Environmental Chemistry

Chapter 5:Chemistry of the Solid Earth

Copyright © 2009 by DBS

Contents

• Introduction

Chemistry of the Solid EarthIntroduction

• Soil – formed from physical, chemical and biological weathering of rocks

• Minerals found in these rocks are predominantly silicates

Chemistry of the Solid EarthIntroduction

• 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 EarthIntroduction

• 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 EarthIntroduction

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 EarthIntroduction

• Clay Minerals– 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 EarthIntroduction

• Textural Classes– Particle size distribution:

sand (0.02-2.00 mm)

silt (0.002-0.02 mm)

clay (<0.002 mm)

– Loam = good combination of soil

– Sci. explanation = good mix of fine particles

Chemistry of the Solid EarthIntroduction

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 EarthIntroduction

• Soil forming factors:– Climate– Macro- and micro-organisms– Topography– Parent material– Time

Chemistry of the Solid EarthIntroduction

• Parent material is acted on as follows…

• Process is VERY slow

Chemistry of the Solid EarthIntroduction

Environmental Compartments

Chemistry of the Solid EarthIntroduction

• 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 EarthIntroduction

• “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 EarthIntroduction

• Solid components (mineral and organic) make up ~ 50% by volume

Soil is a 3-phase material

Chemistry of the Solid EarthIntroduction

Chemistry of FreshwatersFundamentals

• g

Chemistry of the Solid Earth

Chemistry of the Solid Earth

• A

Chemistry of the Solid EarthSummary

• A

References

• A