ESS 210 Exam 2 Study Guide
ESS 210 Exam 2 Study Guide ESS 210 001
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This 5 page Study Guide was uploaded by Michaela Humby on Sunday February 21, 2016. The Study Guide belongs to ESS 210 001 at University of Tennessee - Knoxville taught by Andrew Conrad Sherfy (P) in Fall 2015. Since its upload, it has received 219 views. For similar materials see Intro to Soil Science in Environmental Science at University of Tennessee - Knoxville.
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Date Created: 02/21/16
ESS 210 EXAM 2 STUDY GUIDE What is the difference between gravimetric and volumetric soil water content? Given data you should be able to calculate both of these. Gravimetric weigh moist sample dry for 24 hr at 105 C weigh oven-dry soil %θ m =(mass of water (g) / mass of oven dry soil (g)) * 100 Volumetric water plants use water from a volume of soil more important parameter %θ v = (volume of water/volume of soil) * 100 What are some of the unique properties of water? Polar molecule o Slightly positive end and slightly negative end Polarity results in many important properties o High Specific Heat o Expansion of freezing contracts until 4 C o o expands from 4 C to 0 C These properties result in thermal buffering, ice floating What are adhesion, cohesion and capillarity? Cohesion: attraction of water for other water molecules Adhesion: attraction of water for other substances and surfaces Results in soil’s ability to hold water Results in water moving in soil Two forces cause capillarity o attraction of water for the solid (adhesion) o the surface tension of water (cohesion) Height of rise is inversely proportional to tube diameter, o Subsequent change in surface tension What is the concept of soil water potential? SWP is the work water can do as it moves from present state to free pool Adsorbed water in soil less free to move than water in pool Requires energy to remove from soil What determines the energy (or work) potential of soil water? Water in soil is held by surface attractive forces – adhesion/cohesion As surface area increases, amount of water a soil can hold increases (again surface tension) The strength with which water is held can be measured in energy terms ESS 210 EXAM 2 STUDY GUIDE Related to free energy of water - the ability to do work What are the four components of soil water potential? Matric Potential – Ym Attraction of water for soil surfaces and itself Adhesion/cohesion As soil dries, energy of the least tightly held water decreases (lower SWP) Causes movement from moist to dry Most important in humid regions Osmotic or Solute Potential – Ys Attraction of water for dissolved solutes As salt concentration increases, free energy decreases Water moves from areas of low salt (high FE) to high salt (low FE) Important in arid, semi-arid regions, and salt-affected soils Pressure Potential – Yp Gas pressure effects - MINOR High atmospheric pressure can move water in soil Gravitational Potential – Yg Downward movement of water in response to gravity Water in macro-pores responds to this Water in micropores is influenced, but matric is more important What is field capacity? Field Capacity = -10 to -33 kPa greatest amount held against gravity all micro-pores filled macro-pores are drained What is permanent wilting point? - 1500 kPa; work access to water is high and there is a limit for most plants What is gravitational and plant available water? Gravitational water water between 0 and - 10 to -33 kPa drains freely plant unavailable - moves too fast Plant-available water ESS 210 EXAM 2 STUDY GUIDE held between -10 to -33 and -1500 kPa total plant available = FC - PWP water stored in larger micro-pores Unavailable water water held at SWP of < -1500 kPa small micro-pores water held at >-33 kPa How does plant available water differ between soil types? Passive absorption (>90%): Due to transpiration Evaporative loss of water at leaves results in water being pulled up the xylem tubes. How does water move in soil? Water moves from moist to dry; dry soil has higher attraction for water than wet soil; The water moves sideways and downward at the same rate. This is because of adhesion and cohesion. How about under saturated conditions vs. unsaturated conditions? Rapid movement = gravity potential This is SATURATED FLOW, water moves in response to gravity At soil water potentials > -33 kPa Preferential flow--through cracks in matrix Slow flow, independent of gravity is UNSATURATED FLOW Matric and osmotic potentials Movement from high SWP to low SWP What causes flow constraints in the soil? Unsaturated flow slower in fine textures Slower in compacted soils What controls infiltration and percolation? Why are these processes important? What is soil consistence or soil consistency? What are the differences if any between the two and how are they interpreted or measured? Degree to which soils resist deformation a. Rupture or penetration resistance ESS 210 EXAM 2 STUDY GUIDE Why is soil strength important? How do we measure soil strength? How does soil strength differ between cohesive and non-cohesive soils? What is liquefaction? Cohesive vs. Non-Cohesive b. Collapsible soils i. Thixotrophy (liquefaction) What is soil compressibility? What controls soil compression? How can it be measured? How can soil compaction be limited in practice? Compressibility and structural stability Compressibility and soil texture Method: Standard Proctor Test Compaction control in the field? Why is shear strength important? What are Atterberg limits? How can they be measured? What does soil plasticity mean? Atterberg Limits c. Shrinkage Limit d. Plastic Limit e. Liquid Limit f. How measure? Plasticity (P) = LL - PL What kinds of processes do soil temperature influence? Temperature Governs Rates of: a. Biological Processes i. Seed Germination and Root Function ii. Microbial Activity b. Chemical Processes i. Rates of reactions and sorption ii. Viscosity and Solubility c. Physical Processes i. Freeze thaw cycles ii. Evaporation and Aeration Soils have incredible ability to store thermal energy Temperature is a measure of the thermal state (energy) considered in reference to its ability to transfer heat (potential and the driving force) Varies diurnally, seasonally and with depth How is thermal energy transferred? Conduction Convection Radiation What are the definitions of temperature, conduction and convection with respect to soil heat? Temperature is a measure of the thermal state (energy) considered in reference to its ability to transfer heat (potential and the driving force) ESS 210 EXAM 2 STUDY GUIDE Heat conduction is the transfer of thermal energy between neighboring molecules due to a temperature gradient Does not require any bulk motion of matter Due to vibrations of the molecules and electron transfe Convective heat transfer is a mechanism occurring because of bulk movement of mass (observable movement), in this case soil water or gasses Natural (or free) convection and forced (or advective) convection What do the terms heat capacity, thermal conductivity and thermal diffusivity quantify? What other physical properties of the soil influence these three and how? How can we go about measuring these in the field or lab? Heat Capacity (C) Simply, the amount of heat which can be stored in the soil. Or, the heat energy which can be added/removed per degree change in temperature. Thermal Conductivity (λ) Simply, the soils ability to transmit heat, mainly through conduction. Defined as the amount of energy per time (heat power) which can travel a length (meter) per unit area, per unit temperature gradient. Thermal Diffusivity (α) Ratio of thermal conductivity to heat capacity α = λ / C Absolute temp. Electrically Thermocouples Thermistors Integrated Circuit Non-electric Infrared Predictive methods Heat Capacity de Vries (1963) Approximation Sum of the constituents Can do this for thermal conductivity too