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Environmental Chemistry
Chapter 5:
Chemistry of the Solid Earth
Copyright © 2009 by DBS
Contents
• Introduction
Chemistry of the Solid Earth
Introduction
• Soil – formed from physical, chemical and biological weathering of
rocks
• Minerals found in these rocks are predominantly silicates
Chemistry of the Solid Earth
Introduction
• Importance of aluminosilicates in soil
• Loss of K, Fe, Ca, Na, and Mg as a result of soil processes
• C and N are enriched in soil due to organic matter
Chemistry of the Solid Earth
Introduction
• Organic matter is a significant component of soil
• Decomposition of plants, animal waste and microorganisms
• Amounts of mineral vs organic components leads to large variety of
soil classes
Chemistry of the Solid Earth
Introduction
The Mineral Fraction
• Texture
– Particle size distribution of mineral components in a soil is described
by its texture
sand (0.02-2.00 mm)
silt
(0.002-0.02 mm)
clay (< 0.002 mm)
Chemistry of the Solid Earth
Introduction
•
Clay Minerals
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Relative surface area
It is on the surface that many chemical and
physical processes take place.
Smaller = more surface area (clay is tiny!)
Chemistry of the Solid Earth
Introduction
•
Textural Classes
– Particle size distribution:
sand
silt
clay
(0.02-2.00 mm)
(0.002-0.02 mm)
(<0.002 mm)
– Loam =
good combination of soil
– Sci. explanation
= good mix of fine particles
Chemistry of the Solid Earth
Introduction
Definitions:
1. “The unconsolidated mineral material on the immediate surface of the earth
that serves as a natural medium for the growth of plants.”
2. “The unconsolidated mineral matter on the surface of the earth that has been
subjected to and influenced by genetic and environmental factors of parent
material, climate, macro- and micro-organisms, and topography, all acting over
a period of time and producing a product – soil – that differs from the material
from which it is derived in many physical, chemical, biological and
morphological properties and characteristics.”
Chemistry of the Solid Earth
Introduction
• Soil forming factors:
–
–
–
–
–
Climate
Macro- and micro-organisms
Topography
Parent material
Time
Chemistry of the Solid Earth
Introduction
• Parent material is acted on
as follows…
• Process is VERY slow
Chemistry of the Solid Earth
Introduction
Environmental Compartments
Chemistry of the Solid Earth
Introduction
•
•
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Soil is a combination of all the major components of the surface
(atmosphere, lithosphere, hydrosphere and biosphere)
Leads to variations in soils with location
Chemistry of the Solid Earth
Introduction
•
“Soil Architecture” - a key factor controlling the type and extent of life in soil
– Physical network and size distribution of pores
– Behavior of water and dissolved solutes
– Physical and chemical conditions of soil determine the types and
conditions for biological communities and soil quality/health
Chemistry of the Solid Earth
Introduction
•
Solid components (mineral and organic) make up ~ 50% by volume
Soil is a
3-phase
material
Chemistry of the Solid Earth
Introduction
Chemistry of Freshwaters
Fundamentals
•
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Chemistry of the Solid Earth
Chemistry of the Solid Earth
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Chemistry of the Solid Earth
Summary
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References
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