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Weathering and Soils - New Jersey City University

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									Soils and Environment
WEATHERING
  Physical
    and
  Chemical
   Effects
      WEATHERING, EROSION,
        TRANSPORTATION
• Weathering- Physical disintegration and
  chemical decomposition of rocks
• Erosion- Physical removal
• Transportation- Movement of eroded particles
• Chemical vs. Physical Weathering
• Effects of weathering
  –   Surface alteration of outcrops
  –   Spheroidal weathering
  –   Differential weathering
        Mechanical Weathering
•   Freeze-Thaw Weathering
•   Salt Weathering
•   Wetting and Drying
•   Insolation Weathering
•   Pressure Release
•   Stress Corrosion Cracking
          CHEMICAL WEATHERING
• Decomposition of rock to form new substances
  –   Changes in Equilibrium
• Water
  – Congruent solution (limestones) vs incongruent
    solution (clay minerals)
• Carbon Dioxide- changes in pH change
  solubility of minerals
• Role of Oxygen
  –   Fe in ferromagnesian minerals becomes oxidized
      •   Hematite and Limonite
        Chemical Weathering
• Solution of ions and molecules
• Production of new materials
  – clay minerals
  – oxides
  – hydroxides
• Release of residual unweathered materials
  – quartz and gold
                   Chemical Weathering of
                         Silicates
Interlayer Cations
                   hydrolysis
   Na, K
   Ca, Mg          Hydration, solution
                                            Solutions of Na+, K+, Ca2+, Mg2+

 Aluminosilicate sheets (e.g. as part of feldspars)
                      solution
                                               Silicic acid (H4SiO4)
   Al 3+ & Si 4+    Hydrolysis, hydration
                          Secondary minerals, e.g. clays
 Brucite and alumina sheets and incorporated ions, e.g. Fe2+
                           Oxidation, hydrolysis
       Brucite
                                                   Hydrous oxides, e.g. FeO(OH)
                          hydration
       Alumina
        Fe2+              hydrolysis               Chelate complexes
                          chelation
   Results of Weathering: Clay
             Mineral
• Clay minerals give information about
  weathering conditions
• Kaolinite: humid, acid conditions, alteration
  of K-Feldspar
• Illite: weathering of feldspars and micas
  under alkaline conditions where leaching of
  mobile K does not occur
• Montmorillonite: weathering of basic
  igneous rocks under alkaline conditions with
  a deficit of K+ ions
                   Clays
•   Kaolinite
•   Illite
•   Montmorillonite
•   Chlorite
•   Mixed-layer clays
              Soils: Definitions
• Loose unconsolidated material composed of
  regolith and partially decayed organic matter,
  water and gases
• A soil profile is a vertical face of soil that can be
  exposed and includes all the layers (horizons)
  from the surface to the parent rock (bedrock)
• The solum is that part of the profile that is
  influenced by plant roots
• A pedon is a 3-D representation, the smallest
  volume that can be called a soil
    Soils and Food Production
• Roots of Agriculture
  – Middle East (Iraq) origins
• Roman techniques of soil fertility
• Terrace building in Meso-America and
  South East Asia
• Increasing world population reliance on
  pesticides and fertilizers
       Useful Properties of Soils
• Provides water, nutrients and anchorage for
  vegetation
• Provides habitat for decomposers, essential in
  carbon cycle and mineral cycling
• Acts as a buffer for temperature changes and
  for the flow of water between atmosphere and
  groundwater
• Because of its cation exchange properties,
  acts as a pH buffer, retains nutrients and
  other element loss by leaching and
  volatilization
  Soils as part of the Ecosystem
• An ecosystem is a community of interacting
  organisms and their physical-chemical environment
  that function as a self sufficient whole
• Soils are an essential part of the Carbon cycle due to
  the effects of microorganisms

                    Atmospheric CO2


        Primary                       Decomposers
        Producers

                    Organic Compounds
      Soils and Geologic Time
• Soils could only exist after the colonization of land
  by organisms, in particular vegetation
• First land plants in the Ordovician (450 my)
• By the Devonian the land had been colonized (370
  my)
• By the Carboniferous (300 my) extensive forest
  habitat generated soils similar to today
• Properties of soils determined by climate,
  organisms, relief, parent material and time, thus
  we can extrapolate the conditions that formed
  paleosols
              Soils and Humans
• Cultivation of soils began about 10,000 BP in
  Mesopotamia (Tigris and Euphrates rivers of Iraq)
• The land was a porous friable silt loam that required
  irrigation.
• The civilization ended due to wars, floods, infilled
  irrigation channels, erosion (gullying), salinization,
  loss of food production and famine
• Other centers of agriculture in the fertile Nile valley,
  Indus and the river valleys of China
• In Europe soil erosion instigated colonization of other
  lands and remains the worst problem facing humans.
• In other areas terracing became the primary farming
  technique (Southeast Asia, Peru)
 The Green Revolution: An Idea of
           the 1960’s
• Increase world population demands the increase of food
  production
• Increases in land under cultivation, more intensive agriculture
  (mechanization) or both
• The introduction of fertilizers, pesticides, irrigation, varietal
  seeds (seed banks), Population growth 2% WHILE food
  growth 4%.
• In 1970, Norman Borlaug received the Nobel Peace Price
• However, not a panacea >> potential realized, need for
  irrigation,constant inputs of fertilizers, pesticides, and energy
  intensive mechanized labor, benefit large land holders,
  detrimental to most 3rd world countries
                   Soils
• Pebbles, gravel and sand particles
• Aggregates (mm to cm) of clays
• Roots
• Partially decayed to totally decayed
  vegetation (Humus)
• Organisms (earthworms, arthropods)
• Pore spaces filled with air and gases
• Water
                SOIL Texture
• Texture: Relative proportions of sand, silt
  and clay
  –Dominant size fraction as a descriptor [clay,
   sandy clay, silty clay]
  –If no dominant fraction then >> Loam {40%
   sand; 40% silt; 20% clay}
• Clay-sized particles vs. clay minerals
  – type of clay not just % clay
• Texture is an indicator of other properties
  (ease of cultivation)
Soil Textural Classification
            Soil Structure
• Arrangement of soil particles into
  cemented aggregates
• Aggregates are secondary units or
  granules composed of many soil particles
  held together by organic substances, iron
  oxides, carbonates, clays and/or silica
• Natural aggregates are called PEDS
• A CLOD is a coherent mass of soil broken
  apart by artificial means
               Bulk Density

• Density of soil minerals ranges between 2.6
  to 2.7 g/cm3
• When dry, the bulk density is about half the
  above value, because voids are filled with air
• Defined as rb = M/V;
• Commonly 1.0-1.6 g/cm3
• Varies over small distances due to weather,
  cultivation, compression by animals
• Increases with depth
Core sampler for determination of bulk density. The sampler
yields a core of a fixed volume. The core is dried and weighed
The weight divided into volume gives the bulk density of soil
                   Porosity
• Calculated from the dry bulk density and
  the particle density
  – e = 1 - (rb / rs) x 100 = % porosity
• Where rs is usually between 2.6-2.7 g/cm3
• The pore space is occupied by water and
  air
• Transmission pores >50mm
• Storage pores 0.5-50 mm
• Residual pores <0.5 mm
Relationship Between Texture
 Bulk Density, and Porosity
                                SOIL
• Various definitions
    – Unconsolidated material above bedrock
    – weathered material & organic matter
        •   supports plant life [air, water, organic matter &
            mineral material]
•   Loam {40% sand; 40% silt; 20% clay}
•   Clay-sized particles vs. clay minerals
•   Soil Horizons
•   Residual Soil (on bedrock)
•   Transported Soil (alluvium)
                             SOIL
• Parent Rock, Time, and Slope
• Organic Activity
• Soils and Climate
  – Pedalfer- aluminum and iron rich clays
  – Pedocal- calcium rich
  – Hardpan- crusts (Fe and caliche)
  – Laterites- tropical soils
      •   Bauxite- Principal ore of Al
• Buried soils
                   Soil Horizons
• Identified, named, by symbols consisting of
  upper and lower case letters
• Each symbol recognizes a formational
  property
  – O- organic material
  – A (A1)-accumulation of decomposed org. matter
  – E (A2)- mineral layer, loss of silicate, eluviation (leaching)
    horizon
  – B (B2)-Illuviated humus, silicate clay or hydrous oxides
  – C (C)- mineral horizon above parent
  – R (R)- Consolidated Bedrock
 Soil Structure: Pan Structures
• Dense layers or pans
• Interference with root and water
  penetration
• Produce shallow soils
• Due to compaction, filling of pores with
  clays or chemical cements
• Very firm layers are called hardpans
                   Types of Pans
• Claypan
   – Dense soil layers produced by downward migration of clay and
     accumulation in subsoil as a B-horizon material
• Duripan
   – Layers cemented by precipitates of silica, alone or in combination
     with iron oxides or calcium carbonates
• Fragipan
   – Fragilis (brittle), dense subsoil layers (50-60 cm beneath surface)
     bonded into a hard, brittle form by clay
• Caliche
   – Hard lime-cemented white crust in arid regions
• Plinthite
   – Laterite, precipitated sesquioxides as cements. Weathered soils of
     the tropics formed at depth
• Plowpan
   – Artificially produced, due to compaction by plows.
Caliche
             Soil Taxonomy
• Organization into 11 orders*, 54
  suborders, 238 great groups, 1922
  subgroups and then families and series,
  each series subdivided into mapping units
  called phases of series
  – * including a tentative order andisols (soils
    with over 60% volcanic ejecta)
                           Orders
• Most general category
• 5 of the orders exist in a wide variety of climates
   – Histosols (organic soils); Entisols (undeveloped);
     Inceptisols (slightly developed); Andisols (volcanic);
     Vertisols (swelling-clay)
• 6 are the product of time and the microclimate in
  which they develop
   – Mollisols- naturally fertile, slightly leached, semiarid to
     subhumid, grassland
   – Alfisols- fertile soils in good moisture regimes
   – Ultisols-leached, acidic soils, warm climates, low-
     moderate fertility
   – Aridisols-arid region soils
   – Oxisols- infertile, hot humid tropics
   – Spodosols- cool climate, acidic sandy
               Soil Orders
• In the US Mollisols cover 25% of the land
• Worldwide distribution
  – Aridisols 19%
  – Alfisols 13%
  – Inceptisols 9%
  – Mollisols 8%
  – Oxisols 8%
                 Soil Taxonomy
• Classification at 6 different levels
• Level of generalization relates to the range in
  properties allowed in the different classes
• Soil Orders
   – Suborders
      • Great Groups
         – Subgroups
             » Families
             » Series
Soil Orders
        Engineering Properties
• Plasticity-water content of soil
• Soil Strength-ability to resist deformation
   – Cohesion-ability of particles to stick together
   – Friction-fnc. Density, size, shape of soil particles
   – Sensitivity-measures changes in soil strength, clay
     soils very sensitive to disturbance (liquifaction)
• Compressibility- soils tendency to consolidate
  (decrease in volume), settling causes foundation
  cracks
• Erodibility- ease of removal by wind and water
• Corrosion- function of soil chemistry
• Ease of Excavation
• Shrink-swell potential- gain or loose water
  (expansive soils)
              Soil Erosion
• Soil Erosion: Removal in part or whole of
  soil by wind or water
• Natural process
• Erosion is slight from areas covered by
  dense grasses or forest but increases
  dramatically in exposed steep, poorly
  covered soils
• Increased by human activity especially
  poor agricultural practices
                Soil Erosion
• Soil erosion has been documented as early as
  10,000 ybp in Mesopotamia due to agriculture
  that cleared the land (deforestation), overgrazed
  the land by herbivores (sheep, goats)
• Erosion in Europe is believed to have occurred
  5000 ybp with clearing of woodlands
• In the us during the 1930’s (Dust Bowl) wind and
  water erosion left devastating effects
• On a positive note, erosion from Ethiopian
  highlands generated the fertile sediment for
  Egyptian agriculture for 1000’s of years
Erosion by water in 1961 Kentucky
         Environmental Problem
• Human induced activities such as over cultivating can
  deplete soils. Severe erosion can exceed 200
  Mg/ha/yr (90 tons/acre/yr)
• Loss of soil to support growth of crops, grasslands,
  forest
• Soil erosion destroys human-made structures
  (reservoirs), lakes and rivers and badly damages land
• Deposition of sediment in rivers can cause them to
  change course, variable seasonal flow and flooding
• The cost of dredging rivers and harbors each year is
  15X the cost of holding the soil in place
       Environmental Problem
• More than 1 million acre-feet of sediment settles
  annually in reservoirs lowering their capacity
• Water can become polluted. 1 ton of soil
  containing 0.2% N and 0.05% P will transfer 2kg
  N and 0.5Kg P to rivers and lakes causing
  eutrophication
• Air pollution: fine particles can reduce solar
  radiation and affect chemical processes in the
  atmosphere
Poorly Managed Construction Site
City of Ballinger, TX used
water from this reservoir from
1920-1952. By early 1970’s
soil erosion sediments filled
the reservoir to more than 35
feet destroying the dams ability
to hold water.
Dredging of a Sediment Filled Drainage Ditch
Eutrophication of Water Body due to Nutrient Loading
        Environmental Problem
• This high rate of erosion has tried to be controlled
  by laws past. In 1972, US Congressed passed
  P.L. 92-500, The Federal Water Pollution Control
  Act (FWPCA).
• The Clean Water Act amended in 1977 (Section
  208 of FWPCA) required states to develop plans
  to control ‘non-point sources’ such as sediment in
  waterways
• In 1981 renewed effort that targeted areas having
  the most severe erosion
• By 1986 some improvements were evident
               Effects of Soil Loss
• Amount of erosion depends on erodibility of the soil,
  characteristics of the land and land use management
• Universal Soil Loss Equation (USLE)
A = RKLSCP
A: annual soil loss
R: erosivity of rain
K: soil erodibility factor (easily detached particles);
  reference soil plot obtained using standard plot 22.1m long on
  9% slope, bare of vegetation, plowed up and down
L & S: length and angle of slope (in percent)
C: crop management factor and vegetative cover
P: practices for soil conservation (contour, terracing)
Agricultural Soil Erosion
Contour strip croping of hay and corn
Bench Terraces
Calkins sweep plow designed to
provide 90% stubble on soil as mulch
to reduce wind erosion
Field windbreak protecting a corn crop in North Dakota
Soil Erosion
         Soils and Pollution
• Pollution vs. Contamination
• All chemicals are harmful in excess
  concentrations
• Concentrations of chemicals are regulated
  by law in most industrialized countries
• Natural soils can have chemicals in
  excess concentrations (selenium,
  molybdenum, lead)
• Soils are nature’s filters and a receptacle for burial
   – Physical (sieve action)
   – Chemical (adsorption and precipitation)
   – Biological (decomposition of organic material)
• Soils are needed to:
   – Grow crops for food, animal fodder and fibers, trees for
     fuel and timber and to support natural ecosystems
• Increasingly human population explosion has
  increased the amount of land in cultivation, so that
  what remains is marginal or sub-economic land
• The question is sustainable development of resources
  for our increasing population, estimated at 10 billion by
  2050
• The answer of management is not easy since social,
  political, economic and cultural conditions have to be
  met just as the physical ones
 Contamination by Nutrients:
         Nitrates
• Nitrate is present in soils from microbial
  breakdown of organic matter, manures and
  plant residues; fertilizers; the microbial
  oxidation of ammonium (NH4+) and additions
  from the atmosphere as HNO3
• NO3- is not adsorbed by most soils because
  of its negative charge. It remains in solution
  until it is either taken up by plants, leached
  out in drainage water or denitrified
• Loss of nitrate is undesirable because it is a
  health hazard, it causes economic losses
  (fertilizers); it causes eutrophication
                Health Risks of N
• A health hazard from nitrite was first recognized in
  1945 in Iowa- Methemoglobinemia (blue baby
  syndrome), also affects the elderly and livestock
   – Nitrate becomes toxic to any animal with a disrupted
     digestive track that causes microbes to reduce NO3- to NO2-
     in large amounts. The nitrite is absorbed into the
     bloodstream where it oxidizes oxyhemoglobin to
     methemoglobin thus suffocating the young animal, turning it
     blue (cyanosis), when 70% of hemoglobin is changed, death
     ensues
   – Nitrate content of wells is regulated at 45ppm nitrate or
     10ppm Nitrate-nitrogen; many rural wells exceed this by 2X
• Respiratory illnesses from PANS
  (peroxyacetylnitrates)and other nitrogen oxides
• Cancer (gastric) from nitrosamines from NO2- and
  secondary amines in food
                     Pesticides
• Pesticides are extensively used to control harmful
  populations of insects
• Since Greek and Roman times some mixtures have
  been used to control insect populations and fungi
  (sulfur, arsenic and copper compounds)
• In 1930’s 2,4-D and DDT were found to kill weeds and
  insects. It was the ‘magic-bullet’. Its ‘inventor’ was
  awarded the Nobel Prize in Chemistry in 1948
• DDT is still an excellent insecticide (malaria control,
  Chagas disease, typhus ect..). However, its half-life in
  the environment is too long (10-25 years) and it
  bioaccumulates in the fat of animals (Silent Spring-
  Rachael Carson)
• DDT was banned in US in the early 1970’s
                 Pesticides
• All pesticides are organic chemicals
  (chlorinated hydrocarbons, organophosphorus
  compounds, carbamates etc…)
• About 600 commercially important ones exist
  and over 1500 registered for sale
• To be a ‘good pesticide’; it must be 1) short
  lived in the environment, 2) not carcinogenic,
  teratogenic or mutagenic and must 3) be
  effective yet be able to be handled safely
               Pesticides
• Most pesticides are adsorbed to soils
  especially those of a high molecular mass
  that form positively charged ions
• Some pesticides are volatilized and all are
  eventually biodegraded by soil
  microorganisms depending on their half-
  life
• Groundwater contamination is one of the
  greatest threats we face today
                      Soil Degredation
• Erosion: greatest long term hazard to long term maintenance
  of soil fertility
• Acidification: the soil pH of a weakly buffered soil in the
  humid tropics can drop from 6.0 to 4.5 in 3 years when fertilized
  by ammonium sulfate
• Salinization and sodification: particular problems that occur
  in arid and semi-arid environments under irrigation
• Accumulation of toxic elements: from mining and industry
• Depletion of plant nutrients: harvesting of specific crops
• Reduction of soil organic matter content
• Compaction and crusting
• Waterlogging and drought: periods of wet/dry. Sahel has
  been in a drought since the mid 1960’s and the onslaught of
  desertification
  The Ultimate Pollutant: People
• Pollution: the degredation of a substance or
  system for people’s use
• Carrying capacity (limit of an ecosystem to
  support organisms without causing a
  catastrophe)
• The more nature is bent abnormally by more
  and more people, the more catastrophic will
  be the results, whenever we lose control
                  Degradation
• The American Farmland Trust stated that
  unless California’s agricultural problems
  were addressed in the next 10-20 years
  the state farming industry would decline
  – Agricultural land conversion to nonagricultural uses
     • Over 17,00 ha/yr were converted to urban uses, >80% were
       irrigated croplands
  – Soil erosion
  – Increasing salinity of soil and water
  – Diminishing water supply and diversion for
    nonagricultural uses
        Parting Thought
AS IMPORTANT AS TECHNOLOGY,
POLITICS, LAW, AND ETHICS ARE TO THE
POLLUTION QUESTION, ALL SUCH
APPROACHES ARE BOUND TO HAVE
DISSAPPOINTING RESULTS, FOR THEY
IGNORE THE PRIMARY FACT THAT
POLLUTION IS PRIMARILY AN ECONOMIC
PROBLEM, WHICH MUST BE UNDERSTOOD
IN ECONOMIC TERMS

								
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