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ENVB 210- Midterm Exam Guide - Comprehensive Notes for the exam ( 25 pages long!)


Department
Environmental Biology
Course Code
ENVB 210
Professor
Caroline Begg
Study Guide
Midterm

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McGill
ENVB 210
Midterm EXAM
STUDY GUIDE

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Summary Notes - Final Exam - ENVB 210
Week 6 - Soil Water, Removal, & Contamination
Groundwater use = 30% = stream water + infiltration!
Flow always wet => dry, high => low elevation!
Rates of flow depend on elevation !+ permeability!= 30-150 cm/day = 5yrs/2km (clays slower)
River flow comparison - twig moves downstream at 30-60 cm/second - 1hr for 2km!
One Point!!
Livestock wastes!!
Mill tailings in mining areas!
Land spreading of sludge
Runoff of salt from roads and highways!
Non-Point (distributed sources)!
Fertilizers on agricultural land!
Pesticides on agricultural land and forests!
Contaminants in rain, snow, and dry
atmospheric fallout!!
Pollution Plume in groundwater - liquids from solid wastes//leaking liquid pollutants
percolate through soil, simultaneously releasing into the gas-phase
H2O soluble pollutants disperse at capillary fringe
Insoluble pollutants form pollutant lens: floats above water table OR moves down!(high d)
Unconfined//Shallow Aquifer: Separated by impermeable layer!(low hydraulic conductivity)
Subsidence due to water removal
Opposing water pressure reduced by excessive pumping/withdrawal
Upper layers dry out, compress and compact due to downward force of gravity
Reduced pore size - permanent condition, rewetting the soil does not cause it to go back up!
Lessens total storage capacity of the aquifer system!
Severe cases (extensive ground water mining) may case crack in ground => EARTH FISSURE
Salt Water Intrusion into Coastal Wells!
Sea water depth: overlying column of fresh groundwater = column of heavier sea water!
If sea level = constant + uniform recharge from rainfall, interface would be motionless
Neither element is constant + humans use groundwater
Edge of land and water is porous - if excess water is drawn, salt water intrudes
Factors of Salt water intrusion:
-sea level rise//decrease in recharge
-subsidence//increase in pumping!
Problems in the Prairies: said to become drier - need more irrigation. To estimate the salinity in
western Canada is difficult!because salts move with precipitation up and down the soil profile!
Saline Seeps
Excess water in holding capacity raises water table causing groundwater to flow downslope!
Groundwater flowing over salts in bedrock deposits dissolves and transports the salts
If water is (~2m) to the soil surface, capillary action and evaporation draw up the saline water
Water evaporates, leaving the salts behind => gradually accumulate to form saline seep
!1
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Week 7 - Soil Colloids: Clays and Humus
Soil Mineralogy influences…
Soil fertility!
Physical properties!
Soil development: (primary igneous rock minerals => secondary new minerals)e
Silicate Minerals (SiO2) of Sand and Silt!
Mica (layers of silicates) - often weathers into secondary clay materials!
Muscovite (white)!& Biotite (black)!
Quartz (3-D shape)!
resistant b/cu of Si-O bonds - no need for accessory cations!
Feldspars (3-D)!
substituted Al3+ for Si => (-) charges balanced by ‘accessory cations’
more easily weathered !
Non-Silicate minerals - apatite - phosphate mineral!
Properties of the Clay Fraction!(see graph 1)
•Small with large surface area!
Platy//flaky micro-crystals (some are needle shaped or amorphous); result in properties of
slipperiness, stacking, coating, lining pores!
Surface (-) charge; must be balanced w/ accessory cations
•Adsorb water on surface//or between layers within the crystal (shrink-swell clays)!
Alumino-Silicate Clays!
Basic Building Blocks of Clay Minerals:
-Al3+ + 6 OH- or O atoms => 8-sided octahedral sheet
-Silicon (Si4+ ) + 4 Oxygen => 4-sided tetrahedral sheet
Alumni-silicate minerals divided into groups based on…
-# Si-Tetrahedral: # of Al-Octahedral!
-Oxygen shared between layers!
Interlayers: adsorbed cations and water
How do Clays Get Their Charge => Isomorphous Substitution!
formations secondary mineral types usually alters electrical charge (fixed or
permanent charge until it weathers away)!
Must be balanced by accessory cations in crystal structure//surface
Substitution by similar size not charge
Unbalance negative charge restored by K+, Na+, Ca 2+, Mg2+
Types of Clays!
sheets => layers => clay mineral type
Different combinations given in ratios of tetrahedral: octahedral (eg. 1:1, or 2:1)!
Amount of isomorphous substitution determines the charge of the clay or the "cation
exchange capacity” CEC - Ability to absorb cations to the surface.!
!2
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