EXAM 2 - Chapter 6 & 7 Flashcards
What is Darcy’s law? What do the variables mean?
The quantity of water per unit of time that flows through a column of saturated soil; A is the area in which water flows, Ksat is the saturated hydraulic conductivity, Y is the change in water potential between the ends of the column, L is the length of the column
Unsaturated flow vs saturated flow.
Unsaturated flow occurs when the soil pores are filled with air leaving only smaller pores to hold and transmit water; Saturated flow takes place when the soil pores are completely saturated with water
Vapor flow (in response to temperature and salinity gradients)
occurs as vapor pressure differences develop in relatively dry soils; water vapor will move from a zone of low salt to high salt where it lows the vapor pressure; if temperature of a uniformly moist soil is decreased, the vapor pressure will decrease and it will move toward the cooler part
Evaporation
considered a “waste” of water from the standpoint of plant productivity
Transpiration
an essential component for plant growth that provides the water plants need for cooling, nutrient transport, photosynthesis, and turgor maintenance
Evapotranspiration
The combination of Evaporation and Transpiration
Potential Evapotranspiration
the rate that tells us how fast water vapor would be lost from a densely vegetated plant-soil system if soil water content were continuously maintained at an optimal level; determined by the vapor pressure gradient
Soil Water Discharge
Water that does not enter the soil, but runs off instead
Perched Water Table
when water enters a system more rapidly than lateral capillarity can carry it away, water sits
Water Balance Equation
Precipitation - Soil Storage + Evapotranspiration + Discharge
Evaporation Pan
Used to help estimate potential evapotranspiration; reflects relative humidity, temperature, wind speed, and other climatic variables related to the vapor pressure gradient
Water Stress
when soil water content is less than optimal, the plant will not be able to withdraw water from the soil fast enough to satisfy PET, and the plant will lose turgor pressure and wilt; ET < PET
Water Deficit
the difference between PET and actual ET; a large deficit is indicative of high water stress and aridity
Leaf Area Index
the ratio between leaf and unit land area which increases in vegetated areas that more radiation will be absorbed by foliage to stimulate transpiration and less will reach the soil to promote evaporation
What industry uses the most water?
Agriculture
Consumptive Use
Freshwater withdrawals which are not immediately available for further use because they have been evaporated, embodied in products and waste, or discharged after use into different watersheds or the sea
Blue water vs green water
Blue water is the freshwater available for removal from surface water bodies and aquifers; green water is water stored in the soil as soil moisture and used by plants in evapotranspiration
Furrow and Flood Irrigation
Water is applied to the upper end of a field and allowed to distribute itself by gravity flow through furrows; all plants aren’t getting an accurate amount of wter
Center Pivot Irrigation
low-energy, precision application according to soil properties; very high equipment costs
Micro-irrigation (Drip irrigation)
A small portion of the soil is wetted using a drip system where tubing and emitters are buried 20-50cm deep so water soaks directly into the root zone
Aquifer
a saturated, permeable layer of sediment or rock that can transmit significant quantities of water under normal pressure conditions
How do drainage systems work?
they hasten the removal of excess water from the soil and lower the water table; septic tank drain fields operate in reverse by carrying wastewater to the soil
Ditch
diverts water from rivers to other areas
What is the usage of a drainage pipe? Which orientation should it be placed in?
Placed downward to lower the water table and or absorb excess water to prevent waterlogging
What is a percolation test?
A measurement of the rate of percolation of water in a soil profile, usually to determine the suitability of a soil for use as a septic tank drain field
What are the main gases in the atmosphere?
78% N, 21% O2, 0.035% CO2
What are the main gases in soil air?
~78% N, lower in O2 and higher in CO2; Higher in water vapour
How is CO2 and O2 diffused into and out of soil?
The partial pressure of oxygen is greater in the atmosphere and will diffuse into soil pores; The partial pressure of carbon dioxide is greater in the soil and will diffuse into the atmosphere
What are redox reactions?
Redox reactions take place when the reduced state of an element is changed to the oxidized state
What is the Eh scale?
redox potential; the tendency or potential for electrons to be transferred from one substance to another
What order do elements get reduced in?
O, N, Mn, Fe, S, CH4
What are the reduced forms of C, S, N, Fe, and Mn?
CO2 -> methane SO4 -2 -> S-2 -> H2S NO3 - -> N2 -> NH4+ Fe 3+ - > Fe 2+ Mn 4+ -> Mn 2+
What is the role of soil microorganisms in redox chemistry?
microorganisms use organic matter and the electron sources as sources of oxygen
What is the relationship between the sequence of redox changes with the time soil is saturated?
Once a soil is fully saturated and under conditions in which organisms have decreased the oxygen supply, they begin to use elements in the order of redox potential
What are the effects of redox changes on greenhouse gases?
production of N2O and CH4 are responsible for about 80% of anthropogenic global warming caused by the greenhouse effect
What is the relationship between soil redox and soil pH?
pH increases as H+ ions are consumed in reactions (when the reaction proceeds to the left)
What is the relationship between chromium toxicity and soil reduction?
Oxidized Cr 6+ is movable and very toxic to humans; in neutral to acid soils, easily decomposed organic materials can be used to reduce chromium to the Cr 3+ forms which can not be reoxidized
What is containerized soil waterlogging?
the root zone of containerized plants has limited volume to store water is exposed to fluctuations in air temperature and lacks pore continuity that leads to drought and waterlogging
Hydric soil indicators
features associated with the occurrence of saturation and reduction; redox depletions, redoximorphic features
What is the oxidized roots zone?
reddish, oxidize iron around root channels where O2 diffused out from the aerenchyma-fed roots of a hydrophyte
Gleyed soil
low-chroma colors, colors with a chroma of 1 or less
Redoximorphic features
the contrasting colors of redox depletions or reduced iron and zones of reddish oxidized iron
Hydrophytes
Plants adapted to life in waterlogged soils
What are the requirements to be considered a wetland?
wetland hydrology (anaerobic, slow water over a period of 2-3 months), hydric soils (histosols, aquic suborders), and hydrophytic plants (vegetation that has adapted to low water contents); wetland chemistry (low redox potential, to Fe)
What are the functions of wetland soils?
Species habitat, water filtration, flooding reduction, shoreline protection, commercial and recreational activities, natural products
What are the types of wetlands?
Inland (swamps, bogs); riparian or ephemeral; organic (histosols); salt-affected, permafrost-affected (Histels)
What processes are affected by soil temperature?
plant processes, microbial processes, freezing and thawing, permafrost, soil heating by fire, contaminant removal,
How do recent events with permafrost affect land features?
melting permafrost can cause trees to fall and buildings to collapse by turning the soil into noncohesive mud
Frost Heaving
Alternate freezing and thawing which forces objects upward into the soil; most severe where the soil is silty in texture, wet, and lacking a covering of insolation
Albedo
the fraction of incident radiation that is reflected by the land surface
What are the effects of surface mulches on soil temperatures?
Surface mulches is a material used to cover the soil surface primarily for controlling evaporation, soil erosion, temperature, and/or weeds
What are the effects of clear plastic on soil temperature? What are some cons of this method?
greater heating effect than black plastic because it allows light in and traps it; nonrenewable fossil fuels, removal
What are the effects of black plastic on soil temperature?
black, opaque plastics can help control weeds and eliminate the need for the cultivation
What are the effects of biodegradable plastic on soil temperature?
the heating effect, a biodegradable plastic film made from cornstarch that can stay on the soil and degrade naturally
What are the effects of organic plastic on soil temperature?
cools regulates soil temperature; provides great control over erosion but causes the soil to warm more slowly during spring than where the soil is left bare; conserves soil moisture by decreasing evaporation
How is heat transferred from the soil to the air?
conduction
What are the diurnal profile patterns of soil temperature?
soil reaches its max temperature later in the afternoon/evening than air, the lag time is greater and the fluctuation less pronounced for depths
What are the seasonal profile patterns of soil temperature?
seasonal temperatures increase and decrease with a lag behind air temperature
When does percolation occur and what is it influenced by?
When the amount of rainfall entering a soil exceeds the water-holding capacity of the soil; influenced by the amount of rainfall and its distribution, runoff from the soil, evaporation, the character of the soil, and the nature of the vegetation
Vadose Zone
the unsaturated zone above the water table
