1. Soil Structure and Composition

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1. Soil Structure and Composition

• Chapter 2
• For review see any soils textbook

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What is the importance of soil in pollution
science?

• 1. Landscape productivity can be adversely
  affected by pollutants deposited on the soil.
• e.g. acid rain, improper application of waste,
  chemical spills
• 2. Soils can alleviate the effects of pollution.
• e.g. acid rain, industrial pollution

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What is the importance of soil in pollution
science?

• 3. Soil mismanagement can result in groundwater
  and surface water pollution.
• e.g. over application of pesticides and
  fertilizer, over application of animal manure.
• 4. Soil is used for beneficial utilization of
  waste.
• e.g. sewage sludge, coal ash, composts

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The Solum and Vadose Zone
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Composition of Soil

• Organic matter (humus).
• Finely divided minerals.
• silts and clays
• Coarse minerals-sands and stones.
• Humus, silts, and clays are the most reactive
  fractions.

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Mineral Particle Sizes
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Soil Texture
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Clays

• Have cation exchange capacity.
• Can absorb many metal ions, as well as anions at
  the edges of clay particles.

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Oxides of Fe and Al

• Can absorb cations and anions

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Soil Organic Matter

• Undecayed or partially decayed plant residues
• Microbial biomass
• Humus 1-18 in a mineral soil, typically 1-5
• Humic acid 80-90 of humus
• Fulvic acid 20-30 of humus

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Formation of Soil Organic Matter
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Function of Humus

• Supply N, P, and S
• Retain metal cations
• Retain xenobiotic organic compounds

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Soil Structure
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Soil Horizons
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Soil Horizons
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Decay of Organic Matter in Soils

• Changes the composition of soil air
• Lower PO2 from 21 to 19-20
• Raises PCO2 from 0.035 to as much as 1

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Soil Water

• w wet weight
• d dry weight

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Definition of Soil pH

• pH of water mixed 11 with soil
• pH of 0.01 M CaCl2 mixed 11 with soil
• pH -log H

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Soil pH
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Summary Soils Review

• Soils are made up of
• minerals
• organic matter
• living organisms
• Soils retain cations, anions, and organic
  compounds.
• Soil organic components are sources of N, P, and
  S.
• Soils retain water.
• Soils vary in pH from about 3.5 to 10.
• pH is and important variable for many reactions.

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Problem for next lecture

• The standard way of reporting concentrations in
  soil is dry wt.
• If a sample of soil that has a 20 moisture has
  1000 mg kg-1 Pb (ppm Pb), What is the field moist
  concentration?