CHEM340 Unit 1 - Chemical Speciation, Bioavailability, Soil Minerals, Soil Organic Matter

soil

biologically active, structured, organic and inorganic material which forms a 3D continuum of layers as part of the weathered mantle of the earth

examples of essential plant nutrients

• Macronutrients N, P, K, S, Ca, Mg 

• Micronutrients B, Cl, Mn, Fe, Cu, Zn, Mo

examples of essential animal nutrients

• Macronutrients N, P, K, S, Ca, Mg 

• Micronutrients F, Cl, Cr, Mn, Fe, Co, Cu, Zn, Se, I

essential nutrient

organism requires some concentration to complete its lifestyle

background concentration

concentration of an element that would occur in the absence of anthropogenic input

pollution

damage caused to water, air, soil etc by harmful substances or waste

contamination

the presence of unwanted or dangerous substances

chemical speciation

the specific chemical form of an element in a chemical system, including oxidation state, complexation, isotopic composition and molecular structure

bioavailability

the fraction of a contaminant, nutrient or chemical that is freely available for absorption by living organisms, determining toxicity and bioaccumulation potential

minerals

homogenous, naturally occurring, solid, inorganic substances which have a unique chemical formula

geogenic element

elements that come from minerals

geochemical affinity

tendency of chemical elements to associate with a specific host phase/element based on their chemical and physical properties

4 types of geochemical affinities

1. lithophile

2. atmophile

3. siderophile

4. chalcophile

lithophile

elements that prefer to bond with oxygen and concentrate in the silicate crust/mantle

atmophile

elements that prefer to occur in the atmosphere or in the gas phase

chalcophile

elements that prefer to bond with sulfur and form sulfide ores

siderophile

elements that dissolve in molten iron, predominantly found in the earth’s cor e

relative composition of soil

45% mineral/inorganic

5% organic

25% air

25% water

composition of the inorganic fraction

primary minerals, secondary minerals, carbonates

primary minerals definition

minerals that form at high temperatures and pressures and form from parent rocks without chemical alterations

key point about primary minerals reactivity

most often associated with sand and silt - low reactivity due to low surface area to volume ration

secondary minerals definition

minerals that form at the earth’s surface due to weathering of primary or by precipitation from soil solutions minerals

key point about secondary minerals reactivity

most associated with clay - very reactive due to high surface area to volume ration

3 types of secondary minerals

1. layer silicates

2. non-crystalline/amporphous minerals

3. oxides

two types of non-crystalline/amorphous minerals and why they are important

1. imogolite

2. allophane

3. they are the only minerals that have a variable charge/can have a positive charge

soil organic matter

fraction of soil containing non-carbonate carbon

5 reasons soil organic matter is important

1. nutrient cycling

2. soil structure

3. chemical retention and detoxification

4. energy for soil microbes and organisms

5. ecosystem processes

2 types of humus

1. fulvic

2. humic

fulvic

soluble at all pHs

humic

insoluble humus

2 toes of resistant SOM

1. particulate organic matter (POM)

2. mineral associated organic matter

MAOM definition

mineral associated organic matter formed from the binding of particular organic matter with clays (imogolite, allophone)

how does SOM-clay form

through a Ca2+ bridge, a divalent cation which acts as a bridge between the clay minerals and SOM which have a negative surface charge

mineral specific surface area

total surface area of particles per unit mass

relationship between som and mineral specific surface area

soils with high mineral specific surface area tend to be more clay-like and have a higher som

chemically protected SOM

stable fraction of soil carbon that is resistant to microbial degradation and decomposition due to its close interaction with the mineral soil components