Salinity and Sodicity

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Salinity and Sodicity

• Kristie Watling
• NRW, Toowoomba
• Ph 4688 1092
• E-mail kristie.watling_at_nrw.qld.gov.au

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• Salinity is the presence of excess salt
  (influences the growth of plants)
• Sodicity is the presence of excess sodium
  (influences how soil behaves)

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Types of salt

• The most familiar form of salt is table salt,
  which is almost pure sodium chloride
• But there are other types of salt that may occur
  in soil and water, depending on the
  geology/location etc

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Salt sources

• Dominant sources are rainfall and rock weathering
• Rain
• Dilute source of salt, but over time salt
  deposited by rain accumulates in the landscape

• Concentration of salt in rainfall varies
  (distance from coast, topography)
• If rain is the dominant source of salt, NaCl is
  the most common salt

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Salt sources

• Weathering
• Salts are released as minerals weather
• Amount of salt released differs
• Marine sediments release more salt than
  freshwater sediments
• Constant, but slow source
• Rainfall patterns and soil properties determine
  how much salt remains in the profile (tropics vs
  inland)

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Salt sources

• Other sources
• Aeolian salt wind-transported materials from
  soil or lake surfaces comparatively small source
  in Qld due to general absence of saline soils and
  lakes
• Connate salt salt trapped in rocks and marine
  sediments deposited during periods when Australia
  was partly covered by sea

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• Our landscapes have been storing salt for
  thousands of years
• Salts vary in their solubility, so they therefore
  concentrate to differing levels
• Salt only moves with water
• Its all about mobilisation, concentration and
  redistribution!

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Hydrological Cycle
Figure 4, pg 6, NSW Salinity Glove Box Guide
(Slinger and Tenison 2005)
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Types of salinity

• Primary natural occurrence of salts in the
  landscape eg. salt marshes, salt lakes
• Secondary salinisation of soil, surface water
  or groundwater due to human activity eg.
  urbanisation and agriculture

? Salt ? Moving salt
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Secondary salinity can be further divided based
on the processes contributing to salting

• 1. Dryland salinity changes in the water
  balance (from clearing etc)
• 2. Irrigation salinity source of water used for
  irrigation and quality of irrigation water
• 3. Urban salinity usually due to excess water
  use, and/or water of poor quality
• 4. Scalding primarily caused by erosion
  processes surface soils are eroded by surface
  water flow or wind, exposing saline and/or sodic
  subsoils not associated with watertables

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Dryland Salinity
Figure 10, pg 14, NSW Salinity Glove Box Guide
(Slinger and Tenison 2005)
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Deep drainage under different vegetation types on
similar landscapes
Figure 14, pg 20, NSW Salinity Glove Box Guide
(Slinger and Tenison 2005)
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Irrigation Salinity
Figure 11, pg 15, NSW Salinity Glove Box Guide
(Slinger and Tenison 2005)
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Urban Salinity
Figure 12, pg 16, NSW Salinity Glove Box Guide
(Slinger and Tenison 2005)
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How salt moves to the soil surface
Figure 8, pg 12, NSW Salinity Glove Box Guide
(Slinger and Tenison 2005)
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For salinity to occur, need to have all of these

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• Stores of salt to remobilise
• soil, regolith, groundwater
• Shallow soil/groundwater systems
• to trap and transport salt and water
• Hydrologic change
• more deep drainage
• more water and salt to groundwater
• this is a function of land use ? the only bit we
  can manage!

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Where does salinity occur?

• Where water and salt discharge!
• Some landscapes are naturally more susceptible to
  salinity than others

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The national scene

• Secondary salinity is prevalent in
• WA
• SA
• Vic
• ACT
• NSW
• Qld
• Tas

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Salinity models

• Salinity conceptual models in the Salinity
  Management Handbook define possible discharge
  areas/saline sites
• Examples

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Basalt form
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Catena form
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Catena form and erosion
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Catchment constriction (natural)
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Catchment restriction (artificial)
Figure 21, pg 26, NSW Salinity Glove Box Guide
(Slinger and Tenison 2005)
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Dams
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• Salinity is a landscape phenomenon

• Salt is not a static entity it moves through
  the landscape

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Impacts of salinity

• Damage to civil infrastructure
• Lost agricultural production (affects plant
  growth, can make areas more susceptible to
  erosion etc)
• Biodiversity
• Water quality
• Health

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Some costs

• 1 km major road 1 million
• 1 bridge 1-5 million
• Hot water systems 500 each
• Prime ag land 3000-5000 /ha
• Poor grazing land 100 /ha

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Civil infrastructure

• Major infrastructure road, rail, bridges etc
• Urban houses, footpaths, services
• Water quality
• Hot water systems
• Construction
• Direct and indirect costs
• Damage vs prevention

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Salinity plant effects
0 uM
100 uM
200 uM
Saline conditions reduce plant growth
Osmotic effects can influence water
availability Specific ion effects toxic effects
of Na, Cl, (B, HCO3) Nutritional effects
competition for uptake (Na may affect
availability of K, Mg2 or Ca2)
Influence of NaCl on the growth of sweet potato
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Salinity
Table 8.7 Grouping of crops according to the
conductivity of saturation extract of saline soil
corresponding to a 50 yield decrease (from that
on a nonsaline soil) (Black, 1968)
Tolerance to salinity varies between species and
even within cultivars of one species
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• Salinity was first recognised 150 yrs ago (Vic)
• Observed in the Qld Murray-Darling Basin in the
  1950s
• Australia-wide currently affects 2.5 million ha
  15 million ha threatened
• Queensland 48 000 ha currently affected
• Major areas include the lower Central Coast,
  Burdekin, Southeast, Murray-Darling Basin

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How do we measure/model/predict salinity?

• To determine where salinity occurs
• Measure by drilling, sampling, assessing soil,
  water and regolith
• Models (conceptual and mechanistic)
• Geophysical techniques

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Direct measurements water

• Electrical Conductivity EC (?S/cm)
• Total Dissolved Solids or Ions TDS or TDI
  (mg/l)
• EC x 0.64 ? TDI
• Sodium Absorption Ratio SAR

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• Typical EC values for water
• Rainfall 30 ?S/cm
• Sewage effluent 840
• Drinking upper limit 1600
• Stock upper limit 7000
• Irrigation upper limit 8000
• Freshwater 0-1500
• Brackish 1500-15 000
• Seawater 55 000

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Direct measurements soil

• Electrical Conductivity (dS/m)
• EC15 15 soilwater suspension
• ECse saturation extract EC
• To convert from EC15 to ECse, x texture
• Exchangeable Sodium Percentage ESP ()
• Typical EC values ECse lt1.5 dS/m non-saline

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Soil salt profiles

• Intermittent fluctuating water table
• Normal low conductivity, plants use water and
  leave salts behind
• Discharge shallow water table
• Recharge flushing of accumulated salts

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Salinity modelling

• Modelling of salinity concepts in a landscape
• Landscape shapes salinity (FLAG, MrVBF)
• Groundwater dynamics (Flowtube, MODFLOW)
• System response time (BC2C)
• Land management and groundwater / stream response
  (2C Salt)
• Salinity routing in streams (IQQM)

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Geophysics

• Electromagnetics
• Induction of current and EM field in conducting
  materials in the earth
• Range of depths
• Airborne EM (AEM) a key technology for NAPSWQ
• Gamma radiometrics
• Senses natural radiation in top 30 cm
• Magnetics
• Gravity
• Example Lower Balonne project

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Reuse pumped groundwater
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Dispose of pumped groundwater
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Implement subsurface drainage
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Umbiram, 1990-1991
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Umbiram, 2006
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Pastures
Drainage for alternative land uses
Source Jo Owens, grey vertosol
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Grazing management
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Plants use water differently
Natural vegetation
Winter crop
Depth of active roots
Water use through the year
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Convert land use
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Convert land use
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Convert land use
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Retain and/or establish trees
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Millmerran
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Umbiram 1991-2006
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Fence and forget areas
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Jimbour
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Irrigation Salinity Management
Figure 34, pg 53, NSW Salinity Glove Box Guide
(Slinger and Tenison 2005)
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Management conclusions

• Salinity management is complex
• Salinity management will often require a
  combination of management options at any one site
• Management of salinity requires an approach based
  on an understanding of
• the relevant salinity processes and timescales
• the technical, economic and social feasibility of
  the available solutions
• a willingness to monitor the effectiveness of the
  chosen approach
• a multi-generational commitment

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Where we are with salinity?

• There is less salinity in Qld compared to other
  states
• Risk mitigated by
• Climate - summer dominant rainfall, high rate of
  water use
• Predominance of low permeability clay soils in
  cropping
• More recent clearing patterns

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Salinity a puzzle

• You cant see it easily causes are underground
• There is a long lag time between cause and effect
• It takes even longer to reverse salinity
• It moves (in space and time)