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Soil Solutions Continued
aqueous liquid phase of the soil and its solutes
A letter from an expert…
Atomic structure of water
nutrition.jbpub.com/.../chemistryreview6.cfm
Hydrogen Bonding
Water is a powerful solvent
How salt dissolves in water
nutrition.jbpub.com/.../chemistryreview6.cfm
http://www.chem1.com/acad/sci/aboutwater.html
Hydrated ion
http://nmr.ioc.ac.ru/Staff/AnanikovVP/127i-nmr/127i.htm
Inner-sphere complexes
• Interaction between metal ions and ligands where no water molecules are present
• Ions are 'fixed' irreversibly or tightly bound, thus not water-extractable or plant available
Outer-sphere complexes and ion pairs
• Water molecules are positioned between the metal ion and the ligand
• These ions are loosely bound and easily exchanged with other ions in solution
• Ion pairs are uncharged outer-sphere complexes in solution
Schematic diagram illustrating the outer- and inner-sphere Fe-sulfate complexes in water.
http://geoweb.princeton.edu/research/geochemistry/research/aqueous-sulfate-fig1.jpg
http://www.nsls.bnl.gov/newsroom/science/2003/images/01-Peak-figure2.jpg
Fe or Al
O or OH
Surface Complexation of Uranium(VI) Carbonate Adsorbed on Montmorillonite
jeffcatalano.googlepages.com/U_montmor.html
Solvated ion pair
www.theochem.ruhr-uni-bochum.de
Ion pair solvated by water molecules
nmr.ioc.ac.ru/Staff/AnanikovVP/127i-nmr/127i.htm
Speciation - the distribution of ions and complexes in their various forms (species)
http://www-ocean.tamu.edu/Quarterdeck/QD2.2/Sant-Gill/sant-gillfig2.html
Measurement of soil solution
What to measure: • "intensity" or concentration (how much is
there) – total dissolved quantity of an element,
moles/L, mg/L, or some amount per volume
• "capacity factor" - ability of solids to resupply depleted ions through dissolution, weathering, geochemical cycling, etc.
How to measure soil solution
• In situ – Use lysimeters, suction cups, or collect
drainage from soil. – very difficult due to changing water contents
and redox conditions, precipitation of compounds near collection points, access to soil pores, etc
http://www.maf.govt.nz/mafnet/schools/activities/swi/swi-04.htm
Combined tensiometer-
soil solution sampler
hopmans.lawr.ucdavis.edu/images/research_2_5.jpg www.decagon.com
Pore water
sampler
Measuring soil solution in laboratory more common, but not as accurate
• Displacement techniquesWith or w/o non-polar displacing chemicals
• Centrifugation (spinning the soil at a high speed pulls the liquid out of the pores)
• Saturation paste extracts or any ratio of soil to water mixture
Displacement by a non-polar chemical (e.g., CCl4)
http://commons.wikimedia.org/wiki/Image:Carbon-tetrachloride-3D-balls.png
Saturated Paste Extracts
Collecting soil solution
http://www.envisci.ucr.edu/faculty/graham/students/photos/blee05.jpg