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SUPPORTING MATERIAL
TABLE S1 – Model parameters and their sources
Soil Physics
Volumetric water content: 24%
(Measured)
Soil density: 1.45 g cm-3
(Adjusted)
Soil impedance factor: 0.34
(Estimated using the Millington-Quirk model)
Water flux: derived from plant transpiration in compartment system experiments (Szegedi, 2009)
Geometry: linear
Soil chemistry – Initial concentrations (before calculating initial soil solution equilibrium)
Solute
H2PO4Ca+2
SO4-2
NO3AmmH+
ClK+
CitrateH-2
Fe+3
H2AsO4Edta-4
Mg+2
FeEdtaH+
Diffusion coefficient (cm2 s-1)
from phreeqcd.dat and from
the CRC Handbook of Physics
and Chemistry
0.846 x10-5
0.793 x10-5
1.07 x10-5
1.9e x10-5
1.98 x10-5
2.03 x10-5e-5
1.96 x10-5
0.623 x10-5
8.46 x10-5
0.905 x10-5
8.46 x10-5
0.705 x10-5
8.46 x10-5
9.31 x10-5
Initial concentration (mM cm-3)
(based on modelling initial
soil solution samples)
7.7 x10-4
3 x10-4 (will increase as gypsum dissolves)
3 x10-4 (will increase as gypsum dissolves)
10.85 x10-3
17.66 x10-3 (set to maintain electroneutrality)
1.62 x10-2
6.67 x10-3
0
0.025 x10-3
1.22 x10-4
0.025 x10-3
1.90 x10-3
0
2.5x10-6 / 0.95x10-6 (G-1/G-4)
FeEdta Assumed to be transported and taken up together (almost all Fe and EDTA exist in complexed form
Soil chemistry – Initial phases
Phase
Gypsum
CO2(g)
Saturation index
0.0
-3.5 (partial pressure)
Amount (M l-1)
0.015
10
Soil chemistry – Sorption parameters
Binding site
Hfo_w
Hfo_s
Amount per g goethite
5.83 x10-5
1.45 x10-6
Soil chemistry – stoichiometric reactions and their equilibrium constants (the reduced
database, PHREEQC formulation, without the definition of species included in table 1,
wihout gamma values) The tableau method (Morel and Hering, 1993) was used to reformulate
the stoichiometric reactions by making dominant species to be master species.
SOLUTION_SPECIES
H2O = OH- + H+
log_k -13.998
delta_h 13.345 kcal
-gamma 3.5 0
# Source: minteq.dat
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CO3-2 + H+ = HCO3log_k 10.33
delta_h -3.617 kcal
# Source: minteq.dat
CO3-2 + 2H+ = H2CO3
log_k 16.681
# Source: minteq.dat
3H+ + Edta-4 = EdtaH3log_k 18.86
delta_h 0
kcal
# Source: minteq.dat
Fe+3 + Edta-4 = FeEdtalog_k 27.7
# Source: minteq.dat
PHASES ##########################################################
Gypsum
# Source: Bennett and Adams (1972) Soil Sci Soc Am Proc 36:288-291.
CaSO4:2H2O = + 1.0000 Ca++ + 1.0000 SO4-- + 2.0000 H2O
log_k
-4.53
CaHPO4
# Derived from llnl.dat using the tableu method
CaHPO4 + H+ = Ca+2 + H2PO4log_k -0.437
CO2(g)
# minteq.dat
CO2 + H2O = CO3-2 + 2H+
log_k -18.16
O2(g)
O2 = O2
log_k -2.8983
# minteq.dat
SURFACE_SPECIES
Hfo_sOH2+ + H2PO4- = Hfo_sH2PO4 + H2O
log_k = 4.45
# Derived from phreeqc.dat using the tableu method
Hfo_wOH2+ + H2PO4- = Hfo_wH2PO4 + H2O # Derived from phreeqc.dat using the tableu method
log_k = 4.45
Hfo_wH2PO4 + H2AsO4- = Hfo_wH2AsO4 + H2PO4log_k = 0.6168
# Derived from optimized values using
# the tableu method
Hfo_wH2PO4 + CitrateH-2 = Hfo_wCitrateH- + H2PO4log_k = 12.8
Hfo_wH2AsO4 + CitrateH-2 = Hfo_wCitrateH- + H2AsO4log_k = -0.12
Hfo_wOH2+ + CitrateH-2 = Hfo_wCitrateH- + H2O
log_k = 16.8
Hfo_wOH2+ + CO3-2 + H+ = Hfo_wHCO3 + H2O # Derived after Appelo et al (2002) Environ Sci and
log_k = 14.03
# Technol 36:3096-3103 using the tableu method
Root uptake (Parameters of the Michaelis Menten kinetics)
Solute
H2PO4Ca+2
*Jmax(mM cm-1 s-1) Km (mM cm-3) Cmin(mM cm-3) Source
1e-9
16e-6
2e-7
Jungk & Barber (1975)
8.5e-9
3.9e-5
0
Barber (1995)
2
1
2
3
4
5
6
7
8
9
10
11
12
13
SO4-2
NO3AmmH+
ClK+
Fe+3
H2AsO4Edta-4
Mg+2
FeEdta-
5e-9
0.9e-8
1e-9
3.5e-8
1.2e-8
7.5e-12
2.98e-9
7.5e-12
1e-9
7.5e-12
2.8e-5
1e-5
5.39e-5
1e-6
1.5e-5
1e-6
2.4e-5
1e-6
1.5e-5
1e-6
0
4e-6
0
0
3e-6
0
0
0
0
0
Barber (1995)
Barber (1995)
Barber (1995)
Maas and Ogata (1971)
Claassen and Barber (1974)
Barber (1995)
Abbas and Meharg (2008)
Barber (1995)
Barber (1995)
Barber (1995)
*Adjusted to achieve the best model performance
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