Gibbsite aloh3s 3h al3 aq 3h2o ex kaolinite

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Unformatted text preview: d Ca2+ (Text box 4.11) •  BASE SATURATION is the propor0on of CEC sites occupied by base ca0ons (Ca2+, Mg2+, K+, Na+) A schema0c representa0on of the exchange of the heavy metal lead (Pb+2 ) replacing Na+1. Soil water pH •  Strong interac0on between CEC and pH •  High CEC soils can buffer low pH water by removing H+ •  BUT causes leaching of other ca0ons (base ca0ons) from soils •  Important interac0on with mobility of Al 3+ Idealized soil column subjected to acid rain inputs over an extended period of 0me 2 H+ SO4 2- 1 2 H+ SO4 2- 2 2 H+ SO4 2- 3 Acidifica0on Front Majority of CEC sites occupied by a base ca0ons Ca 2+ SO4 2- Acidifica0on Front Ca 2+ SO4 2- Majority of CEC sites occupied by H+ or Al 3+ 2 H+ SO4 2- Under low pH (<5): •  Secondary minerals become soluble: –  Ex. gibbsite •  Al(OH3)(s) + 3H + <- > Al3+ (aq) + 3H2O –  Ex. Kaolinite •  Al2Si2O5(OH) (s) + 6H+ <- > 2 Al3+(aq) + 2H4SiO4(aq) + H2O Consequences of soil acid inputs: •  Increase base ca0ons losses from soils (net loss of soil ca0on store) •  Reduce exchangeable base ca0ons in upper soil profile •  As front moves down profile get: –  Above front: Low pH and mobile Al –  Below front: no change in pH, exchangeable base ca0ons •  Sudden acidifica0on when front reaches boUom of profile (acidify streams, lakes etc.) •  May takes decades to deplete soils of base ca0ons that have taken 100’s to 1000’s of years to accumulate via weathering UNI...
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This note was uploaded on 01/30/2014 for the course ESCI 271 taught by Professor Lisakellman during the Fall '12 term at St. Francis Xavier, Antigonish.

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