Lake Salinity, Chemistry and Mineral Precipitation

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Lake Salinity, Chemistry and Mineral Precipitation

• What are some sources of salts to lakes, and how
  do they affect lake salinity and ionic
  composition?
• How do biological and chemical processes affect
  lakes chemical compositions?
• What are some common minerals that precipitate
  from lakes at different salinities?

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Rainfall Salinity

• Source Berner and Berner, 1987, Meybeck and
  Helmer (1989)
• All data in ppm

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Rock-derived Chemistry
Ca gtMg gt Na gt K HCO3 gt SO4 gt Cl
Data in µeq/L
Average 551 198 77 14 764 70 3 147
Total 475 529 1069 593
1662 6627
Particles source of Fe, Si, P
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Bowen Low T High T
Goldich
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Open lake chemistry
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Lake Salinity (g/L) Na Ca Mg Cl SO4 HCO3
Mirror 0.06 0.01 0.02 0.004 0.0009 0.004 0.02
Edward (Ug) 0.7 0.18 0.02 0.08 0.04 0.04 0.2
Redberry (CA) 18 1.9 0.1 2.3 0.2 12.5 0.7
Van (TR) 23 8.1 0 0.1 5.9 2.4 5.9
Seawater 35 10.8 0.4 1.3 19.4 2.7 0.1
Bogoria (KE) 36 14.4 0 0 3.4 0.2 17.7
Mono (CA) 89 29.5 0 0 17.6 10.3 30.1
Great Salt Lake 332 105.4 0.3 11.1 181 27 0.8
Don Juan 339 11.5 114 1.2 212 0 0
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Gorham et al., 1983
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Solubilities of stuff

• Solubility of mineral Ks XX-
  _at_ eqm.
• Ion activity product IAP XX- measured
• IAP lt Ks gt Dissolution
• IAP gt Ks gt precipitation
• Conservative vs. non-conservative

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Data from Africa (Kilham, 1990). Why doesnt it
fit the Gibbs Boomerang?
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Mineral Precipitates from Lakes

• Common minerals
• Calcite Ca CO3 --gt CaCO3
• Mg-Calcite Ca Mg CO3 --gt (Ca,Mg)CO3
• Aragonite Ca CO3 --gt CaCO3
• Dolomite Ca Mg CO3 --gt (Ca, Mg)CO3
• Gypsum Ca SO4 --gt CaSO4
• Mirabilite/Thenardite Na2SO4(H2O)
• Natron/Trona NaCO3, NaHCO3(H2O)
• Halite NaCl

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Carbonates and Mg/Ca
Calcite Mg-Calcite Aragonite
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1900
Variable
1800
1700
Low- to High-Mg Calcite
Dry
Year A.D.
1600
1500
1400
Wet
1300
Aragonite
Lamongan Mg
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Saline Lakes
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Evaporites
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Ca2 Cl-
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Summary

• Salt inputs are largely from rock weathering,
  secondarily rainfall
• Outputs are to outflow and sedimentation, the
  balance balance is controlled by water balance
• Sedimentation in partially open and closed lakes
  alters lake chemistry
• Lacustrine carbonate mineralogy changes as a
  function of Mg/Ca
• Salt lake brine chemistry dictated by initial
  chemistry and mineral solubility

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POUT POND

• Summarize the main differences in 2008 and 2007.
  What are hypotheses that could explain the
  differences/similarities?
• What are possible origins for the temperature
  and salinity changes below 15 m water depth?
  What do you think the mixing regime of this lake
  is?
• What additional measurements should we make to
  identify the mixing regime and origins of the
  deep water mass?