the late 1980s and early 1990s and a database
of dryland salinity in Victoria was created which recorded every mapped discharge
site in the state (Allan 1994). With the advent of Geographic Information Systems
(GIS), the soil salinity database was loaded onto the CSDL in the early 1990s. This
database has been maintained on the CSDL since that time by DPI on behalf of DSE.
The last coordinated, regional mapping programs were
completed in North East Victoria in 1998 and the Glenelg Hopkins region in 1999.
The extent of soil salinity in the Mallee has only recently been mapped using a
combination of spatial modelling based on ortho-rectified airphotos from autumn 2003,
Ecological Vegetation Condition (EVC) mapping, a digital elevation model (DEM) and
limited ground truthing. This survey identified areas of moderate to extreme levels of
soil salinity typically characterized by halophytic plant communities. It was not able to
identify slightly saline areas or areas where salinity is transient (Grinter and Mock
Mapping since the late 1990s has been ad hoc and limited in extent, although some
small areas are being remapped to monitor change over time, notably in the North East
and Corangamite CMA catchments. Almost a decade of below average rainfall has seen a
general fall in watertables across Victoria and many saline areas shrank in size,
although it is becoming clear that there may not always be a direct correlation
between a change in the depth to watertable and change in the extent and severity of
soil salinity at a site.
Allan (1994) identified two types of dryland salinity, primary and secondary. Both of
which are mapped using the same salinity severity class criteria:
Primary (or natural) salinity, which existed long before European settlement
and is held to be the result of natural environmental processes.
Secondary (or induced) salinity, which has occurred since European settlement and is
considered to be the result of changes in land and water management practices.
When the salinity monitoring project commenced, the focus was on identifying
secondary saline sites as they were considered as areas of productivity loss that
were more amenable to reclamation. At such sites efforts were frequently made to
rehabilitate the site or at least stop it degrading further and regain some productivity
for the landholder. With productivity as the focus, it appeared there was little to be
gained from investing in salinity treatments in areas that were saline prior to
European settlement (Allen 2006) and primary sites tended to be ignored. However, in
recent years the community’s understanding of salinity has become more
sophisticated and primary saline sites have been recognised as natural assets from a
biodiversity perspective and the salinity program aims to identify primary saline sites
to support their management and preservation.
2 Primary salinity
Natural or primary salinity existed for thousands of years in many parts of
Victoria before European settlement and is considered to be a natural feature of the
landscape. Many saline areas were permanently or seasonally inundated, or frequently
became waterlogged. Over geological time periods, patterns of waterlogging,
inundation and the salinity of soil, ground and surface waters has changed with
climate (Allen 2006). Secondary salinity (as distinct from primary salinity), by
definition is a direct consequence of post-European settlement activity.
Primary salinity sites tend to be populated by a highly diverse and stable
community of salt-tolerant vegetation where the vegetation community, climate and
the environmental conditions at the site have achieved a state of equilibrium over
many years. There may be relatively small seasonal fluctuations in the vegetation
community as some species are either favoured or disadvantaged by short-term
climatic variation (Matters 1987) or where annual species may dominate in years
when conditions are most favourable. Longer-term change in climate may cause
some species to disappear or enable other species to colonise a site (Allen 2006). The
total area of primary salinity in Victoria is estimated to be 250 000 ha (Allan 1994) and
includes semipermanent and permanent wetlands on the coast and inland as well as
dryland areas such as salt flats and drainage lines. A significant number of these sites
have not been included in the soil salinity database as its focus was primarily on
A classification of primary salinity may be as follows:
Salt marshes and saline swamps (coastal and inland)
Salt marshes are not restricted to the coast and may well occur inland. Typical
examples are tidal flats or periodically inundated depressions inland. Salt marshes tend
to be treeless and dominated by grasses.
Saline swamps are similar to salt marshes, but tend to be dominated by trees e.g.
mangrove or tea tree. Not many inland saline swamps remain.
Although salt marshes are a distinct class of primary salinity from salt swamps, they
tend to occur in similar parts of the landscape.
Approximately 100 000 ha of coastal salt marshes and swamps exist in Victoria,
with major occurrences at Discovery Bay (western Victoria), Westernport Bay,
Andersons Inlet, north of Wilsons Promontory, and along the Gippsland Lakes 2
(Corrick pers.comm. ). To date, salt marshes and swamps within the tidal influence of
the sea have generally not been included in soil salinity surveys and as a consequence
are not represented in the soil salinity layer on the CSDL. This may change as local
government authorities come under increased pressure to allow residential
development closer to the coast.
Salt lakes may be distinguished from salt flats and salt pans as they have permanent
or near permanent water under ‘natural’ conditions and as a consequence only
support vegetation around the edges. Typical examples are Lake Corangamite or Lake
Albacutya, although alteration to water flows has changed their primary status to some
Salt flats (including playa) and salt pans
Salt pans and flats are saline areas of low relief generally associated with arid or
desert environments—pans are notably hard and flats are dry lake beds or adjacent
to large water bodies. Playas are a special form of salt flat that are alkaline in nature
and tend to be of uncertain surface strength and often overlie soft mud. Salt flats and
salt pans are commonly found in the north-western Victoria.
Natural salt springs, seepages and drainage lines
These arise where natural upwelling or drainage of saline water occurs. Examples of
this type of primary salinity can be found in south-western Victoria around Dundas
Identifying primary salinity in the field
Primary salinity must be distinguished from secondary salinity in the field because
secondary dryland salinity is regarded as a land degradation problem while naturally
saline ecosystems are considered natural assets. However, in practice it can be difficult
to distinguish between primary and secondary salinity in the field. Adding to the
complexity is that primary sites may also have a secondary salinity component if
changes in land management and land use lead to an increase in salinity severity at the
site, an expansion of the original site, or both.
Allen (2006) developed a field-based method based on composition of the
vegetation community for discriminating between primary and secondary saline
sites. The method is based on the premise that long established sites contain species
that are adapted to saline environments that may have a relatively limited ability to
disperse and colonise new sites. The following criteria result from this premise:
• A site is likely to be a primary site if it has a high diversity of native salt tolerant
species that have low capacities for dispersing and colonising newly salinised sites.
This criterion may not
hold true where a secondary saline site adjoins a primary site from which otherwise
poor colonisers may more readily disperse.
A site with few species considered to be poor colonisers, may be a secondary
site or it may be a highly disturbed primary saline site. In some instances, the grazing
of primary sites may lead to the introduction of volunteer salt-tolerant species and
other weeds, making the distinction between primary and secondary salinity difficult.
Primary salinity tends to occur at certain positions in the landscape as a result of interaction between surface water, groundwater and the landscape. Some region
specific examples of the links between primary salinity, landscape and process are:
The presence of clay lunettes, typically on the eastern side of lakes or
depressions—is also an indicator of natural salinity in the north-west and west of the
state. Clay lunettes are formed down-wind of a saline lake that periodically dries out.
High levels of soil salinity impact on the soil structure of the exposed lake bed leaving
it prone to wind erosion. Deposition of the lake bed sediment forms the distinctive
crescent-shaped lunettes over time (e.g. Lake Tyrell). However, sand lunettes may also
be formed adjacent to freshwater lakes by wave and wind action at times of high water
level (Allen 2006).
Primary salinity may form within water bodies found at the terminal end of a
surface water and/or groundwater drainage system within basalt terrain in southern
Victoria. Over time salts may accumulate as a result of evaporation. An example of
this process is Lake Corangamite.
Natural wetlands and depressions that act as windows to naturally saline
groundwater bodies. An example of this is the salt lakes within the Douglass
Depression in the Wimmera (Swane et al 2001).
3 Secondary salinity
Secondary salinity is characterized by sites that have become affected by increasing
levels of soil salinity since European settlement due to the impacts of changing land
management practices and land use. Originally, mapping was restricted to
secondary soil salinity in non-irrigated agricultural areas, however as community
attitudes to salinity matured, the environmental value of primary sites was recognized
and a number of primary salinity sites were also mapped. Over 260 000 ha of land has
been identified and mapped as saline, including natural dryland salt flats and
wetlands inland and some of the saline wetlands along the coast. These areas are
recorded on the soil salinity layer held on the CSDL.
Across Victoria approximately 25 000 ha of the mapped area has been positively
identified as purely secondary salinity. Over 8000 ha of the mapped dryland salinity
was positively identified as primary salinity, almost 12000 was considered to be a
combination of primary and secondary salinity, while around 217 000 ha of land
mapped as saline has not been identified as either primary or secondary salinity. It is
not possible to state conclusively how much of the state is affected by secondary
salinity, but if we accept Allan’s estimate (Allan 1994) of 15 000 ha of secondary
salinity in the Mallee as reasonable, the mapped area affected by secondary dryland
soil salinity in Victoria could range from 40 000 ha to as much as 160 000 ha.
By implication, secondary salinity occurs at disturbed sites (created either by direct
destruction of vegetation or loss of vegetation and topsoil caused by increased soil
salinity levels) which may not yet have achieved a state of equilibrium between the
vegetation community, climate and other environmental features of the site. The
vegetation community at such sites may see an initial influx of species capable of
dealing with the changing environment. The composition of the vegetation
community may stabilize if the site attains some degree of equilibrium, but is open to
change if this new found equilibrium is disrupted (Brown pers. comm.).
Secondary dryland saline sites may be populated by both native and non-native
plant species with differing tolerance of salinity from many plant groups e.g. grasses,
legumes, native forbs and 3
Austin Brown (Statewide Leader, Pedology and Soil Physics, Future Farming
Sytems Division, DPI) June 2007 herbs (Matters 1987). One characteristic common to most species at a secondary site
is the ability to adapt to change and/or an ability to colonise disturbed areas. Species
with this characteristic are known as ruderal plants, and they tend to be efficient seed
producers and have relatively short life cycles and are. Fewer salt-tolerant native
species have these characteristics than introduced species, and as a consequence
vegetation communities at secondary saline sites are usually dominated by introduced
species (Allen 2006). There are some exceptions to these principles. For example, in the
Victorian Mallee, members of the Halosarcia and Sarcocornia species are not short lived
or known as particularly efficient seeders and are often the only vegetation apart
from annuals to colonise secondary saline sites (Brown pers.comm.).
3.1 Drivers of secondary salinity
Several causal mechanisms, all linked to changed land management practices and
land use since European settlement, have been identified and are believed to lead to
increased levels of secondary dryland salinity:
Increased groundwater recharge
The clearing of deep-rooted perennial native vegetation and its replacement with
shallow-rooted low water-using annual plants common in pasture and cropping
enterprises generates increased accessions to groundwater leading to raised
groundwater levels and increased groundwater discharge (Cook et al 2001, Cope
1958, Jenkin 1981, Rowan 1971). Some examples of secondary dryland salinity
resulting from increased accession to watertables and the geophysical features that
control this expression of salinity within the landscape are:
The presence of aquitards (clay units) within sand dunes that cause
perched saline watertables; typical example Victorian Mallee (Rowan 1971).
Where weak points in aquitards of regional groundwater systems allow for
upward groundwater flow and discharge at the soil surface; typical example along the
Riverine Plains of Victoria (Macumber 1978).
Groundwater discharge occurring at the break-of-slope caused by a change
in hydraulic gradient; typical example Palaeozoic sediments, central Victoria
Increased base flow to streams, which leads to an increase in stream
saltloads. Typical examples include Collie River basin Western Australia (Peck and
Williamson 1987) and Moorabool River, Victoria (Evans 2006).
Altered surface and sub surface environments
While increased recharge following European settlement is considered the most
common cause of secondary salinity, there exist examples where dryland salinity has
been attributed to other processes, such as:
Transient salinity. This type of salinity is not related to shallow watertables.
Transient salinity occurs in cropping and pasture areas overlaying sodic subsoils,
and results from a combination of reduced leaching associated with sodic clays, low
rainfall in dryland areas, transpiration by vegetation and high evaporation in summer.
More than 60% of the 20 million ha of cropping soil in Australia has the potential to be
affected by transient salinity as opposed to about 16% likely to be affected by salinity
resulting from shallow watertables (Rengasamy 2002).
Alteration of shallow regolith flow systems and accumulation of salt caused by
post clearing and geomorphological processes, such as landslide and debris flows.
Typical examples include the Heytsbury region of Victoria (MacEwan et al 1996) and the southern Tablelands of NSW (Acworth et al 1997).
The removal/disturbance of vegetation communities in primary
groundwater discharge zones, which leads to increased evaporation and alterations in
soil chemistry resulting in increased salinity levels in soil and groundwater and
decreased soil pH (Fawcett 2004; Dahlhaus and Cox 2005).
Salinity in and around wetlands and watercourses caused by disruption of the
existing local salt and water budget; typical example Lake Wallace, Edenhope (Fawcett
and Huggins 2004, Vinall 2000).
4Austin Brown, (Statewide Leader, Pedology and Soil Physics, Future Farming
Sytems Division, DPI), June 2007
• Alteration of watercourses and shallow regolith groundwater systems due to 19th
mining activities, typical examples around the Ballarat goldfields (Dahlhaus and Cox
4 Major indicators of dryland salinity
This methodology for dryland salinity assessment is based on a visual appraisal of
locations as salinity affects the soil and vegetation at salinised sites. These effects
frequently produce or initiate changes in the environment that form the distinctive
characteristics common to salt-affected landscapes that are readily observed in the
field. The major visual indicators of salinity are: vegetation species and community,
surface moisture, bare soil, soil surface condition, salt accumulation and organic
matter stains. The position in the landscape where these indications occur is
contextually valuable and can significantly inform site evaluation.
Excess salt levels in the soil can produce two major effects to visually alter a site:
1. Plant growth may be inhibited as a result of increased osmotic pressure of the
soil solution making it difficult for plants to absorb water from the soil. At low to
moderate salt concentrations, plants are able to manage the osmotic balance between the
soil and their root system by accumulating internal salts. This process maintains an
osmotic gradient that enables water influx to continue. However there is a penalty,
for under such conditions energy used to accumulate solutes is no longer available
for plant growth. As salinity increases, individual plants may be affected to a greater
degree. Typical symptoms are: severe leaf tip burning, disturbance of cell membrane
function, internal solute balances and even death (Matters 1987). Less commonly, toxic
effects due to excessive accumulation of ions may directly affect the surface membranes of
plant roots or tissues, or the uptake or metabolism of essential nutrients (United States
Salinity Laboratory staff 1954).
2. Increased percentages of exchangeable sodium on the soil cation exchange
process leading to a deterioration in the soil structure (Cope 1958). Loss of structure can
lead to hard-set surfaces which decrease water infiltration, increase runoff and overland
salt movement, decrease seed germination and emergence and increase the potential for
surface soil erosion. In addition, poor subsurface soil structure will reduce both internal
drainage during wet conditions and moisture holding capacity during dry conditions
(significant factors contributing to transient salinity unrelated to shallow watertable
processes). Reduced subsoil stability can lead to tunnel and gully erosion and increase
the connectivity of saline groundwater to surface streams and rivers.
4.1 Vegetative indicators Dryland salinity assessment based on an assessment of the vegetation community
largely relies on observation of ground and under-storey species of plants. As most salt-
tolerant species will also grow in non-saline soil, it is variation in the composition of the
plant community compared to the surrounding area rather than the presence of one or
two salt-tolerant species that is the key to identifying a salt-affected site. When
traversing a site from non-saline to saline soil, the number of salt-tolerant plants will
tend to increase and the number of salt-sensitive plants will tend to decrease. Sites
should only be classified as saline if there is a significant change in the plant
community from a mix of both salt-tolerant and salt-sensitive species to one dominated
by salt-tolerant species that cannot be plausibly explained by some other management
or environmental factor. The presence of a vegetation community dominated by salt-
tolerant species and with decreased numbers or total absence of salt-sensitive
species in conjunction with any of the physical signs (presence of groundwater, bare
soil, deteriorating soil surface structure, salt or organic stains or the position in the
landscape where saline soil is commonly found) is a good indication of salinity without
the need to take soil samples.
Plant response to salt
Excessive levels of soil salinity can effect vegetation in several ways:
1. Increased concentration of salts in the soil water may increase the osmotic
gradient between plant and soil by reducing a plant’s ability to take up the moisture
required to balance moisture loss via the leaf canopy. The total concentration of
solute particles rather than their chemical nature is responsible for this effect. In such
cases the plant tends to dehydrate and in severe cases die. A common symptom of
plants affected in this manner is a cupping or rolling of the leaves, however water
deficient plants in non-saline soil may show similar symptoms (United States Salinity
Laboratory Staff, 1954).
2. In saline soils the presence of excessive concentrations of ions such as chloride,
sulfate, bicarbonate, sodium, calcium, magnesium and less frequently potassium and
nitrate may lead to injury such as firing of the leaf margins, chlorotic and necrotic
areas on the foliage or simply depressed plant growth. These symptoms may be partly
caused by a reduced ability to metabolise essential nutrients, although it is not always
possible to clearly distinguish the mechanisms related to specific ions (United States
Salinity Laboratory Staff, 1954).
At the upper end of a plant’s salinity tolerance range morphological changes such as
stunting, thickening of the leaf surface, reduction of leaf hairiness, semi-succulence in
leaves and reddening of the plant may occur. These are common stress responses and
may be brought on by any one of a number of environmental factors such as soil
moisture deficit, poor cultivation practices, water logging, spray drift, root disease and
insect attack as well as increasing soil and water salinity levels. Stress symptoms can
be useful in the field to show that a plant may be at the upper end of its tolerance
range and therefore helpful when assessing severity levels. However, it is important to
remember that rising salinity levels are only one of a number of possible stress factors and
field observation combined with knowledge of the likely management and
environmental processes influencing a site should be considered when looking at stress
response. Stress response alone is not sufficient grounds to classify an area as saline as
many other processes can evoke a similar response.
Not all of the relationships between plant and soil are fully understood and
although it is generally acknowledged that while increasing salt concentrations in the soil profile generally have a negative effect on plant growth, vegetation sometimes
shows little effect from increased salinity levels or moisture stress. Vegetation response
to salinity may vary with climate and soil type and there are examples in both the
Corangamite (Allan 1994) and Glenelg Hopkins regions where laboratory measurement
of levels of soil salinity were higher than expected given the vegetation present and the
general physical conditions at the site. It is not known exactly why this occurs, but it is
presumably a function of the variation of the soil water conditions within the root zone
and atmospheric conditions (particularly those conditions that affect evaporation) that
allow species to establish and grow more successfully than predicted. At times of the
year when surface salinity is leached by rainfall, seed often has a much better opportunity
to establish and develop salt tolerant mechanisms before salt levels increase again with
evaporation. In some regions the climatic factors may combine to reduce the osmotic
pressure gradient between soil and leaf thereby limiting water utilisation and loss.
Regional differences in vegetation response to salinity need to be known and
understood to produce accurate maps of soil salinity. To do this adequately, it will be
necessary to collect and analyse soil samples and correlate them with the vegetation
community and condition for different regions. It is hoped that regional salinity
field guides will be developed for all of Victoria.
Salt-tolerant species have physiological mechanisms that allow them to cope with
high salinity levels and grow in saline environments, each species having a specific
range of tolerable soil salinity in a particular climatic zone. In saline areas, this
capability gives these plants a competitive advantage over salt-sensitive species, and
as soil salinity levels increase, species with a higher tolerance tend to replace less
tolerant species. However, these physiological mechanisms have a downside, as less
energy is available for plant growth because much energy is used in accumulating
solutes to maintain the osmotic gradient. They cannot be switched on and off and in
non-saline environments, halophytic plants are at a competitive disadvantage to more
vigorous, glycophytic species, which do not employ such mechanisms.
Appendix 1 lists some of the salt-tolerant species found in Victoria, but it is by no
means a comprehensive list of all Victorian salt-tolerant plants. Some species are
rated in terms of their ability to tolerate soil salinity and others are only listed as
Salt-sensitive species do not have the physiological mechanisms that allow them to
cope with the effects of increased soil salinity levels and suffer reductions in yield/
growth when salinity levels increase beyond a tolerable threshold. The United States
Department of Agriculture (USDA) accepted 2 dSm -1as a threshold above which
yields of sensitive crops may be restricted (United States Salinity Laboratory Staff
An important indicator of salinity is a noticeable reduction in the number of salt-
sensitive species from a suspected discharge site compared to the adjacent non-
saline area. This is a useful indicator, but taken on its own could be misleading and
it should always be examined in conjunction with an assessment of change in the
distribution of salt-tolerant species.
Morphologic changes in salt-sensitive species may result from increased soil
salinity. Matters (Matters 1987) states that such changes may take the form of
decreased germination rate, slow growth rate, incomplete life cycle (e.g. plants do not flower), diminished abundance, depressed health (commonly apparent by
characteristic yellowing and stunting of crop or pasture species), greater susceptibility
to disease and decreased seed viability. These changes may also result from water-
logging, nutrient deficiency or other limiting environmental factors, and there should be
a thorough examination of the surrounding area to determine if the changes are
limited to a particular location and if there is a corresponding increase in salt-tolerant
species. In the absence of any other indicators, it is not good practice to classify such a
site as saline based solely on morphological change.
Appendix 2 lists some of the known salt-sensitive species found in Victoria, but it
is by no means a comprehensive list of all Victorian salt-sensitive plants.
Dieback or death of trees may be due to salinity, though other factors such as
drought, flooding, insect attack, damage by stock or wildlife, soil compaction,
cultivation or other forms of disturbance must be exhaustively ruled out before
salinity is attributed as the cause.
Limitations on assessment using vegetative indicators
Given that the main assessment criterion is identification of vegetation, it is essential
that field assessment be restricted to the time of year when the critical vegetation is
present and can be easily and reliably identified. This is usually around flowering time in
late spring through to early summer but will vary depending on the species, region
and season. Failure to observe this restriction may reduce the accuracy of the field
As an example, subterranean clover (Trifolium. subterraneum) is a salt-sensitive
pasture species common across much of Victoria. It is an annual, highly palatable and
frequently not visible after mid-summer. Sea barley grass (Hordeum marinum), like
subterannean clover has an annual life cycle, however it is generally not palatable to
stock or native wildlife and frequently persists in an identifiable form after setting seed
for most, if not all the year. Sea barley grass is found across much of Victoria, but its
concentration is generally higher in saline sites. It is not uncommon to find
subterannean clover thriving in areas around but not in discharge sites. These same
areas may also carry a relatively small population of sea barley grass, which increases
within the saline area. An assessment in autumn, based solely on the area of sea barley
grass may over-classify the salt affected area by mapping all of the sea barley grass
cover as saline. A more accurate assessment at such a site would take place in late
spring or early summer when both species are easily identified and the areas where
subterannean clover dominated would be assessed as non-saline.
Field assessment should not be based on the presence or absence of a single
species, but should take into account the whole plant community present at a site and
the non-saline areas adjacent and the physical characteristics of the whole site and
If assessment is taking place in years of below average rainfall, there may be very
little plant germination or growth and flowering may be brought forward or limited.
This is likely to reduce the window of opportunity to conduct vegetation-based
assessments. In years of severe water shortage and high temperatures, some annual
species may not germinate at all and increased grazing pressure from stock and
wildlife brought on by the general shortage of feed may further shorten any window of
opportunity. In extreme years the option exists to delay the assessment until
favourable climatic conditions return. To state the obvious; if the indicator species are not present then a vegetation-based assessment is not feasible at that time.
Changes in land management and ground cover may also reduce the
usefulness of this vegetation-based assessment. This is covered in more detail in
the section titled ‘masking’.
This field assessment method relies on a visual assessment of vegetation communities
and other physical indicators by individual officers in the field. This involves subjective
judgement and will vary from individual to individual. One of the aims of publishing
this methodology is to set out clear guidelines that will assist field officers to make
judgements consistent with other field officers. To further reduce the subjective
nature of the field assessment, it is recommended that:
• All staff members are trained in using the method prior to commencing field
work. Training is currently funded by the Statewide Salinity Monitoring Program.
The number of staff working on a mapping project is kept to a minimum i.e.
It is better to have two people working for two weeks each than four staff working
for one week each.
All staff working on a mapping project should spend the first day or two
mapping sites together. This will assist them to bring their assessments into alignment
and will produce a more consistent assessment.
4.2 Physical indicators of salinity
Free water or dampness at the ground surface (particularly in summer) may be
due to groundwater discharge. Recent rainfall events and waterlogging are other
possible causes. Free water should be analysed for salt using a field
electroconductivity (EC) meter. Any water registering above 0.5 dSm in winter may
reasonably be assumed to be discharging saline groundwater and therefore the site
is deemed to be salt affected. See the section titled ‘waterlogging’.
If soil salinity levels rise to critical levels, salt-sensitive vegetation may die. Salt-
tolerant species may then establish, though this is dependent on the proximity of a
suitable seed source, the amount of traffic, grazing and cultivation and susceptibility
of the site to water and wind erosion. At extremely high levels of salinity no plant
species can persist, bare soil is exposed and a damaging cycle commences, as bare
soil is more prone to erosion by wind, water or traffic. Evaporation rates are likely to
increase, as there is no barrier to water being drawn to the surface by capillary action
leading to an accumulation of salt near the soil surface. This will accelerate the risk of
erosion, as excess salt in a soil tends to break down soil structure. Stock frequently
exacerbate baring as they like the cool and salty conditions found at a discharge site,
often preferentially grazing the salt-affected vegetation and camping on these sites.
The process of ‚baring‛ due to salinity usually begins in depressions, these being
marginally but critically closer to the watertable.
Not all bare sites will be associated with salinity. It is important to thoroughly
examine a site in the field to determine if salinity is the prime cause of bare soil or some
other agent such as stock or human traffic, wind or water erosion or cultivation is the
underlying cause. Often several processes will be occurring simultaneously at a site
and there may be some evidence of soil salinity nearby. Areas around gates and dams
are often bare because of traffic, water erosion may be the primary cause on some
slopes and in gullies or stock may wallow in a depression that is wet but not salty. Salt stain or crystals
Salt is sometimes observable (more so on bare soil) as minerals (evaporites) that
form a white stain, or actual salt crystals (encrustation). This is one of the more
definitive indications of salinity. The evaporite stain or encrustation may be tasted for
Position in the landscape
Regional groundwater aquifer systems have flat or gently sloping watertables that
extend under a number of surface water catchments. Due to the evapo-transpiration
process, discharge generally occurs where the watertable reaches to within 2 m of the
ground surface. However, this may vary depending on soil type and climate and
topography. Discharge tends to appear at topographically low sites, i.e. on flats,
drainage lines, lake margins, depressions and stream banks.
Local groundwater aquifer systems have watertables that generally follow surface
topography. Perched watertables, caused by an aquifer overlying a confining
(usually clay) layer, may discharge as seeps along slopes. Salinity may occur at the
break-of-slope where a change in surface gradient leads to a corresponding decrease in
hydraulic gradient and a consequent rise in groundwater. Local groundwater systems
may overlie and interact with regional groundwater systems.
Salt-affected soil that is also low in phosphorus and nitrogen can sometimes be
recognised by a characteristic blackening due to the dispersion of dark coloured
organic matter (Matters 1987).
4.3 Factors affecting recognition of dryland salinity
There a number of factors affecting the recognition of dryland salinity. Two types of
recognition errors can be produced, omission and commission errors. Omission error
results when an area is classed as non-saline when it is in fact saline. Commission error
results when an area is classed as saline when it is non-saline. Some of the factors
affecting recognition of dryland salinity may produce both types of error.
Site disturbance or modification such as cultivation, slashing or harvesting can
conceal the presence of salinity at a site. This is termed ‘masking’, and to determine
if this effect is in operation it may be necessary to take a soil sample for analysis or
make a return visit to assess the site when a crop, pasture or other vegetation regime
has developed. Masking generally increases the likelihood of omission errors and may
dampen assessments of severity levels at a site.
Another form of masking occurs when the vegetation community within an area
has been modified by external factors to favour saline tolerant species i.e. ‘salinity
treatments’. Treatment of discharge sites usually incorporates non-saline areas bordering
the saline site. Planting the treated area with salt-tolerant species such as tall wheat
grass, strawberry clover or Puccinellia may make it difficult to identify the extent of the
saline area and its severity given the ability of these species to grow on both saline and
non-saline soil. This form of masking favors commission error. At such sites the salt-
tolerant vegetation often follows paddock boundaries. If the site has been treated for a
long period and has had time for the vegetation to reflect the underlying soil salinity
levels, the non-saline areas may contain a number of salt-sensitive species that have
been able to out-compete the salt-tolerant species. The areas of higher soil salinity
may be showing degradation and reduced plant cover, or invasion by species with a
higher level of tolerance if a source of seed exists nearby. As a rule of thumb, unless there is invasion by species with higher tolerance or bare ground to indicate increasing
soil salinity, or invasion by salt-sensitive species, the mapping officer can assume that
the salinity must have been at least moderate (class 2 severity) for the landholder to
have bothered treating the site. Although the mapped extent of the salt-tolerant
vegetation may well reflect paddock boundaries, mapping the edge of the salt-tolerant
vegetation will place the site on the data base for future monitoring and contribute
to a greater understanding of the distribution of soil salinity across a catchment.
Another form of masking may arise during seasonal wet periods if salt-sensitive
plants with a short life cycle can complete their growth and reproductive stages before
salt levels in the soil rise again. These oppor