Hyrogeochemical modelling of natural systems

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Hyrogeochemical modelling of natural systems

• Use of environmental tracers that supplement
  hydrological techniques

Liz Irvine Environmental Engineering Supervisors
Justin Costelloe, Andrew Western (UoM), Andrew
Herczeg (CSIRO)
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Occasions for chemistry

• Scarce standard hydrological data
• Water chemistry, isotopes ? (semi)-quantitative
  results
• Combined with hydrological modelling ?
  quantitative results
• Fast, rapid, cheap, lots of information about
  water and salt balances, origin and movement of
  salt.

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What is geochemical modelling?

• Not simply EC and TDS
• Uses water chemistry 7 major ions? the aqueous
  species in water (i.e. dissolved)
• Trends (spatial temporal)
• Water balance studies

TDS (mg/L) 0.7 EC (mS/cm)
Cl- Na K SO4-2 HCO3-/CO3-2 (DIC)
Mg2 Ca2
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Conservative vs non-conservative ions

• Distinct advantage over gross EC/TDS balances

• Conservative ions
• Remain soluble at relatively high salinities
• No ions produced or consumed
• Chloride, Bromide, (Magnesium, Sodium)
• Mixing models, evaporation

• Non-conservative ions
• participate in phase change reactions
• aqueous concentration of the ion may increase or
  decrease.
• Calcium, Sulphate, DIC
• Mineral precipitation an dissolution reactions

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Non-conservative ions

• Processes mineral precipiation and dissolution
• Dependent on mineral Saturation Index (SI)
• SIgt0 mineral precipiation
• SIlt0 mineral dissolution
• e.g. Gypsum
• CaSO4.2H2O ?Ca2 SO42- 2H2O

calcite
gypsum
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Tracing water and salt fluxes

• The Coongie Lakes arid zone, ephemeral, large,
  fresh
• Spatial and temporal variability in lake
  salinity.
• Lakes in terminal or sub terminal positions more
  saline

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Tracing water and salt fluxes
TDS 230mg/L
Lake filling phase
TDS 780mg/L
TDS 198mg/L
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Lake filling phase

• Flow through lakes Na-HCO3 type
• typical of Australian rivers
• (sub)-terminal lake Na-Cl-SO4 type
• loss of DIC,
• Mix with evolved waters
• 3 end members
• Inflow
• soil water
• soil minerals
• Processes
• Evapoconcentration?
• Groundwater?
• Flushing salts?

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Lake filling phase
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In summary

• Geochemical modeling is proving to be a promising
  technique for increasing understanding of water
  and solute transport
• Differences in surface water chemistries can be
  attributed to local processes

Thank you!