lecture 9 Flashcards
how does soil impact organisms
- Important for why you see organisms where you see them
Abiotic components are often not explicitly included in studies
how can u describe the study of ecology
The study of ecology can be described as the observation of patterns and processes
how does biota impact soil development
- Vegetation - soil stability, biological weathering
- Source of organic matter
- Modifies microclimate- due to vegetation
○ Climactic factors changed under and around the plants - ex. Reduced exposure of the surface to wind
○ Slowing wind
○ Shading
○ Retaining snow - Decomposition and movement of material
- Ex. Earth worms move the soil throughout the layers and transport things + physically break down organic matter
The reason you see a conc. Pattern when looking at soil horizons is bc light hits above ground most = more PP = more organic matter
how does time influence soil development
- Time over which soils develop influences their properties (will depend on PM)
- Many soil forming processes occur slowly
○ Glacial retreat (till)
○ Wind deposited sediment (eolian) - Some occur quickly -
*
- Many soil forming processes occur slowly
what happens to phosphorus in soil over time?
- Over time, secondary and organic phosphorus are found in larger quantities - chemical reaction with the soil
Part of the natural cycle
How can human activity influence soil development
- Extending agricultural footprint
- Replacing communities that evolved under natural conditions with ones that are not adapted - crops fail, loss of vegetation cover, exposure of soil
○ Increasing dust after great depression - Nitrogen fixation decreased
○ Historical fixation due to plants - lost when they are replaced - Certain environments are not great for supporting primary productivity
Ie. California is too dry, but introducing water can lead to issues such as salt accumulation in soil
- Replacing communities that evolved under natural conditions with ones that are not adapted - crops fail, loss of vegetation cover, exposure of soil
direct impacts of humans on soil development
○ Nutrient inputs
○ Irrigation
○ Alteration of microenvironment
○ Increased erosional loss
indirect impacts of humans on soil development
- Indirect:
○ Changes in atmospheric composition (deposition, climate)
○ Addition and deletion of species
Acid rain caused by smelting activity = alters the ecosystem bc of change in PH - availability and chemistry of nutrients changed
what interactions take place in developing soil profiles
- Development of soil profiles
- Vast network of interactions taking place
- Additions
- Transformations
- Transfers
Losse
describe additions
precip (ions and soild particles)
organic matter
onto ground surface
describe transformations
- Plant material and primary minerals
- Addition of rainwater
- Decomposition of OM; releasing CO2 and nutrients (N and P)
physical, chemical weathering
biological contributions
desribe physical weathering
○ Breakdown of parent material with no change in chemical composition
○ Expansion and contraction of rocks (freeze-thaw, heating-cooling, wet-dry cycles)
○ Roots growing into rock fissures
Roots will also push the rock as they establish
describe chemical weathering
○ Rocks react with acidic or oxidizing substances, usually in the presence of H2O
○ Primary broken down into secondary minerals
○ Stimulated by the Prescence of acids, water, and heat
Roots in rock fissures- - produce carbon dioxide + water = carbonic acid = far higher rate of acidification
describe biological contributions
- Biological contributions
○ Decomposers, roots, lichen, etc
describe transfers
- Usually down bc of gravity, but can be up
- Usually result in losses
- Vertical transfers- layering of soil
○ Downward: leaching and particulate transport in water
○ Upward movement and mixing:
Capillary action (clay> sand), soil organisms
describe losses
- Primarily solutions and gas; particles also lost via erosion
- Amount lost due to leaching dependas on water and flow and solute conc.
Gaseous losses depend on rate of gas production by microbes + diffusional paths through soil
- Amount lost due to leaching dependas on water and flow and solute conc.
how do ecosystems differ in soil ? what is soil important for
- Ecosystem differences in additions, transformations, transfers, and loss give rise to distinct soils and soil profiles
- Soil is the 3rd most important factor in determining biota
- Horizons may be thicker or even absent depending on the area
*
which horizon is LFH
O - ORGANIC MATTER DECOMPOSINF
which horizons are mineral
A, E, B , C R
les than 30% OM by weight
soil profiles in diff biomes ex
- Dots are organic matter - distinct difference in the distrbution in the different systems
- Bog/tundra: tremendous amount of organic matter at the top
○ Frozen ground for many months - Grasslands: greater gradient of distribution from the top down
○ Bc the amount of plants that are below ground can be up to 50% of the plant
○ Moderate precip and high variation
Desert - low organic matter bc of lack of precip
- Bog/tundra: tremendous amount of organic matter at the top
describe the LFH horizon
- Forest floor
○ Litter: relatively fresh organic residues in which original structures are virtually intact
○ Fermented: dominated by partly decomposed organic materials, original structures are breaking down and discolored but still recognizable
○ Humus: organic residues in advanced stage of decomposition, original structures no longer discernable
AH - upper mineral soil enriched in organic matter
describe the A horizon
- First layer where organic matter from LFH interacts with mineral soil
- Zone of incorporation of OM into mineral soil
- Generally rich in nutrients
- High biological activity
- Generally dark in color
- Topsoil
- Roots
Important layer, when lost takes a long time to rebuild
describe the E horizon
- Zone of eluviation (leaching)
- Soluble minerals and OM move out of this horizon
- Generally a lighter “washed” appearance in color
- Roots
describe the B horizon
- Zone of illuviation (deposition)
- Accumulation of materials leached from above
- Commonly clay, humus, and iron
- Variable in color from reds and yellows to browns and greys
Roots
