Monday Oct 4 1 Field trip A1 A2 signups make sure you are where you think you should be 2 5 credit people field trip introduction in lab today 1 If you are unable to attend THIS SATURDAY let Aaron know by 5PM TODAY 2 You will get a ZERO for the field trip if you do not participate Soils We know more about the movement of celestial bodies than about the soil underfoot Leonardo da Vinci Soil Definition Solid earth material that has been altered by physical chemical and organic processes so that it can support rooted plant life Engineering definition Anything that can be removed without blasting Soil Production Soil Production Inputs Conversion of rock to soil Soil Production Outputs Downslope movement of soil Soil Thickness Storage input output soil thickness or rock conversion soil transport thickness that is soil thickness reflects the balance between rates of soil production and rates of downslope soil movement Slope Weathering Rate Factors of Soil Formation Climate Organisms Parental Material Topography Time Factors of Soil Formation Climate Temperature and precipitation Indirect controls e g types of plants Weathering rates The greater the rainfall amount the more rapid the rate of both weathering and erosion Factors of Soil Formation Organisms Types of native vegetation Weathering is dependent of plant growth Plant and animal activity produces humic acids that are powerful weathering agents acids derived from chemical breakdown of organic matter Plants can physically as well as chemically break down rocks Plants stabilize soil profiles Animals including humans tend to increase erosion Factors of Soil Formation Parent Material Chemistry Mineralogy Grain size Factors of Soil Formation Topography Ground slope Elevation Aspect north vs south facing slopes Factors of Soil Formation Downslope transport of soil is a function of slope Erosion rate f S Steeper slopes erode faster The steeper the surface slope the more likely any eroded material is to be transported out of the system Factors of Soil Formation Soils on hillslopes reach an equilibrium thickness often about 1m Soils on flat surfaces such as floodplains or plateaus tend to thicken through time due to weathering rates being greater than sediment transport rates Factors of Soil Formation Time for development and destruction of soil profiles Typical chemical reaction rates are slow the longer a rock unit has been exposed the more likely it is to be weathered And the longer soil waits before transport the thicker it can become Processes of Soil Development combined effects of additions to ground surface chemical transformations vertical transfers removals from soil relative importance varies Additions to soils Inputs from outside ecosystem Atmospheric inputs Precipitation dust deposition Horizontal inputs Floods tidal exchange erosion landwater movement Inputs from within ecosystem Litterfall and root turnover Transformations Decomposition of organic matter Breakdown to form soluble compounds that can be absorbed leached away Depends on input quantity location roots leaves environment temp precip Humification to form complex organic matter Weathering of rocks Physical weathering fragmentation of rock Freeze thaw drying wetting fire Chemical weathering primary secondary minerals Parent material bedrock undergoes weathering to become regolith soil saprolite Soil is a mixture of mineral and organic matter lacking any inherited rock structure Soil Saprolite is weathered rock that retains remnant rock structure Saprolite Saprolite Soil Horizons and Profiles Soil Horizons over time soil layers differentiate into distinct horizons not deposited but zones of chemical action Chemical reactions and formation of secondary minerals clays Leaching by infiltrating water elluviation Deposition and accumulation of material leached from higher levels in the soil illuviation Soil Profile Suite of horizons at a given locality Typical soil profile Cookport soil Pennsylvania A Horizon B Horizon C Horizon Soil classification messy Soil classification soil orders Aridisols Mollisols Alfisols Ultisols Spodosols Oxisols Histosols Gelisols Andosols Vertisols Entisols Inceptisols arid zone soils calcic horizons grassland soils thick A horizon and forest soils thick B horizon tropical soils quite oxidized wetland soils polar soils volcanic parent material swelling clays weak A over C horizon weak B horizon Soil classification soil orders Aridisols Mollisols Alfisols Ultisols Spodosols Oxisols Histosols Gelisols Andosols Vertisols Entisols Inceptisols arid zone soils calcic horizons grassland soils thick A horizon and forest soils thick B horizon tropical soils quite oxidized wetland soils polar soils volcanic parent material swelling clays weak A over C horizon weak B horizon Soil types more simply Aridisols Physical weathering breaks rocks into small mineral particles Soil types Oxisols Chemical weathering dissolves and changes minerals at the Earth s surface Soil types Mollisols Decomposing organic material from plants and animals mixes with accumulated soil minerals Limits on soil development Balance Between Downward Lowering of Ground Surface Downward Migration of Soil Horizons If erosion rapid or soil evolution slow soils may never mature beyond a certain point Extremely ancient soils may have lost everything movable Rates of Soil Development U S Department of Agriculture estimates that it takes 500 years to form an inch of topsoil That s less than 0 01 mm yr 1 Modern rates of soil loss are 100 to 1000 times rates of soil formation typically mm yr 1 to cm yr 1 in agricultural settings Sets up a fundamental problem due to the erosion of natural capital Soil and the Life Cycle of Civilizations How long would it take to erode a 1m thick soil Thickness of soil divided by the difference between Rate of soil production and erosion 1m 1000 years 1 mm yr 1 01 mm yr 1 This is about the life span of most major civilizations Man despite his artistic pretensions his sophistication and his many accomplishments owes his existence to a six inch layer of topsoil and the fact that it rains Author Unknown A nation that destroys its soils destroys itself President Franklin D Roosevelt Feb 26 1937 National Archives 114 SC 5089 and finally sign up for field trip A1 or A2 by 5 TODAY On Wednesday we will discuss erosion how to get rid of the materials created by physical chemical weathering and soil formation
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