Chemical Weathering

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Chemical Weathering

• Most chemical weathering occurs in the vadose
  zone of soils
• Rate of chemical weathering increases if the rate
  of physical weathering increases
• Rate of chemical weathering is proportional to
  soil organic/biological activity

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Chemical Weathering

• Rate of chemical weathering is proportional to
  the infiltration rate
• I P -R -ET
• Rate of chemical weathering increases with
  increasing temperature
• Involves attack of H2O (and acidity) and
  atmospheric O2 on parent material

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Rate of Weathering
Anorthite 112 yr
Forsterite 2,300 yr
1mm cube pH 5 25C
Diopside 6,800 yr
Tremolite 58,000 yr
Albite 575,000 yr
Biotite 38,000 yr
K-feldspar 921,000 yr
Muscovite 2,600,000 yr
Quartz 24,000,000 yr
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Changes During Weathering
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Compositional Changes
Fwt
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Soils
Rain
A0 or O
Organic Debris, partially decomposed
A1 or A
Organic and mineral matter
A2 or E
Eluviation light colored horizon
B
Illuviation Blocky structure, accumulation of
material
C
Weathered parent material
Dry Weather
D
Parent material
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Silicate Weathering
Si
K
HCO3-
Si
K
HCO3-
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Silicate Weathering
Ca
HCO3-
Ca
HCO3-
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Mass Balance
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Matrix Solutions
unknowns
Known Concentrations
Mineral stoichiometry
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Statistics

• Correlation Analysis
• Multiple Linear Regression
• Factor Analysis

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Surface Water Chemistry
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Groundwater Chemistry