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 Diffusion coefficient (cm2 s-1) Initial concentration (mM cm-3)
from phreeqcd.dat and from (based on modelling initial
the CRC Handbook of Physics soil solution samples)
and Chemistry
H2PO4- 0.846 x10-5 7.7 x10-4
Ca+2 0.793 x10-5 3 x10-4 (will increase as gypsum dissolves)
SO4-2 1.07 x10-5 3 x10-4 (will increase as gypsum dissolves)
NO3- 1.9e x10-5 10.85 x10-3
AmmH+ 1.98 x10-5 17.66 x10-3 (set to maintain electroneutrality)
Cl- 2.03 x10-5e-5 1.62 x10-2
K+ 1.96 x10-5 6.67 x10-3
CitrateH-2 0.623 x10-5 0
Fe+3 8.46 x10-5 0.025 x10-3
H2AsO4- 0.905 x10-5 1.22 x10-4
Edta-4 8.46 x10-5 0.025 x10-3
Mg+2 0.705 x10-5 1.90 x10-3
FeEdta- 8.46 x10-5 0
H+ 9.31 x10-5 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 Saturation index Amount (M l-1)
Gypsum 0.0 0.015
CO2(g) -3.5 (partial pressure) 10
Soil chemistry – Sorption parameters
Binding site Amount per g goethite
Hfo_w 5.83 x10-5
Hfo_s 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+ # Source: minteq.dat
log_k -13.998
delta_h 13.345 kcal
-gamma 3.5 0
CO3-2 + H+ = HCO3- # Source: minteq.dat
log_k 10.33
delta_h -3.617 kcal
CO3-2 + 2H+ = H2CO3 # Source: minteq.dat
log_k 16.681
3H+ + Edta-4 = EdtaH3- # Source: minteq.dat
log_k 18.86
delta_h 0 kcal
Fe+3 + Edta-4 = FeEdta- # Source: minteq.dat
log_k 27.7
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 + H2PO4-
log_k -0.437
CO2(g) # minteq.dat
CO2 + H2O = CO3-2 + 2H+
log_k -18.16
O2(g) # minteq.dat
O2 = O2
log_k -2.8983
SURFACE_SPECIES
Hfo_sOH2+ + H2PO4- = Hfo_sH2PO4 + H2O # Derived from phreeqc.dat using the tableu method
log_k = 4.45
Hfo_wOH2+ + H2PO4- = Hfo_wH2PO4 + H2O # Derived from phreeqc.dat using the tableu method
log_k = 4.45
Hfo_wH2PO4 + H2AsO4- = Hfo_wH2AsO4 + H2PO4- # Derived from optimized values using
log_k = 0.6168 # the tableu method
Hfo_wH2PO4 + CitrateH-2 = Hfo_wCitrateH- + H2PO4-
log_k = 12.8
Hfo_wH2AsO4 + CitrateH-2 = Hfo_wCitrateH- + H2AsO4-
log_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 *Jmax(mM cm-1 s-1) Km (mM cm-3) Cmin(mM cm-3) Source
H2PO4- 1e-9 16e-6 2e-7 Jungk & Barber (1975)
Ca+2 8.5e-9 3.9e-5 0 Barber (1995)
SO4-2 5e-9 2.8e-5 0 Barber (1995)
NO3- 0.9e-8 1e-5 4e-6 Barber (1995)
AmmH+ 1e-9 5.39e-5 0 Barber (1995)
Cl- 3.5e-8 1e-6 0 Maas and Ogata (1971)
K+ 1.2e-8 1.5e-5 3e-6 Claassen and Barber (1974)
Fe+3 7.5e-12 1e-6 0 Barber (1995)
H2AsO4- 2.98e-9 2.4e-5 0 Abbas and Meharg (2008)
Edta-4 7.5e-12 1e-6 0 Barber (1995)
Mg+2 1e-9 1.5e-5 0 Barber (1995)
FeEdta- 7.5e-12 1e-6 0 Barber (1995)
*Adjusted to achieve the best model performance
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