Unit 3 Notes
Weathering Notes
• Porder
o Plant activity weathers soils
§ When stomata are closed, no photosynthesis because CO2 cannot enter
leaf
o Cluster roots provide carboxylates in low phosphorous soils
§ Liberates phosphorous or iron from goethite
§ Organic acids form complexes with metals
• Transfer minerals to plants
o Phosphorous least abundant in rocks/soils
§ Phosphorous from mining helps expand industrial agriculture
• Popkin
o Up to 50% of living biomass in soil is networks
o Plants get up to 80% of phosphorous from fungi
• Weathering
o Soil is Critical Zone
§ Everything integrated here
• Lithosphere, biosphere, atmosphere, hydrosphere
§ Foundation of terrestrial ecosystems
§ Foundation for agriculture
§ Net sink for energy
• Not sustainable
§ Soil is complex system
• Interactions between water, air, minerals, organic matter,
organisms
o Interaction between weathering system and detrital
system
o Decomposition of rocks and minerals + decomposition of
organic matter
• Humus: highly decomposed organic matter
o Mostly from plant material
o Crucial to store nutrients and retain water
• Bacteria and other organisms
o Plants and roots
o Fungi
o Protists
o Animals
• O2 and CO2
• SOC: soil organic carbon
• Pedogenic processes are complex and organism-mediated
§ Soil is emergent property
, • Before life on land, there were no soils
• Before plants on land, there were no meandering rivers
o All flat and wide
o Rock Cycle
§ Outcrop à sediment through weathering, erosion, transportation,
deposition
§ Sediment à sedimentary rock through burial, compaction, and
cementation
§ Sedimentary rock à metamorphic rock through deeper burial, heat,
pressure
• Sedimentary rock à outcrop through uplift
§ Metamorphic rock à magma through melting
• Metamorphic rock à outcrop through uplift
• Metamorphic rock à metamorphic rock through burial
§ Magma à extrusive/intrusive igneous rock through cooling
§ Extrusive/intrusive igneous rock à outcrop through uplift
• Extrusive/intrusive igneous rock à metamorphic rock through
burial
o Weathering processes are central at many temporal and spatial scales
§ Fractal
§ Can study at many levels
§ Linked in many feedback loops
• Linked to hydrology, climate, erosion, and biology
§ The Weathering System
• Rock fragmentation à mineral fragmentation à mineral
decomposition à mineral formation
o Mineral fragmentation à mineral decomposition is
mechanical
o Mineral decomposition à mineral formation is chemical
§ Weathering Processes
• Weathering is breaking and dissolution of minerals
• Biologically-mediated process
o Plant roots contribute to physical and chemical weathering
§ At macro- and micro-scale
o Lichens contribute to chemical and mechanical weathering
§ Micro-scale
o Bacteria and fungi contribute to chemical weathering
§ Micro-scale
• Mechanical
o Biotic or abiotic
o Increases SA:V ratio
o Allows for faster chemical weathering
o Fragmentation of rocks
, § Freezing and thawing of water
§ Growth of salt crystals
§ Release of pressure
§ Roots
o Fragmentation of minerals
§ Freezing and thawing of water
§ Fungal hyphae
§ Fine roots
• Chemical
o Crystal lattice breakdown
o Organic acids dominate weathering in A and B horizons
§ Carbonic acid (H2CO3) dominates in C horizon
o Organic acids produced by
§ Organic matter decomposition
§ Organisms, directly
o CO2 produced by respiration of
§ Plants
§ Macroinvertebrates
§ Soil microbes
o Active biological is release of organic acids by
§ Roots
§ Hyphae
§ Bacteria
§ Overall decomposition of organic matter
o Passive biological is carbonic acid formation due to cellular
respiration
§ CO2 release from soil organisms
o Abiotic acid rain
§ Carbonic, nitric, sulfuric acid in rainwater
§ Strong acids contribute to chemical weathering
• Reinforcing feedback loop
o Minerals + Acid = Ions in solution ± Residual Minerals
§ Minerals are primary minerals
• Feldspar
• Hornblende
• Micas
§ Acid is (in)organic acids
• Organic acids like oxalic acids
• Inorganic acids like carbonic acid
§ Ions in solution are
• Major cations
o Sodium (Na+)
o Magnesium (Mg2+)
Weathering Notes
• Porder
o Plant activity weathers soils
§ When stomata are closed, no photosynthesis because CO2 cannot enter
leaf
o Cluster roots provide carboxylates in low phosphorous soils
§ Liberates phosphorous or iron from goethite
§ Organic acids form complexes with metals
• Transfer minerals to plants
o Phosphorous least abundant in rocks/soils
§ Phosphorous from mining helps expand industrial agriculture
• Popkin
o Up to 50% of living biomass in soil is networks
o Plants get up to 80% of phosphorous from fungi
• Weathering
o Soil is Critical Zone
§ Everything integrated here
• Lithosphere, biosphere, atmosphere, hydrosphere
§ Foundation of terrestrial ecosystems
§ Foundation for agriculture
§ Net sink for energy
• Not sustainable
§ Soil is complex system
• Interactions between water, air, minerals, organic matter,
organisms
o Interaction between weathering system and detrital
system
o Decomposition of rocks and minerals + decomposition of
organic matter
• Humus: highly decomposed organic matter
o Mostly from plant material
o Crucial to store nutrients and retain water
• Bacteria and other organisms
o Plants and roots
o Fungi
o Protists
o Animals
• O2 and CO2
• SOC: soil organic carbon
• Pedogenic processes are complex and organism-mediated
§ Soil is emergent property
, • Before life on land, there were no soils
• Before plants on land, there were no meandering rivers
o All flat and wide
o Rock Cycle
§ Outcrop à sediment through weathering, erosion, transportation,
deposition
§ Sediment à sedimentary rock through burial, compaction, and
cementation
§ Sedimentary rock à metamorphic rock through deeper burial, heat,
pressure
• Sedimentary rock à outcrop through uplift
§ Metamorphic rock à magma through melting
• Metamorphic rock à outcrop through uplift
• Metamorphic rock à metamorphic rock through burial
§ Magma à extrusive/intrusive igneous rock through cooling
§ Extrusive/intrusive igneous rock à outcrop through uplift
• Extrusive/intrusive igneous rock à metamorphic rock through
burial
o Weathering processes are central at many temporal and spatial scales
§ Fractal
§ Can study at many levels
§ Linked in many feedback loops
• Linked to hydrology, climate, erosion, and biology
§ The Weathering System
• Rock fragmentation à mineral fragmentation à mineral
decomposition à mineral formation
o Mineral fragmentation à mineral decomposition is
mechanical
o Mineral decomposition à mineral formation is chemical
§ Weathering Processes
• Weathering is breaking and dissolution of minerals
• Biologically-mediated process
o Plant roots contribute to physical and chemical weathering
§ At macro- and micro-scale
o Lichens contribute to chemical and mechanical weathering
§ Micro-scale
o Bacteria and fungi contribute to chemical weathering
§ Micro-scale
• Mechanical
o Biotic or abiotic
o Increases SA:V ratio
o Allows for faster chemical weathering
o Fragmentation of rocks
, § Freezing and thawing of water
§ Growth of salt crystals
§ Release of pressure
§ Roots
o Fragmentation of minerals
§ Freezing and thawing of water
§ Fungal hyphae
§ Fine roots
• Chemical
o Crystal lattice breakdown
o Organic acids dominate weathering in A and B horizons
§ Carbonic acid (H2CO3) dominates in C horizon
o Organic acids produced by
§ Organic matter decomposition
§ Organisms, directly
o CO2 produced by respiration of
§ Plants
§ Macroinvertebrates
§ Soil microbes
o Active biological is release of organic acids by
§ Roots
§ Hyphae
§ Bacteria
§ Overall decomposition of organic matter
o Passive biological is carbonic acid formation due to cellular
respiration
§ CO2 release from soil organisms
o Abiotic acid rain
§ Carbonic, nitric, sulfuric acid in rainwater
§ Strong acids contribute to chemical weathering
• Reinforcing feedback loop
o Minerals + Acid = Ions in solution ± Residual Minerals
§ Minerals are primary minerals
• Feldspar
• Hornblende
• Micas
§ Acid is (in)organic acids
• Organic acids like oxalic acids
• Inorganic acids like carbonic acid
§ Ions in solution are
• Major cations
o Sodium (Na+)
o Magnesium (Mg2+)
