Soil and Geochemistry
Soil and geochemistry studies the chemical composition and reactions of soils and the near-surface earth, where minerals, water, organic matter, and organisms interact.
Definition
The branch of environmental chemistry concerned with the composition, reactions, and surface chemistry of soils and the near-surface geosphere.
Scope
This area covers the chemistry of the solid earth at low temperatures: mineral weathering and soil formation, the nature and reactivity of soil organic matter, soil acidity and redox, and the sorption and ion-exchange processes at mineral and organic surfaces. It links elemental cycling, nutrient availability, and contaminant behavior in the terrestrial environment.
Sub-topics
Core questions
- How do rocks weather to form soils and release elements?
- What controls soil acidity and redox status?
- How do mineral and organic surfaces retain ions and contaminants?
- How is soil organic matter formed, stabilized, and degraded?
Key theories
- Surface complexation at soil interfaces
- Ion retention in soils is described by adsorption and surface-complexation at charged mineral and organic surfaces, governed by pH, ionic strength, and competing ions, which controls nutrient and contaminant mobility.
- Weathering and pedogenesis
- Chemical weathering of primary minerals drives soil formation, releasing nutrients and forming secondary clays and oxides whose surfaces dominate soil chemical behavior.
Mechanisms
Soil chemistry is governed by interfaces. Variable- and permanent-charge surfaces on clays, oxides, and humus exchange cations and bind anions and metals; pH and redox set speciation; and weathering continually supplies reactive secondary phases. These processes determine the partition of elements between solution and solid.
Clinical relevance
Soil and geochemistry underlie soil fertility, the retention or release of heavy metals and contaminants, and remediation strategy, and they document the worldwide spread of trace-metal contamination.
History
Environmental soil chemistry developed from classical soil science and geochemistry, with surface-complexation theory and spectroscopic surface studies maturing the field through the late 20th century.
Key figures
- Garrison Sposito
- Donald L. Sparks
- Victor Goldschmidt
Related topics
Seminal works
- sparks2003
- sposito2008
- nriagu1988
Frequently asked questions
- How does this differ from agricultural soil science?
- It focuses on the underlying chemistry of soils and the geosphere, including contaminant behavior, rather than on crop production practices specifically.