Chapter 17 Soils and Environment

Environmental  Geology   Chapter  17  SOILS  and  ENVIRONMENT     Soil  supports  rooted  plant  life  and  is  composed  of  solid  earth  materials  altered  by   physical,  chemical,  and  biological  processes.    In  land-­‐use  planning:  Soil  suitability  is   large  part  of  land  capability.    For  waste  disposal:  Soil  properties  are  critical.    And,   the  impact  of  natural  hazards:  Affected  by  soil  properties     Soil  Profile  -­‐  Soil  horizons:    Distinct  layers  roughly  parallel  to  the  surface  as  soil   develops  over  time.    Soil  Structure  -­‐  Particle  size  increases  with  depth   Clays  are  usually  found  in  the  A  horizon     Soil’s  General  Properties   • Color:  Depending  on  the  amount  of  organic  matter,  iron  oxides,  and  soil   water  retention   • Texture:  Relative  proportions  of  sand,  silt,  and  clay-­‐sized  particles,  affect   soil’s  strength  and  ability  to  retain  water  and  nutrients   • Structure:   Ø Aggregates  of  soil  as  peds   Ø The  more  developed  over  time,  the  more  complex  a  soil’s  structure     Soil  Fertility  -­‐  Soil’s  capability  to  supply  nutrients  needed  for  plant  growth,  such  as   Nitrogen  (N),  Phosphorous  (P),  and  Potassium  (K)     Fertility  changes   Ø Increase:  Applying  fertilizers  or  mixing   materials  to  improve  soil  texture   Ø Decrease:  Leaching  or  soil  erosion;  overuse,  especially  by  agriculture     Soil  Taxonomy  -­‐  Soil  classification  based  on  physical  and  chemical  properties  of  the   soil  profile     Sixfold  hierarchy:  Orders,  suborders,  groups,  subgroups,  families,  and  series  (more   detail  than  we  need  for  this  class)     Useful  for  agricultural  and  related  land  use  planning     Engineering  Properties  of  Soils  (1)   • Strength:  Soil’s  ability  to  resist  deformation,  function  of  cohesive  and   frictional  forces  between  soil  particles.    Partially  saturated  soil-­‐surface   tension  between  particles  and  water  holds  soil  together-­‐cohesion   • Sensitivity:  Measuring  the  changes  in  soil  strength  from  disturbances   • Compressibility:  Soils  tendency  to  consolidate  or  decrease  in  volume   • Erodibility:  The  ease  with  which  soil  is  removed  by  wind  or  water   • Hydraulic  conductivity:  The  ease  of  water  to  allow  water  to  move  through   Corrosion  potential:  Depending  on  the  chemistry  of  soil,  water  content  of   soil,  and  the  type  of  buried  materials  in  the  soil   • Ease  of  excavation:  The  degree  of  ease  to  remove   soil  using  certain  equipment  during  construction   • Caliche  makes  excavation  very  difficult  in  SW  U.S.   • Shrink-­‐swell  potential:  Soil’s  tendency  to  gain  or   lose  water.    Expansive  soils  (clayey  soils):  Causing  significant  environmental   problems  in  the  U.S.    This  is  a  big  issue  in  Phoenix  area  –  e.g.,  Anthem   •   Rates  of  Soil  Erosion   Volume,  mass,  or  weight  of  soil  removed  from  a  specific  area  during  a  specific   period  of  time     The  Universal  Soil  Loss  Equation:  A  =  RKLSCP   A:  Long-­‐term  average  annual  soil  loss  for  the  site   R:  Long-­‐term  rainfall  runoff  erosion  factor   K:  Soil  erodibility  index  factor   L:  Hillslope/length  factor   C:  Soil  cover  factor   P:  Soil  erosion-­‐control  practice  factor     Soil  Erosion   • Urbanization:  Rapid  development  and  construction     • Desertification:  Over-­‐grazed  or  disturbed     • Deforestation:  Forest  over-­‐logged  or  burned   • Surface  mining  (in  2000,  65%  coal  produced  from  surface  mining)   • Soil  erosion  and  deposition  by  natural  hazards,  such  as  floods     Sediment  Pollution   • One  of  the  greatest  pollutants  by  volume/mass   Ø A  resource  “out  of  place”   • Choking  the  waterways,  burying  vegetation,  causing  dust  storms   • Adverse  impact  on  water  and  air  quality,  land  productivity   • Preventive  measures   Ø Conservation  practices:  Better  land-­‐use  and  urban  development   planning,  sediment  control  basins   Ø   Land-­‐Use  and  Soil  Problems  (1)   Agriculture:  Estimated  10%  of  the  world  best  agricultural  land  damaged  due  to   soil  erosion  and  overuse  of  soil  during  the  last  50  years   Better  practice  to  sustain  soils   Ø Contour  plowing   Ø No-­‐till  agriculture  (no  plowing)   Ø Terracing  slopes,  retaining  walls  for  steep  slopes   Ø Planting  more  than  one  crop,  particularly  in  tropical  areas   •   Land-­‐Use  and  Soil  Problems  (2)   • Urbanization:  Conversion  of  agricultural,  forest,  and  rural  lands   • Soil  scraped  off  and  lost   • Changes  of  soil  properties   • Soil  pollution:  Use  of  chemicals   • Changes  of  surface  runoff,  sediment  yield,  and   stream  dynamics  affecting  soil  and  soil  erosion   • Off-­‐road  vehicles:  Recreation,  tourism,  etc.   • In  deserts,  coastal  dunes,  forested  mountains   • Cause  changes  in  rates  of  soil  erosion,  hydrology,  habitats  of  plants   and  animals   • Impacts  from  the  increased  number  of  mountain   bikes  in  parks,  national  forests,  etc.     Soil  Pollution:  By  any  materials  detrimental  to  human  and  other  living  organisms,   such  as  organic  chemicals,  inorganic  chemicals,  toxic  substances   • Intentionally  or  accidentally  applied  to  soils   • Inappropriate  disposal  of  waste  materials   • Treatment:  Excavation,  disposal,  incineration,  and  bioremediation     Soil  Survey  and  Land-­‐Use  Planning   • Soil  survey:  Providing  important  information  about  soils   • Soil  properties:  Critical  for  the  best  use  of  land;  specific  soils  suitable  for   certain  land  use   • Soil’s  engineering  properties:  Necessary  info  for  identifying  potential   problems  before  construction   • Detailed  soil  maps:  Helpful  and  important  in  land  use  planning