When does run off occur
When accumulation exceeds rare if infiltration or soil storage capacity
Precipitation that never reaches soil due to vegetation
Material that reduces evaporation and controls weeds
Excess nutrients (phosphorus) that leads to excessive aquatic growth and ultimately oxygen depletion
Oxidation if pyrite produces extreme acidity and soluble iron and sulfur
Acid mine drainage
The ability if soils to bind chemical substances depends on these 3 things:
Chemical characteristics if substance
Characteristics if soil
Provides maximum opportunity for soils to bind chemicals:
Greatly decreases the ability if a soil to bond chemicals
Preferential or bypass flow
Transports chemicals to groundwater more rapidly via macro pores
Oxygen concentration does what as soil depth increases?
High saturation levels does what to o2 content?
What are concentrations of co2 like beneath the soil surface.
It can be 10 to 100 times greater and be toxic
What can anaerobic conditions in soil lead to?
Production of reduced nitrogen gases, methane gases, hydrogen sulfide, ethylene
What 2 things regulate o2 availability?
Soil macro porosity and water content
What two ways does soul gas exchange?
Mass flow and diffusion
What is the more important form of soil gas exchange?
What is mass flow?
Physical movement if air due to fluctuations in moisture content
Why does diffusion occur?
What is the partial pressure gradient?
A difference in every potential of gas concentration
At what percentage air porosity dies microbial and root respiration cease?
What does water do to diffusion?
Slows it because it moves 10000 times slower
Loss of electrons in a substance
The gain of electrons
What is the electron receptor for respiration?
The measure in volts of how aerobic or anaerobic a system is. A measure of electrical potential of a substance to give up electrons
What happens if Eh falls below .32 volts
A soil is devoid of o2 and other elements are used for microbial metabolism
Anaerobic decomposition can lead to…
What 3 factors affect soil aeration and Eh?
Drainage and nacroporosity
Is reduction good for plants?
What kinds if soils are under frequent reducing conditions?
Wetland soils —> histosols
What is a veal action process?
Seeds needing cold treatment to germinate
What is biological 0?
5 degrees centigrade
What happens to microbial activity as temperature rises?
It doubles for every 10 degrees and dies around 50 or 60
What is albedo?
The fraction of sunlight reflected?
What is aspect?
The direction of slope of a surface