Liquids and Gases Flashcards
Soil air compared to atmospheric…
Similar composition however organism influences with increased CO2 relative to O2
Importance of air/water independently?
Air allows aerobic organisms to thrive whilst rain causes saturation
Contamination in soils…
Volatile Organic Compounds, contaimination varying with organism presence, so anaerobic organisms produce CH4, N2O, H2S when low in O2
Relative Humidity
Measure of how much water vapor in a water air mixture compared to the maximum amount possible
What is the average relative humidity in soils?
99-100%
What does RH depend on?
Increased temperature holds more water vapour
What does diffusion depend on?
Conc Grad, water content, size/number of pores, temperature and molecule type
Diffusion and pores?
Total porosity more important than pore size, and pore continuity with increasing speed with higher connectivity
When does mass flow of gases happen in soil?
Soil temp changes, gas velocity, atmosphere pressure changes, plant water extraction, wind blowing over surface increasing evaporation, flooding
Tortuosity
Ratio of actual flow path relative to straight distance from end to end
Bulk Density
This is the weight of material including the air space in unit volume
What does bulk density indicate?
Compaction and porosity, being soill mass/V
Specific Gravity
This is mass to volume ratio of a mineral relative to water at 4C
Unique proeprties of water?
Polarity, hydrogen bonding, surface tension, cationic hydration with binding
Common H2O binding cations…
Na, Ca, Mg, K attracted to O
What are the most common solutes?
Ca, Mg, K, Cl, NO3, SO42, H2PO4, HPO42, HCO3
When does leaching occur?
Water enters soil, dissolving soluble compounds, redistributing nutrients
How may climate influence soil?
Tropics high temp and precip means high biological activity, whilst humid climates with cold temp not
Field Capacity
This is the amount of water within a soil after excess water has drained away
Permanent Wilting Point
The point at which no water is avaiable to the plant
What two states represent moisture of soils?
Field Capacity
Permanent Wilting Point
Ion Exchange
Electrostatic interactions between ions, or solute/surface binding, solid phase dissolution in solution, solid precipitation, organic molecule weak soprtion pore retention and phase partinioning
Charge of clays and OM?
Anionic: clays due to isomorphic substituion and H+ loss in humus
Why does ionic exchange occur?
Coulombic forces being weaker than the covalent ones
What determines equilibrium of cationic exchange?
Small hydrated radius held tighter and exchange less easily than larger cations due to closeness to exchange complex and larger size meaning tighter hold
What element has highest electrostatic adsorption?
Al
How may elements with lower electrostatic adosrption displace higher?
High concentrations
Why is H+ low competitive?
Larger hydrated radius, singular charge and low concentrations, however acidificfaction for pH-dependent surface charge readily adsorb it
Importance of Anionic Exchange Capacity…
Lower influence but affects anionic pesticides like 2, 4-D and retention of Cl-, NO3- and SO42-
Cation Exchange Capacity
This measures total amount of cations that can be held by a given mass of soils
How is ions equivalent weight measured?
Atomic Weight divided by charge
How many CEC be determined by Clay/OM?
Isomorphic Substitution, pH, Humus greatly increases CEC
London Forces
Resonances between transient dipoles of adjacent atoms
Hydrogen Bonding
Electron sharing between two permanent dipoles
Impotance of Van der Waals forces…
Ionicaly bind organic ions to clays or humus allows pesticide retention and proteins acting as external enzymes
Soils anti-pollutant affects?
Sorption of nonpolar, hydrophobic organic compounds, assimilate alkenes, aromatics, petroelum, pesticides
